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Page 1: Lightning Protection Guide

LIGHTNINGPROTECTION

GUIDE2nd updated edition

Page 2: Lightning Protection Guide

LIGHTNINGPROTECTION

GUIDE2nd updated edition

Page 3: Lightning Protection Guide

DEHN + SÖHNE – LIGHTNING PROTECTION GUIDE

2nd updated edition

ISBN 3-00-015975-4

Lightning Protection

Surge Protection

Safety Equipment

DEHN + SÖHNE

GmbH + Co.KG.

Hans-Dehn-Str. 1

Postfach 1640

92306 Neumarkt

Germany

Phone +49 9181 906-0

FAX +49 9181 906-333

www.dehn.de

[email protected]

Editorial state: September 2007

We reserve the right to introduce changes inperformance, configuration and technology,dimensions, weights and materials in the course of technical progress.

The figures are shown without obligation. Mis-prints, errors and omissions excepted.

Reproduction in any form whatsoever is forbiddenwithout our permission.

Brochure No. DS702/E/2007© Copyright 2007 DEHN + SÖHNE

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Since its foundation in 1980, the IEC TC 81 “Light-ning Protection“ of the International Electrotech-nical Commission (IEC) has drawn up diverse stan-dards for the protection of buildings from light-ning, for the protection of electronic systems, forrisk analysis and for the simulation of the effects oflightning. These standards were compiled oneafter the other as they were required, and pub-lished under different numbers with no recognis-able system. The standards work therefore becamemore and more unsystematic to the user. In Sep-tember 2000, the IEC TC 81 therefore decided tointroduce a new, clearly arranged structure forlightning protection standards (series: IEC 62305).Revised and new standards will be integrated intothis new structure.

The new International Lightning Protection Stan-dards IEC 62305 (Parts 1 to 4) were published at thebeginning of 2006. Almost at the same time theycame into force as new European Lightning Pro-tection Standards EN 62305-1 to 4.The standards IEC 62305 and EN 62305 providecompact information as required for the protec-

tion of electrical and electronic systems in build-ings and structures. So, this complex protectionsuccessfully has been subdivided into a number ofconcrete individual protective measures which thedesigner and installer can compose to an overallsystem adjusted and specific to the respective tar-get of protection.When signing new contracts on designing andinstallation of lightning protection systems, infuture the contractor has to follow the series ofstandards IEC 62305 or EN 62305 to work in com-pliance with the State of the Art. For this to be possible, the contractor must famil-iarise himself with the contents of the new light-ning protection standards.With this completely revised LIGHTNING PROTEC-TION GUIDE, we would like to support you as thespecialists in this field, regardless of whether youare involved in design or executing, in becomingfamiliar with the new series of lightning protec-tion standards.

DEHN + SÖHNE

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Preface

Aerial photo of DEHN + SÖHNE

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www.dehn.de4 LIGHTNING PROTECTION GUIDE

Trademarks

– BLITZDUCTOR®

– BLITZPLANER®

– DEHNALU-DRAHT®

– DEHNbloc®

– DEHNfix®

– DEHNgrip®

– DEHNguard®

– DEHNport®

– DEHNQUICK®

– DEHNrapid®

– DEHNsnap®

– DEHNventil®

– HVI®

– LifeCheck®

– ... MIT SICHERHEIT DEHN.

and our logo

are registered trademarks of

DEHN + SÖHNE GmbH + Co.KG.

Product terms mentioned in the book that

are also registered trademark have not been

clearly marked. Therefore, it cannot be con-

cluded from an absent TM or ® marking that

a term is an unregistered trademark. Equally,

it cannot be determined from the text if

patents or protection of utility patents exist

for a product.

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Signs and symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

1. State of the art for the installation of lightning protection systems . . . . . . . . . . . . . . . . . . . . . .11

1.1 Installation standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

1.2 Work contracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

1.3 Product standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

2. Characteristics of lightning current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

2.1 Lightning discharge and sequence of lightning current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

2.2 Peak value of lightning current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

2.3 Steepness of lightning current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

2.4 Charge of lightning current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

2.5 Specific energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

2.6 Assignment of lightning current parameters to lightning protection levels . . . . . . . . . . . . . . . . .22

3. Designing a lightning protection system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

3.1 Necessity of a lightning protection system – legal regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

3.2 Assessment of the risk of damage and selection of protective components . . . . . . . . . . . . . . . . .29

3.2.1 Risk management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

3.2.2 Fundamentals of risk assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

3.2.3 Frequency of lightning strikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

3.2.4 Probabilities of damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

3.2.5 Types of loss and sources of damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

3.2.6 Loss factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

3.2.7 Relevant risk components for different lightning strikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

3.2.8 Tolerable risk of lightning damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

3.2.9 Choice of lightning protection measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

3.2.10 Economic losses / Economic efficiency of protective measures . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

3.2.11 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

3.2.12 Designing aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

3.3 Inspection and maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

3.3.1 Types of inspection and qualification of the inspectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

3.3.2 Inspection measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

3.3.3 Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

3.3.4 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

4. Lightning protection system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

5. External lightning protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

5.1 Air-termination systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

5.1.1 Designing methods and types of air-termination systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

5.1.2 Air-termination systems for buildings with gable roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

5.1.3 Air-termination systems for flat-roofed structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

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Contents

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5.1.4 Air-termination systems on metal roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

5.1.5 Principle of an air-termination system for structures with thatched roof . . . . . . . . . . . . . . . . . . .65

5.1.6 Walkable and trafficable roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68

5.1.7 Air-termination system for green and flat roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

5.1.8 Isolated air-termination systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71

5.1.9 Air-termination system for steeples and churches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74

5.1.10 Air-termination systems for wind turbines (WT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75

5.1.11 Wind load stresses on lightning protection air-termination rods . . . . . . . . . . . . . . . . . . . . . . . . . .76

5.2 Down-conductor system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81

5.2.1 Determination of the number of down conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

5.2.2 Down-conductor system for a non-isolated lightning protection system . . . . . . . . . . . . . . . . . . .82

5.2.2.1 Installation of down-conductor systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83

5.2.2.2 Natural components of a down-conductor system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84

5.2.2.3 Measuring points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

5.2.2.4 Internal down-conductor systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

5.2.2.5 Courtyards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

5.2.3 Down conductors of an isolated external lightning protection system . . . . . . . . . . . . . . . . . . . . .87

5.2.4 High voltage-resistant, isolated down-conductor system – HVI conductor . . . . . . . . . . . . . . . . . .87

5.2.4.1 Installation and performance of the isolated down-conductor system HVI . . . . . . . . . . . . . . . . .89

5.2.4.2 Installation examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90

5.2.4.3 Project example: Training and residential building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93

5.2.4.4 Separation distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95

5.3 Materials and minimum dimensions for air-termination conductors and down conductors . . . .97

5.4 Assembly dimensions for air-termination and down-conductor systems . . . . . . . . . . . . . . . . . . . .97

5.4.1 Change in length of metal wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

5.4.2 External lightning protection system for an industrial structure and a residential house . . . . . .99

5.4.3 Application tips for mounting roof conductors holders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102

5.5 Earth-termination systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105

5.5.1 Earth-termination systems in accordance with IEC 62305-3 (EN 62305-3) . . . . . . . . . . . . . . . . . .116

5.5.2 Earth-termination systems, foundation earth electrodes and foundation earth electrodes for special structural measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118

5.5.3 Ring earth electrodes – Earth electrodes Type B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .124

5.5.4 Earth rods – Earth electrodes Type A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125

5.5.5 Earth electrodes in rocky ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125

5.5.6 Intermeshing of earth-termination systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125

5.5.7 Corrosion of earth electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127

5.5.7.1 Earth-termination systems with particular consideration of corrosion . . . . . . . . . . . . . . . . . . . .127

5.5.7.2 Formation of voltaic cells, corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128

5.5.7.3 Choice of earth electrode materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132

5.5.7.4 Combination of earth electrodes made of different materials . . . . . . . . . . . . . . . . . . . . . . . . . . .132

5.5.7.5 Other anticorrosion measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133

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5.5.8 Materials and minimum dimensions for earth electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135

5.6 Electrical isolation of the external lightning protection system – Separation distance . . . . . . .135

5.7 Step and touch voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .140

5.7.1 Control of the touch voltage at down conductors of lightning protection systems . . . . . . . . . .144

6. Internal lightning protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147

6.1 Equipotential bonding for metal installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147

6.2 Equipotential bonding for low voltage consumer’s installations . . . . . . . . . . . . . . . . . . . . . . . . .151

6.3 Equipotential bonding for information technology installations . . . . . . . . . . . . . . . . . . . . . . . .151

7. Protection of electrical and electronic systems against LEMP . . . . . . . . . . . . . . . . . . . . . . . . . . .155

7.1 Lightning protection zones concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155

7.2 LEMP protection management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156

7.3 Calculation of the magnetic shield attenuation of building/room shielding . . . . . . . . . . . . . . .158

7.3.1 Cable shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162

7.4 Equipotential bonding network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164

7.5 Equipotential bonding on the boundary of LPZ 0A and LPZ 1 . . . . . . . . . . . . . . . . . . . . . . . . . . .166

7.5.1 Equipotential bonding for metal installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166

7.5.2 Equipotential bonding for power supply installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167

7.5.3 Equipotential bonding for information technology installations . . . . . . . . . . . . . . . . . . . . . . . .170

7.6 Equipotential bonding on the boundary of LPZ 0A and LPZ 2 . . . . . . . . . . . . . . . . . . . . . . . . . . .171

7.6.1 Equipotential bonding for metal installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171

7.6.2 Equipotential bonding for power supply installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .171

7.6.3 Equipotential bonding for information technology installations . . . . . . . . . . . . . . . . . . . . . . . .172

7.7 Equipotential bonding on the boundary of LPZ 1 and LPZ 2 and higher . . . . . . . . . . . . . . . . . .173

7.7.1 Equipotential bonding for metal installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173

7.7.2 Equipotential bonding for power supply installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174

7.7.3 Equipotential bonding for information technology installations . . . . . . . . . . . . . . . . . . . . . . . .175

7.8 Coordination of the protective measures at various LPZ boundaries . . . . . . . . . . . . . . . . . . . . . .175

7.8.1 Power supply installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .175

7.8.2 IT installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .176

7.9 Inspection and maintenance of the LEMP protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .179

8. Selection, installation and assembly of surge protective devices (SPDs) . . . . . . . . . . . . . . . . . .180

8.1 Power supply systems (within the scope of the lightning protection zones concept according to IEC 62305-4 (EN 62305-4)) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .180

8.1.1 Technical characteristics of SPDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181

8.1.2 Use of SPDs in various systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .182

8.1.3 Use of SPDs in TN Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184

8.1.4 Use of SPDs in TT systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185

8.1.5 Use of SPDs in IT systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .192

8.1.6 Rating the lengths of the connecting leads for SPDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197

8.1.7 Rating of the terminal cross-sections and the backup protection of surge protective devices . .201

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8.2 Information technology systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .206

8.2.1 Measuring and control systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .214

8.2.2 Technical property management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .215

8.2.3 Generic cabling systems (EDP networks, TC installations) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .216

8.2.4 Intrinsically safe circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .218

8.2.5 Special features of the installation of SPDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .223

9. Application proposals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .227

9.1 Surge protection for frequency converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .227

9.2 Lightning and surge protection for outdoor lighting systems . . . . . . . . . . . . . . . . . . . . . . . . . . .230

9.3 Lightning and surge protection for biogas plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .234

9.4 Lightning and surge protection retrofitting for sewage plants . . . . . . . . . . . . . . . . . . . . . . . . . .244

9.5 Lightning and surge protection for cable networks and antennas for TV, sound signals and interactive services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .250

9.6 Lightning and surge protection in modern agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .255

9.7 Lightning and surge protection for video surveillance systems . . . . . . . . . . . . . . . . . . . . . . . . . .259

9.8 Surge protection for public address systems (PA systems) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262

9.9 Surge protection for hazard alert systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .264

9.10 Lightning and surge protection for KNX systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .268

9.11 Surge protection for Ethernet and Fast Ethernet networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . .271

9.12 Surge protection for M-Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .273

9.13 Surge protection for PROFIBUS FMS, PROFIBUS DP, and PROFIBUS PA . . . . . . . . . . . . . . . . . . . .278

9.14 Surge protection for telecommunication accesses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282

9.15 Lightning and surge protection for intrinsically safe circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . .285

9.16 Lightning and surge protection of multi-megawatt wind turbines . . . . . . . . . . . . . . . . . . . . . . .291

9.17 Surge protection for radio transmitter /receiver stations (mobile radio) . . . . . . . . . . . . . . . . . . .295

9.17.1 Power supply 230/400 V a.c. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .295

9.17.2 Fixed network connection (if existing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .297

9.17.3 Radio transmission technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .297

9.17.4 Lightning protection, earthing, equipotential bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .297

9.18 Lightning and surge protection for PV systems and solar power plants . . . . . . . . . . . . . . . . . . .298

9.18.1 Lightning and surge protection for photovoltaic (PV) systems . . . . . . . . . . . . . . . . . . . . . . . . . . .298

9.18.2 Lightning and surge protection for solar power plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .304

Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .308

DEHN + SÖHNE Brochures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .314

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .315

Figures and Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .321

Answer Sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .329

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Signs and symbols

ϑ

A

B

C

D

M

L

K

K

k

Q

Symbol* Description Symbol* Description Symbol* Description

PEN conductor

Semiconductor

Lightning equipotential bondingLightning current arresterN conductor

PE conductor

Movable conductor,e.g. expansion piece

Expansion loop(at concrete joints)

Adjustable resistor

Thermistor, adjustable

Socket (of a socket outletor a plug-in connection)

Suppressordiode, bipolar

Earth (general)

Signal lamp

Fuse (general)

Lightning equipotential bondingLightning current arresterYellow/Line TYPE 1

Gas discharge tube (basic)

Local equipotential bondingSurge arresterYellow/Line TYPE 2-4

Resistor,Decoupling element (general)

Lightning equipotential bondingLightning current arrester(SPD Type 1)

Transformer

Local equipotential bondingSurge arrester(SPD Type 2, SPD Type 3)

Zener diode, unipolar

Isolating spark gap

Capacitor

Isolating point /Measuring point

Combined surge protectivedevice for power supplyand IT systems

Interface

Surge arresterfor hazardous/explosive areas

ClampExternal lightning protection

Varistor

Local equipotential bondingSurge arrester

Equipotential bonding bar

* according to IEC 62305-3 (EN 62305-3): 2006 and EN 60617: 1997-08

Lightning protection zone

Explosive area

Lightning electromagnetic pulse

Switching electromagnetic pulse

Discharge capacity of an SPD(acc. to categories of IEC 61643-21)

Protective effect of an SPD(limitation below the test levelsacc. to EN 61000-4-5)

Energy coordination(with another Yellow/Line arrester)

Characteristic Symbol Legend

The symbols of the Yellow/Line SPD Classes

Enclosure with terminals

LifeCheck arrester testing

Impulse D1 (10/350 μs), lightning impulse current ≥ 2.5 kA/ line or ≥ 5 kA/total• exceeds the discharge capacity of B – D

Impulse C2 (8/20 μs), increased impulse load ≥ 2.5 kA/ line or ≥ 5 kA/total• exceeds the discharge capacity of C – D

Impulse C1 (8/20 μs), impulse load ≥ 0.25 kA / line or ≥ 0.5 kA / total• exceeds the discharge capacity of D

Load < C

Test level required for the terminal device: 1 or higher

Test level required for the terminal device: 2 or higher

Test level required for the terminal device: 3 or higher

Test level required for the terminal device: 4

SPD has a decoupling impedance and is suitable forcoordination with an arrester labelled Q

SPD suitable for coordination with an arresterhaving a decoupling impedance k

Inductor

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a.c. Alternating Current

ADSL Asymmetric Digital Subscriber Line

ATM Asynchronous Transfer Mode

BA Building Automation

BTS Base Transceiver Station

CHP Combined Heat and Power Unit

d.c. Direct Current

DDC Direct Digital Control

DNO Distribution Network Operator

EB Equipotential Bonding

EBB Equipotential Bonding Bar

EDP Electronic Data Processing

EMC Electromagnetic Compatibility

ERP Earthing Reference Point

FEM Finite Elements Method

GDT Gas Discharge Tube

GDV Gesamtverband der Deutschen Ver-sicherungswirtschaft e.V. (German Insurance Association)

GPS Global Positioning System

GRP Glass-fibre Reinforced Plastic

HVI High Voltage Resistant Insulating DownConductor

ISDN Integrated Services Digital Network

IT Information Technology

KNX Open standard for home and buildingcontrol

LEMP Lightning Electromagnetic Pulse

LPC Lightning Protection Components

LPL Lightning Protection Level

LPMS LEMP Protection Measures System

LPS Lightning Protection System

LPZ Lightning Protection Zone

l.v. Low Voltage

MDB Main Distribution Board

MEB Main Equipotential Bonding Bar

MEBB Main Equipotential Bonding Bar

MOEB Meshed Operational Equipotential Bonding

MSC Mobile Switching Centre

NTBA Network Termination for ISDN Basic RateAccess

NTPM Network Termination for Primary RateMultiplex Access

PABX Private Automatic Branch Exchange

PE Protective Conductor

PEB Protective Equipotential Bonding

PEN Protective and Neutral Conductor

PEX Polymerised Polyethylene

PSU Power Supply Unit

PV Photovoltaic

PVC Polyvinyl Chloride

RBS Radio Base Station

RCD Residual Current Protective Device

SAK Shield Terminal (Schirmanschlussklemme)

SD Sub-Distribution

SDB Sub-Distribution Board

SEB Service Entrance Box

SEMP Switching Electromagnetic Pulse

SLK Protective Conductor Terminal(Schutzleiterklemme)

SPC Stored Program Control

SPD Surge Protective Device

TC Telecommunication

TEI Terminal Equipment Interface

TOV Temporary Overvoltage

UPS Uninterruptible Power Supply

VDN Association of German Network Operators

VdS VdS Schadenverhütung GmbH(VdS Loss Prevention)

WT Wind Turbine

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Abbreviations

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1.1 Installation standardsAt the beginning of 2006, the new IEC standardson lightning protection, Parts 1 to 4 of the seriesIEC 62305 were published. Almost at the same timethey became effective as new European LightningProtection Standards EN 62305-1 to 4.

The new standards of the series EN 62305 specifythe state of the art in the field of lightning protec-tion on a uniform and up-to-date European basis.The actual protection standards (EN 62305-3 and -4) are preceded by two generally valid standardparts (EN 62305-1 and -2) (Table 1.1.1).

IEC 62305-1 (EN 62305-1): General principlesThis section contains information about the riskposed by lightning, lightning characteristics, andthe parameters derived therefrom for the simula-tion of the effects of lightning. In addition, anoverall view of the IEC 62305 (EN 62305) series ofstandards is given. Procedures and protection prin-ciples which form the basis of the following sec-tions are explained.

IEC 62305-2 (EN 62305-2): Risk managementRisk management in accordance with IEC 62305-2(EN 62305-2) uses risk analysis to first establish thenecessity for lightning protection. The optimumprotective measure from a technical and economicpoint of view is then determined. Finally, theremaining residual risk is ascertained. Startingwith the unprotected state of the building, theremaining risk is reduced and reduced until it isbelow the tolerable risk. This method can be usedboth for a simple determination of the class oflightning protection system in accordance with IEC62305-3 (EN 62305-3), and also to establish a com-

plex protection system against lightning electro-magnetic impulse (LEMP) in accordance with EN 62305-4.

IEC 62305-3 (EN 62305-3): Physical damage to structures and life hazardThis section deals with the protection of buildingsand structures and persons from material damageand life-threatening situations caused by theeffect of lightning current or by dangerous spark-ing, especially in the event of direct lightningstrikes. A lightning protection system comprisingexternal lightning protection (air-termination sys-tem, down-conductor system and earth-termina-tion system) and internal lightning protection(lightning equipotential bonding and separationdistance) serves as a protective measure. The light-ning protection system is defined by its class, Class I being more effective than Class IV. The classrequired is determined with the help of a riskanalysis carried out in accordance with IEC 62305-2(EN 62305-2), unless otherwise laid down in regu-lations (e.g. building regulations).

IEC 62305-4 (EN 62305-4): Electrical and electronic systems within structuresThis section deals with the protection of buildingsand structures with electrical and electronic sys-tems against the effects of the lightning electro-magnetic impulse. Based on the protective meas-ures according to IEC 62305-3 (EN 62305-3), thisstandard also takes into consideration the effectsof electrical and magnetic fields, and induced volt-ages and currents, caused by direct and indirectlightning strikes. Importance and necessity of thisstandard derives from the increasing use of diverseelectrical and electronic systems which aregrouped together under the heading informationsystems. For the protection of information systems,the building or structure is divided up into light-

ning protection zones (LPZ).This allows local differencesin the number, type andsensitivity of the electricaland electronic devices to betaken into considerationwhen choosing the protec-tive measures. For eachlightning protection zone, arisk analysis in accordancewith IEC 62305-2 (EN 62305-2) is used to select those

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1. State of the art for the installation of lightning protection systems

Classification TitleIEC 62305-1: 2006-01 Protection against lightning(EN 62305-1) Part 1: General principlesIEC 62305-2: 2006-01 Protection against lightning(EN 62305-2) Part 2: Risk managementIEC 62305-3: 2006-01 Protection against lightning Part 3: Physical(EN 62305-3) damage to structures and life hazardIEC 62305-4: 2006-01 Protection against lightning Part 4: Electrical(EN 62305-4) and electronic systems within structures

Table 1.1.1 Lightning protection standard valid since January 2006

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protective measures which provide optimum pro-tection at minimum cost.

These standards can be applied to the design,installation, inspection and maintenance of light-ning protection systems for buildings and struc-tures, their installations, their contents and thepersons within.

1.2 Work contractsA work contractor is fundamentally liable forensuring that his service is free of deficiencies.Compliance with the recognised engineering rulesis the decisive starting point for work and servicefree of deficiencies. Relevant national standardsare used here in order to fill the factual character-istic of the “recognised engineering rules” withlife. If the relevant standards are complied with, itis presumed that the work and service is free fromdeficiencies. The practical significance of such aprima facie evidence lies in the fact that a cus-tomer who lodges a complaint of non-conformservice by the work contractor (for example for theinstallation of a lightning protection system) hasbasically little chance of success if the work con-tractor can show that he complied with the rele-vant technical standards. As far as this effect is con-cerned, standards and prestandards carry equalweight. The effect of the presumption of technicalstandards is removed, however, if either the stan-dards are withdrawn , or it is proven that the actu-al standards no longer represent the state of theart. Standards cannot statically lay down the stateof the recognised engineering rules in tablets ofstone, as technical requirements and possibilities

are continually changing. So, if standards are with-drawn and replaced with new standards or pre-standards, then it is primarily the new standardswhich then correspond to the state of the art.Contractors and those placing an order for workregularly agree that the work must conform to thegeneral state of the art without the need to makespecific mention of this. If the work shows a nega-tive deviation from this general state of the art, itis faulty. This can result in a claim being madeagainst the contractor for material defect liability.The material defect liability only exists, however, ifthe work was already faulty at the time of accept-ance! Circumstances occurring subsequently – suchas a further development of the state of the art –do not belatedly make the previously accepted,defect-free work faulty!For the question of the deficiency of work andservice, the state of the recognised engineeringrules at the time of the acceptance is the soledeciding factor.Since, in future, only the new lightning protectionstandards will be relevant at the time of comple-tion and acceptance of lightning protection sys-tems, they have to be installed in accordance withthese standards. It is not sufficient that the serviceconformed to the engineering rules at the time itwas provided, if, between completion of a con-tract, service provision and acceptance of the con-struction work, the technical knowledge andhence the engineering rules have changed.Hence works which have been previously installedand already accepted under the old standards donot become defective because, as a result of theupdating of the standards, a “higher technicalstandard” is demanded.

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SPDs which withstand the partial lightning current with a typical waveform10/350 μs require a corresponding impulse test current IimpThe suitable test current Iimp is defined in the Class I test procedure of IEC 61643-1

Definition acc.to IEC 61643

SPD class II

SPD class III

SPD class I

SPDs which withstand induced surge currents with a typical waveform8/20 μs require a corresponding impulse test current InThe suitable test current In is defined in the Class II test procedure of IEC 61643-1

SPDs that withstand induced surge currents with a typical waveform8/20 μs and require a corresponding impulse test current IscThe suitable combination wave test is defined in the Class III test procedure of IEC 61643-1

Definition acc.to EN 61643

SPD Type 2

SPD Type 3

SPD Type 1

Table 1.1.2 Equivalents for SPD classifications (In the following the Lightning Protection Guide uses the designation SPD Type 1, SPD Type 2,SPD Type 3)

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With the exception of lightning protection systemsfor nuclear facilities, lightning protection systemshave only to conform to the state of the art at thetime they are installed, i.e. they do not have to beupdated to the latest state of the art. Existing sys-tems are inspected in the course of maintenancetests according to the standards in force at thetime they were installed.

1.3 Product standards

Materials, components and units for lightning pro-tection systems must be designed and tested forthe electrical, mechanical and chemical stresseswhich have to be expected during their use. Thisaffects both the components of the external light-ning protection as well as units of the internallightning protection system.

EN 50164-1: Requirements for connection components

This standard describes inspection and test proce-dures for metal connecting units. Units fallingwithin the scope of this standard are:

⇒ Clamps

⇒ Connectors

⇒ Terminal components

⇒ Bridging components

⇒ Expansion pieces

⇒ Measuring points

Our clamps and connectors meet the requirementsof this standard.

EN 50164-2: Requirements for conductors and earth electrodesThis standard specifies the requirements on con-ductors, air-termination rods, lead-in componentsand earthing electrodes.

EN 61643-11: Surge protective devices connected to low voltagesystemsSince 1 December 2002, the requirements on, andinspections of, surge protective devices in low volt-age systems have been governed by EN 61643-11.This product standard is the result of internationalstandardisation as part of IEC and CENELEC.

EN 61643-21: Surge protective devices connectedto telecommunications and signalling networksThis standard describes the performance require-ments and testing methods for surge protectivedevices used for the protection of telecommunica-tions and signal processing networks including e.g.

⇒ data networks,

⇒ voice transmission networks,

⇒ alarm systems,

⇒ automation systems.

CLC/TS 61643-22 (IEC 61643-22:2004, modified):2006-04; Low-voltage surge protective devices,Part 22:Surge protective devices connected to telecommu-nications and signalling networks - Selection andapplication principles

EN 61663-1Lightning protection - Telecommunication lines -Fibre optic installations

EN 61663-2Lightning protection - Telecommunication lines -Lines using metallic conductors

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2. Characteristics of lightning current

2.1 Lightning discharge and sequenceof lightning current

Every year, an average of around 1.5 million light-ning strikes discharge over Germany. For an areaof 357,042 km2 this corresponds to an averageflash density of 4.2 lightning discharges per squarekilometre per year. The actual lightning density,however, depends to a large extent on geographicconditions. An initial overview can be obtainedfrom the lightning density map contained in Fig-ure 3.2.3.1. The higher the resolution of the light-ning density map, the more accurate the informa-tion it provides about the actual lightning fre-quency in the area under consideration.Using the BLIDS Blitzinformationsdienst vonSiemens (lightning information service bySiemens), it is now possible to locate lightning towithin 200 m in Germany. For this purpose, eight-een measuring outposts are spread throughoutthe country. They are synchronised by means ofthe highly accurate time signal of the global posi-tioning system (GPS). The measuring posts recordthe time the electromagnetic wave produced bythe lightning discharge arrives at the receiver.From the differences in the times of arrival of theelectromagnetic wave recorded by the variousreceivers, and the corresponding differences in thetimes it takes the electromagnetic wave to travelfrom the location of the lightning discharge to thereceivers, the point of strike is calculated. The datadetermined in this way are filed centrally andmade available to the user in form of various pack-ages. Further information about this service can beobtained from www.blids.de.Thunderstorms come into existence when warmair masses containing sufficient moisture are trans-ported to great altitudes. This transport can occurin a number of ways. In the case of heat thunder-storms, the ground is heated up locally by intenseinsolation. The layers of air near the ground heatup and rise. For frontal thunderstorms, the inva-sion of a cold air front causes cooler air to bepushed below the warm air, forcing it to rise. Oro-graphic thunderstorms are caused when warm airnear the ground is lifted up as it crosses risingground. Additional physical effects furtherincrease the vertical upsurge of the air masses. Thisforms updraught channels with vertical speeds ofup to 100 km/h, which create towering cumu-lonimbus clouds with typical heights of 5 – 12 kmand diameters of 5 – 10 km.

Electrostatic charge separation processes, e.g. fric-tion and sputtering, are responsible for chargingwater droplets and particles of ice in the cloud. Positively charged particles accumulate in theupper part, and negatively charged particles in thelower part of the thundercloud. In addition, thereis again a small positive charge centre at the bot-tom of the cloud. This originates from the coronadischarge which emanates from sharp-pointedobjects on the ground underneath the thunder-cloud (e.g. plants), and is transported upwards bythe wind.

If the space charge densities, which happen to bepresent in a thundercloud, produce local fieldstrengths of several 100 kV/m, leader discharges(leaders) are formed which initiate a lightning dis-charge. Cloud-to-cloud flashes result in chargeneutralisation between positive and negativecloud charge centres, and do not directly strikeobjects on the ground in the process. The lightningelectromagnetic impulses (LEMP) they radiatemust be taken into consideration, however,because they endanger electrical and electronicsystems.

Fig. 2.1.1 Downward flash (cloud-to-earth flash)

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Lightning flashes to earth lead to a neutralisationof charge between the cloud charges and the elec-trostatic charges on the ground. We distinguishbetween two types of lightning flashes to earth:

⇒ Downward flash (cloud-to-earth flash)

⇒ Upward flash (earth-to-cloud flash)

In the case of downward flashes, leader dischargespointing towards the ground guide the lightningdischarge from the cloud to the earth. Such dis-charges usually occur in flat terrain and near lowbuildings and structures. Downward flashes can berecognised by the branching (Figure 2.1.1) which isdirected earthwards. The most common type oflightning is negative lightning flashes to earth,where a leader filled with negative cloud chargepushes its way from the thunder cloud to earth(Figure 2.1.2). This leader propagates in a series ofjerks with a speed of around 300 km/h in steps of afew 10 m. The interval between the jerks amountsto a few 10 μs. When the leader has drawn close tothe earth, (a few 100 m to a few 10 m), it causesthe strength of the electric field of objects on thesurface of the earth in the vicinity of the leader(e.g. trees, gable ends of buildings) to increase.The increase is great enough to exceed the dielec-

tric strength of the air. These objects involvedreach out to the leader by growing positivestreamers which then meet up with the leader, ini-tiating the main discharge.Positive flashes to earth can arise out of the lower,positively charged area of a thundercloud (Figure2.1.3). The ratio of the polarities is around 90 %negative lightning to 10 % positive lightning. Thisratio depends on the geographic location.On very high, exposed objects (e.g. radio masts,telecommunication towers, steeples) or on thetops of mountains, upward flashes (earth-to-cloud

leader leader

Fig. 2.1.2 Discharge mechanism of a negative downward flash(cloud-to-earth flash)

Fig. 2.1.3 Discharge mechanism of a positive downward flash(cloud-to-earth flash)

Fig. 2.1.4 Upward flash (earth-to-cloud flash)

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flashes) can occur. It can be recognised by theupwards-reaching branches of the lightning dis-charge (Figure 2.1.4). In the case of upwardflashes, the high electric field strength required totrigger a leader is not achieved in the cloud, butrather by the distortion of the electric field on theexposed object, and the associated high strengthof the electric field. From this location, the leaderand its charge channel propagate towards thecloud. Upward flashes occur with both negativepolarity (Figure 2.1.5) and also with positive pola-rity (Figure 2.1.6). Since, with upward flashes, theleaders propagate from the exposed object on thesurface of the earth to the cloud, high objects canbe struck several times by one lightning dischargeduring a thunderstorm.Objects struck by lightning are subject to higherstress by downward flashes (cloud-to-earthflashes) than by upward flashes (earth-to-cloudflashes). The parameters of downward flashes aretherefore taken as the basis when designing light-ning protection measures.Depending on the type of lightning flash, eachlightning discharge consists of one or more partialstrikes of lightning. We distinguish between shortstrikes with less than 2 ms duration and longstrikes with a duration of more than 2 ms. Further

distinctive features of partial lightning strikes aretheir polarity (negative or positive), and their tem-poral position in the lightning discharge (first, sub-sequent or superimposed partial strikes of light-ning). The possible combinations of partial light-ning strikes are shown in Figure 2.1.7 for down-ward flashes, and Figure 2.1.8 for upward flashes.The lightning currents consisting of both impulsecurrents and continuing currents are load-inde-pendent currents, i.e. the objects struck exert noeffect on the lightning currents. Four parametersimportant for lightning protection technology canbe obtained from the lightning current profilesshown in Figure 2.1.7 and 2.1.8:

⇒ The peak value of lightning current I

⇒ The charge of the lightning current Qflash, com-prising the charge of the short strike Qshort andthe charge of the long strike Qlong

⇒ The specific energy W/R of the lightning cur-rent

⇒ The steepness di/dt of the lightning current.

The following chapters show which of the individ-ual efficiency parameters are responsible for whicheffects, and how they influence the dimensioningof lightning protection systems.

leader leader

Fig. 2.1.5 Discharge mechanism of a negative upward flash (earth-to-cloud flash)

Fig. 2.1.6 Discharge mechanism of a positive upward flash (earth-to-cloud flash)

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±I

long-time current

positive or negative t

−I

negative t

±I

first impulse current

positive or negative t

−I

sequential impulse currents

negative t

±I

short stroke

positive or negative t

−I

subsequentshort strokes

negative t

first long stroke

superimposedshort strokes

±I

positive or negative t

single longstroke

±I

long stroke

positive or negative t

−I

negative t

Fig. 2.1.7 Possible components of downward flashes

Fig. 2.1.8 Possible components of upward flashes

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2.2 Peak value of lightning currentLightning currents are load-independent currents,i.e. a lightning discharge can be considered analmost ideal current source. If a load-independentactive electric current flows through conductivecomponents, the amplitude of the current, and theimpedance of the conductive component the cur-rent flows through, help to regulate the potentialdrop across the component flown through by thecurrent. In the simplest case, this relationship canbe described using Ohm´s Law.

U I R= ⋅

If a current is formed at a single point on a homo-geneously conducting surface, the well-knownpotential gradient area arises. This effect alsooccurs when lightning strikes homogeneousground (Figure 2.2.1). If living beings (people oranimals) are inside this potential gradient area, astep voltage is formed which can cause a shock cur-rent to flow through the body (Figure 2.2.2). Thehigher the conductivity of the ground, the flatterthe shape of the potential gradient area. The riskof dangerous step voltages is thus also reduced.If lightning strikes a building which is alreadyequipped with a lightning protection system, thelightning current flowing away via the earth-ter-mination system of the building gives rise to apotential drop across the earthing resistance RE ofthe earth-termination system of the building (Fig-ure 2.2.3). As long as all conductive objects in thebuilding, which persons can come into contactwith, are raised to the same high potential, per-sons in the building cannot be exposed to danger.This is why it is necessary for all conductive parts inthe building with which persons can come intocontact, and all external conductive parts entering

www.dehn.de18 LIGHTNING PROTECTION GUIDE

ϕ potential

r distance frompoint of strike

ϕ

r

Î

Û

Î

air-terminationsystem

down-conductorsystem

earth-termination systemwith earth resistance RE

remote earth

lightning current

time

curr

ent

Fig. 2.2.1 Potential distribution of a lightning strike into homoge-nous soil

Fig. 2.2.2 Animals killed by shock current due to hazardous stepvoltage

Fig. 2.2.3 Potential rise of the earth-termination system of a build-ing compared to the remote earth due to the peak valueof the lightning current

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the building, to have equipotential bonding. If thisis disregarded, there is a risk of dangerous shockhazard voltages if lightning strikes.The rise in potential of the earth-termination sys-tem as a result of the lightning current also createsa hazard for electrical installations (Figure 2.2.4).In the example shown, the operational earth ofthe low-voltage supply network is located outsidethe potential gradient area caused by the light-ning current. If lightning strikes the building, thepotential of the operational earth RB is thereforenot identical to the earth potential of the con-sumer system within the building. In the presentexample, there is a difference of 1000 kV. Thisendangers the insulation of the electrical systemand the equipment connected to it.

2.3 Steepness of lightning currentThe steepness of lightning current Δi/Δt, which iseffective during the interval Δt, determines theheight of the electromagnetically induced volt-ages. These voltages are induced in all open or

closed conductor loops located in the vicinity ofconductors through which lightning current isflowing. Figure 2.3.1 shows possible configura-tions of conductor loops in which lightning cur-rents could induce voltages. The square wave volt-age U induced in a conductor loop during theinterval Δt is:

M Mutual inductance of the loop

Δi/Δt Steepness of lightning current

As already described, lightning discharges com-prise a number of partial strikes of lightning. As faras the temporal position is concerned, a distinctionis made between first and subsequent short strikeswithin a lightning discharge. The main differencebetween the two types of short strikes consists inthe fact that, because the lightning channel has tobe built, the gradient of the lightning current ofthe first short strike is not as steep as that of thesubsequent short strike, which can use an existing,

U M i t= ⋅ / Δ Δ

distance r

1000 kV

UE

L1 L2 L3 PEN

RE = 10 Ω UE

I = 100 kAsubstation

RB 100% lightning current90%

10%

front time T1

U

T1

induced square-wave voltage

time

time

curr

ent

volta

ge

Î

s 3

s2

s 1

1

2

3

1 Loop in the down con-ductor with potentialflashover distance s1

2 Loop in the down con-ductor and installationcable with potentialflashover distance s2

3 Installation loop withpotential flashoverdistance s3

Î / T1building down conductor

Fig. 2.2.4 Threat to electrical installations by potential rise at theearth-termination system

Fig. 2.3.1 Induced square-wave voltage in loops via the currentsteepness Δi/Δt of the lightning current

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fully conductive lightning channel. The steepnessof lightning current of the subsequent lightningstrike is therefore used to assess the highestinduced voltage in the conductor loops. An example of how to assess the induced voltagein a conductor loop is shown in Figure 2.3.2.

2.4 Charge of lightning currentThe charge Qflash of the lightning current is madeup of the charge Qshort of the short strike and thecharge Qlong of the long strike. The charge

of the lightning current determines the energydeposited at the precise striking point, and at allpoints where the lightning current continues in

Q idt= ∫

the shape of an electric arc along an insulatedpath. The energy W deposited at the base of theelectric arc is given by the product of the charge Qand the anode-/cathode voltage drop with valuesin the micrometer range UA,K (Figure 2.4.1).

The average value of UA,K is a few 10 V anddepends on influences such as the height andshape of the current:

Q Charge of lightning current

UA,K Anode/cathode voltage drop

Hence, the charge of the lightning current causesthe components of the lightning protection systemstruck by lightning to melt down. The charge isalso relevant for the stresses on isolating sparkgaps and protective spark gaps and by spark-gapbased surge protective devices.

Recent examinations have shown that, as the elec-tric arc acts for a longer time, it is mainly the con-tinuing charge Qlong of the continuing currentwhich is able to melt or vaporise large volumes ofmaterials. Figure 2.4.2 and 2.4.3 show a compari-son of the effects of the short strike charge Qshortand the long strike charge Qlong.

W Q UA K= ⋅ ,

10

1

0.1

0.01

0.001

0.1 · 10-3

0.01 · 10-3

0.1 0.3 1 3 10 30

Δ iΔ t

1

1

a

a

U

s

s (m)

a = 10 m

a = 3 m

a = 1 m

a = 0.1 m

a = 0.3 ma = 0.03 ma = 0.01 m

Example of calculationbased on an installation loop (e.g. alarm system)

From the above diagram results: M2 ≈ 4.8 μH

U = 4.8 · 150 = 720 kV

M2 (μH)

a

s

10 m

ΔiΔt

kAμs

3 m

150

(high requirement)

smelt metal

tip of the down conductor

Q

UA,K

time

lightningcurrent

Qshort = ∫idt

Qlong = ∫idt

long stroke current

time

curr

ent

curr

ent

Fig. 2.3.2 Example for calculation of induced square-wave voltagesin squared loops

Fig. 2.4.1 Energy deposited at the point of strike by the load of thelightning current

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2.5 Specific energyThe specific energy W/R of an impulse current isthe energy deposited by the impulse current in aresistance of 1 Ω. This energy deposition is theintegral of the square of the impulse current overthe time for the duration of the impulse current:

The specific energy is therefore often called thecurrent square impulse. It is relevant for the tem-perature rise in conductors through which a light-ning impulse current is flowing, as well as for theforce exerted between conductors flown throughby a lightning impulse current (Figure 2.5.1).

For the energy W deposited in a conductor withresistance R we have:

R (Temperature dependent) d.c. resistance ofthe conductor

W/R Specific energy

The calculation of the temperature rise of conduc-tors through which a lightning impulse current isflowing, can become necessary if the risks to per-sons, and the risks from fire and explosion, have tobe taken into account during the design andinstallation of lightning protection systems. Thecalculation assumes that all the thermal energy isgenerated by the ohmic resistance of the compo-

W R i dt R W R= ⋅ ∫ = ⋅ / 2

W R i dt/ = ∫ 2

0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100

Galvanised steel100 kA (10/350 μs)

Copper100 kA (10/350 μs)

10.00 mm

Aluminiumd = 0.5 mm; 200 A, 350 ms

10.00 mm

Copperd = 0.5 mm; 200 A, 180 ms

10.00 mm

Stainless steeld = 0.5 mm; 200 A, 90 ms

10.00 mm

Steeld = 0.5 mm; 200 A, 100 ms

10.00 mm

Galvanised steeld = 0.5 mm; 200 A, 100 ms

specific energyW/R

force onparallel

conductors

heatinglightningcurrent

time

specificenergy

force

Fig. 2.4.2 Effect of an impulse current arc on a metal surface

Fig. 2.4.3 Plates perforated by the effects of long-time arcs

Fig. 2.5.1 Heating and force effects by the specific energy of light-ning current

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nents of the lightning protection system. Further-more, it is assumed that, because of the brevity ofthe process, there is no perceptible heat exchangewith the surrounding. Table 2.5.1 lists the tempera-ture rises of different materials used in lightningprotection, and their cross sections, as a functionof the specific energy.

The electrodynamic forces F generated by a cur-rent i in a wire with a long, parallel section oflength I and a distance d (Figure 2.5.2) can be cal-culated as an approximation using the followingequation:

F(t) Electrodynamic force

i Current

μ0 Magnetic constant in air (4π ⋅ 10-7 H/m)

l Length of conductor

d Distance between the parallel conductors

The force between the conductors is attractive ifthe two currents flow in the same direction, andrepulsive if the currents flow in opposite direc-tions. It is proportional to the product of the cur-rents in the conductors, and inversely proportionalto the distance of the conductors. Even in the caseof a single, bent conductor, a force is exerted onthe conductor. Here, the force is proportional tothe square of the current in the bent conductor.The specific energy of the impulse current thusdetermines the load which causes a reversible orirreversible deformation of components and arraysof a lightning protection system. These effects aretaken into consideration in the test arrangementsof the product standards concerning the require-ments made on connecting components for light-ning protection systems.

2.6 Assignment of lightning currentparameters to lightning protec-tion levels

In order to define lightning as a source of interfer-ence, lightning protection levels I to IV are laiddown. Each lightning protection level requires aset of

⇒ maximum values (dimensioning criteria usedto design lightning protection components tomeet the demands expected to be made ofthem) and

⇒ minimum values (interception criteria neces-sary to be able to determine the areas withsufficient protection against direct lightningstrikes (radius of rolling sphere)).

F t μ i t l d( ) ( )= / ⋅ ⋅ / 022π

I

d

F

i i

F

i i

4 10 16 25 50 100Cross section[mm2]

AluminiumW/R [MJ/Ω]

IronW/R [MJ/Ω]

CopperW/R [MJ/Ω]

Stainlesssteel

W/R [MJ/Ω]

Mat

eria

l

2.5 – 564 146 52 12 3

5.6 – – 454 132 28 7

10 – – – 283 52 12

2.5 – – 1120 211 37 9

5.6 – – – 913 96 20

10 – – – – 211 37

2.5 – 169 56 22 5 1

5.6 – 542 143 51 12 3

10 – – 309 98 22 5

2.5 – – – 940 190 45

5.6 – – – – 460 100

10 – – – – 940 190

Table 2.5.1 Temperature rise ΔT in K of different conductor mate-rials

Fig. 2.5.2 Electrodynamic effect between parallel conductors

Page 24: Lightning Protection Guide

The Tables 2.6.1 and 2.6.2 show the assignment ofthe lightning protection levels to maximum andminimum values of the lightning current parame-ters.

www.dehn.de LIGHTNING PROTECTION GUIDE 23

Lightningprotection

level

Max.lightningcurrent

peak value

Probability ofthe actually

upcoming light-ning current tobe less than themax. lightningcurrent peak

value

I

II

III

IV

200 kA

150 kA

100 kA

100 kA

99 %

98 %

97 %

97 %

Maximum values(Dimensioning criteria)

Lightningprotection

level

Min.lightning

current peakvalue

Probability ofthe actually

upcoming light-ning current tobe higher thanthe min. light-ning currentpeak value

Radiusof therollingsphere

I

II

III

IV

3 kA

5 kA

10 kA

16 kA

99 %

97 %

91 %

84 %

20 m

30 m

45 m

60 m

Minimum values(Interception criteria)

Table 2.6.1 Maximum values of lightning current parameters andtheir probabilities

Table 2.6.2 Minimum values of lightning current parameters andtheir probabilities

Page 25: Lightning Protection Guide

3.1 Necessity of a lightning protec-tion system – legal regulations

The purpose of a lightning protection system is toprotect buildings from direct lightning strikes andpossible fire, or from the consequences of theload-independent active lightning current (non-igniting flash of lightning).If national regulations, e.g. building regulations,special regulations or special directives requirelightning protection measures, they must beinstalled.Unless these regulations contain specifications forlightning protection measures, a lightning protec-tion system (LPS) Class III meeting the require-ments of IEC 62305-3 (EN 62305-3) is recommend-ed as minimum.

Otherwise, the need for protection and the choiceof appropriate protection measures, should bedetermined by risk management.The risk management is described in IEC 62305-2(EN 62305-2) (see subclause 3.2.1).

Of course other additional corresponding nationalstandards and legal requirements may be applica-ble and have to be taken into account. In the fol-lowing some examples of German directives, stan-dards and legal regulations.

In Germany further information on how to deter-mine the type of lightning protection systems forgeneral buildings and structures can be found inthe following directive of the VdS:

⇒ VdS-Richtlinie 2010 “Risikoorientierter Blitz-und Überspannungsschutz, Richtlinien zurSchadenverhütung”. [engl.: “Risk orientatedlightning and surge protection, guideline forprevention of damage”]

For example, the building regulations of the Stateof Hamburg (HbauO § 17, Abs. 3) require a light-ning protection system to be installed if lightningcan easily strike a building because of:

⇒ its length,

⇒ its height or

⇒ the use to which it is put,

or if

⇒ it is expected that a lightning strike wouldhave serious consequences.

This means:“A lightning protection system must be built evenif only one of the requirements is met.“

A lightning strike can have particularly seriousconsequences for buildings and structures owingto their location, type of construction or the use towhich they are put.A nursery school, for example, is a building wherea lightning strike can have serious consequencesbecause of the use to which the building is put.The interpretation to be put on this statement ismade clear in the following court judgement:

Extract from the Bavarian Administrative Court,decision of 4 July 1984 – No. 2 B 84 A.624.

1. A nursery school is subject to the requirementto install effective lightning protection sys-tems.

2. The legal requirements of the building regula-tions for a minimum of fire-retardant doorswhen designing staircases and exits also applyto a residential building which houses a nurs-ery school.

For the following reasons:According to the Bavarian building regulations,buildings and structures whose location, type ofconstruction or the use to which they are put,make them susceptible to lightning strikes, orwhere such a strike can have serious consequences,must be equipped with permanently effectivelightning protection systems. This stipulates therequirement for effective protective devices in twocases. In the first case, the buildings and structuresare particularly susceptible to lightning strikes(e.g. because of their height or location); in theother case, any lightning strike (e.g. because of thetype of construction or the use to which it is put)can have particularly serious consequences. Theplaintiff´s building falls within the latter categorybecause of its present use as a nursery school. Anursery school belongs to the group of buildingswhere a lightning strike can have serious conse-quences because of the use to which the buildingis put. It is of no consequence that, in the annota-tions to the Bavarian building regulations, nurseryschool are not expressly mentioned in the illustra-tive list of buildings and structures which are par-ticularly at risk, alongside meeting places.

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3. Designing a lightning protection system

Page 26: Lightning Protection Guide

The risk of serious consequences if lightning strikesa nursery school arises because, during the day, alarge number of children under school age arepresent at the same time.

The fact that the rooms where the children spendtheir time are on the ground floor, and that thechildren could escape to the outside through seve-ral windows – as put forward by the plaintiff – isnot a deciding factor. In the event of fire, there isno guarantee that children of this age will reactsensibly and leave the building via the windows ifnecessary. In addition, the installation of sufficientlightning protection equipment is not too much toexpect of the operator of a nursery school. A fur-ther section of the Bavarian building regulationsrequires that, amongst other things, staircasesmust have entrances to the cellar which have self-closing doors which are, at least, fire-retardant.The requirements do not apply to residentialbuildings with up to two flats. The respondentonly made the demand when the plaintiff convert-ed the building, which was previously residential,into a nursery school as well, in accordance withthe authorised change of use. The exemption pro-vision cannot be applied to buildings which werebuilt as residential buildings with up to two flats,but which now (also) serve an additional purposewhich justifies the application of the safetyrequirements.

Serious consequences (panic) can also arise whenlightning strikes assembly rooms, schools, hospi-tals.For these reasons, it is necessary that all buildingsand structures which are at risk of such events areequipped with permanently effective lightningprotection systems.

Lightning protection systems always requiredBuildings and structures where a lightning protec-tion system must always be included because, inthese cases, the German law has affirmed theneed, are

1. Assembly places with stages or covered stageareas and assembly places for the showing offilms, if the accompanying assembly rooms ineach case, either individually or together, canaccommodate more than 100 visitors;

2. Assembly places with assembly rooms whichindividually or together can accommodate

more than 200 visitors; in the case of schools,museums and similar buildings, this regula-tion only applies to the inspection of techni-cal installations in assembly rooms whichindividually can accommodate more than 200visitors, and their escape routes;

3. Sales areas whose sales rooms have morethan 2000 m2 of floor space;

4. Shopping centres with several sales areaswhich are connected to each other eitherdirectly or via escape routes, and whose salesrooms individually have less than 2000 m2 offloor space but having a total floor space ofmore than 2000 m2;

5. Exhibition spaces whose exhibition roomsindividually or together have more than 2000m2 of floor space;

6. Restaurants with seating for more than 400customers, or hotels with more than 60 bedsfor guests;

7. High-rise buildings as defined in the Ham-burg building regulations (HbauO);

8. Hospitals and other buildings and structureshaving a similar purpose;

9. Medium-sized and large-scale garages asdefined in the Hamburg regulations forgarages (Hamburgisches Gesetz- und Verord-nungsblatt);

10. Buildings and structures

10.1 with explosive materials, such as ammunitionfactories, depots for ammunition and explo-sives,

10.2 with factory premises which are at risk ofexplosion, such as varnish and paint factories,chemical factories, larger depots of com-bustible liquids and larger gas holders,

10.3 particularly at risk of fire, such as

– larger woodworking factories,

– buildings with thatched roofs, and

– warehouses and production plants with ahigh fire load,

10.4 for larger numbers of people such as

– schools,

– homes for the elderly and children´s homes,

– barracks,

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Page 27: Lightning Protection Guide

– correctional facilities

– and railway stations,

10.5 with cultural assets, such as

– buildings of historic interest,

– museums and archives,

10.6 towering above their surroundings, such as

– high chimneys,

– towers

– high buildings.

The following list provides an overview of the rel-evant “General Provisions” in Germany which dealwith the issue of requirement, design and inspec-tion of lightning protection systems.

General international and national (German) pro-visions:

DIN 18384: 2000-12Contract procedure for building worksPart C: General technical specifications for buildingworks; Lightning protection systems

Lightning protection systems:

Standardleistungsbuch für das Bauwesen (StLB)Leistungsbereich 050, Blitzschutz- und Erdungsan-lagen (Translation: Standard services book for theconstruction industry, Service sector 050, lightningprotection and earth-termination systems)The purpose of this standard services book is toensure conformity of the texts used in the servicedescriptions, and also to facilitate data processing. The texts are used for public tenders by all buildingauthorities, and by federal, state and local govern-ments.

IEC 62305-1: 2006-01EN 62305-1: 2006-02Lightning protection – Part 1: General principles

IEC 62305-2: 2006-01EN 62305-2: 2006-02Lightning protection – Part 2: Risk management

IEC 62305-3: 2006-01EN 62305-3: 2006-02Lightning protection – Part 3: Physical damage tostructures and life hazard

IEC 62305-4: 2006-01EN 62305-4: 2006-02Lightning protection – Part 4: Electrical and elec-tronic systems within structures

DIN 48805 ... 48828Components for external lightning protectionThis series of standards specifies dimensions andmaterial thicknesses.It is being replaced step by step by the followingstandard.

EN 50164-1: 1999-09Lightning protection components (LPC)Part 1: Requirements for connection componentsDefines the requirements which metal connectioncomponents such as connectors, terminals andbridging components, expansion pieces and meas-uring points for lightning protection systems haveto meet.

EN 50164-2: 2002-08Lightning protection components (LPC)Part 2: Requirements for conductors and earthelectrodesThis standard describes, for example, dimensionsand tolerances for metal conductors and earthelectrodes as well as the test requirements to theelectrical and mechanical values of the materials.

Special standards for earth–termination systems:

DIN 18014: 2007-09Foundation earth electrode – General planning cri-teria

DIN VDE 0151: 1986-06Material and minimum dimensions of earth elec-trodes with respect to corrosionThis VDE guideline applies to corrosion protectionwhen installing and extending earth electrodesand earthing-termination systems. It providesinformation on how to avoid or reduce the risk ofcorrosion to earth electrodes and with earth elec-trodes of other systems installed. Moreover, it pro-vides information to assist in making the correctchoice of earth electrode materials, and also aboutspecial anticorrosion measures.

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Page 28: Lightning Protection Guide

EN 50162: 2004-08Protection against corrosion by stray current fromdirect current systemsAmong others this standard requires that forunderground storage tanks being electrically sepa-rated from the electrical installation in the houseby insulating parts, the connection between thetank and the lightning protection system must beeffected via an isolating spark gap.

HD 637 S1: 1999-05Power installations exceeding 1 kV

EN 50341-1: 2001-10Overhead electrical lines exceeding a.c. 45 kV – Part 1: General requirements; Common specifica-tions;Special consideration also is given to the require-ments of protection against lightning.Reference is made to the risk of back flashover,and a relationship is established between theimpulse earthing resistance of the mast or frame-work earthing, the impulse withstand voltage ofthe insulation and the peak value of the lightningcurrent.Furthermore attention is drawn to the fact that itis more effective to install several individual earthelectrodes (meshed or star-type earth electrodes)than a single, very long earth rod or surface earthelectrode.

Special standards for internal lightning and surgeprotection, equipotential bonding:

IEC 60364-4-41: 2005, modHD 60364-4-41: 2007Erection of power installations – Part 4-41: Protec-tion against electric shock

IEC 60364-5-54: 2002, modHD 60364-5-54: 2007Erection of low voltage installations – Part 5-54:Selection and erection of electrical equipment –earthing arrangements, protective conductors,equipotential bonding.

IEC 60364-5-53/A2: 2001IEC 64/1168/CDV: 2001-01Erection of low voltage installations – Part 5: Selec-tion and erection of electrical equipment; Chapter53: Switchgear and controlgear; Section 534:

Devices for protection against overvoltages;Amendment A2This standard deals with the use of surge protec-tive devices Type I, II and III in low-voltage con-sumer’s installations in accordance with the pro-tection at indirect contact.

IEC 60364-4-44: 2001 + A1: 2003, modHD 60364-4-443: 2006Erection of low voltage installations – Part 4: Pro-tection for safety; Chapter 44: Protection againstovervoltages; Section 443: Protection against over-voltages of atmospheric origin or due to switching.

IEC 109/44/CD: 2005EN 60664-1: 2003-04Isolation coordination for equipment within low-voltage systems – Part 1: Principles, requirementsand tests (IEC 60664-1: 1992 + A1: 2000 + A2: 2002)This standard defines the minimum insulation dis-tances, their selection and the rated impulse volt-ages for overvoltage categories I to IV.

VDEW Directive: 2004-08(German Directive)Surge protective devices Type 1 – Use of surge pro-tective devices (SPD) Type 1 (previously Class B) inthe upstream area of the meter.Describes the use and the installation of surge pro-tective devices Type 1 in the upstream area of themeter.

Especially for electronic systems such as televi-sion, radio, data systems technology (telecommu-nications systems):

IEC 60364-5-548: 1996Electrical installations of buildings – Part 5: Selec-tion and erection of electrical equipment – Section548: Earthing arrangements and equipotentialbonding for information technology installations.

IEC/DIS 64(CO)1153: 1981MOD IEC 60364-4-41: 1982Earthing and equipotential bondingPart 2 summarises all requirements on the functionof a telecommunications system with respect toearthing and equipotential bonding.

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Page 29: Lightning Protection Guide

DIN VDE 0800-10: 1991-03(German standard)Transitional requirements on erection and opera-tion of installationsPart 10 contains requirements for the installation,extension, modification and operation of telecom-munications systems. Section 6 of this part laysdown the requirements for surge protective meas-ures.

IEC 61643-21: 2000-08 + Corrigendum: 2001EN 61643-21: 2001-07Low-voltage surge protective devices – Part 21:Surge protective devices connected to telecommu-nications and signalling networks; Performancerequirements and testing methods.

IEC 60728-11: 2005-01EN 60728-11: 2005-05Cable networks for television signals, sound signalsand interactive services – Part 11: Safety Part 11 requires measures to protect againstatmospheric discharges (earthing of the antennamounting, equipotential bonding).

VDE 0855 Part 300: 2002-07(German standard)Transmitting / receiving systems for transmitter RFoutput power up to 1 kW; Safety requirementsSection 12 of Part 300 describes the lightning andsurge protection and the earthing of antenna sys-tems.

IEC 61663-1: 1999-07EN 61663-1: 1999-11Lightning protection – Telecommunication lines,Part 1: Fibre optic installationsOn this subject, the standard describes a methodfor calculating the possible number of incidencesof damage for selecting the protective measureswhich can be used, and gives the permissible fre-quency of incidences of damage. Only primaryfaults (interruption of operations) and not second-ary faults (damage to the cable sheath (formationof holes)), however, are considered.

IEC 61663-2: 2001-03EN 61663-2: 2001-06Lightning protection – Telecommunication lines,Part 2: Lines using metallic conductors.

This standard must only be applied to the light-ning protection of telecommunication and signallines with metal conductors which are located out-side buildings (e.g. access networks of the landlineproviders, lines between buildings).

Special installations:

EN 1127-1: 1997-08Explosive atmospheres – Explosion prevention andprotection – Part 1: Basic concepts and method-ologyThis standard is a guide on how to prevent explo-sions, and protect against the effects of explosionsby employing measures during the drafting anddesign of devices, protection systems and compo-nents.Part 1 requires also protection against the effectsof a lightning strike which put the installations atrisk.

pr EN 1127-1: 2004-12Explosive atmospheres – Explosion prevention andprotection – Part 1: Basic concepts and method-ology.

IEC 60079-14: 2002EN 60079-14: 2003-08Electrical apparatus for explosive gas atmos-pheres – Part 14: Electrical installations in haz-ardous areas (other than mines)Section 6.5 draws attention to the fact that theeffects of lightning strikes must be taken into con-sideration.Section 12.3 describes the detailed stipulations forinstallations for the ex zone 0.Extremely extensive equipotential bonding isrequired in all ex zones.

IEC 31J/120/CDV: 2006pr EN 60079-14: 2006-06Explosive atmospheres – Part 14: Electrical installa-tions design, selection and erection

IEC 61241-17: 2005-01EN 61241-17: 2005-05Electrical apparatus for use in the presence of com-bustible dust – Part 17: Inspection and mainte-nance of electrical installations in hazardous areaswith explosive atmospheres (other than mines)

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Page 30: Lightning Protection Guide

VDE document series 65: “Elektrischer Explosions-schutz nach DIN VDE 0165“; VDE Verlag Berlin[engl.: “Electrical explosion protection accordingto DIN VDE 0165”], Annex 9: “PTB-Merkblatt fürden Blitzschutz an eigensicheren Stromkreisen, diein Behälter mit brennbaren Flüssigkeiten einge-führt sind“ [engl.: “PTB bulletin for protection ofintrinsically safe circuits installed in containerswith flammable liquids against lightning”]

In Germany standards can be obtained from thefollowing addresses:

VDE VERLAG GMBHBismarckstraße 3310625 BerlinGermanyPhone: +49 30 34 80 01-0Fax: +49 30 341 70 93eMail: [email protected]: www.vde-verlag.de

or

Beuth-Verlag GmbHBurggrafenstraße 4-1010787 BerlinGermanyPhone: +49 30 2601-2240Fax: +49 30 2601-1724Internet: www.din.de/beuth

3.2 Assessment of the risk of dam-age and selection of protectivecomponents

3.2.1 Risk managementRisk management with foresight includes calculat-ing the risks for the company. It provides the basison which decisions can be made in order to limitthese risks, and it makes clear which risks should becovered by insurance. When considering the man-agement of insurances, it should be borne in mind,however, that insurance is not always a suitablemeans of achieving certain aims (e.g. maintainingthe ability to deliver). The probabilities that cer-tain risks will occur cannot be changed by insur-ance.Companies which manufacture or provide servicesusing extensive electronic installations (and nowa-days this applies to most companies), must alsogive special consideration to the risk presented bylightning strikes. It must be borne in mind that thedamage caused by the non-availability of electron-ic installations, production and services, and alsothe loss of data, is often far greater than the dam-age to the hardware of the installation affected.In the case of lightning protection, innovativethinking about damage risks is slowly gaining inimportance. The aim of risk analysis is to objectifyand quantify the risk to buildings and structures,and their contents, as a result of direct and indirectlightning strikes. This new way of thinking hasbeen embodied in the international standard IEC 62305-2: 2006 or the European standard EN62305-2: 2006.

The risk analysis presented in IEC 62305-2 (EN62305-2) ensures that it is possible to draw up alightning protection concept which is understoodby all parties involved, and which meets optimumtechnical and economic requirements, i.e. the ne-cessary protection can be guaranteed with as littleexpenditure as possible. The protective measureswhich result from the risk analysis are thendescribed in detail in the later parts of the stan-dard, in the new IEC 62305 (EN 62305) series.

3.2.2 Fundamentals of risk assessmentAccording to IEC 62305-2 (EN 62305-2), risk R oflightning damage can generally be found usingthe relationship:

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Fig. 3.2.3.1 Lightning density in Germany (average of 1999 – 2005)

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N Number of hazardous events, i.e. frequency oflightning strikes in the area under considera-tion (How many lightning strikes occur peryear in the area under consideration?);

P Probability of damage (What is the probabilitythat a lightning strike causes a quite specifictype of damage?);

L Loss, i.e. the quantitative evaluation of thedamage (What are the effects, amount of loss,extent, and consequences of a very specifictype of damage?).

The task of the risk assessment therefore involvesthe determination of the three parameters N, Pand L for all relevant risk components. Thisinvolves establishing and determining of manyindividual parameters. A comparison of the risk Rthus established with a tolerable risk RT thenenables a statement to be made about the require-ments and the dimensioning of lightning protec-tion measures.An exception is the consideration of the economiclosses. For this kind of damage the protectivemeasures have to be justified strictly by the eco-nomical point of view. There is no tolerable risk RT,but rather a cost-benefit analysis. An exception isthe consideration of the economic losses. For thiskind of damage the protective measures have tobe justified strictly by the economical point ofview. There is no tolerable risk RT, but rather acost-benefit analysis.

3.2.3 Frequency of lightning strikesWe distinguish between the following frequenciesof lightning strikes which can be relevant for abuilding or structure:

R N P L= ⋅ ⋅ ND Frequency of direct lightning strikes to thebuilding or structure;

NM Frequency of close lightning strikes with elec-tromagnetic effects;

NL Frequency of direct lightning strikes in utilitylines entering the building or structure;

NI Frequency of lightning strikes adjacent to util-ity lines entering the building or structure.

The calculation of the frequencies of lightningstrikes is given in detail in Annex A of IEC 62305-2(EN 62305-2). For practical calculations it is re-commendable to take the annual density of thecloud-to-earth flashes Ng for the region under con-sideration from Figure 3.2.3.1. If a finer grid isused, the local values of the lightning densities canstill deviate noticeably from these averages.Owing to the relatively short time of seven yearsthe map has been recorded, and to the large areaaveraging according to licence plate numberareas, the application of a safety factor of 25 % tothe values given in Figure 3.2.3.1 is recommended.

For the frequency of direct lightning strikes ND tothe building or structure we have:

Ad is the equivalent interception area of the isolat-ed building or structure (Figure 3.2.3.2), Cd a sitefactor so that the influence of the surroundings(built-up, terrain, trees, etc.) can be taken intoaccount (Table 3.2.3.1).

Similarly, the frequency of close lightning strikesNM can be calculated:

N N AM g m= ⋅ ⋅ 10-6

N N A CD g d d= ⋅ ⋅ ⋅ 10-6

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Relative site of the building or structure Cd

Object is surrounded by higher objects or trees 0.25

Object is surrounded by objects or trees of the same or lower height 0.5

Free-standing object: no further objects near by (within a distance of 3H) 1

Free-standing object on top of a moutain or a rounded hilltop 2

Table 3.2.3.1 Site factor Cd

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Am is arrived at by drawing a line at a distance of250 m around the building or structure (Figure3.2.3.3). The equivalent interception area Ad Cd ofthe building or structure estimated using the envi-ronmental coefficients is then subtracted from thearea thus enclosed. Lightning strikes on the areaAm lead exclusively to magnetically induced surgesin installation loops in the interior of the buildingor structure.

The frequency of direct lightning strikes in a utilityline entering a building or structure NL is:

The area Al (Figure 3.2.3.3) is a function of the typeof line (overhead line, cable), the length LC of theline; in the case of cables, it is a function of theearth resistivity ρ; and for overhead lines it is a function of height HC of the line above groundlevel (Table 3.2.3.2). If the length of the line is notknown, or if it is very time-consuming to ascertainit, then, as a worst-case scenario, a value of LC = 1000 m can be set.

HC Height (m) of the line above ground level;

ρ Earth resistivity (Ωm) in, or on, which the line islaid, up to a maximum value of ρ = 500 Ωm;

LC Length (m) of the line, measured from thebuilding or structure to the first distributionjunction, or to the first location where surge

N N A C CL g l e t= ⋅ ⋅ ⋅ ⋅ 10-6

protective devices are installed, up to a maxi-mum length of 1000 m;

H Height (m) of the building or structure;

Hb Height (m) of the building or structure;

Ha Height (m) of the neighbouring building orstructure connected via the line.

If, within the area Al there is a medium voltageline rather than a low voltage one, then a trans-former reduces the intensity of the surges at theentrance to the building or structure. In such cases,this is taken into account by the correction factorCt = 0.2. The correction factor Ce (environment fac-tor) is ultimately a function of the building density(Table 3.2.3.3).

The frequency NL must be determined individuallyfor each utility line entering the building or struc-ture. In the building or structure under considera-tion, lightning strikes within the area Al lead, as arule, to a high energy discharge which can gener-ate a fire, an explosion, a mechanical or chemicalreaction. The frequency NL therefore, does notcomprise pure surges which result in faults or dam-age to the electrical and electronic systems, butmechanical and thermal effects which arise whenlightning strikes.

Surges to utility lines entering the building orstructure are described by the frequency of light-ning strikes next to such a utility line NI:

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3HW

L

H

1:3

Hb

Am

Ad

Al Ha

Aa

Ai

250 m

L

W

3Hb

3Ha

L a

Wa

Lc

2 .Di

end of con-ductor“b”

end of con-ductor“a”

Fig. 3.2.3.2 Equivalent interception area Adfor direct lightning strikes into astand-alone structure

Fig. 3.2.3.3 Equivalent interception areas Ad , Al , Aa for direct lightning strikes into structures/supply lines and Am , Ai for indirect lightning strikes near the structures/supply lines

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The area Ai (Figure 3.2.3.3) is again a function ofthe type of line (overhead line, undergroundcable), the length LC of the line; in the case ofcables, it is a function of the earth resistivity ρ; andfor overhead lines it is a function of the height HCof the line above ground level (Table 3.2.3.3). Thesame worst-case scenario applies. The area Ai isusually significantly larger than Al. This makesallowance for the fact that surges resulting infaults or damage to electrical and electronic sys-tems can also be caused by lightning strikes furtheraway from the line.

The correction factors Ct und Ce correspond tothose already stated above. The frequency Nl mustthen also be determined individually for each util-ity line entering the building or structure.

3.2.4 Probabilities of damage

The damage probability parameter gives the prob-ability that a supposed lightning strike will cause aquite specific type of damage. It is thereforeassumed that there is a lightning strike on the re-levant area; the value of the damage probabilitycan then have a maximum value of 1. We differen-tiate between the following eight damage proba-bilities:

PA Electric shock suffered by living beings as aresult of a direct lightning strike to the build-ing or structure;

PB Fire, explosion, mechanical and chemical reac-tions as a result of a direct lightning strike tothe building or structure;

PC Failure of electrical / electronic systems as aresult of a direct lightning strike to the build-ing or structure; PC = PSPD

PM Failure of electrical / electronic systems as aresult of a lightning strike to the ground nextto the building or structure;

PU Electric shock suffered by living beings as aresult of a direct lightning strike to the utilitylines entering the building or structure;

PV Fire, explosion, mechanical and chemical reac-tions as a result of a direct lightning strike to autility line entering the building or structure;

PW Failure of electrical / electronic systems as aresult of a direct lightning strike to a utilityline entering the building or structure;

PZ Failure of electrical / electronic systems as aresult of a lightning strike to the ground nextto a utility line entering the building or struc-ture.

This damage probabilities are presented in detailin Annex B of IEC 62305-2 (EN 62305-2). They canbe taken either directly from tables or they are theresulting function of a combination of further

N N A C Cl g i t e= ⋅ ⋅ ⋅ ⋅ − 10 6

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Table 3.2.3.2 Equivalent interception areas Al and Ai in m2

Table 3.2.3.3 Environment factor Ce

Underground cableOverhead line

Al

Ai

L H H HC a b C− ⋅ +( )⎡⎣ ⎤⎦ ⋅ ⋅3 6

1000 ⋅ LC

L H HC a b− ⋅ +( )⎡⎣ ⎤⎦ ⋅3 ρ

25 ⋅ ⋅LC ρ

Environment Ce

Urban with high buildings or structures (higher than 20 m) 0

Urban (buildings or structures of heights between 10 m and 20 m) 0.1

Suburban (buildings or structures not higher than 10 m) 0.5

Rural 1

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influence factors. There is no more subdivision intosimple (basic) probabilities and reduction factors.Some reduction factors now rather have beenassigned to the Annex C, i.e. to the losses, forexample PB and PC representing damage factors.Both parameter values are presented in Tables3.2.4.1 and 3.2.4.2. Attention still is drawn to thefact that also other, deviating values are possible,if based on detailed examinations or estimations.

3.2.5 Types of loss and sources of damageDepending on the construction, use and substanceof the building or structure, the relevant types ofdamage can be very different. IEC 62305-2 (EN62305-2) recognises the following four types ofdamage:

L1 Loss of human life (injury to, or death of, per-sons);

L2 Loss of services for the public;

L3 Loss of irreplaceable cultural assets;

L4 Economic losses.

The types of loss stated can arise as a result of thedifferent sources of damage: The sources of dam-age thus literally represent the “cause” in a causalrelationship, the type of loss the “effect” (seeTable 3.2.5.1). The possible sources of damage forone type of loss can be manifold. It is thereforenecessary to first define the relevant types of dam-age for a building or structure. It is then subse-quently possible to stipulate the sources of dam-age to be determined.

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Lightning protection level (LPL) Damage factor PSPD

No coordinated surge protection 1

III – IV 0.03

II 0.02

I 0.01

Surge protective devices (SPD) having a protective characteristic better than for 0.005 – 0.001LPL I (higher lightning current carrying capability, lower protection level, etc.)

Table 3.2.4.2 Damage factor PSPD to describe the protective measures surge protective devices as a function of the lightning protection level

Table 3.2.4.1 Damage factor PB to describe the protective measures against physical damage

Characteristics of building or structure Class of lightning PBprotection system (LPS)

Building or structure is not protected by LPS – 1

Building or structure is protected by LPS IV 0.2

III 0.1

II 0.05

Building or structure with air-termination system according to class of LPS and a 0.01metal facade or a concrete reinforcement as natural down conductor system

I 0.02

Building or structure with metal roof or with air-termination system, preferably 0.001including natural components, which protect all roof superstructues entirely againstdirect lightning strikes, and a metal facade or concrete reinforcement a naturaldown conductor system.

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Table 3.2.5.1 Sources of damage, types of damage and types of loss according to the point of strike

Point of Strike Sourceof damage

Typeof damage

Typeof loss

Example

Building or structure S1 D1

D2

D3

L1, L4b

L1, L2, L3, L4

L1a, L2, L4

Earth next to thestructure

S2 D3 L1a, L2, L4

Entering supply line S3 D1

D2

D3

L1, L4b

L1, L2, L3, L4

L1a, L2, L4

Earth next to theentering supply line

S4 D3 L1a, L2, L4

a For hospitals and buildings or structures with hazard of explosionb For agricultural properties (loss of animals)

Source of damage in relation to the point of strikeS1 Direct lightning strike to the building or structure;S2 Lightning strike to the earth near the building or structure;S3 Direct lightning strike to the entering supply line;S4 Lightning strike to the earth close to the entering supply line.

Type of damageD1 Electric shock to living beings as a result of contact and step voltage;D2 Fire, explosion, mechanical and chemical reactions as a result of the physical effects of the lightning discharge;D3 Failure of electrical and electronic sytems as a result of surges.

Type of lossL1 Injury to, or death of, persons;L2 Loss of services for the public;L3 Loss of irreplaceable cultural assets;L4 Economic losses.

Building or structure

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3.2.6 Loss factorIf a particular type of damage has occurred in abuilding or structure, then the effect of this dam-age must be assessed. It is possible, for example,for a fault or damage to a DP system (L4 type ofloss: economic losses) to have very different conse-quences. If no data appertaining to the business islost, then the claim will only be for the damage tothe hardware to the value of a few thousand Euro.If, however, the complete business of a company isdependent on the permanent availability of theDP system (call centre, bank, automation engineer-ing) then, in addition to the hardware damage,there is also disproportionately high consequentialdamage as a result of customer dissatisfaction, cus-tomers going to other suppliers, overlooked busi-ness processes, loss of production, etc.The effects of the damage are assessed using theloss factor L.

Basically divided up into the following:

Lt Loss by injury as a result of contact and stepvoltages;

Lf Loss as a result of physical damage;

Lo Loss as a result of failure of electrical and elec-tronic systems.

Depending on the relevant type of damage, thisenables the extent of the damage, its value or theconsequences to be assessed. Annex C of IEC62305-2 (EN 62305-2) gives the fundamentals ofthe calculation of the loss of the four types of dam-age. It is frequently the case, however, that it isextremely time-consuming to apply the equations.For usual cases, the aforementioned Annex Ctherefore also provides suggestions for typical val-ues for the damage factor L, depending on theunderlying causes of the damage.

In addition to the actual loss factors Annex C alsooutlines three reduction factors rx and an increas-ing factor h:

ra Reduction factor for effects of step and con-tact voltages depending on the kind of groundor floor;

r Reduction factor for measures to mitigate theconsequences of fire;

rf Reduction factor to describe the risk of fire toa building or structure;

h Factor increasing the relative value of a loss, ifthere is special hazard (e.g. as a result of pan-ic, potential endangering of the environmentby the building or structure).

Although shifted from IEC 62305-2 (EN 62305-2)Annex B (damage factors) to Annex C now, theparameter values, however, remained almostunchanged.

3.2.7 Relevant risk components for differentlightning strikes

There is close correlation between the cause of thedamage, the type of damage and the resulting rel-evant risk components. Initially, it serves to repre-sent the dependence on the point of strike of thelightning discharge, and the risk componentswhich are derived from this. If lightning directly strikes a building or structure,the following risk components arise (Table 3.2.7.1):

RA Risk component for electric shocks to livingbeings as a result of direct lightning strikes;

RB Risk component for physical damage as aresult of direct lightning strikes;

RC Risk of malfunctioning of electrical and elec-tronic systems as a result of surges caused bydirect lightning strikes.

If lightning strikes the earth near a building orstructure, or neighbouring buildings, the follow-ing risk component is created:

RM Risk of malfunctioning of electrical and elec-tronic systems as a result of surges caused bydirect lightning strikes to the ground next tothe building or structure.

If lightning directly strikes utility lines entering abuilding or structure, the following risk compo-nents arise:

RU Risk components for electric shocks to livingbeings in the event of direct lightning strikesto utility lines entering the building or struc-ture;

RV Risk components for physical damage in theevent of direct lightning strikes to utility linesentering the building or structure;

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RW Risk of failure of electrical and electronic sys-tems as a result of surges caused by directlightning strikes to utility lines entering thebuilding or structure.

If lightning eventually strikes the ground next tothe utility lines entering a building or structure,the following risk component is created:

RZ Risk of failure of electrical and electronic sys-tems as a result of surges caused by directlightning strikes to the ground next to the util-ity lines entering the building or structure.

The eight risk components in total (which basicallymust be determined individually for each type ofdamage) can now be combined according to twodifferent criteria: the point of strike of lightningand the cause of the damage.

If the combination according to the point of strikeis of interest, i.e. the evaluation of Table 3.2.7.1according to columns, then the risk

⇒ as a result of a direct lightning strike to thebuilding or structure is:

⇒ as a result of an indirect lightning strike nextto the building or structure is:

If, on the other hand, it is desired to investigatethe cause of the damage, then the risks can becombined as follows:

⇒ For electric shock to humans or animals as aresult of contact and step voltages:

R R Rs A U= +

R R R R R Ri M U V W Z= + + + +

R R R Rd A B C= + +

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S1

Direct lightningstrike into thestructure

S2

Lightning strikeinto the earthnext to the structure

S3

Direct lightningstrike into theentering supplyline

S4

Lightning strikeinto the earthnext to the ente-ring supply line

Direct Indirect

Lightning strike (with regard to the structure)

D1

Electric shock toliving beings

D2

Fire, explosions,mechanical andchemical effects

D3

Interferences onelectrical and electronic systems

Source ofdamage

Type ofdamage

RA = ND . PA . ra . LtRU = (NL + NDA) .

PU . ra . Lt

RC = ND . PC . Lo RM = NM . PM . Lo

Rs = RA + RU

Rf = RB + RV

Ro = RC + RM

+ RW+ RZ

Rd = RA + RB + RC Ri = RM + RU + RV + RW + RZ

RB = ND . PB . r . h .rf . Lf

RV = (NL + NDA) .PV . r . h . rf . Lf

RW = (NL + NDA) .PW . Lo

RZ = (NI – NL) .PZ . Lo

Table 3.2.7.1 In addition to the risk components RU , RV and RW , there is the frequency of direct lightning strikes into the supply line NL andthe frequency of direct lightning strikes into the connected building or structure NDA (compare Figure 3.2.3.3). In case of the riskcomponent RZ , however, the frequency of lightning strikes next to the supply line Nl has to be reduced by the frequency of directlightning strikes into the supply line NL.

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⇒ For fire, explosion, mechanical and chemicalreaction, caused by mechanical and thermaleffects of a lightning strike:

⇒ For failure of electrical and electronic systemsdue to surges:

R R R R Ro C M W Z= + + +R R Rf B V= +

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Types of loss RT

L1 Loss of human life (injury to, or death of, persons) 10-5/year

L2 Loss of services for the public 10-3 /year

L3 Loss of irreplaceable cultural asset 10-3 /year

Fig. 3.2.9.1 Flow chart for selection of protective measures for the types of loss L1 ... L3

Table 3.2.8.1 Typical values for the tolerable risk RT

Identify the building or structure to be protected

Identify the relevant types of damage

For the types of damage:Identify and calculate the risk components

RA, RB, RC, RM, RU, RV, RW, RZ

R > RT

Is LPSinstalled

Building or structureProtected

No

No

Yes

Is LPMSinstalled

Yes

No

RB > RT

Yes

Installcorresponding

type of LPS

Installcorresponding

LPMS

Installother

protective measures

No

Yes

Calculate newvalues of the risk

components

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3.2.8 Tolerable risk of lightning damageWhen making a decision on the choice of lightningprotection measures, one has to examine whetherthe damage risk R determined for each relevanttype of damage exceeds a tolerable (i.e. a stillacceptable) value RT or not. This, however, is onlyapplicable for the three types of loss L1 – L3, whichare of so-called public interest. For a building orstructure which is sufficiently protected againstthe effects of lightning, then must hold:

R represents the sum over all risk componentswhich are relevant for the respective type of lossL1 – L3:

IEC 62305-2 (EN 62305-2) provides acceptable max-imum values RT for these three types of loss (Table3.2.8.1).

3.2.9 Choice of lightning protection mea-sures

The measures for protection against lightning areintended to lead to the limiting of the damage riskR to values below the tolerable risk of damage RT.Using a detailed calculation of the damage risksfor the types of damage which are relevant to aspecific building or structure in each case, i.e. bydividing them into the individual risk componentsRA , RB , RC , RM , RU , RV , RW and RZ , it is possible tochoose lightning protection measures in anextremely targeted way. The flow chart in IEC 62305-2 (EN 62305-2) (Figure3.2.9.1) illustrates the procedure. Starting from thefact that the calculated damage risk R exceeds thetolerable damage risk RT, the first thing to beexamined is whether the risk of physical damagecaused by a direct lightning strike to a building orstructure RB exceeds the tolerable damage risk RT.If this is the case, a complete lightning protectionsystem with suitable external and internal light-ning protection must be installed. If RB is sufficient-ly small, the second step is to examine whether therisk can be sufficiently reduced by protective mea-

sures against the lightning electromagnetic pulse(LEMP).

Proceeding according to Figure 3.2.9.1 makes itpossible to choose those protective measureswhich lead to a reduction in the risk componentswhich have relatively high values in each case, i.e.protective measures whose degrees of effective-ness in the case under inspection are comparative-ly high.

3.2.10 Economic losses / Economic efficiencyof protective measures

The type of loss L4, economic losses, is relevant formany buildings or structures. Here it is no longerpossible to work with a tolerable risk of damageRT. One rather has to compare, whether the pro-tective measures are justifiable from an economi-cal point of view. Not an absolute parameter, suchas a specified tolerable risk of damage RT, is stan-dard of comparison, but a relative one: Differentstates of protection of the building or structure arecompared and the optimal solution, i.e. the cost ofdamage as a result of lightning strikes remainingas low as possible, will be realised. So several vari-ants can and shall be examined.

The basic procedure is represented in Figure3.2.10.1, Figure 3.2.10.2 shows the correspondingflow chart from IEC 62305-2 (EN 62305-2). At thebeginning this new method certainly will arousenew discussions among experts because it allows a(rough) estimation of costs even before the actualdesigning of lightning protection measures. Here adetailed and administered respective data basecan render good service.

Usually not only the type of loss L4, but also one orseveral of the other types of loss L1 – L3 are rele-vant for a building or structure. In these cases firstof all the proceeding represented in Figure 3.2.9.1is applicable, i.e. the damage risk R for the each ofthe losses L1 – L3 must be lower than the tolerabledamage risk RT. In this case a second step is toexamine the efficiency of the planned protectivemeasures according to Figure 3.2.10.1 and Figure3.2.10.2. Of course, also here again several variantsof protection are possible, the most favourableone finally to be realised, however, provided that

R RV= ∑

R RT≤

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for all relevant types of loss of public interest L1 – L3 is always R < RT.

3.2.11 SummaryIn practice, it is time-consuming and not alwayseasy to apply the procedures and data given. Thisshould not prevent the experts in the field of light-ning protection and, in particular, those at thesharp end, from studying this material. The quanti-tative assessment of the risk of lightning damagefor a building or structure is a considerableimprovement on the situation often encounteredbefore, where decisions for or against lightningprotection measures were frequently made solelyon the basis of subjective considerations whichwere not always understood by all parties.A quantitative assessment of this type is thereforean important pre-requirement for the decisionwhether to designate lightning protection meas-ures for a building or structure and, if so, to whatextent and which ones. In the long term it will thusmake a contribution to the acceptance of light-ning protection and damage prevention.

Author of Chapters 3.2.1 – 3.2.11:Prof. Dr.-Ing. Alexander KernAachen Technical College, Abt. JülichGinsterweg 152428 JülichGermanyPhone: +49 (0)241/6009-53042Fax: +49 (0)241/[email protected]

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Calculate all risk components RXrelevant for R4

Calculate the yearly costs of the totalloss CL and the costs of the remaininglosses CRL if protective measures are

applied

Calculate the yearly costs ofprotective measures CPM

CPM + CRL > CL

Application ofprotective measuresis economically not

advantageous

yes

no

Application of protective measuresis economically advantageous

Fig. 3.2.10.2 Flow chart for the choice of protective measures incase of economic losses

Fig. 3.2.10.1 Basic procedure in case of a purely economic consideration and calculation of the yearly costs

Yearly costsdue to lightning

hazard

Yearly costsdue to lightning

hazard

Costs of theprotectivemeasures

Yearly costsdue to lightning

hazard

Costs of theprotectivemeasures

Economicallymost favour-able variant

Costsper year

MeasureWithoutprotectivemeasures

With protectivemeasuresvariant 1

With protectivemeasuresvariant 2

Tota

l cos

ts

Yearly costs as a result of lightning strike

Loss amount x yearly occurrence probability

Where:Loss amount is the replacement cost plusfollow-up costs (e.g. production loss, dataloss)

Occurrence probability depends on theprotective measures

Yearly costs of the protective measures

Depreciation, maintenance, interest loss(per year)

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3.2.12 Designing aidsFor practical applications, the time-consuming andnot always simple application of the procedure forassessing the risk of damage for buildings andstructures can be noticeably improved by the useof a PC-aided solution. In “DEHNsupport” the pro-cedures and date from IEC 62305-2 (EN 62305-2)have been converted into a user-friendly software.With “DEHNsupport” the user has a purposefulassistance for designing. The following designingaids are available:

⇒ Risk analysis according to IEC 62305-2 (EN62305-2)

⇒ Calculation of the separation distance

⇒ Calculation of the length of earth electrodes

⇒ Calculation of the length of air-terminationrods

3.3 Inspection and maintenance

3.3.1 Types of inspection and qualificationof the inspectors

Other and additional national standards and legalrequirements have to be taken into account.

To guarantee that the building or structure, thepersons therein, and the electrical and electronicsystems have permanent protection, the mechani-cal and electrical characteristics of a lightning pro-tection system must remain completely intact forthe whole of its service life. To ensure this case, acoordinated programme of inspection and mainte-nance of the lightning protection system shall belaid down by an authority, the designer of thelightning protection system, or the personinstalling the lightning protection system, and theowner of the building or structure. If faults arefound during the inspection of a lightning protec-tion system, the operator / owner of the buildingor structure is responsible for the immediateremoval of the faults. The inspection of the light-ning protection system must be carried out by alightning protection specialist.

A lightning protection specialist is due to his tech-nical training, knowledge and experience, alsowith regard to the applicable standards, able todesign, install and inspect lightning protection sys-tems.

The criteria – technical training, knowledge andexperience – usually are met after several years ofpractical and professional experience and duringan occupational activity in the field of lightningprotection. The fields designing, installation andinspection require different skills from the light-ning protection specialist.A lightning protection specialist is a competentperson who is familiar with the relevant safetyequipment regulations, directives and standards tothe extent that he is in a position to judge if tech-nical work equipment is in a safe working condi-tion. Competent persons are, for example, after-sales service engineers. A training course leadingto recognition as a competent person for lightningand surge protection, as well as for electricalinstallations conforming to EMC (EMC approvedengineer), is offered by the VdS Loss Prevention,which is part of the Joint Association of GermanInsurers (GDV e.V.), in cooperation with the Com-mittee for Lightning Protection and LightningResearch of the Association of German ElectricalEngineers (ABB of the VDE).Note: A competent person is not an expert!An expert has special knowledge because of histraining and experience in the field of technicalwork equipment which requires testing. He isfamiliar with the relevant safety equipment regu-lations, directives and standards to the extent thathe is in a position to judge if complex technicalwork equipment is in a safe working condition. Heshall be able to inspect technical work equipmentand provide an expert opinion. An expert is a spe-cially trained, officially approved competent per-son. Persons who are eligible to be experts are, forexample, engineers at the German TechnicalInspectorate or other specialist engineers. Installa-tions which are subject to monitoring require-ments generally have to be inspected by experts.

Regardless of the required inspector’s qualifica-tions, the inspections shall ensure that the light-ning protection system fulfils its protective func-tion of protecting living beings, stock, technicalequipment in the building or structure operationaltechnology, safety technology, and the building orstructure, against the effects of direct and indirectlightning strikes when combined with any mainte-nance and service measures which may be neces-sary. A design report of the lightning protectionsystem containing the design criteria, designdescription and technical drawings shall therefore

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be available to the inspector. The inspectionswhich need to be carried out are distinguished asfollows:

Inspection of the designThe inspection of the design shall ensure that allaspects of the lightning protection system with itscomponents correspond to the state of the art inforce at the time the designing is undertaken. Itmust be carried out before the service is provided.

Inspections during the construction phaseSections of the lightning protection system whichwill not be accessible when the building work iscomplete must be inspected as long as this is possi-ble. These include:

⇒ Foundation earth electrodes

⇒ Earth-termination systems

⇒ Reinforcement connections

⇒ Concrete reinforcements used as room shield-ing

⇒ Down-conductor systems and their connec-tions laid in concrete

The inspection comprises the control of the techni-cal documentation, and on-site inspection andassessment of the work carried out.

Acceptance inspectionThe acceptance inspection is carried out when thelightning protection system has been completed.The following must be thoroughly inspected:

⇒ Compliance with the protection plan conform-ing to the standards (design),

⇒ the work done (technical correctness)

taking into consideration

⇒ the type of use,

⇒ the technical equipment of the building orstructure and

⇒ the site conditions.

Repeat inspectionRegular repeat inspections are the preconditionfor a permanently effective lightning protectionsystem. In Germany they shall be carried out every2 to 4 years. Table 3.3.1.1 contains recommenda-tions for the intervals between the full inspectionsof a lightning protection system under averageenvironmental conditions. If official instructions orregulations with inspection deadlines are in force,these deadlines have to be considered as minimumrequirements. If official instructions prescribe thatthe electrical installation in the building or struc-ture must be regularly inspected, then the func-tioning of the internal lightning protection mea-sures shall be inspected as part of this inspection.

Visual inspectionLightning protection systems Type I or II in build-ings and structures, and critical sections of light-ning protection systems (e.g. in cases where thereis considerable influence from aggressive environ-mental conditions) have to undergo a visualinspection between repeat inspections (Table3.3.1.1).

Additional inspectionIn addition to the repeat inspections, a lightningprotection system must be inspected if

⇒ fundamental changes in use,

⇒ modifications to the building or structure,

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Type of LPS Visual inspection

(Year)

I and II

III and IV

1

2

Complete inspection

(Year)

2

4

Complete inspectionof critical systems

(Year)

1

1

Note: In buildings or structures with hazard of explosion a visual inspection of the lightning protection systemshould be carried out every 6 months. Once in a year the electrical installations should be tested. A deviationfrom these yearly inspection plan is accepted if it makes sense to carry out the tests in intervals of 14 to 15months in order to measure the conductivity of the ground at different times of the year in order to getknowledge of seasonal changes.

Table 3.3.1.1 Longest interval between inspections of the LPS acc. to IEC 62305-3, Table E.2

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⇒ restorations,

⇒ extensions or

⇒ repairs

on a protected building or structure have been car-ried out.

These inspections shall also be carried out when itis known that a lightning has struck the lightningprotection system.

3.3.2 Inspection measures

The inspection comprises the control of the techni-cal documentation, on-site inspection and mea-surement.

Control of the technical documentation

The technical documentation must be inspected toensure it is

⇒ complete and

⇒ in accordance with the standards.

On-site inspection

The on-site inspection shall examine whether

⇒ the complete system corresponds to the tech-nical documentation,

⇒ the complete system of external and internallightning protection is in an acceptable condi-tion,

⇒ there are any loose connections and interrup-tions in the lines of the lightning protectionsystem,

⇒ all earthing connections (if visible) are in order,

⇒ all lines and system components are correctlysecured, and units with a mechanical protec-tive function are in working order,

⇒ modifications requiring additional protectivemeasures have been made at the protectedbuilding or structure,

⇒ the surge protective devices installed in powersupply systems and information systems arecorrectly installed,

⇒ there is any damage, or whether there are anydisconnected surge protective devices,

⇒ upstream overcurrent protection devices ofsurge protective devices have tripped,

⇒ in the case of new supply connections orextensions which have been installed in theinterior of the building or structure since thelast inspection, the lightning equipotentialbonding was carried out,

⇒ equipotential bonding connections within thebuilding or structure are in place and intact,

⇒ the measures required for proximities of thelightning protection system to installationshave been carried out.

Note: For existing earth-termination systems whichare more than 10 years old, the condition andquality of the earth conductor line and its connec-tions can only be assessed by exposing it at certainpoints.

MeasurementsMeasurements are used to inspect the conductivityof the connections and the condition of the earth-termination system.

⇒ Conductivity of the connectionsMeasurements must be made to examinewhether all the conductors and connections ofair-termination systems, down-conductor sys-tems, equipotential bonding lines, shieldingmeasures etc. have a low-impedance conduc-tivity. The recommended value is < 1 Ω.

⇒ Condition of the earth-termination systemThe contact resistance to the earth-termina-tion system at all measuring points must bemeasured to establish the conductivity of thelines and connections (recommended value < 1 Ω).Further, the conductivity with respect to themetal installations (e.g. gas, water, ventilation,heating), the total earthing resistance of thelightning protection system, and the earthingresistance of individual earth electrodes andpartial ring earth electrodes must be mea-sured.

The results of the measurements must be com-pared with the results of earlier measurements. Ifthey deviate considerably from the earlier mea-surements, additional examinations must be per-formed.

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3.3.3 DocumentationA report must be compiled for each inspection.This must be kept together with the technical doc-umentation and reports of previous inspections atthe installation/system operator´s premises or atthe offices of the relevant authority.

The following technical documentation must beavailable to the inspector when, for example, hecarries out his assessment of the lightning protec-tion system:

⇒ Design criteria

⇒ Design descriptions

⇒ Technical drawings of the external and inter-nal lightning protection

⇒ Reports of previous services and inspections

An inspection report shall contain the followinginformation:

⇒ General

a) Owner, address

b) Installer of the lightning protection system,address

c) Year of construction

⇒ Information about the building or structure

a) Location

b) Use

c) Type of construction

d) Type of roofing

e) Lightning protection level (LPL)

⇒ Information about the lightning protectionsystem

a) Material and cross section of the lines

b) Number of down conductors, e.g. inspectionjoints (designation corresponding to the infor-mation in the drawing)

c) Type of earth-termination system (e.g. ringearth electrode, earth rod, foundation earthelectrode)

d) Design of the lightning equipotential bondingto metal installations, to electrical installationsand to existing equipotential busbars

⇒ Inspection fundamentals

a) Description and drawings of the lightning pro-tection system

b) Lightning protection standards and provisionsat the time of the installation

c) Further inspection fundamentals (e.g. regula-tions, instructions) at the time of the installa-tion

⇒ Type of inspection

a) Inspection of the design

b) Inspections during the construction phase

c) Acceptance inspection

d) Repeat inspection

e) Additional inspection

f) Visual inspection

⇒ Result of the inspection

a) Any modifications to the building or structureand / or the lightning protection system deter-mined

b) Deviations from the standards, regulations,instructions and application guidelines appli-cable at the time of the installation

c) Defects determined

d) Earthing resistance or loop resistance at theindividual inspection joints, with informationabout the measuring method and the type ofmeasuring device

e) Total earthing resistance (measurement withor without protective conductor and metalbuilding installation)

⇒ Inspector

a) Name of inspector

b) Inspector´s company / organisation

c) Name of person accompanying

d) Number of pages in inspection report

e) Date of inspection

f) Signature of the inspector´s company / organi-sation

3.3.4 MaintenanceThe maintenance and inspection of lightning pro-tection systems must be coordinated. In addition to the inspections, regular mainte-nance routines should therefore also be estab-lished for all lightning protection systems. Howfrequently the maintenance work is carried outdepends on the following factors:

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⇒ Loss of quality related to weathering and theambient conditions

⇒ Effects of direct lightning strikes and possibledamage arising therefrom

⇒ Class of lightning protection system requiredfor the building or structure under considera-tion

The maintenance measures should be determinedindividually for each lightning protection systemand become an integral part of the completemaintenance programme for the building or struc-ture.

A maintenance routine should be drawn up. Thisallows a comparison to be made between resultsrecorded now, and those from an earlier service.These values can also be used for comparison witha subsequent inspection.

The following measures should be included in amaintenance routine:

⇒ Inspection of all conductors and componentsof the lightning protection system

⇒ Measuring of the electrical conductivity ofinstallations of the lightning protection system

⇒ Measuring of the earthing resistance of theearth-termination system

⇒ Visual inspection of all surge protectivedevices (relates to surge protective devices onthe lines of the power supply and informationsystem entering the building or structure) todetermine if there has been any damage or ifany disconnections are present

⇒ Refastening of components and conductors

⇒ Inspection to ascertain that the effectivenessof the lightning protection system isunchanged after installation of additionalfixed equipment or modifications to the build-ing or structure

Complete records should be made of all mainte-nance work. They should contain modificationmeasures which have been, or are to be, carriedout.These records serve as an aid when assessing thecomponents and installation of the lightning pro-tection system. They can be used to examine andupdate a maintenance routine. The maintenancerecords should be kept together with the designand the inspection reports of the lightning protec-tion system.

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4. Lightning protection system

Lightning protection systems shall protect build-ings and structures from fire or mechanicaldestruction, and persons in the buildings frominjury or even death.A lightning protection system comprises an exter-nal and an internal lightning protection (Figure4.1).

The functions of the external lightning protectionare:

⇒ Directing direct lightning strikes into an air-termination system

⇒ Safe conduction of the lightning current to theearth by means of a down-conductor system

⇒ Distribution of the lightning current in theearth via an earth-termination system

The function of the internal lightning protection is

⇒ to prevent hazardous sparking inside thebuilding or structure.This is achieved by means of equipotentialbonding or a safety distance between thecomponents of the lightning protection sys-tem and other conductive elements inside thebuilding or structure.

The lightning equipotential bonding reduces thepotential drops caused by the lightning current.This is achieved by connecting all separate, con-ductive parts of the installation directly by meansof conductors or surge protective devices (SPDs)(Figure 4.2).

Lightning ProtectionSystem (LPS)

Air-

term

inat

ion

syst

em

Dow

n-co

nduc

tor

syst

em

Eart

h-te

rmin

atio

n sy

stem

Sepa

rati

on d

ista

nces

Ligh

tnin

g eq

uipo

tent

ial b

ondi

ng

according to IEC 62305 (EN 62305)

Fig. 4.1 Components of a lightning protection system

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The four classes of lightning protection systems(LPS) – I, II, III and IV – are determined using a set ofconstruction rules which are based on the corre-sponding lightning protection level. Each set com-prises class dependent (e.g. radius of the rollingsphere, mesh size) and class independent (e.g.cross-sections, materials) construction rules.

To ensure the continuous availability of complexinformation technology installations even in theevent of a direct lightning strike, it is necessary tohave continuing measures for the surge protectionof electronic installations which supplement thelightning protection system. This extensive cata-logue of measures is described in Chapter 7 underthe concept of lightning protection zones.

down-conductorsystem

earth-termination system

separationdistance

air-terminationsystem

serviceentrancebox

lightning currentarrester for230/400 V, 50 Hz

lightning currentarrester fortelephone line

equipotential bondingfor heating,air-conditioning, sanitation

foundation earth electrode

lightningequipotential bonding

Fig. 4.2 Lightning protection system (LPS)

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5. External lightning protection

5.1 Air-termination systemsThe function of the air-termination systems of alightning protection system is to prevent directlightning strikes from damaging the volume to beprotected. They must be designed to preventuncontrolled lightning strikes to the structure tobe protected.By correct dimensioning of the air-termination sys-tems, the effects of a lightning strike to a structurecan be reduced in a controlled way.

Air-termination systems can consist of the follow-ing components and can be combined with eachother as required:

⇒ Rods

⇒ Spanned wires and cables

⇒ Intermeshed conductors

When determining the siting of the air-termina-tion systems of the lightning protection system,special attention must be paid to the protection ofcorners and edges of the structure to be protected.This applies particularly to air-termination systemson the surfaces of roofs and the upper parts offacades. Most importantly, air-termination systemsmust be mounted at corners and edges.

Three methods can be used to determine thearrangement and the siting of the air-terminationsystems (Figure 5.1.1):

⇒ Rolling sphere method

⇒ Mesh method

⇒ Protective angle method

The rolling sphere method is the universal methodof design particularly recommended for geometri-cally complicated applications.The three different methods are described below.

5.1.1 Designing methods and types of air-termination systems

The rolling sphere method – “geometric-electricalmodel”For lightning flashes to earth, a downward leadergrows step-by-step in a series of jerks from thecloud towards the earth. When the leader has gotclose to the earth within a few tens, to a few hun-dreds of metres, the electrical insulating strengthof the air near the ground is exceeded. A further“leader” discharge similar to the downward leaderbegins to grow towards the head of the down-ward leader: the upward leader. This defines the

h 1

h 2

air-termination rod

α

protective angle

mesh size M

down conductor

r

rolling sphere

earth-termination system

I 20 m 5 x 5 mII 30 m 10 x 10 mIII 45 m 15 x 15 mIV 60 m 20 x 20 m

Class of LPS Radius of therolling sphere (r)

Mesh size(M)

Max. building height

Fig. 5.1.1 Method for designing of air-termination systems for high buildings

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point of strike of the lightning strike (Figure5.1.1.1).

The starting point of the upward leader and hencethe subsequent point of strike is determined main-ly by the head of the downward leader. The headof the downward leader can only approach theearth within a certain distance. This distance isdefined by the continuously increasing electricalfield strength of the ground as the head of thedownward leader approaches. The smallest dis-tance between the head of the downward leaderand the starting point of the upward leader iscalled the final striking distance hB (corresponds tothe radius of the rolling sphere).

Immediately after the electrical insulating strengthis exceeded at one point, the upward leader whichleads to the final strike and manages to cross thefinal striking distance, is formed. Observations ofthe protective effect of guard wires and pylonswere used as the basis for the so-called“geometric-electrical model”.

This is based on the hypothesis that the head ofthe downward leader approaches the objects onthe ground, unaffected by anything, until it reach-es the final striking distance.

The point of strike is then determined by theobject closest to the head of the downward leader.The upward leader starting from this point “forcesits way through” (Figure 5.1.1.2).

Classification of the lightning protection systemand radius of the rolling sphereAs a first approximation, a proportionality existsbetween the peak value of the lightning currentand the electrical charge stored in the downwardleader. Furthermore, the electrical field strength ofthe ground as the downward leader approaches isalso linearly dependent on the charge stored inthe downward leader, to a first approximation.Thus there is a proportionality between the peakvalue I of the lightning current and the final strik-ing distance hB (= radius of the rolling sphere):

r in m

I in kA

The protection of structures against lightning isdescribed in IEC 62305-1 (EN 62305-1). Among other things, this standard defines the classifica-tion of the individual lightning protection systemand stipulates the resulting lightning protectionmeasures.

It differentiates between four classes of lightningprotection system. A Class I lightning protectionsystem provides the most protection and a Class IV,by comparison, the least. The interception effec-

r I= ⋅10 0 65 .

point afar from thehead of the down-ward leader

startingupward leader

downwardleader

head of thedownward leader

startingupward leader

closest point tothe head of thedownward leader

rolling sphere

final striking

distance hB

A rolling sphere can touch not only thesteeple, but also the nave of the church atseveral points. All points touched arepotential points of strike.

Fig. 5.1.1.1 Starting upward leader defining the point of strike Fig. 5.1.1.2 Model of a rolling sphere Ref: Prof. Dr. A. Kern, Aachen

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tiveness Ei of the air-termination systems is con-comitant with the class of lightning protection sys-tem, i.e. which percentage of the prospectivelightning strikes is safely controlled by the air-ter-mination systems. From this results the final strik-ing distance and hence the radius of the “rollingsphere”. The correlations between class of light-ning protection system, interception effectivenessEi of the air-termination systems, final striking dis-tance / radius of the “rolling sphere” and currentpeak value are shown in Table 5.1.1.1.

Taking as a basis the hypothesis of the “geometric-electrical model” that the head of the downwardleader approaches the objects on the earth in anarbitrary way, unaffected by anything, until itreaches the final striking distance, a generalmethod can be derived which allows the volume tobe protected of any arrangement to be inspected.Carrying out the rolling sphere method requires ascale model (e.g. on a scale of 1:100) of the build-ing / structure to be protected, which includes theexternal contours and, where applicable, the air-termination systems. Depending on the location ofthe object under investigation, it is also necessaryto include the surrounding structures and objects,since these could act as “natural protective mea-sures” for the object under examination.

Furthermore, a true-to-scale sphere is requiredaccording to the class of lightning protection sys-tem with a radius corresponding to the final strik-ing distance (depending on the class of lightningprotection system, the radius r of the “rollingsphere” must correspond true-to-scale to the radii20, 30, 45 or 60 m). The centre of the “rollingsphere” used corresponds to the head of thedownward leader towards which the respectiveupward leaders will approach.

The “rolling sphere” is now rolled around theobject under examination and the contact pointsrepresenting potential points of strike are markedin each case. The “rolling sphere” is then rolledover the object in all directions. All contact pointsare marked again. All potential points of strike arethus shown on the model; it is also possible todetermine the areas which can be hit by lateralstrikes. The naturally protected zones resultingfrom the geometry of the object to be protectedand its surroundings can also be clearly seen. Air-termination conductors are not required at thesepoints (Figure 5.1.1.3).

It must be borne in mind, however, that lightningfootprints have also been found on steeples inplaces not directly touched as the “rolling sphere”rolled over. This is traced to the fact that, amongother things, in the event of multiple lightningflashes, the base of the lightning flash movesbecause of the wind conditions. Consequently, anarea of approx. one metre can come up around the

Fig. 5.1.1.3 Schematic application of the “rolling sphere” method ata building with considerably structured surface

Table 5.1.1.1 Relations between lightning protection level, interception criterion Ei , final striking distance hB and min. peak value of current IRef.: Table 5, 6 and 7 of IEC 62305-1 (EN 62305-1)

Lightning protectionlevel LPL

Probabilities for the limit valuesof the lightning current parameters

Radius of the rolling sphere(final striking distance hB)

r in m

Min. peak valueof current

I in kA

IV

III

II

I

0.84

0.91

0.97

0.99

60

45

30

20

16

10

5

3

< Max. values acc. to Table 5IEC 62305-1 (EN 62305-1)

> Min. values acc. to Table 6IEC 62305-1 (EN 62305-1)

0.97

0.97

0.98

0.99

r

r

r

r

rr

building

rolling sphere

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point of strike determined where lightning strikescan also occur.

Example 1: New administration building inMunichDuring the design phase of the new administra-tion building, the complex geometry led to thedecision to use the rolling sphere method to iden-tify the areas threatened by lightning strikes.This was possible because an architectural modelof the new building was available on a scale of1:100.It was determined that a lightning protection sys-tem Class I was required, i.e. the radius of therolling sphere in the model was 20 cm (Figure5.1.1.4).The points where the “rolling sphere” touchesparts of the building, can be hit by a direct light-ning strike with a corresponding minimum currentpeak value of 3 kA (Figure 5.1.1.5). Consequently,these points required adequate air-terminationsystems. If, in addition, electrical installations werelocalised at these points or in their immediatevicinity (e.g. on the roof of the building), addition-al air-termination measures were realised there.

The application of the rolling sphere methodmeant that air-termination systems were notinstalled where protection was not required. Onthe other hand, locations in need of more protec-tion could be equipped accordingly, where neces-sary (Figure 5.1.1.5).

Example 2: Aachen CathedralThe cathedral stands in the midst of the old townof Aachen surrounded by several high buildings.Adjacent to the cathedral there is a scale model(1:100) whose purpose is to make it easier for visi-tors to understand the geometry of the building.The buildings surrounding the Aachen Cathedralprovide a partial natural protection against light-ning strikes.Therefore, and to demonstrate the effectivenessof lightning protection measures, models of themost important elements of the surroundingbuildings were made according to the same scale(1:100) (Figure 5.1.1.6).

Figure 5.1.1.6 also shows “rolling spheres” forlightning protection systems Class II and III (i.e.with radii of 30 cm and 45 cm) on the model.

Fig. 5.1.1.4 Construction of a new administration building:Model with “rolling sphere” acc. to lightning protectionsystem Type I Ref.: WBG Wiesinger

Fig. 5.1.1.5 Construction of a DAS administration building:Top view (excerpt) on the zones threatened by lightningstrikes for lightning protection system Class I Ref.: WBG Wiesinger

Fig. 5.1.1.6 Aachen Cathedral: Model with environment and “rollingspheres” for lightning protection systems Class II and III Ref.: Prof. Dr. A. Kern, Aachen

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The aim here was to demonstrate the increasingrequirements on the air-termination systems as theradius of the rolling sphere decreases, i.e. whichareas of Aachen Cathedral had additionally to beconsidered at risk of being hit by lightning strikes,if a lightning protection system Class II with a high-er degree of protection was used. The “rolling sphere” with the smaller radius(according to a class of lightning protection systemwith a higher lightning protection level) naturallytouches also the model at all points alreadytouched by the “rolling sphere” with the largerradius. Thus, it is only necessary to determine theadditional contact points.As demonstrated, when dimensioning the air-ter-mination system for a structure, or a structuremounted on the roof, the sag of the rolling sphereis decisive.The following formula can be used to calculate thepenetration depth p of the rolling sphere whenthe rolling sphere rolls “on rails”, for example. Thiscan be achieved by using two spanned wires, forexample.

r Radius of the rolling sphere

d Distance between two air-termination rods ortwo parallel air-termination conductors

Figure 5.1.1.7 illustrates this consideration.Air-termination rods are frequently used to pro-tect the surface of a roof, or installations mountedon the roof, against a direct lightning strike. Thesquare arrangement of the air-termination rods,over which no cable is normally spanned, meansthat the sphere does not “roll on rails” but “sitsdeeper” instead, thus increasing the penetrationdepth of the sphere (Figure 5.1.1.8).

The height of the air-termination rods Δh shouldalways be greater than the value of the penetra-tion depth p determined, and hence greater thanthe sag of the rolling sphere. This additionalheight of the air-termination rod ensures that therolling sphere does not touch the structure to beprotected.

p r r d= − − /( )⎡⎣

⎤⎦

2 21

2 2

Fig. 5.1.1.9 Calculation Δh for several air-termination rods accord-ing to rolling sphere method

domelightinstalled on the roof

d diagonal

Δh

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Fig. 5.1.1.7 Penetration depth p of the rolling sphere

Δh

d

r air-terminationconductor

pene

trat

ion

dept

h p

Fig. 5.1.1.8 Air-termination system for installations mounted on theroof with their protective area

d

Δh

r

p

Class of LPSI II III IV

r 20 30 45 60

Cuboidal protective area bet-ween four air-termination rods

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Another way of determining the height of the air-termination rods is using Table 5.1.1.2. The pene-tration depth of the rolling sphere is governed bythe largest distance of the air-termination rodsfrom each other. Using the greatest distance, thepenetration depth p (sag) can be taken from thetable. The air-termination rods must be dimen-sioned according to the height of the structuresmounted on the roof (in relation to the location ofthe air-termination rod) and also the penetrationdepth (Figure 5.1.1.9).

If, for example, a total height of an air-terminationrod of 1.15 m is either calculated or obtained fromthe table, an air-termination rod with a standardlength of 1.5 m is normally used.

Mesh method

A “meshed” air-termination system can be useduniversally regardless of the height of the struc-ture and shape of the roof. A reticulated air-termi-nation network with a mesh size according to theclass of lightning protection system is arranged onthe roofing (Table 5.1.1.3).

To simplify matters, the sag of the rolling sphere isassumed to be zero for a meshed air-terminationsystem.

By using the ridge and the outer edges of thestructure, as well as the metal natural parts of thestructure serving as an air-termination system, theindividual cells can be sited as desired.

The air-termination conductors on the outer edgesof the structure must be laid as close to the edgesas possible.A metal attic can serve as an air-termination con-ductor and / or a down-conductor system if therequired minimum dimensions for natural compo-nents of the air-termination system are compliedwith (Figure 5.1.1.10).

Protective angle methodThe protective angle method is derived from theelectric-geometrical lightning model. The protec-tive angle is determined by the radius of therolling sphere. The comparable protective anglewith the radius of the rolling sphere is given whena slope intersects the rolling sphere in such a waythat the resulting areas have the same size (Figure5.1.1.11).This method must be used for structures with sym-metrical dimensions (e.g. steep roof) or roof-mounted structures (e.g. antennas, ventilationpipes).The protective angle depends on the class of light-ning protection system and the height of the air-

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e.g. gutter

Class of LPS

I

II

III

IV

Mesh size

5 x 5 m

10 x 10 m

15 x 15 m

20 x 20 m

Table 5.1.1.3 Mesh size

Fig. 5.1.1.10 Meshed air-termination system

I (20 m) II (30 m) III (45 m) IV (60 m)

Class of LPS with rolling sphere radius in meters

Sag of the rolling sphere [m] (rounded up)d

Distancebetween air-termniation

rods [m]

2 0.03 0.02 0.01 0.014 0.10 0.07 0.04 0.036 0.23 0.15 0.10 0.088 0.40 0.27 0.18 0.1310 0.64 0.42 0.28 0.2112 0.92 0.61 0.40 0.3014 1.27 0.83 0.55 0.4116 1.67 1.09 0.72 0.5418 2.14 1.38 0.91 0.6820 2.68 1.72 1.13 0.8423 3.64 2.29 1.49 1.1126 4.80 2.96 1.92 1.4329 6.23 3.74 2.40 1.7832 8.00 4.62 2.94 2.1735 10.32 5.63 3.54 2.61

Table 5.1.1.2 Sag of the rolling sphere over two air-terminationrods or two parallel air-termination conductors

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α1

α 2

h 2

Hh 1h 1

Note:Protective angle α1 refers to the height of the air-termination systemh1 above the roof surface to be protected (reference plane);Protective α2 refers to the height h2 = h1 + H, while the earthsurface is the reference plane.

h1: Physical height of the air-termination rod

Fig. 5.1.1.16 External lightning protection system, volume protectedby a vertical air-termination rod

Fig. 5.1.1.14 Example of air-termination systems with protectiveangle α

angle α

angle α

Fig. 5.1.1.13 Cone-shaped protection zone

h 1

α° α°

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Fig. 5.1.1.11 Protective angle and comparable radius of the rollingsphere

Fig. 5.1.1.12 Protective angle α as a function of height h dependingon the class of lightning protection system

Fig. 5.1.1.15 Area protected by an air-termination conductor

base

equal surface areasair-termi-nation rod

r

α°

rolling sphere

protectiveangle

h[m]

α°

I II III

80

70

60

50

40

30

20

10

00 2 10 20 30 40 50 60

IV

α° h1

air-terminationconductor

Angle α depends on the class of lightning protection systemand the height of the air-termination conductor above ground

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Height of the air-termination rod

h in m

Class of LPS IAngle Distance

α a in m

Class of LPS IIAngle Distance

α a in m

Class of LPS IIIAngle Distance

α a in m

Class of LPS IVAngle Distance

α a in m

αangle

height hof the air-

termination rod

distance a

Table 5.1.1.4 Protective angle α depending on the class of lighting protection system

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termination system above the reference plane(Figure 5.1.1.12).

Air-termination conductors, air-termination rods,masts and wires should be arranged to ensure thatall parts of the building to be protected are situa-

ted within the volume of protection of the air-ter-mination system.The protection zone can be “cone-shaped” or“tent-shaped”, if a cable, for example, is spannedover it (Figures. 5.1.1.13 to 5.1.1.15).If air-termination rods are installed on the surfaceof the roof to protect structures mounted thereon,the protective angle α can be different. In Figure5.1.1.16, the roof surface is the reference plane forprotective angle α1. The ground is the referenceplane for the protective angle α2. Therefore theangle α2 according to Figure 5.1.1.12 and Table5.1.1.4 is less than α1.Table 5.1.1.4 provides the corresponding protec-tive angle for each class of lightning protectionsystem and the corresponding distance (zone ofprotection).

Protective angle method for isolated air-termina-tion systems on roof-mounted structuresSpecial problems may occur when roof-mountedstructures, which are often installed at a later date,protrude from zones of protection, e.g. the mesh.If, in addition, these roof-mounted structures con-tain electrical or electronic equipment, such asroof-mounted fans, antennas, measuring systemsor TV cameras, additional protective measures arerequired.

If such equipment is connected directly to theexternal lightning protection system, then, in theevent of a lightning strike, partial currents are con-ducted into the structure. This could result in thedestruction of surge sensitive equipment. Directlightning strikes to such structures protrudingabove the roof can be prevented by having isolat-ed air-termination systems.Air-termination rods as shown in Figure 5.1.1.17are suitable for protecting smaller roof-mountedstructures (with electrical equipment).They form a “cone-shaped” zone of protectionand thus prevent a direct lightning strike to thestructure mounted on the roof.

The separation distance s must be taken intoaccount when dimensioning the height of the air-termination rod (see Chapter 5.6).

Isolated and non-isolated air-termination systemsWhen designing the external lightning protectionsystem of a structure, we distinguish between twotypes of air-termination system:

Fig. 5.1.1.18 Gable roof with conductor holder

Fig. 5.1.1.19 Flat roof with conductor holders: Protection of thedomelights

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Fig. 5.1.1.17 Protection of small-sized installations on roofs againstdirect lightning strikes by means of air-terminationrods

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⇒ isolated

⇒ non-isolated

The two types can be combined.

The air-termination systems of a non-isolatedexternal lightning protection system of a structurecan be installed in the following ways:

If the roof is made of non-flammable material, theconductors of the air-termination system can beinstalled on the surface of the structure (e.g. gableor flat roof). Normally non-flammable buildingmaterials are used. The components of the exter-nal lightning protection system can therefore bemounted directly on the structure (Figures 5.1.1.18and 5.1.1.19).

If the roof is made of easily inflammable materiale.g. thatched roofs, then the distance between theflammable parts of the roof and the air-termina-tion rods, air-termination conductors or air-termi-nation meshes of the air-termination system mustnot be less than 0.4 m.Easily inflammable parts of the structure to be pro-tected must not be in direct contact with parts ofthe external lightning protection system. Neithermay they be located under the roofing, which canbe punctured in the event of a lightning strike (seealso Chapter 5.1.5 Thatched roofs).

With isolated air-termination systems, the com-plete structure is protected against a direct light-ning strike via air-termination rods, air-termina-tion masts or masts with cables spanned overthem. When installing the air-termination systems,the separation distance s to the structure must bekept (Figures 5.1.1.20 and 5.1.1.21).

The separation distance s between the air-termina-tion system and the structure must be kept.

Air-termination systems isolated from the struc-ture are frequently used, when the roof is coveredwith inflammable material, e.g. thatch or also forex-installations, e.g. tank installations.

See also Chapter 5.1.5 “Air-termination system forstructures with thatched roofs”.

A further method of designing isolated air-termi-nation systems consists in securing the air-termina-tion systems (air-termination rods, conductors orcables) with electrically insulating materials such asGRP (glass fibre-reinforced plastic).This form of isolation can be limited to local use orapplied to whole parts of the installation. It isoften used for roof-mounted structures such as fansystems or heat exchangers with an electricallyconductive connection into the structure (see alsoChapter 5.1.8).

s s

α α

reference plane

protectedstructure

air-termi-nation mast

air-termi-nation mast

s separation distance acc. to IEC 62305-3 (EN 62305-3)α protective angle acc. to Table 5.1.1.4

s2

s 1

s2

reference plane

protectedstructureair-termi-

nation mast

s1, s2 separation distance acc. to IEC 62305-3 (EN 62305-3)

horizontal air-termination conductor

air-termi-nation mast

Fig. 5.1.1.20 Isolated external lightning protection system with twoseparate air-termination masts according to the pro-tective angle method: Projection on a vertical area

Fig. 5.1.1.21 Isolated external lightning protection system, consist-ing of two separate air-termination masts, connectedby a horizontal air-termination conductor: Projectionon a vertical surface via the two masts (vertical sec-tion)

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Natural components of air-termination systemsMetal structural parts such as attics, guttering, rail-ings or cladding can be used as natural compo-nents of an air-termination system.

If a structure has a steel skeleton construction witha metal roof and facade made of conductive mate-rial, these can be used for the external lightningprotection system, under certain circumstances.

Sheet metal cladding on the walls or roof of thestructure to be protected can be used if the electri-cal connection between the different parts is per-manent. These permanent electrical connectionscan be made by e.g. brazing, welding, pressing,screwing or riveting, for example.If there is no electrical connection, a supplemen-tary connection must be made for these elementse.g. with bridging braids or bridging cables.

If the thickness of the sheet metal is not less thanthe value t' in Table 5.1.1.5, and if there is norequirement to take account of a through-meltingof the sheets at the point of strike or the ignition offlammable material under the cladding, then suchsheets can be used as an air-termination system.

The material thicknesses are not distinguished ac-cording to the class of lightning protection system.

If it is, however, necessary to take precautionarymeasures against through-melting or intolerableheating-up at the point of strike, if the thickness ofthe sheet metal shall not be less than value t inTable 5.1.1.5.

The required thicknesses t of the materials cangenerally not be complied with, for example, formetal roofs.For pipes or containers, however, it is possible tomeet the requirements for these minimum thick-nesses (wall thickness). If, though, the temperaturerise (heating-up) on the inside of the pipe or tankrepresents a hazard for the medium containedtherein (risk of fire or explosion), then these mustnot be used as air-termination systems (see alsoChapter 5.1.4).

If the requirements on the appropriate minimumthickness are not met, the components, e.g. con-duits or containers, must be situated in an areaprotected from direct lightning strikes.

A thin coat of paint, 1 mm bitumen or 0.5 mm PVCcannot be regarded as insulation in the event of adirect lightning strike. Such coatings break downwhen subjected to the high energies depositedduring a direct lightning strike.There must be no coatings on the joints of the na-tural components of the down-conductor systems.

If conductive parts are located on the surface ofthe roof, they can be used as a natural air-termina-tion system if there is no conductive connectioninto the structure.By connecting, e.g. pipes or electrical conductorsinto the structure, partial lightning currents canenter the structure and affect or even destroy sen-sitive electrical / electronic equipment.In order to prevent these partial lightning currentsfrom penetrating, isolated air-termination systemsshall be installed for the aforementioned roof-mounted structures.The isolated air-termination system can bedesigned using the rolling sphere or protectiveangle method. An air-termination system with amesh size according to the class of lightning pro-tection system used can be installed if the wholearrangement is isolated (elevated) from the struc-ture to be protected by at least the required sepa-ration distance s.

Table 5.1.1.5 Min. thickness of metal plates

Material

-

4

4

5

7

-

2.0

0.5

0.5

0.5

0.65

0.7

Lead

Steel (stainless,galvanised)

Titanium

Copper

Aluminium

Zinc

Thick-nessa t

mm

Thick-nessb t`

mm

Class of LPS

I to IV

a t prevents from puncturing, overheating, and inflamming

b t` only for metal plates, if the prevention of puncturing, overheating, and inflamming is not important

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A universal system of components for the installa-tion of isolated air-termination systems is descri-bed in Chapter 5.1.8.

5.1.2 Air-termination systems for buildingswith gable roofs

Air-termination systems on roofs are the metalcomponents in their entirety, e.g. air-terminationconductors, air-termination rods, air-terminationtips.The parts of the structure usually hit by lightningstrikes, such as the top of the gable, chimneys,ridges and arrises, the edges of gables and eaves,parapets and antennas and other protruding struc-tures mounted on the roof, must be equipped withair-termination systems.Normally, a reticulated air-termination network is installed on the surface of gabled roofs, said network corresponding to the mesh size of theappropriate class of lightning protection system(e.g. 15 m x 15 m for a lightning protection systemClass III) (Figure 5.1.2.1).By using the ridge and the outer edges of thestructure, as well as the metal parts of the struc-ture serving as an air-termination system, the indi-vidual meshes can be sited as preferred. The air-termination conductors on the outer edges of thestructure must be installed as close to the edges aspossible.

Generally, the metal gutter is used for closing the“mesh” of the air-termination system on the roofsurface. If the gutter itself is connected so as to beelectrically conductive, a gutter clamp is mounted

at the crossover of the air-termination system andthe gutter.

Roof-mounted structures made of electrically non-conductive material (e.g. PVC vent pipes) are con-sidered to be sufficiently protected if they do notprotrude more than h = 0.5 m from the plane ofthe mesh (Figure 5.1.2.2).

If the protrusion is h > 0.5 m, the structure must beequipped with an air-termination system (e.g.interception tip) and connected to the nearest air-termination conductor. One way of doing thiswould be to use a wire with a diameter of 8 mm up to a maximum free length of 0.5 m, as shown inFigure 5.1.2.3.

Metal structures mounted on the roof withoutconductive connection into the structure do notneed to be connected to the air-termination sys-tem if all the following conditions are met:

⇒ Structures mounted on the roof may protrudea maximum distance of 0.3 m from the planeof the mesh

⇒ Structures mounted on the roof may have amaximum enclosed area of 1 m2 (e.g. dormerwindows)

⇒ Structures mounted on the roof may have amaximum length of 2 m (e.g. sheet metal roof-ing parts)

Only if all three conditions are met, no terminal isrequired.

h

Fig. 5.1.2.1 Air-termination system on agable roof

Fig. 5.1.2.2 Height of a roof superstructuremade of electrically non-conduc-tive material (e.g. PVC), h ≤ 0.5 m

Fig. 5.1.2.3 Additional air-termination systemfor ventilation pipes

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Furthermore, with the conditions stated above,the separation distance to the air-termination con-ductors and down-conductor systems must bemaintained (Figure 5.1.2.4).

Air-termination rods for chimneys must be erectedto ensure that the whole chimney is in the zone ofprotection. The protective angle method is appliedwhen dimensioning the air-termination rods.

If the stack is brick-built or constructed with pre-formed sections, the air-termination rod can bemounted directly on the stack.

If there is a metal insert pipe in the interior of thestack, e.g. as found when redeveloping old build-ings, the separation distance to this conductivecomponent must be kept. This is an examplewhere isolated air-termination systems are usedand the air-termination rods are erected with dis-tance holders. The inserted metal pipe must beconnected to the equipotential bonding.Theassembly to protect parabolic antennas in particu-lar is similar to that to protect stacks with an inter-nal stainless steel pipe.

In the event of a direct lightning strike toantennas, partial lightning currents can enter thestructure to be protected via the shields of thecoaxial cables and cause the effects and destruc-tion previously described. To prevent this, anten-nas are equipped with isolated air-termination sys-tems (e.g. air-termination rods) (Figure 5.1.2.5).

Air-termination systems on the ridge have a tent-shaped zone of protection (according to the pro-tective angle method). The angle depends on theheight above the reference plane (e.g. surface of

the earth) and the class of lightning protection sys-tem chosen.

5.1.3 Air-termination systems for flat-roofedstructures

An air-termination system for structures with flatroofs (Figures 5.1.3.1 and 5.1.3.2) is designed usingthe mesh method. A mesh-type air-terminationsystem with a mesh size corresponding to the classof lightning protection system is installed on theroof (Table 5.1.1.3).

Figure 5.1.3.3 illustrates the practical applicationof the meshed air-termination system in combina-tion with air-termination rods to protect the struc-tures mounted on the roof, e.g. domelights, pho-tovoltaic cells or fans. Chapter 5.1.8 shows how todeal with these roof-mounted structures.

Roof conductor holders on flat roofs are laid atintervals of approx. 1 m. The air-termination con-ductors are connected with the attic, this being anatural component of the air-termination system.As the temperature changes, so does the length ofthe materials used for the attic, and hence theindividual segments must be equipped with “slideplates”.If the attic is used as an air-termination system,these individual segments must be permanentlyinterconnected so as to be electrically conductivewithout restricting their ability to expand. This can

Fig. 5.1.2.5 Antenna with air-termination rodFig. 5.1.2.4 Building with photovoltaic system Ref.: Wettingfeld Lightning Protection, Krefeld, Germany

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be achieved by means of bridging braids, straps orcables (Figure 5.1.3.4).

The changes in length caused by changes in tem-perature must also be taken into account with air-termination conductors and down-conductor sys-tems (see Chapter 5.4).A lightning strike to the attic can cause the materi-als used to melt through. If this is unacceptable, a

expansion piece

distance between theroof conductor holdersapprox. 1 m

flexible connection

Bridging braidPart No. 377 015

Roof conductor holder Type FB2Part No. 253 050

Roof conductor holder Type FBPart No. 253 015

Fig. 5.1.3.1 Air-termination system

Fig. 5.1.3.2 Air-termination system on a flat roof

Fig. 5.1.3.5 Example how to protect a metal roof attic, if meltingthrough is unacceptable (front view)

Fig. 5.1.3.3 Use of air-termination rods

Fig. 5.1.3.4 Bridged attic

bridging braid

air-termination tip

rolling sphere

parapet

metal attic

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supplementary air-termination system, e.g. withair-termination tips, must be installed, its locationbeing determined by using the rolling spheremethod (Figure 5.1.3.5).

Conductor holders for flat roofs, homogeneouslywelded

In the wind, roof sheetings can move across theroof surface horizontally, if they are only fixedmechanically / laid on the surface. A special posi-tion fixing is required for the air-termination con-ductor for preventing the conductor holders forair-termination systems from being displaced onthe smooth surface. Conventional roof conductorholders cannot be permanently bonded to roofsheetings since the latter do not usually permit theapplication of adhesives.

A simple and safe way of fixing the position is touse roof conductor holders Type KF in combinationwith straps (cut the strips to fit) made of the roofsheeting material. The strap is clamped into theplastic holder and both sides are welded onto theseal. Holder and strap should be positioned imme-diately next to a roof sheeting joint at a distanceof approx. 1 m. The strip of foil is welded to theroof sheeting according to the manufacturer ofthe roof sheeting. This prevents air-terminationconductors on flat roofs from being displaced.

If the slope of the roof is greater than 5 °, eachroof conductor holder must be equipped with aposition fixing element. If the synthetic roof sheet-ings are secured by mechanical means, the roofconductor holders must be arranged in the imme-diate vicinity of the mechanical fixing elements.

When carrying out this work, it must be consideredthat welding and bonding work on the seal affectthe guarantee provided by the roofer.The work to be carried out must therefore only bedone with the agreement of the roofer responsi-ble for the particular roof, or be carried out by himhimself (Figure 5.1.3.6).

5.1.4 Air-termination systems on metalroofs

Modern industrial and commercial purpose-builtstructures often have metal roofs and facades. Themetal sheets and plates on the roofs are usually 0.7 – 1.2 mm thick.

Figure 5.1.4.1 shows an example of the construc-tion of a metal roof.When the roof is hit by a direct lightning strike,melting through or vaporisation can cause a holeformed at the point of strike. The size of the holedepends on the energy of the lightning strike and

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Fig. 5.1.3.6 Synthetic flat roof sheetings – Roof conductor holder Type KF / KF2

~300~ 300

~90

~70

distance between theroof conductor holdersapprox. 1 m

flexible connection

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the characteristics of the material, (e.g. thickness).The biggest problem here is the subsequent dam-age, e.g. water entering at this point. Days orweeks can pass before this damage is noticed. The

roof insulation becomes damp and / or the ceilingbecomes wet and is no longer rainproof.One example of damage, assessed using BLIDS(Blitz-Informations Dienst von Siemens – SiemensLightning Information Service) illustrates thisproblem (Figure 5.1.4.2). A current of approx.20,000 A struck the sheet metal and made a hole(Figure 5.1.4.2: Detail A). Since the sheet metal wasnot earthed by a down-conductor system, flash-overs to natural metal components in the walloccurred in the area around the fascia (Figure5.1.4.2: Detail B), which also caused a hole.To prevent such kind of damage, a suitable exter-nal lightning protection system with wires andclamps capable of carrying lightning currents mustbe installed even on a “thin” metal roof. The IEC62305-3 (EN 62305-3) lightning protection stan-dard clearly illustrates the risk of damage to metalroofs. Where an external lightning protection sys-tem is required, the metal sheets must have theminimum values stated in Table 5.1.1.5.

The thicknesses t are not relevant for roofingmaterials. Metal sheets with a thickness t’ may onlybe used as a natural air-termination system ifpuncturing, overheating and melting is tolerated.The owner of the structure must agree to toleratethis type of roof damage, since there is no longerany guarantee that the roof will offer protectionfrom the rain. Also the Rules of the German Roof-ing Trade concerning lightning protection on andattached to roofs require the agreement of theowner.

If the owner is not prepared to tolerate damage tothe roof in the event of a lightning strike, then aseparate air-termination system must be installed

Distance of thehorizontal conductors

3 m

4 m

5 m

6 m

Height of theair-termination tip*)

0.15 m

0.25 m

0.35 m

0.45 m

Suitable for all classes of lightning protection system

*) recommended values

rolling sphere with a radiusacc. to class of LPS

air-termination tip

Evaluation: BLIDS – SIEMENSI = 20400 A residential building

Detail B

Detail A

Fig. 5.1.4.2 Example of damage: Metal plate cover

Table 5.1.4.1 Lightning protection for metal roofs – Height of theair-termination tips

Fig. 5.1.4.3 Air-termination system on a metal roof – Protectionagainst holing

Fig. 5.1.4.1 Types of metal roofs, e.g. roofs withround standing seam

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on a metal roof. The air-termination system mustbe installed to ensure that the rolling sphere(radius r which corresponds to the class of light-ning protection system chosen) does not touch themetal roof (Figure 5.1.4.3).

When mounting the air-termination system it isrecommended to install a so-called “hedgehogroof” with longitudinal conductors and air-termi-nation tips.

In practice, the heights of air-termination tipsaccording to Table 5.1.4.1 are tried and tested,regardless of the class of lightning protection sys-tem involved.

Holes must not be drilled into the metal roof whenfixing the conductors and air-termination tips. Var-ious conductor holders are available for the differ-ent types of metal roofs (round standing seam,standing seam, trapezoidal). Figure 5.1.4.4a showsone possible design for a metal roof with roundstanding seam.

When installing the conductors, care must be tak-en that the conductor holder located at the high-est point of the roof must be designed with a fixedconductor leading, whereas all other conductorholders must be designed with a loose conductorleading because of the linear compensation

2

1 3

Parallel conectorSt/tZn Part No. 307 000

Roof conductor holderfor metal roofs, loose con-ductor leading, DEHNgripconductor holderStSt Part No. 223 011Al Part No. 223 041

Roof conductor holderfor metal roofs fixed con-ductor leading with clampingframeStSt Part No. 223 010Al Part No. 223 040

1

2

3

roof connection

bridging braid

conductor holder withloose conductor leading

bridging cable

KS connector

air-termination tip

Fig. 5.1.4.4a Conductor holders for metal roofs – Round standing seam Fig. 5.1.4.4b Conductor holder for metal roofs –Round standing seam

Fig. 5.1.4.5 Model construction of a trape-zoidal sheet roof, conductorholder with clamping frame

Fig. 5.1.4.6 Model construction of a roofwith standing seam

Fig. 5.1.4.7 Air-termination rod for a dome-light on a roof with round stand-ing seam

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caused by changes in temperature (Figure5.1.4.4b).

The conductor holder with fixed conductor lead-ing is illustrated in Figure 5.1.4.5 using the exam-ple of a trapezoidal sheet roof.

Figure 5.1.4.5 also shows an air-termination tipnext to the conductor holder. The conductor hold-er must be hooked into the fixing screw above thecovering plate for the drill hole to prevent anyentering of water.

Figure 5.1.4.6 uses the example of a round stand-ing seam roof to illustrate the loose conductorleading.Figure 5.1.4.6 also shows the connection to theroof with round standing seam at the roof edge,which is capable of carrying currents.Unprotected installations projecting above theroof, e.g. domelights and chimney covers, areexposed points of strike for a lightning discharge.In order to prevent these installations from beingstruck by a direct lightning strike, air-terminationrods must be installed adjacent to the installationsprojecting above the roof. The height of the air-termination rod results from the protective angle α(Figure 5.1.4.7).

5.1.5 Principle of an air-termination systemfor structures with thatched roof

The design of lightning protection systems Class IIIgenerally meets the requirements of such a struc-ture. In particular individual cases, a risk analysisbased on IEC 62305-2 (EN 62305-2) can be carriedout.

The air-termination conductors on such roofs(made of thatch, straw or rushes) must be fastenedacross isolating supports to be free to move. Cer-tain distances must also be maintained around theeaves.

In case of subsequent installation of a lightningprotection system on a roof, the distances must beincreased. This allows to maintain the necessaryminimum distances when re-roofing is carried out.For a lightning protection system Class III, the typi-cal distance of the down-conductor system is 15 m.

The exact distance of the down-conductor systemsfrom each other results from calculating the sepa-ration distance s in accordance with IEC 62305-3(EN 62305-3).

Chapter 5.6 explains how to calculate the separa-tion distance.

Ideally, ridge conductors shouldhave spans up to around 15 m, anddown-conductor systems up toaround 10 m without additionalsupports.Fastening posts must be tightlyconnected to the roof structure(rafters and rails) by means of boltsand washers (Figures 5.1.5.1 to5.1.5.3).

Metal components situated abovethe roof surface (such as weathervanes, irrigation systems, anten-nas, metal plates, conductors) mustbe entirely in the protected vol-ume of isolated air-terminationsystems.In such cases, effective protectionagainst lightning can only beachieved with an isolated externallightning protection system with

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Fig. 5.1.5.1 Air-termination system for buildings with thatched roofs

Signs and symbolsAir-termination conductorConnecting pointIsolating point /Measuring pointEarth conductorDown conductor

Important distances (min. values)a 0.6 m Air-term. conductor / Gableb 0.4 m Air-term. conductor/Roofingc 0.15 m Eaves / Eaves supportd 2.0 m Air-termination conductor /

Branches of trees

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air-termination rods near the structure, or air-ter-mination conductors or interconnected air-termi-nation masts adjacent to the structure.

If a thatched roof borders onto metal roofingmaterial, and if the structure has to be equippedwith an external lightning protection system, thenan electrically non-conductive roofing material atleast 1 m wide, e.g. in plastic, must be insertedbetween the thatched roof and the other roof.

Tree branches must be kept at least 2 m away froma thatched roof. If trees are very close to, and high-er than, a structure, then an air-termination con-ductor must be mounted on the edge of the rooffacing the trees (edge of the eaves, gable) and

This method can be found in Chapter 5.1.8 isolatedair-termination system (steel telescopic lightningprotection masts).A new and architecturally very attractive possibili-ty of isolated lightning protection is the use of iso-lated down conductor systems.Example for the installation of isolated down con-ductor systems: Redevelopment of the roof of ahistorical farmhouse in Lower Saxony (Figure5.1.5.4).

Referring to the building regulations (LBO) of therespective federal state as well as to the modelbuilding regulations (MBO), the competent build-ing authority decides about the necessity of alightning protection system.

connected to thelightning protectionsystem. The necessarydistances must bemaintained.

A further way of pro-tecting structureswith thatched roofsagainst a strike oflightning is to erectair-termination mastsso that the wholestructure is in the pro-tected volume.

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6

3

4

5

Pos Description DIN Part No.1 Clamping cap with 48811 A 145 309

air-termination rod2 Wood pile 48812 145 2413 Support for roof conductors − 240 0004 Eaves support 48827 239 0005 Tensioning block 48827 B 241 0026 Air-term. conductor, e.g. Al cable − 840 050

1

2

Fig. 5.1.5.2 Components for thatched roofs

Fig. 5.1.5.3 Thatched roof Fig. 5.1.5.4 Historical farmhouse with external lightning protection(Ref. Photo: Hans Thormählen GmbH & Co.KG)

Page 68: Lightning Protection Guide

The building regulations of LowerSaxony (NBauO) for example stipu-late in § 20 (3) that:“Buildings or structures which dueto the location, type of constructionor use are particularly susceptibleto lightning strikes, or where such astrike can have serious conse-quences, must be equipped withpermanently effective lightningprotection systems.”

With regard to the increasing dam-age events caused by lightningstrikes and surges, property insurersrequire that measures of lightningand surge protection are taken pri-or to the conclusion of new, oradjustment of existing insurancecontracts. Basis for the risk assess-ment is a risk analysis according toIEC 62305-2 (EN 62305-2).At the historical farmhouse a light-ning protection system Class III hasbeen installed, which meets thestandard requirements for buildingswith thatched roofs IEC 62305-3 (EN62305-3).

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Fig. 5.1.5.5 Sectioning at the central building

rolling sphere with r = 45 m

2 m

10 m

1.5

m1

m

13 m

GRP/Al insulating pipe ∅ 50 mm

Legend:

Down conductor

HVI® conductor(under roof)

Earth conductor

Isolating point

Thatched roof

Fig. 5.1.5.6 Schematic diagram and diagram of the down conductor installation at the rafter

insulating pipe withinterior HVI® conductor

heather or divot-cladded ridge

boltedwooden traverse HVI® conductor led under

the roof to the eaves

mast sealing film

cornice plank

EBB

MEBB

Legend:

Down conductor

HVI® conductor(under roof)

Earth conductor

Isolating point

Thatched roof

HVI® conductorinside

Page 69: Lightning Protection Guide

(EN 62305-3). The isolated HVI conductor is speci-fied with an equivalent separation distance in airof s = 0.75 m or s = 1.50 m for solid building mate-rials. Figure 5.1.5.6 shows how the down conduc-tor system is arranged.

The HVI conductor is run in an insulating pipe. Theconstruction requires a down leading of the HVIconductor via a central earthing busbar, theequipotential bonding measures being performedby a flexible conductor H07V-K 1 x 16 mm2. Theinsulating pipe is fixed at a special construction(wooden traverse) and further down, the downconductors are routed along the rafters of the roofconstruction underneath the battens (Figure5.1.5.6).At the eaves, the HVI conductors are led throughthe cornice plank (Figure 5.1.5.7).For architectural reasons aluminium down conduc-tors are installed further down. Like for the wholeinstallation, the crossover of the HVI conductor tothe uninsulated, bare down conductor near theearthing system is effected on the basis of themounting instructions of the DEHNconductor sys-tem. A sealing unit was not necessary.

5.1.6 Walkable and trafficable roofs

It is not possible to mount air-termination conduc-tors (e.g. with concrete blocks) on trafficable roofs.One possible solution is to install the air-termina-tion conductors in either concrete or in the jointsbetween the sections of the roadway. If the air-ter-mination conductor is installed in these joints,mushroom head collectors are installed at theintersections of the mesh as defined points ofstrike.

The mesh size must not exceed the value accordingto the class of lightning protection system (seeChapter 5.1.1, Table 5.1.1.3).

If it can be guaranteed that no persons will be onthis area during a thunderstorm, then it is suffi-cient to install the measures described above.Persons who can go onto this storey of the car parkmust be informed by means of a sign that theymust immediately clear this storey when a thun-derstorm occurs, and not return for the durationof the storm (Figure 5.1.6.1).

The heather-cladded ridge of the object is protect-ed by a reticulated plastic cover to avoid abrasionby birds.

Before designing of the air-termination system,the protected volumes are to be determined bythe rolling sphere method. A rolling sphere radiusof 45 m is applicable in case of a lightning protec-tion system Class III according to the standard spec-ifications. The height of the air-termination systemwas ascertained to be 2.30 m, thus the two stacksat the ridge and the three new dormers at the oneside of the roof are within the protected volume(Figure 5.1.5.5).

An insulating pipe (Glass Fibre Reinforced Unsatu-rated Plastic) was chosen to keep the air-termina-tion system correspondingly elevated and to sup-port the isolated down-conductor system. The low-er part of the insulating pipe is aluminium toensure the mechanical stability. Due to the induc-tion of neighbouring components unwantedsparking is possible in this section. To avoid this,there are no earthed parts or electrical equipmentwithin a distance of 1 m from the air-terminationsystem.The electrical isolation of air-termination systemsand down-conductor systems on the one hand andof the metal installations to be protected and thesystems of power supply and information technology of the building or structure to be protectedon the other hand, can be achieved by the separa-tion distance s between these conductive parts.This must be determined according to IEC 62305-3

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HVI® conductor

leading through the cornice

Fig. 5.1.5.7 HVI conductor led through the cornice plank

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If it is also possible that persons are on the roofduring a thunderstorm, then the air-terminationsystem must be designed to protect these persons,assuming they have a height of 2.5 m (with out-stretched arm) from direct lightning strikes.

The air-termination system can be dimensionedusing the rolling sphere or the protective anglemethod according to the class of lightning protec-tion system (Figure 5.1.6.2).

These air-termination systems can also be con-structed from spanned cables or air-terminationrods. These air-termination rods are secured tostructural elements such as parapets or the like, forexample. Furthermore, lightning masts, for example, canalso act as air-termination rods to prevent life haz-ard. With this version, however, attention must bepaid to the partial lightning currents which can beconducted into the structure via the power lines. Itis imperative to have lightning equipotentialbonding measures for these lines.

5.1.7 Air-termination system for green andflat roofs

A planted roof can make economic and ecologicalsense. This is because it provides noise insulation,

protects the roof skin, suppresses dust from theambient air, provides additional heat insulation,filters and retains rainwater and is a natural way ofimproving the living and working conditions.Moreover, in many regions it is possible to obtaingrants from public funds for cultivating plants onthe roof. A distinction is made between so-calledextensive and intensive cultivation. An extensiveplanted area requires little care, in contrast to anintensive planted area which requires fertiliser,irrigation and cutting. For both types of plantedarea, either earth substrate or granulate must belaid on the roof.It is even more expensive if the granulate or sub-strate has to be removed because of a direct light-ning strike.

If there is no external lightning protection system,the roof seal can be damaged at the point ofstrike.

Experience has shown that, regardless of the typeof care required, the air-termination system of anexternal lightning protection system can, andshould, also be installed on the surface of a greenroof.

For a meshed air-termination system, the IEC62305-3 (EN 62305-3) lightning protection stan-

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Fig. 5.1.6.1 Lightning protection for car park roofs – Building protec-tion

Fig. 5.1.6.2 Lightning protection for car park roofs – Building andlife protection IEC 62305-3 (EN 62305-3); Annex E

Down conducting via steel reinforcement

Conductors installed withinconcrete or in the joints ofthe roadway (plates)

Warning!Keep off the car parkduring thunderstorms

Mushroom headcollectorArt.-Nr. 108 001

Mushroom headcollector after asphalting

hh

r

Height of the air-termination roddimensioned according to therequired protective angle

Additionalair-terminationcable

h = 2.5 m + s

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dard prescribes a mesh size which depends on theclass of lightning protection system chosen (seeChapter 5.1.1, Table 5.1.1.3). An air-terminationconductor installed inside the covering layer is dif-ficult to inspect after a number of years becausethe air-termination tips or mushroom head collec-tors are overgrown and no longer recognisable,and frequently damaged by maintenance work.Moreover, air-termination conductors installedinside the covering layer are more susceptible tocorrosion. Conductors of air-termination meshesinstalled uniformlyon top of the cover-ing layer are easier toinspect even if theybecome overgrown,and the height of theinterception systemcan be lifted up bymeans of air-termi-nation tips and rodsand “grown” withthe plants on theroof. Air-terminationsystems can be de-signed in differentways. The usual wayis to install a meshedair-termination netwith a mesh size of 5 m x 5 m (lightningprotection systemClass I) up to a max.mesh size of 15 m x15 m (lightning pro-tection system ClassIII) on the roof sur-face, regardless of

the height of the structure. It is preferable todetermine the installation site of the mesh consid-ering the external edges of the roof and any met-al structures acting as an air-termination system.

Stainless steel (Material No. 1.4571) has proven tobe a good material for the conductors of air-termi-nation systems on planted roofs.Aluminium wire must not be used for installingconductors in the covering layer (in the earth sub-strate or granulate), (Figures 5.1.7.1 to 5.1.7.3).

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Fig. 5.1.7.1 Green roof

Fig. 5.1.8.1 Connection of roof-mounted structures

Fig. 5.1.7.3 Conductor leading on the cover-ing layer

Fig. 5.1.7.2 Air-termination system on agreen roof

roof

1st floor

ground floor

basement

connection viaisolating spark gapdirect connection

EBB

data lines

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5.1.8 Isolated air-termination systems

Roof-mounted structures such as air conditioningand cooling systems, e.g. for mainframes, arenowadays used on the roofs of larger office blocksand industrial structures. Antennas, electricallycontrolled domelights, advertising signs with inte-grated lightning and all other protruding roof-mounted structures having a conductive connec-tion, e.g. via electrical cables or ducts, into thestructure, must be treated in a similar way.According to the state of the art for lightning pro-tection, such roof-mounted structures are protect-ed against direct lightning strikes by means of sep-arately mounted air-termination systems. This pre-vents partial lightning currents from entering thestructure, where they would affect or even destroythe sensitive electrical /electronic installations.In the past, these roof-mounted structures wereconnected directly. This direct connection meant that parts of thelightning current were conducted into the struc-ture. Later, “indirect connection” via a spark gapwas introduced. This meant that direct lightningstrikes to the roof-mounted structure could alsoflow away via the “internal conductors” to someextent, and in the event of a more distant light-ning strike to the structure, the spark gap shouldnot operate. The operating voltage of approx. 4 kV was almost always attained and hence partial

lightning current was also carried into the struc-ture via the electrical cable, for example. This canaffect or even destroy electrical or electronicinstallations inside the structure.

The only way of preventing these currents to becarried in is to use isolated air-termination systemswhich maintain the separation distances.

Figure 5.1.8.1 shows a partial lightning currentpenetrating the inside of the structure.

These widely different roof-mounted structurescan be protected by various designs of isolated air-termination systems.

Air-termination rods

For smaller roof-mounted structures (e.g. smallfans) the protection can be achieved by using indi-vidual, or a combination of several, air-termina-tion rods. Air-termination rods up to a height of2.0 m can be fixed with one or two concrete basespiled on top of each other (e.g. Part No. 102 010)as self supporting installation (Figure 5.1.8.2).

If air-termination rods are higher than 2.5 m or 3.0 m, they must be fixed at the object to be pro-tected by distance holders made of electricallyinsulating material (e.g. DEHNiso distance holder)(Figure 5.1.8.3).

Angled supports are a practical solution when air-termination rods also have to be secured against

www.dehn.de LIGHTNING PROTECTION GUIDE 71

Fig. 5.1.8.2 Isolated air-termination system, protection provided byan air-termination rod

Fig. 5.1.8.3 Air-termination rod with distance holder

Page 73: Lightning Protection Guide

the effects of side winds (Figures 5.1.8.4 and5.1.8.5).If higher air-termination rods are required, e.g. forlarger roof-mounted structures, which nothing canbe secured to, the air-termination rods can beinstalled by using special supports.Self-supporting air-termination rods up to a heightof 8.5 m can be installed by using a tripod. Thesesupports are fixed to the floor with standard con-crete bases (one on top of another). Additionalguy lines are required above a free height of 6 m inorder to withstand the stresses caused by the wind.

These self-supporting air-termination rods can beused for a wide variety of applications (e.g. anten-nas, PV installations). The special feature of thistype of air-termination system is its short installa-tion time as no holes need to be drilled and onlyfew elements need to be screwed together (Fig-ures 5.1.8.6 to 5.1.8.7).For protecting complete structures or installations(e.g. PV installations, ammunition depots) with air-termination rods, lightning protection masts areused. These masts are installed in a concrete foun-

dation. Free heights of 19 m above ground levelcan be achieved, even higher, if custom-made onesare used. It is also possible to span a cable betweenthese masts if they are especially designed for thispurpose. The standard lengths of the steel tele-scopic lightning protection masts are supplied insections, offering enormous advantages for trans-portation.

Further information (e.g. installation, assembly)about these steel telescopic lightning protectionmasts can be found in Installation Instructions No. 1574 (Figures 5.1.8.8 and 5.1.8.9).

Spanned over by cables or conductors

According to IEC 62305-3 (EN 62305-3), air-termi-nation conductors can be installed above the struc-ture to be protected.

The air-termination conductors generate a tent-shaped protective space at the sides, and a cone-shaped one at the ends. The protective angle αdepends on the class of lightning protection sys-tem and the height of the air-termination systemabove the reference plane.

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Fig. 5.1.8.4 Angled support for air-termina-tion rods

Fig. 5.1.8.6 Isolated air-termination systemfor photovoltaic system

Fig. 5.1.8.5 Supporting element for the air-termination rod

Fig. 5.1.8.7 Isolated air-termination systemfor roof-mounted structures

Fig. 5.1.8.9 Installation of a steel telescopiclightning protection mast

Fig. 5.1.8.8 Additional protection in the tran-sition area by anticorrosive bandfor underground application

Page 74: Lightning Protection Guide

The rolling sphere method with its correspondingradius (according to the class of lightning protec-tion system) can also be used to dimension theconductors or cables.

The mesh type of air-termination system can alsobe used if an appropriate separation distance sbetween the components of the installation andthe air-termination system must be maintained. Insuch cases, isolating distance holders in concretebases are installed vertically, for example, for guid-ing the mesh on an elevated level (Figure 5.1.8.10).

DEHNiso-CombiA user-friendly way of installing conductors orcables in accordance with the three differentdesign methods for air-termination systems(rolling sphere, protective angle, mesh) is providedby the DEHNiso-Combi programme of products.

The aluminium insulating pipes with “isolating dis-tance” (GRP – Glass-fibre Reinforced Plastic) whichare fixed to the object to be protected, provide away of guiding the cables. By means of the GRPdistance holder, a subsequently separate guidingto the down-conductor system or supplementaryair-termination systems (e.g. mesh) is realised.

Further information about the application is con-tained in the brochures DS 123E, DS 111E and inthe set of installation instructions No. 1475.

The types of design described can be combinedwith each other as desired to adapt the isolatedair-termination systems to the local conditions(Figures 5.1.8.11 to 5.1.8.14).

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Fig. 5.1.8.10 Installed air-termination system Ref.: Blitzschutz Wettingfeld , Krefeld. Germany

Fig. 5.1.8.12 Isolated air-termination systems with DEHNiso-Combi

Fig. 5.1.8.11 Tripod support for self-supporting insulating pipes

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5.1.9 Air-termination system for steeplesand churches

External lightning protection systemAccording to the German standard DIN EN 62305-3,Supplement 2, lightning protection systems ClassIII meet the normal requirements for churches andsteeples. In particular individual cases, for example

in the case of culturally significant structures, aspecial risk analysis in accordance with IEC 62305-2(EN 62305-2) must be carried out.

NaveAccording to the German standard DIN EN 62305-3,Supplement 2, the nave must have its own light-ning protection system and, if a steeple isattached, this system must be connected by theshortest route with a down-conductor system ofthe steeple. In the transept, the air-terminationconductor along the transverse ridge must beequipped with a down-conductor system at eachend.

SteepleSteeples up to a height of 20 m must be equippedwith a down-conductor system. If steeple and naveare joined, then this down-conductor system mustbe connected to the external lightning protectionsystem of the nave by the shortest route (Figure5.1.9.1). If the down-conductor system of thesteeple coincides with a down-conductor system ofthe nave, then a common down-conductor systemcan be used at this location. According to the Ger-man standard DIN EN 62305-3, Supplement 2,steeples above 20 m in height must be provided

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Fig. 5.1.8.13 Detail picture of DEHNiso-Combi

Fig. 5.1.9.1 Installing the down-conductor system at a steeple

Fig. 5.1.8.14 Isolated air-termination system with DEHNiso-Combi

Page 76: Lightning Protection Guide

with at least two down conductors. At least one ofthese down conductors must be connected withthe external lightning protection system of thenave via the shortest route.

Down-conductor systems on steeples must alwaysbe guided to the ground on the outside of thesteeple. The installation inside the steeple is notallowed (DIN EN 62305-3 Supplement 2). Further,the separation distance s to metal components andelectrical installations in the steeple (e.g. clockmechanisms, belfry) and under the roof (e.g. airconditioning, ventilation and heating systems)must be maintained by suitable arrangement ofthe external lightning protection system. Therequired separation distance can become a prob-lem especially at the clock. In this case, the conduc-tive connection into the structure can be replacedwith an isolating connector (e.g. a GRP pipe) toprevent hazardous sparking in parts of the exter-nal lightning protection system.

In more modern churches built with reinforcedconcrete, the reinforcement steels can be used asdown-conductor systems if it can be ensured thatthey provide a continuous conductive connection.If pre-cast reinforced concrete parts are used, thereinforcement may be used as a down-conductorsystem if terminals to connect the reinforcementcontinuously are provided on the pre-cast concreteparts.

In Germany the lightning equipotential bondingwith the electronic equipment (power system,telephone and public address system) shall beeffected at the entrance to the building and forthe bells control and timing system in the steepleand at the control and timing system, in accor-dance with Supplement 2 of DIN EN 62305-3.

5.1.10 Air-termination systems for wind tur-bines (WT)

Requirement for protection against lightningIEC 61400-24 describes measures required to pro-tect wind turbines against lightning. In the certifi-cation directives of the German Lloyd, a lightningprotection system Class III is required for WT hubsin a height of 60 m and Class II if the hub is in aheight of more than 60 m. In case of offshoreplants a lightning protection system Class I is

required. This can control lightning strikes withcurrents measuring up to 200,000 A. This require-ments are based on the experience made at theoperation of WT and on the assessment of the riskof damage according to IEC 62305-2 (EN 62305-2).

Principle of an external lightning protection sys-tem for wind turbinesThe external lightning protection system compri-ses air-termination systems, down-conductor sys-tems and an earth termination system and protectsagainst mechanical destruction and fire. Lightningstrikes to wind turbines usually affect the rotorblades. Hence, receptors, for example, are inte-grated to determine defined points of strike (Fig-ure 5.1.10.1).

In order to allow the coupled lightning currents toflow to earth in a controlled way, the receptors inthe rotor blades are connected to the hub with ametal interconnecting conductor (solid tape con-ductor St/tZn 30 mm x 3.5 mm or copper cable 50 mm2). Carbon fibre brushes or air spark gapsthen, in turn, bridge the ball-bearings in the headof the nacelle in order to avoid the welding of therevolving parts of the structure.

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Fig. 5.1.10.1 WT with integrated receptors in the rotor blades

receptor

wire meshwork

Page 77: Lightning Protection Guide

In order to protect structures on the nacelle, suchas anemometers in the event of a lightning strike,air-termination rods or “air-termination cages”are installed (Figure 5.1.10.2).The metal tower or, in case of a prestressed con-crete version, the down-conductor systems embed-ded in the concrete (round conductor St/tZn Ø 8 ...10 mm or tape conductor St/tZn 30 mm x 3.5 mm) is used as the down-conductor system. Thewind turbine is earthed by a foundation earthelectrode in the base of the tower and the meshedconnection with the foundation earth electrode ofthe operation building. This creates an “equipo-tential surface” which prevents potential differ-ences in the event of a lightning strike.

5.1.11 Wind load stresses on lightning pro-tection air-termination rods

Roofs are used more and more as areas for techni-cal installations. Especially when extending thetechnical equipment in the structure, extensiveinstallations are sited more than ever on the roofsof larger office blocks and industrial structures. It isessential to protect roof-mounted structures suchas air conditioning and cooling systems, transmit-ters for cell sites on host buildings, lamps, flue gasvents and other apparatus connected to the elec-trical low voltage system (Figure 5.1.11.1).

In accordance with the relevant lightning protec-tion standards contained in the IEC 62305 (EN62305) series, these roof-mounted structures canbe protected from direct lightning strikes with iso-lated air-termination systems. This requires an iso-

lation of both the air-termination systems, such asair-termination rods, air-termination tips or air-ter-mination meshes, and the down-conductor sys-tems, i.e. to be installed with sufficient separationdistance from the roof-mounted structures withinthe zone of protection. The construction of an iso-lated lightning protection system creates a zone ofprotection in which direct lightning strikes cannotoccur. It also prevents partial lightning currentsfrom entering the low voltage system and hencethe structure. This is important as the entering ofpartial lightning currents into the building canaffect or destroy sensitive electrical /electronicinstallations.Extended roof-mounted structures are alsoequipped with a system of isolated air-terminationsystems. These are connected with each other andalso with the earth-termination system. Amongother things the magnitude of the zone of protec-tion created depends on the number and theheight of the air-termination systems installed.A single air-termination rod is sufficient to providethe protection required by smaller roof-mountedstructures. The procedure involves the applicationof the rolling sphere method in accordance withIEC 62305-3 (EN 62305-3) (Figure 5.1.11.2).With the rolling sphere method, a rolling spherewhose radius depends on the class of lightning

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Fig. 5.1.10.2 Lightning protection for wind speed indicators at WT

Fig. 5.1.11.1 Protection against direct lightning strikes by self-sup-porting air-termination rods

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protection system chosen is rolled in all possibledirections on and over the structure to be protect-ed. During this procedure, the rolling sphere musttouch the ground (reference plane) and/or the air-termination system only.This method produces a protection volume wheredirect lightning strikes are not possible.To achieve the largest possible volume of protec-tion, and also to be able to protect larger roof-mounted structures against direct lightningstrikes, the individual air-termination rods shouldideally be erected with a corresponding height. To prevent self-supporting air-termination rodsfrom tilting and breaking a suitably designed baseand supplementary braces are required (Figure5.1.11.3).The requirement for the self-supporting air-termi-nation rods to be built as high as possible must bebalanced against the higher stress exerted by theactive wind loads. A 40 % increase in wind speed,for example, doubles the active tilting moment. Atthe same time, from the application point of view,

users demand a lightweight system of “self-sup-porting air-termination rods”, which are easier totransport and install. To ensure that it is safe to useair-termination rods on roofs, their mechanical sta-bility must be proven.

Stress caused by wind loadsSince self-supporting air-termination rods areinstalled at exposed sites (e.g. on roofs), mechani-cal stresses arise which, owing to the comparablelocation and the upcoming wind speeds, corre-spond to the stresses suffered by antenna frames.Self-supporting air-termination rods must there-fore basically meet the same requirements con-cerning their mechanical stability as set out in theGerman standard DIN 4131 for antenna frames.DIN 4131 divides Germany up into 4 wind zoneswith zone-dependent wind speeds (Figure5.1.11.4).When calculating the prospective actual wind loadstresses, apart from the zone-dependent windload, the height of the structure and the local con-

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Fig. 5.1.11.3 Self-supporting air-termina-tion rod with variable tripod

Fig. 5.1.11.2 Procedure for installation of air-termination systems according to IEC 62305-3 (EN 62305-3)

h 1h 2

air-termination rod

α

protective angle

mesh size M

downconductor

r

rollingsphere

earth-termination system

I 20 m 5 x 5 mII 30 m 10 x 10 mIII 45 m 15 x 15 mIV 60 m 20 x 20 m

Class of LPS Radius of therolling sphere (r)

Mesh size(M)

Max. height of the building

air-terminationrod with air-termination tip

bracing

variabletripod

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When designing self-supporting air-terminationrods, the following requirements must be met forthe wind load stress:

⇒ Tilt resistance of the air-termination rods

⇒ Fracture resistance of the rods

⇒ Maintaining the required separation distanceto the object to be protected even under windloads (prevention of intolerable deflections)

Determination of the tilt resistanceThe dynamic pressure arising (depends on thewind speed), the resistance coefficient cw and thecontact surface of the wind on the air-terminationrod, generate a uniform load q‘ on the surfacewhich generates a corresponding tilting momentMT on the self-supporting air-termination rod. To

ensure that the self-supporting air-termination rod is stable, the tilt-ing moment MT must be opposedby a load torque MO , which is gen-erated by the post. The magnitudeof the load torque MO depends onthe standing weight and the radiusof the post. If the tilting moment isgreater than the load torque, thewind load pushes the air-termina-tion rod over.The proof of the stability of self-supporting air-termination rods isalso obtained from static calcula-tions. Besides the mechanical char-acteristics of the materials used,the following information is in-cluded in the calculation:

⇒ Wind contact surface of theair-termination rod: deter-mined by length and diameterof the individual sections ofthe air-termination rod.

⇒ Wind contact surface of thebracing: Very high self-sup-porting air-termination rodsare anchored with 3 bracesmounted equidistantly aroundthe circumference. The windcontact surface of these bracescorresponds to the area pro-jected by these braces onto aplane in a right angle to thedirection of the wind, i.e. the

ditions (structure standing alone in open terrain orembedded in other buildings) must also be includ-ed. From Figure 5.1.11.4 it can be seen that around95 % of Germany´s surface area lies within WindZones I and II. Air-termination rods are thereforegenerally designed for Wind Zone II. The use ofself-supporting air-termination rods in Wind ZoneIII and Wind Zone IV must be assessed for eachindividual case taking the arising stresses intoaccount.According to DIN 4131 a constant dynamic pres-sure over the height of a structure can be expectedfor structures up to a height of 50 m. For the calcu-lations, the maximum height of the structure wasconsidered 40 m, so that a total height (height ofthe structure plus length of the air-terminationrods) is kept below the 50 m mark.

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Zone IV

Zone III Zone II

Zone I

München

Augsburg

Regensburg

Nürnberg

Würzburg

Stuttgart

Freiburg

Saarbrücken Mannheim

FrankfurtWiesbaden

Köln

Düsseldorf

Bonn

EssenDortmund

Erfurt Chemnitz

DresdenLeipzig

Halle

Magedburg

Berlin

PotsdamHannover

Bremen

HamburgSchwerin

RostockKiel

I

I

II

II

IV

Zone Dynamicpressure

2]q [kN/m

0.8

1.05

1.4

1.7

Windvelocityv [km/h]

126.7

145.1

161.5

184.7

Windstrength

12 - 17

Fig. 5.1.11.4 Division of Germany into wind load zones and corresponding values ofdynamic pressure and max. wind speed Ref.: DIN 4131:1991-11: Steel antenna frames, Berlin: Beuth-Verlag, GmbH

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brace lengths are shortened accordingly whenconsidered in the calculation.

⇒ Weight of the air-termination rod and thebracing: The dead weight of the air-termina-tion rod and the braces is taken into account inthe calculation of the load torque.

⇒ Weight of the post: The post is a tripodweighted down with concrete blocks. Theweight of this post is made up of the deadweight of the tripod and the individualweights of the concrete blocks used.

⇒ Tilting lever of the post: The tilting leverdenotes the shortest distance between thecentre of the tripod and the line or pointaround which the whole system would tilt.

The proof of stability is obtained by comparing thefollowing moments:

⇒ Tilting moment formed from the wind-load-dependent force on the air-termination rod orthe braces and the lever arm of the air-termi-nation rod.

⇒ Load torque formed from the weight of thepost, the weight of the air-termination rodand the braces, and the length of the tilt leverthrough the tripod.

Stability is achieved when the ratio of load torqueto the tilting moment assumes a value >1.Basically: the greater the ratio of load torque totilting moment, the greater the stability.The required stability can be achieved in the fol-lowing ways:

⇒ In order to keep the wind contact surface ofthe air-termination rod small, the cross sec-tions used have to be as small as possible. Theload on the air-termination rod is reduced,but, at the same time, the mechanical strengthof the air-termination rod decreases (risk ofbreaking). It is therefore crucial to make acompromise between a smallest possible crosssection to reduce the wind load and a largestpossible cross section to achieve the requiredstrength.

⇒ The stability can be increased by using largerbase weights and /or larger post radii. Thisoften conflicts with the limited areas for erec-tion and the general requirement for lowweight and easy transport.

ImplementationIn order to provide the smallest possible wind con-tact surface, the cross sections of the air-termina-tion rods were optimised in accordance with theresults of the calculation. For easier transportationand installation, the air-termination rod comprisesan aluminium tube (in sections, if so desired) andan aluminium air-termination rod. The post tohold the air-termination rod is hinged and is avail-able in two versions. Roof pitches up to 10 ° can becompensated..

Determination of the fracture resistanceNot only the stability of the air-termination rodmust be proven, but also the fracture resistance,since the occurring wind load exerts bendingstresses on the self-supporting air-termination rod.The bending stress in such cases must not exceedthe max. permissible stress. The bending stressoccurring is higher for longer air-termination rods.The air-termination rods must be designed toensure that wind loads as can arise in Wind Zone IIcannot cause permanent deformation of the rods.Since both the exact geometry of the air-termina-tion rod and the non-linear performance of thematerials used must be taken into account, theproof of the fracture resistance of self-supportingair-termination rods is obtained using an FEM cal-culation model. The finite elements method, FEMfor short, is a numerical method for calculation ofstresses and deformations of complex geometricalstructures. The structure under examination is bro-ken down into so-called “finite elements” usingimaginary surfaces and lines which are intercon-nected via nodes.The calculation requires the following informa-tion:

⇒ FEM-calculation model

The FEM calculation model corresponds to thesimplified geometry of the self-supporting air-termination rod.

⇒ Material characteristics

The performance of the material is represent-ed by the details of cross-sectional values,modulus of elasticity, density and lateral con-traction.

⇒ Loads

The wind load is applied to the geometricmodel as a pressure load.

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The fracture resistance is determined by compar-ing the permissible bending stress (materialparameter) and the max. bending stress which canoccur (calculated from the bending moment andthe effective cross section at the point of maxi-mum stress).

Fracture resistance is achieved if the ratio of per-missible to actual bending stress is >1. Basically, thesame principle also applies here: the greater theratio of permissible to actual bending stress, thegreater the fracture resistance.

Using the FEM calculation model, the actual bend-ing moments for two air-termination rods (length= 8.5 m) were calculated as a function of theirheight with and without braces (Figure 5.1.11.5).This clearly illustrates the effect of a possible braceon the course of the moments. Whereas the max.bending moment of the air-termination rod with-out a brace in the fixed-end point is around 1270 Nm, the brace reduces the bending momentto around 460 Nm. This brace makes it possible toreduce the stresses in the air-termination rod tosuch an extent that, for the max. expected windloads, the strength of the materials used is not

exceeded and the air-termination rod is notdestroyed.

ImplementationBraces create an additional “bearing point” whichsignificantly reduces the bending stresses occur-ring in the air-termination rod. Without supple-mentary bracing, the air-termination rods wouldnot cope with the stresses of Wind Zone II. There-fore, air-termination rods higher than 6 m areequipped with braces.

In addition to the bending moments, the FEM cal-culation also provides the tensile forces occurringin the bracing, whose strength must also beproven.

Determination of the wind-load-dependent de-flection of the air-termination rodA further important value calculated with the FEMmodel is the deflection of the tip of the air-termi-nation rod. Wind loads cause the air-terminationrods to bend. The bending of the rod results in achange to the volume to be protected. Objects tobe protected are no longer situated in the zone of

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Fig. 5.1.11.5 Comparison of bending moment courses at self-supporting air-termination rods with and without braces (length = 8.5 m)

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protection and /or proximities can no longer bemaintained.The application of the calculation model on a self-supporting air-termination rod without and withbraces produces the following results (Figures5.1.11.6 and 5.1.11.7).For the example chosen, the calculation gives a dis-placement of the tip of the air-termination rodwith bracing of around 1150 mm. Without bracingthere would be a deflection of around 3740 mm, atheoretical value which exceeds the breakingpoint of the air-termination rod under considera-tion.

ImplementationAbove a certain rod height, supplementary bracesreduce this defection significantly. Furthermore,this also reduces the bending load on the rod.

ConclusionTilting resistance, fracture resistance and deflec-tion are the decisive factors when designing air-termination rods. Base and air-termination rodmust be coordinated to ensure that the loadsoccurring as a result of the wind speeds of Zone IIdo not cause a tilting of the rod, nor damage it.It must still be borne in mind that large deflectionsof the air-termination rod reduce the separationdistance and thus intolerable proximities can arise.

Higher air-termination rods require a supplemen-tary bracing to prevent such intolerable deflec-tions of the tips of the air-termination rods.The measures described ensure that self-support-ing air-termination rods can cope with Zone IIwind speeds according to DIN 4131 (German stan-dard).

5.2 Down-conductor systemThe down-conductor system is the electrically con-ductive connection between the air-terminationsystem and the earth-termination system. Thefunction of down-conductor systems is to conductthe intercepted lightning current to the earth-ter-mination system without intolerable temperaturerises, for example, to damage the structure.To avoid damage caused during the lightning cur-rent discharge to the earth-termination system,the down-conductor systems must be mounted toensure that from the point of strike to the earth,

⇒ several parallel current paths exist,

⇒ the length of the current paths is kept as shortas possible (straight, vertical, no loops),

⇒ the connections to conductive components ofthe structure are made wherever required (dis-tance < s; s = separation distance).

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Fig. 5.1.11.6 FEM model of a self-supporting air-termination rodwithout bracing (length = 8.5 m)

Fig. 5.1.11.7 FEM model of a self-supporting air-termination rodwith bracing (length = 8.5 m)

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5.2.1 Determination of the number of downconductors

The number of down conductors depends on theperimeter of the external edges of the roof(perimeter of the projection on the ground sur-face).The down conductors must be arranged to ensurethat, starting at the corners of the structure, theyare distributed as uniformly as possible to theperimeter.Depending on the structural features (e.g. gates,precast components), the distances between thevarious down conductors can be different. In eachcase, there must be at least the total number ofdown conductor required for the respective classof lightning protection system.The IEC 62305-3 (EN 62305-3) standard gives typi-cal distances between down conductors and ringconductors for each class of lightning protectionsystem (Table 5.2.1.1).The exact number of down conductors can only bedetermined by calculating the separation distances. If the calculated separation distance cannot bemaintained for the intended number of down con-ductors of a structure, then one way of meetingthis requirement is to increase the number ofdown conductors. The parallel current pathsimprove the current splitting coefficient kc. Thismeasure reduces the current in the down conduc-tors, and the required separation distance can bemaintained.Natural components of the structure (e.g. rein-forced concrete supports, steel skeleton) can alsobe used as supplementary down conductors if con-tinuous electrical conductivity can be ensured.By interconnecting the down conductors atground level (base conductor) and using ring con-ductors for higher structures, it is possible to bal-

ance the distribution of the lightning currentwhich, in turn, reduces the separation distance s.The latest IEC 62305 (EN 62305) series of standardsattaches great significance to the separation dis-tance. The measures specified can change the sep-aration distance positively for structures and thusthe lightning current can be safely discharged.If these measures are not sufficient to maintain therequired separation distance, it is also possible touse a new type of high voltage-resistant isolatedconductors (HVI). These are described in Chapter5.2.4.Chapter 5.6 describes how the exact separationdistance can be determined.

5.2.2 Down-conductor system for a non-iso-lated lightning protection system

The down-conductor systems are primarily mount-ed directly onto the structure (with no distance).The criterion for installing them directly on thestructure is the temperature rise in the event oflightning striking the lightning protection system.If the wall is made of flame-resistant material ormaterial with a normal level of flammability, thedown-conductor systems may be installed directlyon or in the wall.

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Class of LPS

I

II

III

IV

Typical distance

10 m

10 m

15 m

20 m

Table 5.2.1.1 Distance between down conductors according to IEC 62305-3 (EN 62305-3)

Table 5.2.2.1 Max. temperature rise ΔT in K of different conductor materials

16

50

78

8 mm

10 mm

qmm2

III + IV II IIII + IV II IIII + IV II IIII + IV II I

* * *

190 460 940

78 174 310

56 143 309

5 12 22

3 5 9

1120 * *

37 96 211

15 34 66

146 454 *

12 28 52

4 9 17

Stainless steelCopperIronAluminium

Type of lightning protection system

* melting / vaporising

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Owing to the specifications in the building regula-tions of the German federal states, highly flamma-ble materials are generally not used. This meansthat the down-conductor systems can usually bemounted directly on the structure.Wood with a bulk density greater than 400 kg/m2

and a thickness greater than 2 mm is considered tohave a normal level of flammability. Hence thedown-conductor system can be mounted on wood-en poles, for example.If the wall is made of highly flammable material,the down conductors can be installed directly onthe surface of the wall, provided that the temper-ature rise when lightning currents flow is not haz-ardous.The maximum temperature rise ΔT in K of the var-ious conductors for each class of lightning protec-tion system are stated in Table 5.2.2.1. These valuesmean that, generally, it is even permissible toinstall down conductors underneath heat insula-tion because these temperature rises present nofire risk to the insulation materials.This ensures that the fire retardation measure isalso provided.When installing the down-conductor system in orunderneath heat insulation, the temperature rise(on the surface) is reduced if an additional PVCsheath is used. Aluminium wire sheathed in PVCcan also be used.If the wall is made of highly flammable material,and the temperature rise of the down-conductorsystems presents a hazard, then the down conduc-tors must be mounted to ensure that the distancebetween the down-conductor systems and thewall is greater than 0.1 m. The mounting elementsmay touch the wall. The erector of the structuremust state whether the wall, where a down-con-ductor system is to be installed, is made of flamma-ble material.

In Germany the precise definition of the termsflame-resistant, normal level of flammability andhighly flammable can be taken from Supplement 1of DIN EN 62305-3 (VDE 0185-305-3).

5.2.2.1 Installation of down-conductor sys-tems

The down conductors must be arranged to be thedirect continuation of the air-termination conduc-tors. They must be installed straight and vertically

so as to represent the shortest possible direct con-nection to the earth.Loops, e.g. projecting eaves or structures, must beavoided. If this is not possible, the distance meas-ured where two points of a down-conductor sys-tem are closest, and the length I of the down-con-ductor system between these points, must fulfillthe requirements on the separation distance s (Fig-ure 5.2.2.1.1).The separation distance s is calculated using thetotal length l = l1 + l2 + l3.

Down-conductor systems must not be installed ingutters and downpipes, even if they are sheathedin an insulating material. The damp in the gutterswould badly corrode the down-conductor systems.

If aluminium is used as a down conductor, it mustnot be installed directly (with no distance) on, in orunder plaster, mortar, concrete, neither should itbe installed in the ground. If it is equipped with aPVC sheath, then aluminium can be installed inmortar, plaster or concrete, if it is possible toensure that the sheath will not be mechanicallydamaged nor will the insulation fracture at lowtemperatures.It is recommended to mount down conductors tomaintain the required separation distance s to alldoors and windows (Figure 5.2.2.1.2).

Metal gutters must be connected with the downconductors at the points where they intersect (Fig-ure 5.2.2.1.3).The base of metal downpipes must be connectedto the equipotential bonding or the earth-termi-nation system, even if the pipe is not used as adown conductor. Since it is connected to the eavesgutter, through which the lightning current flows,the downpipe also takes a part of the lightning

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Fig. 5.2.2.1.1 Loop in the down conductor

l 2

l1

l3

s

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current which must be conducted into the earth-termination system. Figure 5.2.2.1.4 illustrates onepossible design.

5.2.2.2 Natural components of a down-con-ductor system

When using natural components of the structureas a down-conductor system, the number of downconductors to be installed separately can bereduced or, in some cases, they can be dispensedwith altogether.

The following parts of a structure can be used as“natural components” of the down-conductor sys-tem:

⇒ Metal installations, provided that the safe con-nection between the various parts is perma-nent and their dimensions conform to theminimum requirements for down conductors.These metal installations may also be sheathedin insulating material. The use of conduits con-taining flammable or explosive materials asdown conductors is not permitted if the sealsin the flanges /couplings are non-metallic orthe flanges/couplings of the connected pipes

are not otherwise connected so as to be elec-trically conductive.

⇒ The metal skeleton of the structure

If the metal frame of structures with a steelskeleton or the interconnected reinforcedsteel of the structure is used as a down-con-ductor system, then ring conductors are notrequired since additional ring conductorswould not improve the splitting of the current.

⇒ Safe interconnected reinforcement of thestructure

The reinforcement of existing structures can-not be used as a natural component of thedown-conductor system unless it can beensured that the reinforcement is safely inter-connected. Separate external down conduc-tors must be installed.

⇒ Precast parts

Precast parts must be designed to provide ter-minal connections for the reinforcement. Pre-cast parts must have an electrically conductiveconnection between all terminal connections.The individual components must be intercon-nected on site during installation (Figure5.2.2.2.1).

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Downpipes mayonly be used asdown conductor, ifthey are soldered orriveted

The connectionmust be asshort as pos-sible, straightand installedvertically StSt wire

Ø 10 mm

Fig. 5.2.2.1.2Down-conductor system Fig. 5.2.2.1.4 Earthed downpipe

Fig. 5.2.2.1.3 Air-termination system withconnection to the gutter

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Note:In the case of prestressed concrete, attention mustbe paid to the particular risk of possible intolera-ble mechanical effects arising from lightning cur-rent and resulting from the connection to thelightning protection system.For prestressed concrete, connections to tension-ing rods or cables must only be effected outsidethe stressed area. The permission of the personresponsible for erecting the structure must be giv-en before using tensioning rods or cables as adown conductor.If the reinforcement of existing structures is notsafely interconnected, it cannot be used as adown-conductor system. In this case, externaldown conductors must be installed.

Furthermore, facade elements, mounting channelsand the metal substructures of facades can be usedas a natural down-conductor system, providedthat:

⇒ the dimensions meet the minimum require-ments of down-conductor systems. For sheetmetal, the thickness must not be less than 0.5 mm. Their electrical conductivity in verticaldirection must be ensured. If metal facades areused as a down-conductor system, they mustbe interconnected to ensure that the individ-ual plates are safely interconnected with each

other by means of screws, rivets, or bridgingconnections. There must be a safe connectioncapable of carrying currents to the air-termi-nation system and also to the earth-termina-tion system.

⇒ If metal plates are not interconnected in accor-dance with the above requirement, but thesubstructure ensures that they are continuous-ly conductive form the connection on the air-termination system to the connection on theearth-termination system, then they can beused as a down-conductor system (Figures5.2.2.2.2 and 5.2.2.2.3).

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Fig. 5.2.2.2.1 Use of natural components – new buildings made ofready-mix concrete

Fig. 5.2.2.2.2 Metal subconstruction, conductively bridged

Fig. 5.2.2.2.3 Earth connection of a metal facade

expansion joint

expansion joint

Bridging braidPart No. 377 115

Fixed earthing terminalPart No. 478 200

vertical box section

wall fixing

horizontal support

Bridging braidPart No. 377 015

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Metal downpipes can be used as natural downconductors, as long as they are safely interconnect-ed (brazed or riveted joints) and comply with theminimum wall thickness of the pipe of 0.5 mm.If a downpipe is not safely interconnected, it canserve as a holder for the supplementary down con-ductor. This type of application is illustrated in Fig-ure 5.2.2.2.4. The connection of the downpipe tothe earth-termination system must be capable ofcarrying lightning currents since the conductor isheld only along the pipe.

5.2.2.3 Measuring pointsThere must be a measuring point at every connec-tion of a down conductor with the earth-termina-tion system (above the lead-in, if possible).

Measuring points are required to allow the inspec-tion of the following characteristics of the light-ning protection system:

⇒ Connections of the down conductors via theair-termination systems to the next down con-ductor

⇒ Interconnections of the terminal lugs via theearth-termination system, e.g. in the case ofring or foundation earth electrodes (earthelectrode Type B)

⇒ Earth electrode resistance of single earth elec-trodes (earth electrode Type A)

Measuring points are not required if the structuraldesign (e.g. reinforced concrete structure or steelskeleton) allows no “electrical” disconnection ofthe “natural” down-conductor system to theearth-termination system (e.g. foundation earthelectrode).

The measuring point may only be opened with thehelp of a tool for the purpose of taking measure-ments, otherwise it must be closed.Each measuring point must be able to be clearlyassigned to the design of the lightning protectionsystem. Generally, all measuring points are markedwith numbers (Figure 5.2.2.3.1).

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Fig. 5.2.2.2.4 Down conductorinstalled along adownpipe

Fig. 5.2.2.3.1 Measuring pointwith number plate

roofingheat insulation

wood insulation

metal construction

internal downconductor

roof bushing

If the separation distance is too short, the conductive parts of the buildingconstruction have to be connected to the air-termination system. The effectsfrom the currents have to be taken into account.

separationdistance s

Courtyards with circumference of morethan 30 m. Typical distances accordingto class of LPS

15 m

7.5

m

30 m

45 m

metal attic

courtyardcircumference> 30 m

Fig. 5.2.2.4.1 Air-termination system installed on large roofs – Internal down-conduc-tor system

Fig. 5.2.2.5.1 Down-conductor systems for court-yards

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5.2.2.4 Internal down-conductor systems

If the edges of the structure (length and width) arefour times as large as the distance of the downconductors which corresponds to the class of light-ning protection system, then supplementary inter-nal down conductors must be installed (Figure5.2.2.4.1).The grid dimension for the internal down-conduc-tor systems is around 40 m x 40 m.Large structures with flat roofs, such as large pro-duction halls or also distribution centres, frequent-ly require internal down conductors. In such cases,the ducts through the surface of the roof shouldbe installed by a roofer because he is responsiblefor ensuring that the roof provides protectionagainst rain.The consequences of the partial lightning currentsthrough internal down-conductor systems withinthe structure must be taken into account. Theresulting electromagnetic field in the vicinity ofthe down conductor must be taken into considera-tion when designing the internal lightning protec-tion system (pay attention to inputs to electrical /electronic systems.)

5.2.2.5 Courtyards

Structures with enclosed courtyards having aperimeter greater than 30 m (Figure 5.2.2.5.1)must have down-conductor systems installed withthe distances shown in Table 5.2.1.1.

5.2.3 Down conductors of an isolated exter-nal lightning protection system

If an air-termination system comprises air-termina-tion rods on isolated masts (or one mast), then this

is both air-termination system and down-conduc-tor system at the same time (Figure 5.2.3.1).Each individual mast requires at least one downconductor. Steel masts or mast with an intercon-nected steel reinforcement require no supplemen-tary down-conductor system.

For optical reasons, a metal flag pole, for examplecan also be used as an air-termination system.The separation distance s between the air-termina-tion and down-conductor systems and the struc-ture must be maintained.If the air-termination system consists of one ormore spanned wires or cables, each end of thecable which the conductors are attached torequires at least one down conductor (Figure5.2.3.2).

If the air-termination system forms an intermeshednetwork of conductors, i.e. the individual spannedwires or cables are interconnected to form a mesh(being cross-linked), there must be at least onedown conductor at the end of each cable the con-ductors are attached to (Figure 5.2.3.3).

5.2.4 High voltage-resistant, isolated down-conductor system – HVI conductor

A multitude of structures is used in order to createan exhaustive network of cell sites. Some of thesestructures have lightning protection systems. Inorder to design and implement the mast infra-structure in accordance with the standards, theactual situation must be taken into account duringthe design phase while the relevant standardshave to be strictly differentiated.

For the operator of a mobile phone network thereare basically three different situations:

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ss

s

mechanical fixing

downconductor

Fig. 5.2.3.1 Air-termination masts isolatedfrom the building

Fig. 5.2.3.2 Air-termination masts spannedwith cables

Fig. 5.2.3.3 Air-termination masts spannedwith cables with cross connection(meshing)

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⇒ Structure has no lightning protection system

⇒ Structure is equipped with a lightning protec-tion system which is no longer capable of func-tioning

⇒ Structure is equipped with a functioning light-ning protection system

Structure has no lightning protection systemIn Germany cell sites are constructed in accordancewith DIN VDE 0855-300. This deals with the earth-ing of the cell site. In accordance with the conceptfor protection against surges of the mobile phonenetwork operators, supplementary protectionagainst surges is integrated into the meter section.

Structure is equipped with a lightning protectionsystem which is no longer capable of functioningIn Germany cell sites are connected to the externallightning protection system as required by theclass of lightning protection system (LPS) deter-mined. The lightning current paths required forthe cell site are investigated and assessed. Thisinvolves replacing non-functional components ofthe existing installation which are required to dis-charge the lightning current, such as air-termina-tion conductor, down-conductor system and con-nection to the earth-termination system. Anyobserved defects to parts of the installation whichare not required must be notified in writing to theowner of the structure.

Structure is equipped with a functioning lightningprotection systemExperience has shown that most lightning protec-tion systems are designed according to LPS Class III.Regular inspections are prescribed for certainstructures. It must be planned to integrate the cellsite installation in accordance with the class oflightning protection system (LPS) determined. Forinstallations with LPS Class I and II, the surround-ings of the installation must be recorded photo-graphically to ensure that, if problems subsequent-ly arise with proximities, the situation at the timeof construction can be proven. If a cell site is erect-ed on a structure with a functional external light-ning protection system, its erection is governed bythe latest lightning protection standard (IEC 62305(EN 62305)). In this case for example, in Germanythe DIN VDE 0855-300 can only be used for theequipotential bonding of the antenna cable. Prox-imities must be calculated as appropriate to the

class of LPS. All mechanical components used mustbe able to cope with the prospective partial light-ning currents. For reasons of standardisation, allthe steel fixing elements and structures for hold-ing antennas of many mobile phone networkoperators must be designed for LPS Class I. Theconnection should be done via the shortest route,which is not a problem, however, as the air-termi-nation conductors on flat roofs are usuallydesigned to be meshed. If there is a functionallightning protection system on the host building,this has a higher priority than an antenna earthinginstallation.

Because of how it is designed, the class of light-ning protection system to be effected must be laiddown at the discussion stage of the project:

⇒ If the system technology components are alsosituated on the roof, it is preferable to installthe electrical cable on the exterior side of thestructure.

⇒ If the system technology components are situ-ated on the roof, and if it is intended to erecta central mast, the installation must beequipped with an isolated lightning protec-tion system.

⇒ If the system technology components arelocated within the structure, it is preferable tohave an isolated lightning protection embed-ment. Care must be taken that the cell siteinfrastructure is designed to be geometricallysmall so that the costs of the isolated lightningprotection system are economically viable.

Experience has shown that, in many cases, existinglightning protection systems have old defectswhich adversely affect the effectiveness of theinstallation. These defects mean that even if thecell site is correctly “tied-in” to the external light-ning protection system, damage can still be causedwithin the structure.

In order to enable a designer of mobile phone net-works to erect antenna installations in accordancewith the standards even in difficult situations, theonly thing available to him used to be the isolatedlightning protection system with horizontal dis-tance holders. In such cases, however, the design ofthe antenna installation, could really not be con-sidered architecturally aesthetic (Figure 5.2.4.1).

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Air-termination systems as shown in Figure 5.2.4.1are not applicable for locations where the anten-nas have to be pleasing to look at.

The isolated HVI conductor is an innovative solu-tion which provides the installer of lightning pro-tection systems with novel possibilities for designand for easy maintaining of the separation dis-tance (Figure 5.2.4.2).

5.2.4.1 Installation and performance of theisolated down-conductor system HVI

Basic conception of the isolated down-conductorsystem is to cover the lightning current carryingconductor with an insulating material, allowingthe necessary separation distance s to other con-ductive parts of the structure, to electrical conduc-tors and conduits to be kept. Incorrect proximitiesmust be avoided. Basically the following require-ments to the isolated down-conductor system haveto be met, if insulating materials are used to avoidinadmissible proximities:

⇒ Possibility of a lightning current proof connec-tion of the down-conductor system with theair-termination system (air-termination rod,air-termination conductor, air-termination tip,etc.) by terminals.

⇒ Compliance with the required separation dis-tance s by sufficient dielectric strength of thedown-conductor system in the range of theinput point as well as in the course of thedown-conductor system.

⇒ Sufficient current carrying capability becauseof an adequate cross section of the down-con-ductor system.

⇒ Possibility of connection to the earth-termina-tion system or of equipotential bonding.

Sheathing of the down conductors with insulatingmaterials of high dielectric strength basicallyallows to reduce the separation distance. Certainhigh voltage technological requirements, howev-er, have to be met. This being necessary as thedielectric strength of the isolated down-conductorsystem depends on its positioning and on theoccurrence of creeping discharges.

The use of unshielded, isolated down-conductorsystems is a fundamental solution to be independ-ent with regard to positioning and laying. A con-ductor, however, which has only a sheathing ofinsulating material does not solve the problem.Already relatively low induced impulse voltageswill release creeping discharges in the range of theproximities (e.g. between metal, earthed conduc-tor holders and the feeding point), which canresult in a total flashover at the surface of longconductor sections. Ranges of insulating material,metal (at high voltage potential or earthed) get-ting in contact with the air are critical with regardto creeping discharges. This range is subject to ahigh voltage stressing because of the potentialarising of creeping discharges, resulting in a con-siderably reduced voltage resistance. Creeping dis-charges have to be taken into account, wheneverusual (vertical to the surface of the insulatingmaterial) components of electrical field strength E,lead to the tripping voltage of the creeping dis-charge being exceeded and, field components tan-gentially enforce the increase of creeping dis-charges (Figure 5.2.4.1.1).

The creeping discharge release-voltage determinesthe resistance of the whole insulation, being in themagnitude of 250 – 300 kV lightning impulse volt-age.

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5.2.4.25.2.4.1

Fig. 5.2.4.1 Isolated air-termination system with distance holderFig. 5.2.4.2 Isolated air-termination system for cell sites –

Application of DEHNconductor system

Page 91: Lightning Protection Guide

By the coaxial single conductor cable – HVI conduc-tor – shown in Figure 5.2.4.1.2 the occurrence ofthe creeping discharge is avoided and the light-ning current is safely conducted to the earth.

Isolated down-conductor systemswith field control and semi-con-ductive shield prevent from creep-ing discharges by a targeted influ-encing of the electric field in therange of the input point. Theyallow the lightning current to beconducted into the special cable,the safe discharge of the lightningcurrent and the required separa-tion distance s to be kept. Thesemi-conductive shield of the coax-ial input cable insulates from theelectric field. It has to be minded,however, that the magnetic fieldsurrounding the current carryinginner conductor is not affected.Optimisation of the field controlallows an adjusted cable sealingunit length of 1.50 m to realise the

required equivalent separation distance in air of s ≤ 0.75 m and in case of solid construction materi-al of s ≤ 1.50 m (Figure 5.2.4.1.3).This special cable sealing unit is realised by anadjusted connection element to the air-termina-tion system (supply point) and the equipotentialbonding terminal in a fixed distance. Comparedwith a coaxial cable with metal shield, the wholesemi-conductive coating of the cable has a clearlyhigher resistance. Even by a multiple equipotentialbonding connection of the cable coating onlyinsignificant partial lightning currents will bedragged into the building.

Apart from the required separation distance s , themaximum conductor length Lmax of such an isolat-ed down-conductor system is calculated with

5.2.4.2 Installation examplesApplication for cell sitesCell site installations are frequently erected onhost structures. There is usually an agreementbetween the operator of the cell site installationand the owner of the structure that the erection ofthe cell site installation must not increase the risk

Lk s

k km

i cmax =

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innerconductor

insulation

proximity

Fig. 5.2.4.1.1 Basic development of a creeping discharge at an isolated down conductorwithout special coating

coupling ofthe lightningimpulse current

air-terminationbonding element

inner conductor

high voltage-resistant insulation equipotential

bonding element

semi-conductivesheath

sealing unit range

Fig. 5.2.4.1.2 Components of HVI Conductor

Fig. 5.2.4.1.3 HVI conductor I and components of the DEHNconduc-tor system

Page 92: Lightning Protection Guide

to the structure. For protection against lightning,this particularly means that no partial lightningcurrents must enter the structure if there is a light-ning strike to the frame structure. A partial light-ning current within the structure would especiallyput the electrical and electronicapparatus at risk.Figure 5.2.4.2.1 shows one possi-ble solution for the “isolated air-termination system” on theframe structure of an antenna.The air-termination tip must befixed to the frame structure ofthe antenna by means of aninsulating pipe in non conduc-tive material so that it is isolated.The height of the air-termina-tion tip is governed by therequirement that the structureof the frame and any electricaldevices which are part of the cellsite installation (BTS – BaseTransceiver Station) must bearranged in the zone of protec-tion of the air-termination tip.

Structures with several antenna systems must beequipped with multiple “isolated air-terminationsystems”.Figures 5.2.4.2.2a and b illustrate the installationon an antenna post.

www.dehn.de LIGHTNING PROTECTION GUIDE 91

Fig. 5.2.4.2.2b Connection to the antennaframe structure for directingpotential

Fig. 5.2.4.2.2a Insulating pipe within theantenna area

Fig. 5.2.4.2.1 Integration of a new 2G/3G antenna into the existing lightning protection system by using the HVI conductor

earth connectionfeeding point

HVI® conductor

insulating pipe

earthingclamp

air-termination tip

feeding point

HVI® conductor

insulatingpipe

earthconnection

α α

antenna cableearthing acc. to VDE 0855-300

HVI® conductor II

insulating pipe GRP/AL

air-termination tip

sealing unitrange

BTS

LV-supply

equipotential bonding line

sealing unit

bare down conductor

Isolated lightning protection

Note: Clarify existing state of protection

air-termination system

Page 93: Lightning Protection Guide

Roof-mounted structuresMetal and electrical roof-mounted structures pro-trude above roof level and are exposed points forlightning strikes. The risk of partial lightning cur-rents flowing within the structure is also existingbecause of conductive connections with conduitsand electrical conductors leading into the struc-ture. To prevent this and to set up the necessaryseparation distance for the complete structure easily, the air-termination system must be instal-led with a terminal to the isolated down-conduc-tor system, as shown in Figure 5.2.4.2.3a and5.2.4.2.3b.

Hence all metal and electrical roof-mounted struc-tures protruding above roof level are within thearea protected against lightning strikes. The light-ning current will be “channeled” along the struc-ture and distributed by the earth-termination sys-tem.

If several structures are mounted on the roof then,according to the basic illustration in Figure5.2.4.2.4, several isolated air-termination systemsmust be installed. This must be done to ensure thatall structures protruding above the roof must bearranged in an area protected from lightningstrikes (lightning protection zone LPZ 0B).

Down-conductor systemEspecially problematical from the optical point ofview often is the integration of a down-conductorsystem, taking into account the required separa-tion distance s.The HVI conductor e.g. can be installed or evenintegrated in the facade (Figure 5.2.4.2.5). Thisnew kind of isolated down-conductor system con-

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α

cable duct

foundation earth electrode

metal earthed roof-mounted structure

reinforcementcable duct

HVI® conductor I

EB terminal

separationdistance s

sealing unit

isolated air-termination system

metal attic cover within the protective area of an isolated air-termination system

ring conductor

HVI® conductor

Fig. 5.2.4.2.3a Fan with air-termination rod and spanned cable

Fig. 5.2.4.2.3b Air-termination rod, elevated ring conductor connect-ed to the isolated down-conductor system

Fig. 5.2.4.2.4 Keeping the required separation distance with volt-age-controlled isolated down conductor (HVI)

Fig. 5.2.4.2.5 Air termination system with spanned cable and isolated down-conductor system

Page 94: Lightning Protection Guide

tributes to an architectural more pleasing struc-ture. Functionality and design can be an entity.Therefore this innovative technology is an impor-tant feature of modern architecture.

5.2.4.3 Project example: Training and resi-dential building

StructureThe structure in Figure 5.2.4.3.1 was built conven-tionally from the ground floor to the 6th floor. Ata later date, the 7th floor was attached to theexisting roof surface.The external facade of the 7th floor consists ofmetal sheets.The media centre is situated on the 3rd floor, theground floor is used for administration. All otherfloors up to the 7th floor are used for apartments.The roof surface of the 6th and 7th floor was fin-ished off with a metal attic whose components areinterconnected so as to be non-conductive.The complete structure is 25.80 m high (withoutattic) up to the roof level.Subsequently, five antenna systems for mobilephone systems and microwaves were installed bydifferent operators of mobile phone networks onthe roof surface of the 7th floor. The antennaswere erected both in the corners and in the middleof the roof surface.The cable (coax cables) from the four antennas inthe corners of the roof surface were installed inthe vicinity of the attic to the south-west corner.From this point, the cables are ledthrough a metal cable duct which isconnected to the attic of the roof sur-faces of the 7th and 6th floors to theBTS room on the 6th floor.The cables from the antenna in themiddle are also installed by means of ametal cable duct directly to the 2ndBTS room on the north-east side of thestructure to the 6th floor. This cableduct is also connected to the surround-ing attics.The structure was equipped with alightning protection system. The newinstallation of the external lightningprotection system to protect againstdamage to the structure and life haz-ards was designed in accordance withthe national lightning protection stan-

dard DIN V VDE V 0185-3, which was applicablewhen the building was erected.

During the installation of the antennas, theequipotential bonding and earthing measures ofthe system were carried out in accordance with theGerman standard DIN VDE 0855 Part 300.

The earthing of the systems, however, was not iso-lated from the existing external lightning protec-tion system at the earth-termination system atground level, but directly at the air-terminationsystem.

Hence, in the event of a lightning discharge, par-tial lightning currents are conducted directly intothe structure via the coax cable shields. These par-tial lightning currents do not only present a lifehazard, they also present a hazard to the existingtechnical equipment of the structure.

New concept

A lightning protection system was required, whichprevents partial lightning currents from being con-ducted directly into the structure via the antennacomponents (frame structures, cable shields andinstallation systems). At the same time, therequired separation distance s between the framestructures of the antennas and the air-terminationsystem on the roof surface of the 7th floor must berealised.

This cannot be effected with a lightning protec-tion system of a conventional design.

www.dehn.de LIGHTNING PROTECTION GUIDE 93

Fig. 5.2.4.3.1 Total view

54

3 cable tray1 2

Antennas of the cell site operators (1 - 5)

Page 95: Lightning Protection Guide

By installing the HVI conductor,a lightning protection systemwas constructed with an isolat-ed air-termination system. Thisrequired the following compo-nents:

⇒ Air-termination tips oninsulating pipes in GRPmaterial, secured directlyto the antenna pole (Fig-ure 5.2.4.2.2a).

⇒ Down conductor from theair-termination tip bymeans of an HVI conductorwith connection to the iso-lated ring conductor (Fig-ure 5.2.4.3.2).

⇒ Sealing end feeding pointto ensure the resistanceagainst creeping flashoversat the input (Figures5.2.4.2.2a and 5.2.4.2.2b).

⇒ Isolated ring conductor oninsulating supports madeof GRP, supports as high asaccording to the calcula-tion of the required sepa-ration distance

⇒ Down conductors installedseparately from the isolat-ed ring conductor via therespective metal attics andmetal facade to the baremetal down conductors onthe 6th floor with therequired separation dis-tance s to the lower attic(Figure 5.2.4.3.3).

⇒ Supplementary ring con-ductor, all down-conductorsystems interconnected ata height of approx. 15 m toreduce the required sepa-ration distance s of theinterception and down-conductor system (Figures5.2.4.3.4 and 5.2.4.4.1).

The various implementationstages explained in detail aresummarised in Figure 5.2.4.3.4.

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air-termination tip

HVI® conductor

isolated ring conductor

bare down conductorcable duct

attic

ring conductor

bare down conductor

isolatedring conductor

HVI® conductorconnection toequipotential bonding

isolated ring conductor

cable tray

HVI®

conductor

Fig. 5.2.4.3.2 Isolated air-terminationsystem and isolated ringconductorRef.: H. Bartels GmbH,Oldenburg, Germany

Fig. 5.2.4.3.3 Down conductor of isolated ring con-ductor

Fig. 5.2.4.3.4 Total view on a newly installed external lightning protection system

Page 96: Lightning Protection Guide

It is also important to note that the proposeddesign concept was discussed in detail with the sys-tem erector in order to avoid mistakes when carry-ing out the work.When designing the external lightning protectionsystem, care was taken that the deck on the 6thfloor (Figure 5.2.4.3.1) and the lower attachments(Figure 5.2.4.3.4) were also arranged in the zone ofprotection/protective angle of the air-terminationsystem.

5.2.4.4 Separation distanceWhen calculating the required separation distances, not only the height of the structure but also theheights of the individual antennas with the isolat-ed air-termination system had to be taken intoconsideration.Each of the four corner antennas protrudes 3.6 mabove the surface of the roof. The antenna in themiddle protrudes 6.6 m above the roof surface.

Considering the height of the structure, result thefollowing total heights to be taken into accountwhen calculating the installation:

⇒ 4 corner antennas to the base of the air-termi-nation tip + 29.40 m

⇒ 1 antenna in the middle of the roof surface tothe base of the air-termination tip + 32.40 m

⇒ Three further, isolated separate air-termina-tion rods on the west side of the roof surfaceand two isolated air-termination masts on thebalcony 6th floor, south side, realise the zoneof protection of the complete roof surface.

A special cable, DEHNconductor, Type HVI, wasused as the isolated down conductor, allowing anequivalent separation distance of s = 0.75 m (air) /1.5 m (solid building materials) to be maintained.

The calculation of the required separation dis-tances was done as shown in Figure 5.2.4.4.1 forthree partial areas:

1. Partial area at a level of + 32.4 m and a level of+ 29.4 m (antennas) to + 27.3 m (isolated ringconductor) on the roof.

2. Partial area at + 27.3 m to + 15.0 m (isolatedring conductor on roof up to lower supple-mentary ring conductor).

3. Partial area at + 15.0 to ± 0 m (lower ring con-ductor to ground level).

The complete down-conductor system comprisessix down conductors from the isolated ring con-ductor at a height of + 27.3 m to the supplemen-tary ring conductor at a level of + 15.0 m. The ringconductor at a level of + 15.0 m is connected withthe earthing ring conductor via the six down con-ductors of the residential structure and four fur-ther down conductors on attached parts of thestructure.This produces a different splitting of the current inthe individual partial areas which had to be takeninto consideration for the design of the lightningprotection system.The equipotential bonding required and theearthing of the antenna components on the roofsurface (including the cable ducts, metal fa-cades and the attics on both roof levels) was done using two supplementary earthing cablesNYY 1 x 25 mm2 connected to the equipotentialbonding of the individual BTS stations.The erection of this isolated air-termination systemon the surface of the roof and on the antenna sys-tems, as well as the isolated down conductorsaround metal parts of the structure, prevent par-tial lightning currents from entering the structure.

www.dehn.de LIGHTNING PROTECTION GUIDE 95

Fig. 5.2.4.4.1Calculation of the required separation distance

ring conductor

EB c

ondu

ctor

dow

nco

nduc

tor

kc1

kc2

kc3

L 1L 2

L 3 1st floor

2nd floor

3rd floor

4th floor

5th floor

7th floor

ground floor

6th floor

Page 97: Lightning Protection Guide

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Remarks10)Min. cross-section mm2

Material Configuration

Copper solid flat materialsolid round material7)

cablesolid round material3), 4)

508)

508)

508)

2008)

min. thickness 2 mmdiameter 8 mmmin. diameter each wire 1.7 mmdiameter 16 mm

Tin platedcopper1)

solid flat materialsolid round material7)

cable

508)

508)

508)

min. thickness 2 mmdiameter 8 mmmin. diameter each wire 1.7 mm

Aluminium solid flat materialsolid round materialcable

70508)

508)

min. thickness 3 mmdiameter 8 mmmin. diameter each wire 1.7 mm

Aluminiumalloy

solid flat materialsolid round materialcablesolid round material3)

508)

50508)

2008)

min. thickness 2.5 mmdiameter 8 mmmin. diameter each wire 1.7 mmdiameter 16 mm

Hot dippedgalvanisedsteel2)

solid flat materialsolid round material9)

cablesolid round material3), 4), 9)

508)

50508)

2008)

min. thickness 2.5 mmdiameter 8 mmmin. diameter each wire 1.7 mmdiameter 16 mm

Stainlesssteel5)

solid flat material6)

solid round material6)

cablesolid round material3), 4)

508)

50708)

2008)

min. thickness 2 mmmin. thickness 8 mmmin. diameter each wire 1.7 mmdiameter 16 mm

1) Hot dipped or electroplated, minimum thickniss of the coating 1 μm.

2) The coating should be smooth, continuous and free of residual flux, minimum thickness 50 μm.

3) For air-termination rods. For applications where mechanical loads, like wind loads are not critical, a max.1 m long air-termination rod with a diameter of 10 mm with an additional fixing may be used.

4) For lead-in earth rods.

5) Chromium 16 %, nickel 8 %, carbon 0.03 %

6) For stainless steel in concrete and/or in direct contact with flammable material, the min. cross sectionfor solid round material has to be increased to 78 mm2 (10 mm diameter) and for solid flat material to75 mm2 (3 mm thickness).

7) For certain applications where the mechnical strength is not important, 28 mm2 (6 mm diameter) materialmay be used instead of 50 mm2 (8 mm diameter). Then distance of the fixing elements has to be reduced.

8) If thermal and mechanical requirements are important, the min. cross section for solid flat material canbe increased to 60 mm2 and for solid round material to 78 mm2.

9) At a specific energy of 10,000 kJ/Ω the min. cross section to prevent from melting is 16 mm2 (copper),25 mm2 (aluminium), 50 mm2 (steel) and 50 mm2 (stainless steel). For further information see Annex E.

10) Thickness, width and diameter are defined at a tolerance of ± 10 %.

Table 5.3.1 Material, configuration and min. cross sections of air-termination conductors, air-termination rods and down conductors accordingto IEC 62305-3 (EN 62305-3) Table 6

Page 98: Lightning Protection Guide

5.3 Materials and minimum dimen-sions for air-termination conduc-tors and down conductors

Table 5.3.1 gives the minimum cross sections, formand material of air-termination systems.

This requirements arise from the electrical conduc-tivity of the materials to carry lightning currents(temperature rise) and the mechanical stresseswhen in use.

When using a round conductor Ø 8 mm as an air-termination tip, the max. free height permitted is0.5 m. The height limit for a round conductor Ø 10mm is 1 m in free length.

Note:According to IEC 62305-3 (EN 62305-3) Clause 1,Table 8, the minimum cross section for an intercon-necting conductor between two equipotentialbonding bars is 14 mm2 Cu.

Tests with a PVC-insulated copper conductor andan impulse current of 100 kA (10/350 μs) deter-mined a temperature rise of around 56 K. Thus, acable NYY 1 x 16 mm2 Cu can be used as a downconductor or as a surface and underground inter-connecting cable, for example.

5.4 Assembly dimensions for air-ter-mination and down-conductorsystems

The following dimensions (Figure 5.4.1) have beentried and tested in practice and are primarilydetermined by the mechanical forces acting on thecomponents of the external lightning protectionsystem.These mechanical forces arise not so much as aresult of the electrodynamic forces generated bythe lightning currents, but more as a result of thecompression forces and the tensile forces, e.g. dueto temperature-dependent changes in length,wind loads or the weight of snow.The information concerning the max. distances of1.2 m between the conductor holders primarilyrelates to St/tZn (relatively rigid). For using alu-minium, distances of 1 m have become the stan-dard in practice.IEC 62305-3 (EN 62305-3) gives the followingassembly dimensions for an external lightning pro-tection system (Figures 5.4.1 and 5.4.2).

Figure 5.4.3 illustrates the application on a flatroof.

www.dehn.de LIGHTNING PROTECTION GUIDE 97

0.3 m

1.0

m

0.3

m1.

5 m

0.5

m

0.05 m

α

e

e = 0.2 mdistanceappropriate1.0 m 0.

15 m

1.0 m

as closeas possible

to the edge

Fig. 5.4.1 Detail examples of an external lightning protection system at a building with a slopedtiled roof

Fig. 5.4.2 Air-termination rod for chim-neys

1 m

Fig. 5.4.3 Application on a flat roof

Page 99: Lightning Protection Guide

If possible, the separation dis-tance to windows, doors andother openings should be main-tained when installing downconductors.Further important assemblydimensions are illustrated in Fig-ures 5.4.3 – 5.4.5.

Installation of surface earth elec-trodes (e.g. ring earth electrodes)around the structure at a depthof > 0.5 m and a distance ofapprox. 1 m from the structure(Figure 5.4.4).

For the earth entries or terminalson the foundation earth elec-trode (ring earth electrodes), cor-rosion protection must be consid-ered. Measures such as anticorrosive bands orwires with PVC sheath at a min. of 0.3 m above andbelow the turf (earth entry) must be employed(Figure 5.4.5) for protection.

An optically acceptable and noncorrosive connec-tion possibility is provided by a stainless steel fixedearthing terminal set to be laid in concrete.Moreover, there must also be corrosion protectionfor the terminal lug for equipotential bondinginside the building in damp and wet rooms.

The material combinations below (within air-ter-mination systems, down conductors and with partsof the structure) have been tried and tested, pro-vided that no particularly corrosive environmentalconditions must be taken into consideration. Theseare values obtained from experience (Table 5.4.1).

5.4.1 Change in length of metal wires

In practice, the temperature-dependent changesin length of air-termination and down conductors are often underestimated.

The older regulations and stipulations recom-mended an expansion piece about every 20 m as ageneral rule in many cases. This stipulation wasbased on the use of steel wires, which used to bethe usual and sole material employed. The highervalues for the coefficients of linear expansion ofstainless steel, copper and especially aluminiummaterials were not taken into account.

In the course of the year, temperature changes of100 K must be expected on and around the roof.The resulting changes in length for different metalwire materials are shown in Table 5.4.1.1. It isnoticeable that, for steel and aluminium, the tem-

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Steel (tZn)

Aluminium

Copper

StSt

Titanium

Tin

Steel (tZn)

yes

yes

no

yes

yes

yes

Aluminium

yes

yes

no

yes

yes

yes

Copper

no

no

yes

yes

no

yes

StSt

yes

yes

yes

yes

yes

yes

Titanium

yes

yes

no

yes

yes

yes

Tin

yes

yes

yes

yes

yes

yes

building

≥ 0.

5 m

≈ 1 m

0.3 m

protectionagainst

corrosion0.3 m

Fig. 5.4.4 Dimensions for ring earth elec-trodes

Table 5.4.1 Material combinations

Fig. 5.4.5 Points threatened by corrosion

Page 100: Lightning Protection Guide

perature-dependent changes in length differ by afactor of 2.The stipulations governing the use of expansionparts in practice are thus as shown in Table 5.4.1.2.When using pieces, care must be taken that theyprovide flexible length equalisation. It is not suffi-cient to bend the metal wires into an S shape sincethese “expansion pieces“, handmade on site, arenot sufficiently flexible.When connecting air-termination systems, forexample to metal attics surrounding the edges ofroofs, care should be taken that there is a flexibleconnection to suitable components or measures. Ifthis flexible connection is not made, there is a riskthat the metal attic cover will be damaged by thetemperature-dependent change in length.To compensate for the temperature-dependentchanges in length of the air-termination conduc-tors, expansion pieces must be used to equalise theexpansion (Figure 5.4.1.1).

5.4.2 External lightning protection systemfor an industrial structure and a resi-dential house

Figure 5.4.2.1a illustrates the design of the exter-nal lightning protection system for a residentialhouse with attached garage and Figure 5.4.2.1bthat for an industrial structure.Figures 5.4.2.1a and 5.4.2.1b and Tables 5.4.2.1aand b show examples of the components in usetoday.No account is taken of the measures required foran internal lightning protection system such aslightning equipotential bonding and surge protec-tion (see also Chapter 6).

Particular attention is drawn to DEHN´s DEHNsnapand DEHNgrip programme of holders.The DEHNsnap generation of synthetic holders(Figure 5.4.2.2) is suitable as a basic component

www.dehn.de LIGHTNING PROTECTION GUIDE 99

Δ ΔL L T= ⋅ ⋅α

Material Coefficientof linear expansion α

Assumed temperature change on the roof: ΔT = 100 K

Steel

StSt

Copper

Aluminium

11.5

16

17

23.5

ΔL = 11.5 • 10-6 • 100 cm • 100 = 0.115 cm • 1.1 mm/m

ΔL = 16 • 10-6 • 100 cm • 100 = 0.16 cm = 1.6 mm/m

ΔL = 17 • 10-6 • 100 cm • 100 = 0.17 cm = 1.7 mm/m

ΔL = 23.5 • 10-6 • 100 cm • 100 = 0.235 cm • 2.3 mm/m

1

106

1

K

ΔL

Calculation formula

X

X

X

X

X

X

15

20

10

15

10

Material Surface under the fixing of the air-terminationsystem or down conductor

Distance ofexpansion pieces

in msoft,

e. g. flat roof with bitumen-or synthetic roof sheetings

hard,e. g. pantilesor brickwork

Steel

StSt/Copper

Aluminium

Use of expansion pieces, if no other length compensation is provided

Table 5.4.1.2 Expansion pieces in lightning protection – Recommended application

Table 5.4.1.1 Calculation of the temperature-related change in length ΔL of metal wires in light-ning protection

Fig. 5.4.1.1 Air-termination system –Compensation of expansionwith bridging braid

Page 101: Lightning Protection Guide

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EBB

3

14

13

15

210

9

7

8

6

1

4

511

Pos. Part description Part No.1 Round conductor 8 mm - DEHNALU,

medium hard soft- twistable840 008840 018

2 Steel strip 30 x 3.5 mm St/tZnRound conductor 10 mm StSt V4A

810 335860 010

3 Roof conductor holders St/tZnfor ridge and hip tiles StSt

StStStStStStStSt

202 020204 109204 249204 269206 109206 239

4 Roof conductor holders StStfor conductors within roof surfaces StSt

St/tZnSt/tZnSt/tZn

StStSt/tZn

204 149204 179202 010202 050202 080206 209206 309

5 DEHNsnapDEHNgripconductor holder with cleat and flangeconductor holder for heat insulation

204 006207 009275 160273 740

6 Gutter clamp for beads St/tZnStSt

Single-screw gutter clamp St/tZnStSt

339 050339 059339 100339 109

7 MV clamp St/tZnMV clamp StSt

390 050390 059

8 Gutter board clamp St/tZn 343 0009 Downpipe clamp adjustable for 60 - 150 mm

Downpipe clamp for any cross sectionsKS connector for connecting conductorsKS connector StSt

423 020423 200301 000301 009

Pos. Part description Part No.

10 MV clamp 390 05111 Bridging bracket Aluminium

Bridging braid Aluminium377 006377 015

12 Lead-in earthing rod 16 mmcomplete

480 150480 175

13

14

Parallel connector

Cross unitSV clamps St/tZnSV clamps StSt

305 000306 020319 201308 220308 229

15

Rod holder with cleat and flangeRod holder for heat insulation

275 260273 730

Number plate for marking isolating points 480 006480 005

16 Air-termination rod with forged tabAir-termination rod with rounded endsRod clamp

100 075483 075380 020

Fig. 5.4.2.1a External lightning protection of a residential building

Table 5.4.2.1a Components for external lightning protection of a residential building

16

12

Page 102: Lightning Protection Guide

(roof and wall). The cap simply snaps in to fix theconductor in the holder while still being looselyguided. The special snap-in technique exerts nomechanical load on the fastening.

DEHNgrip (Figure 5.4.2.2) is a stainless steel systemof holders without screws which was put into the

programme to supplement the DEHNsnap systemof synthetic holders.

This system of holders without screws can also beused as both a roof and a wall conductor holderfor Ø 8 mm conductors.

Simply press in the conductors and the conductor isfixed in DEHNgrip (Figure 5.4.2.2).

www.dehn.de LIGHTNING PROTECTION GUIDE 101

1

2

3

4

5

6

8

9

7

10

11

Pos. Part description Part No.1234567

Stainless steel conductor 10 mm StStSet of lead-in earthing rods St/tZnCross unit StStDEHNALU-DRAHT® AlMgSiConductor holder DEHNsnap®

Bridging braid AlAir-termination rod AlMgSiwith concrete base with adapted flat washer

860 010480 150319 209840 008204 120377 015104 200120 340

Pos. Part description Part No.8910

11

Roof conductor holder for flat roofsDEHNiso distance holder ZDC-St/tZnElevated ring conductorwith concrete base with adapted flat washerand distance holder StStIsolated air-termination rod

253 050106 100

102 340106 160105 500

Fig. 5.4.2.1b External lightning protection of an industrial structure

Table 5.4.2.1b Components for external lightning protection of a residential structure

Page 103: Lightning Protection Guide

5.4.3 Application tips for mounting roofconductors holders

Ridge and hip tiles:Adjust roof conductor holders with adjustingscrew to suit the dimension of the ridge tile (Figure5.4.3.1).The conductor leading can, in addition, be gradu-ally adjusted by means of conductor holders fromthe top centre to the bottom side.

(Conductor holder can be loosened by either turn-ing the holder or opening the fixing screw.)

⇒ SPANNsnap roof conductor holder with DEHN-snap synthetic conductor holder or DEHNgripstainless steel conductor holder (Figure5.4.3.2).Permanent tension due to stainless steel ten-sion spring. Universal tension range from

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1

2

basic component

cap

Conductor holderDEHNgrip

Conductor holderDEHNsnap

Fig. 5.4.2.2 DEHNsnap and DEHNgrip conductor holders

Fig. 5.4.3.1 Conductor holder with DEHNsnap for ridge tiles

Fig. 5.4.3.2 SPANNsnap with plasticDEHNsnap conductor holder

Fig. 5.4.3.3 FIRSTsnap for mounting on existing ridge clamp

Page 104: Lightning Protection Guide

180 – 280 mm with laterally adjustable conduc-tor leading for Rd 8 mm conductors.

⇒ FIRSTsnap conductor holder with DEHNsnapsynthetic conductor holder for putting onexisting ridge clamps for dry ridges.

For dry ridges, the DEHNsnap conductor holder (1)(Figure 5.4.3.3) is put on the ridge clamp alreadyon the structure (2) and tightened manually (onlyturn DEHNsnap).

Grooved pantiles:UNIsnap roof conductor holder with preformedstruts is used for the roof surfaces. The conductorholder is bent by hand before being hooked intothe battens. Additionally, it can also be securedwith nails (Figure 5.4.3.4).

Smooth tiles (Figure 5.4.3.5)

Slate roofs:When using it on slate roofs, the internal hook sys-tem is bent (Figure 5.4.3.6) or equipped with a sup-plementary clamp (Part No. 204 089).

Grooved tiles:⇒ FLEXIsnap roof conductor holder for grooved

tiles, for direct fitting on the groove (Figure5.4.3.7).

The flexible stainless steel strut is pushedbetween the grooved tiles.By pressing on the top grooved tile, the stain-less steel strut is deformed and adapts itself tothe shape of the groove.Thus it is fixed tightly under the tile.This application with an aluminium strutmakes it easy to adapt to the shape of thegroove.A notch is provided for an eventually existingwindow hook. The strut of the holder can alsobe nailed down (holes in the strut).

⇒ Roof conductor holders with preformed strut,for hooking into the bottom grove for pantileroofs (Figure 5.4.3.8).

Flat tiles or slabs:DEHNsnap conductor holder (1) (Figure 5.4.3.9)and its clamping device (2) is pushed in betweenthe flat tiles (3) (e.g. plain tile) or slabs and tight-ened manually (only turn DEHNsnap).

Overlapped constructions:In case of overlapped constructions (3) (e.g. slabsand natural slates), DEHNsnap conductor holder(1) (Figure 5.4.3.10) with clamping terminals (2) ispushed on from the side and secured with a screwdriver when the holder is open.For slabs laid on a slat, DEHNsnap can also beturned to allow a plumb conductor leading.

www.dehn.de LIGHTNING PROTECTION GUIDE 103

angled by hand

angle the inner latchingfor use on slate roofs

Fig. 5.4.3.4 UNIsnap roof conductor holderwith preformed strut – Used ongrooved pantiles

Fig. 5.4.3.5 UNIsnap roof conductor holderwith preformed strut – Used onsmooth tiles, e.g. plain tiles

Fig. 5.4.3.6 UNIsnap roof conductor holderwith preformed strut – Used onslate roofs

Page 105: Lightning Protection Guide

www.dehn.de104 LIGHTNING PROTECTION GUIDE

insert the holderunderneath

lift tile

press tileon it

insert the holderunderneath

lift tile

press tileon it

DEHNsnap

1

2

1

4

3

DEHNsnap

1

2

3

1

3

Fig. 5.4.3.7 Conductor holder for direct fitting on the seams Fig. 5.4.3.8 Roof conductor holder for hanging into the bottomseam of pantile roofs

Fig. 5.4.3.9 ZIEGELsnap, for fixing between flat tiles or plates Fig. 5.4.3.10 PLATTENsnap roof conductor holder for overlapped construction

Page 106: Lightning Protection Guide

5.5 Earth-termination systems

A detailed explanation of the terms used in earth-termination technology is contained in IEC 62305-3 (EN 62305-3) “Lightning protection –physical damage to structures and life hazard”, HD 637 S1 “Power installations exceeding 1 kV”,IEC 60050-826 “International electrotechnicalvocabulary Part 826: Electrical installations” andIEC 60364-5-54 “Electrical installations of buildings– Part 5-54”. In Germany DIN 18014 is additionallyapplicable for foundation of earth electrodes.Below, we repeat only the terminology which isrequired to understand the following designs.

Terminology

Earthis the conductive ground whose electrical poten-tial at each point is set equal to zero as agreed. Theword “earth” also the designation for both theearth as a place as well as earth as a material, e.g.

the type of soil: humus, loam, sand, gravel androck.Reference earth(neutral earth) is the part of the earth, especiallythe surface of the earth outside the sphere ofinfluence of an earth electrode or an earth-termi-nation system, in which, between two arbitrarypoints, no perceptible voltages arising from theearthing current occur (Figure 5.5.1).

Earth electrodeis a conductive component or several conductivecomponents in electrical contact with the earthand forming an electrical connection with it(includes also foundation earth electrodes).

Earth-termination systemis a localised entirety of interconnected conductiveearth electrodes or metal components acting assuch, (e.g. reinforcements of concrete founda-tions, cable metal sheaths in contact with theearth, etc.).

www.dehn.de LIGHTNING PROTECTION GUIDE 105

Fig. 5.5.1 Earth surface potential and voltages at a foundation earth electrode FE and control earth electrode CE flown through by currents

1 m

UB2

ϕFE

US

FE

ϕ

UB1

ϕFE + SE

UE

UE Earth potentialUB Touch voltageUB1 Touch voltage without potential control (at the

foundation earth electrode)UB2 Touch voltage with potential control (foundation

and control earth electrode)US Step voltageϕ Earth surface potentialFE Foundation earth electrodeCE Control earth electrode (ring earth electrode)

reference earth

CE

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Earthing conductoris a conductor connecting a system component tobe earthed to an earth electrode and which isinstalled above the ground or insulated in theground.

Lightning protection earthingis the earthing installation of a lightning protec-tion system to discharge lightning currents intothe earth.

Below some types of earth electrodes and theirclassification are described according to location,form and profile.

Classification according to location

Surface earth electrodeis an earth electrode generally driven in at a shal-low depth down to 1 m. It can consist of roundmaterial or flat strips and be designed as a star-type, ring or meshed earth electrode or a combina-tion thereof.

Earth rodis an earth rod generally driven in plumb down togreater depths. It can consist of round material ormaterial with another profile, for example.

Foundation earth electrodecomprises one or more conductors embedded inconcrete which is in contact with the earth over awide area.

Control earth electrodeis an earth electrode whose form and arrangementserves more to control the potential than to main-tain a certain earth electrode resistance.

Ring earth electrodeis an an earth electrode underneath or on the sur-face of the earth, leading as closed ring around thestructure.

Natural earth electrodeis a metal component in contact with the earth orwith water either directly or via concrete, whoseoriginal function is not as an earth electrode butwhich acts as an earth electrode (reinforcementsof concrete foundations, conduits, etc.).

Classification according to form and profileOne distinguishes between:flat strip earth electrodes, cruciform earth elec-trodes and earth rods.

Types of resistanceSpecific earth resistanceρE is the specific electrical resistance of the earth. Itis given in Ωm and represents the resistancebetween two opposite sides of a cube of earthwith edges of 1 m in length.

Earth electrode resistanceRA of an earth electrode is the resistance of theearth between the earth electrode and referenceearth. RA is practically a resistance.

Impulse earth resistanceRst is the resistance as lightning currents traversefrom one point of an earth-termination system tothe reference earth.

Voltages at current carrying earth-termina-tion systems, control of potentialEarth potentialUE is the voltage arising between an earth-termi-nation system and reference earth (Figure 5.5.1).

Potential of the earth´s surfaceϕ is the voltage between one point of the earth´ssurface and reference earth (Figure 5.5.1).

Touch voltageUB is the part of the potential of the earth´s surfacewhich can be bridged by humans (Figure 5.5.1), thecurrent path via the human body running fromhand to foot (horizontal distance from touchablepart around 1 m) or from one hand to the other.

Step voltageUS is the part of the potential of the earth´s surfacewhich can be bridged by humans taking one step 1m long, the current path via the human body run-ning from one foot to the other (Figure 5.5.1).

Potential controlis the effect of the earth electrodes on the earthpotential, particularly the potential of the earth´ssurface (Figure 5.5.1).

www.dehn.de106 LIGHTNING PROTECTION GUIDE

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Equipotential bondingfor lightning protection system is the connectionof metal installations and electrical systems to thelightning protection system via conductors, light-ning current arresters or isolating spark gaps.

Earth electrode resistance/Specific earthresistance

Earth electrode resistance RA

The conduction of the lightning current via theearth electrode into the ground does not happenat one point but rather energises a particular areaaround the earth electrode.The type of earth electrode and the way it isinstalled must now be chosen to ensure that thevoltages affecting the surface of the earth (touchand step voltages) do not assume hazardous val-ues.The earth electrode resistance RA of an earth elec-trode can best be explained with the help of ametal sphere buried in the ground.If the sphere is buried deep enough, the currentdischarges radially to be equally distributed overthe surface of the sphere. Figure 5.5.2a illustratesthis case; as a comparison, Figure 5.5.2b illustratesthe case of a sphere buried just under the earth´ssurface.The concentric circles around the surface of thesphere represent surface of equal voltage. Theearth electrode resistance RA is composed of thepartial resistances of individual layers of thesphere connected in series.The resistance of such alayer of the sphere is calculated using

where ρE is the specific earth resistance of theground, assuming it is homogeneous,

l the thickness of an imaginary layer of thesphere

and

q the medial surface of this layer of the sphere.

To illustrate this, we assume a metal sphere 20 cmin diameter buried at a depth of 3 m at a specificearth resistance of 200 Ωm.

If now the increase in earth electrode resistancefor the different layers of the sphere is calculated,then as a function of the distance from the centreof the sphere, a curve as shown in Figure 5.5.3. isobtained.

The earth electrode resistance RA for the sphericalelectrode is calculated using:

ρE Specific earth resistance in Ωm

Rr

r

tA

E

K

K

=⋅

⋅⋅

+ρπ

100

2

12

2

Rl

qE= ⋅ρ

www.dehn.de LIGHTNING PROTECTION GUIDE 107

equipotential lines

a) Spherical earthelectrode deep inthe ground

b) Spherical earthelectrode close to the earth surface

1 2 3 4 5

160

140

120

100

80

60

40

20

RA = 161 Ω

Eart

h el

ectr

ode

resi

stan

ce R

A (Ω

)

approx. 90%

Distance x (m)

Fig. 5.5.2 Current distribution from the spherical earth electrode

Fig. 5.5.3 Earth electrode resistance RA of a spherical earth elec-trode with Ø 20 cm, 3 m deep, at ρE = 200 Ωm as a func-tion of the distance x from the centre of the sphere

Page 109: Lightning Protection Guide

t Burial depth in cm

rK Radius of the spherical earth electrode in cm

This formula gives a earth electrode resistance ofRA = 161 Ω for the spherical earth electrode.

The trace of the curve in Figure 5.5.3 shows thatthe largest fraction of the total earth electroderesistance occurs in the immediate vicinity of theearth electrode. Thus, for example, at a distance of5 m from the centre of the sphere, 90 % of thetotal earth electrode resistance RA has alreadybeen achieved.

Specific earth resistance ρEThe specific earth resistance ρE which determinesthe magnitude of the earth electrode resistance RAof an earth electrode, is a function of the composi-

tion of the soil, the amount ofmoisture in the soil and thetemperature. It can fluctuatebetween wide limits.

Values for various types ofsoilFigure 5.5.4 gives the fluctua-tion ranges of the specificearth resistance ρE for varioustypes of soil.

Seasonal fluctuationsExtensive measurements (lit-erature) have shown that thespecific earth resistance varies

greatly according to the burial depth of the earthelectrode. Owing to the negative temperaturecoefficient of the ground (α = 0.02 ... 0.004), thespecific earth resistance attain a maximum in win-ter and a minimum in summer. It is therefore advis-able to convert the measured values obtainedfrom earth electrodes to the maximum prospectivevalues, since even under unfavourable conditions(very low temperatures), permissible values mustnot be exceeded. The curve of the specific earthresistance ρE as a function of the season (groundtemperature) can be represented to a very goodapproximation by a sinus curve having its maxi-mum around the middle of February and its mini-mum around the middle of August. Investigationshave further shown that, for earth electrodesburied not deeper than around 1.5 m, the maxi-mum deviation of the specific earth resistancefrom the average is around ± 30 % (Figure 5.5.5).

www.dehn.de108 LIGHTNING PROTECTION GUIDE

0.1 1 10 100 1000 10000 ρE

Concrete

Boggy soil, turf

Farmland, loam

Humid sandy soil

Dry sandy soil

Rocky soil

Gravel

Lime

River and lake water

Sea water

in Ωm

e e e

a M a’

measuringdevice

30

20

10

0

10

20

30

burial depth < 1.5 m+ ρE in %

burial depth > 1.5 m

− ρE in %

June July Aug. Sept. Oct. Nov.

Jan. Feb. March April May Dec.

Fig. 5.5.4 Specific earth resistance ρE of different ground types

Fig. 5.5.5 Specific earth resistance ρE as a function of the seasonswithout influencing of rainfall (burial depth of the earthelectrode < 1.5 m)

Fig. 5.5.6 Determination of the specific earth resistance ρE with afour-terminal measuring bridge acc. to the WENNERmethod

Page 110: Lightning Protection Guide

For earth electrodes buried deeper (particularly forearth rods), the fluctuation is merely ± 10 %. Fromthe sineshaped curve of the specific earth resist-ance in Figure 5.5.5, the earthing electrode resist-ance RA of an earth-termination system measuredon a particular day can be converted to the maxi-mum prospective value.

MeasurementThe specific earth resistance ρE is determined usingan earthing measuring bridge with 4 clamps whichoperates according to the null method.Figure 5.5.6 illustrates the measuring arrangementof this measuring method named after WENNER.The measurement is carried out from a fixed cen-tral point M which is retained for all subsequentmeasurements. Four measuring probes (earthing

spikes 30 ... 50 cm long) are driven into the soilalong a line a – a' pegged out in the ground. Fromthe measured resistance R one can determine thespecific earth resistance ρE of the ground:

R measured resistance in Ω

e probe distance in m

ρE average specific earth resistance in Ωm downto a depth corresponding to the probe dis-tance e

By increasing the probe distance e and re-tuningthe earthing measuring bridge, the curve of the

ρ πE e R= ⋅ ⋅2

www.dehn.de LIGHTNING PROTECTION GUIDE 109

Table 5.5.1 Formulae for calculating the earth electrode resistance RA for different earth electrodes

Earth electrode Rough estimate Auxiliary

Surface earth electrode(star-type earth electrode)

Earth rod

Ring earth electrode

Meshed earth electrode

Earth plate

Hemispherical earth electrode

RA Earth electrode resistance (Ω)ρE Specific earth resistance (Ωm)l Length of earth electrode (m)d Diameter of a ring earth electrode, of the area of the equivalent circuit or of a hemispherical earth electrode (m)A Area (m2) of the enclosed area of a ring or meshed earth electrodea Edge length (m) of a square earth plate, for rectangular plates value: , while b and c are the

two sides of the rectangleV Content (m3) of a single foundation element

b c⋅

RlA

E=⋅2 ρ

RlAE=

ρ

RdAE=

⋅⋅

2

3

ρd A= ⋅1 13 2.

d A= ⋅1 13 2. RdA

E=⋅

ρ2

RaA

E=⋅

ρ4 5.

RdA

E=⋅

ρπ d V= ⋅1 57. 3

Page 111: Lightning Protection Guide

specific earth resistance can be determined ρE as afunction of the depth.

Calculation of earth electrode resistancesTable 5.5.1 gives the formulae for calculating theearth electrode resistances of the most commontypes of earth electrode. In practice, these approx-imate formulae are quite sufficient. The preciseformulae for the calculations must be taken fromthe following sections.

Straight surface earth electrodeSurface earth electrodes are generally embeddedhorizontally in the ground at a depth of 0.5 ... 1 m.Since the layer of soil covering the earth electrodedries out in summer and freezes in winter, theearth electrode resistance RA of such a surfaceearth electrode is calculated as if it lays on the sur-face of the ground:

RA Earth electrode resistance of a stretched sur-face earth electrode in Ω

ρE Specific earth resistance in Ωm

l Length of the surface earth electrode in m

r Quarter width of steel strip in m or diameterof the round wire in m

The earth electrode resistance RA as a function ofthe length of the earth electrode can be takenfrom Figure 5.5.7.

Rl

l

rAE=⋅

⋅ρ

π

ln

www.dehn.de110 LIGHTNING PROTECTION GUIDE

50 100

100

50

ρE = 100 Ωm

ρE = 200 Ωm

ρE = 500 Ωm

Earth electrode resistance RA (Ω)

Length I of the stretched surface earth electrode (m)

UE

100

80

60

40

20

a

UE

100

80

60

40

20

a

V

a

t

V

V

t

V

a

100 cm

t = 0 cm50 cm

t = 0 cm

50 cm100 cm

LONGITUDINAL DIRECTION

TRANSVERSE DIRECTION

Eart

h po

tent

ial U

E (%

)Ea

rth

pote

ntia

l UE (

%)

Distance a (m) from earth electrode

Distance a (m) from earth electrode

10080604020

0.5 1 1.5 2 m

%

Max

. ste

p vo

ltage

in %

of th

e to

tal v

olta

ge

Burial depth

Fig. 5.5.7 Earth electrode resistance RA as a function of length I ofthe surface earth electrode at different specific earthresistance ρE

Fig. 5.5.9 Max. step voltage US as a function of the burial depth fora stretched earth strip

Fig. 5.5.8 Earth potential UE between supply conductor and earthsurface as a function of the distance from the earth elec-trode, at an earth strip (8 m long) in different depths

Page 112: Lightning Protection Guide

Figure 5.5.8 shows the transverse and longitudinalearthing potential UE for an 8 m long flat stripearth electrode.The effect of the burial depth on the earthingpotential can be clearly seen.

Figure 5.5.9 illustrates the step voltage US as afunction of the burial depth.

In practice, the calculation is done using theapproximate formula in Table 5.5.1:

Earth rodThe earth electrode resistance RA of a earth rod iscalculated using:

RA earth electrode resistance in Ω

ρE Specific earth resistance in Ωm

l Length of the earth rod in m

r Radius of the earth rod in m

As an approximation, the earth electrode resist-ance RA can be calculated using the approximateformula given in Table 5.5.1:

Figure 5.5.10 shows the earth electrode resistanceRA as a function of the rod length I and the specif-ic earth resistance ρE.

Combination of earth electrodesIf the soil conditions require several earth rods, thedriving down depth of the earth rods is applicablefor the corresponding minimum distance of thedifferent earth rods which have to be intercon-nected.The earth electrode resistance calculated using theformulae and the measurement results given inthe diagrams apply to low frequency d.c. current

and a.c. current provided that the expansion of theearth electrode is relatively small (a few hundredmetres). For longer lengths, e.g. for surface earthelectrodes, the a.c. current also has an inductivepart. Furthermore, the calculated earth electrode resist-ances do not apply to lightning currents. This iswhere the inductive part plays a role, which canlead to higher values of the impulse earthingresistance for larger expansion of the earth-termi-nation system. Increasing the length of the surface earth elec-trodes or earth rods above 30 m reduces theimpulse earth electrode resistance by only aninsignificant amount. It is therefore expedient tocombine several shorter earth electrodes. In suchcases, because of their interaction, care must betaken that the actual total earth electrode resist-ance is greater than the value calculated from theindividual resistances connected in parallel.

Star-type earth electrodesStar-type earth electrodes in the form of cruciformsurface earth electrodes are important when rela-tively low earth electrode resistances shall be cre-ated in poorly conducting ground at an affordableprice.

RlAE=

ρ

Rl

l

rAE=⋅

⋅ρ

π2

ln

RlA

E=⋅2 ρ

www.dehn.de LIGHTNING PROTECTION GUIDE 111

2 4 6 8 10 12 14 16 18 20

100

80

60

40

20

Earth electrode resistance RA

Drive-in depth l of the earth rod

ρE = 100 Ωm

ρE = 500 Ωm

ρE = 200 Ωm

Fig. 5.5.10 Earth electrode resistance RA of earth rods as a functionof their length I at different specific earth resistances ρE

Page 113: Lightning Protection Guide

The earth electrode resistance RA of a cruciformsurface earth electrode whose sides are at 90 ° toeach other is calculated using:

RA Earth electrode resistance of the cruciform sur-face earth electrode in Ω

ρE Specific earth resistance in Ωm

l Side length in m

d Half a bandwidth in m or diameter of theround wire in m

As a rough approximation, for longer lengths ofthe star arrangement (l > 10 m), the earth elec-trode resistance RA can be determined using thetotal length of the star obtained from the equa-tions in Table 5.5.1.

Figure 5.5.11 shows the curve of the earth elec-trode resistance RA of cruciform surface earth elec-trodes as a function of the burial depth;

Figure 5.5.12 shows the curve of the earthing volt-age.

For star-type earth electrodes, the angle betweenthe individual arms should be greater than 60 °.According to Figure 5.5.12 the earth electroderesistance of a meshed earth electrode is given bythe formula:

Where d is the diameter of the analogous circlehaving the same area as the meshed earth elec-trode, which is determined as follows:For rectangular or polygonal dimensions of themeshed earth electrode:

A Area of the meshed earth electrode

dA

=⋅4

π

RdA

E=⋅

ρ2

Rl

l

rAE=⋅

⋅ +ρ

π41 75

ln .

www.dehn.de112 LIGHTNING PROTECTION GUIDE

l

Earth electrode resistance RA (Ω)

Burial depth (m)

l = side length

ρE = 200 Ωm

l = 10 m

l = 25 m

%

14

12

10

8

6

4

2

0.5 1 1.5

%

100

80

60

40

20

10 20 30 m

45°

II

I

Voltage

Distance from the centre of the intersection

direction ofmeasurement II

direct

ion of

measu

remen

t I

side length 25 m

Fig. 5.5.11 Earth electrode resistance RA of crossed surface earthelectrode (90 °) as a function of the burial depth

Fig. 5.5.12 Earth potential UE between the supply conductor of theearth electrode and earth surface of crossed surfaceearth electrode (90 °) as a function of the distance fromthe cross centre point (burial depth 0.5 m)

Page 114: Lightning Protection Guide

For square dimensions (edge length b):

Figure 5.5.13 illustrates the curve of the impulseearth electrode resistance of surface earth elec-trodes with single and multiple star for square-wave voltages.

As can be seen from this diagram, for a givenlength, it is more expedient to install a radial earthelectrode than one single arm.

Foundation earth electrode

The earth electrode resistance of a metal conduc-tor in a concrete foundation can be calculated asan approximation using the formula for hemi-spherical earth electrodes:

Where d is the diameter of the analogous hemi-sphere having the same volume as the foundation:

V Volume of the foundation

When calculating the earth electrode resistance,one must be aware that the foundation earth elec-trode can only be effective if the concrete bodyhas a large contact area with the surroundingground. Water repellent, isolating shielding signif-icantly increases the earth electrode resistance, orisolate the foundation earth electrode (see 5.5.2).

Earth rods connected in parallelTo keep the interactions within acceptable limits,the distances between the individual earth elec-trodes and earth rods connected in parallel shouldnot be less than the pile depth, if possible.If the individual earth electrodes are arrangedroughly in a circle and if they all have about thesame length, then the earth electrode resistancecan be calculated as follows:

d V= ⋅1 57. 3

RdA

E=⋅

ρπ

d b= ⋅1 1.

www.dehn.de LIGHTNING PROTECTION GUIDE 113

0 1 2 3 4 5 6

Ω

160

140

120

100

80

60

40

20

0

Impu

lse

eart

h re

sist

ance

Rst

Time μs

n = 12

3

4

RA = 10 Ωl

n = 4Z = 150 ΩRA = 10 Ωn = 1 ... 4n · l = 300 m

Z Surge impedance of the earth conductorRA Earth electrode resistancen Quantity of the parallel connected earth electrodesl Mean length of the earth electrodes

al

p

n = 20

10

5

3

2

p Reduction factorn Quantity of the parallel connected earth electrodesa Mean distance of the earth electrodesl Mean length of the earth electrodes

0.5 1 2 5 10

20

10

5

3

2

1

Fig. 5.5.13 Impulse earth resistance Rst of single or multiple star-type earth electrodes with equal length

Fig. 5.5.14 Reduction factor p for calculating the total earth elec-trode resistance RA of earth rods connected in parallel

Page 115: Lightning Protection Guide

Where RA' is the average earth electrode resistanceof the individual earth electrodes. The reductionfactor p as a function of the length of the earthelectrode, the distance of the individual earth elec-trodes and the number of earth electrodes can betaken from Figure 5.5.14.

Combination of flat strip earth electrodes andearth rodsIf sufficient earth electrode resistance is providedby earth rods, for example from deep water carry-ing layers in sandy soil, then the earth rod shall beas close as possible to the object to be protected. Ifa long feed is required, it is expedient to install aradial multiple star-type earth electrode in parallelto this in order to reduce the resistance as the cur-rent rises.

As an approximation, the earth electrode resist-ance of a flat strip earth electrode with earth rodcan be calculated as if the flat strip earth electrodewere extended by the drive-in depth of the earthrod.

Ring earth electrodeFor circular ring earth electrodes with large diame-ters (d > 30 m), the earth electrode resistance is cal-culated as an approximation using the formula forthe flat strip earth electrode (where the circumfer-ence π ⋅ d is used for the length of the earth elec-trode):

r Radius or the round conductor or quarterwidth of the flat strip earth electrode in m

For non-circular ring earth electrodes, the earthelectrode resistance is calculated by using thediameter d of an analogous circle with the samearea:

A Area enclosed by the ring earth electrode

ImplementationAccording to the standards, each installation to beprotected must have its own earth-terminationsystem which must be fully functional in itselfwithout requiring metal water pipes or earthedconductors of the electrical installation.The magnitude of the earth electrode resistanceRA is of only secondary importance for protecting astructure or installation against physical damage.It is important that the equipotential bonding atground level is carried out systematically and thelightning current is safely distributed in theground.The lightning current i raises the structure to beprotected to the earthing potential UE

with respect to the reference earth.

The potential of the earth´s surface decreases withincreasing distance from the earth electrode (Fig-ure 5.5.1).The inductive voltage drop across the earth elec-trode during the lightning current rise must onlybe taken into account for extended earth-termina-tion systems (e.g. as required for long surfaceearth electrodes in poorly conducting soils withbedrock). In general, the earth electrode resistanceis determined only by the ohmic part.

If isolated conductors are led into the structure,the earthing potential UE has its full value withrespect to the conductor.In order to avoid the risk of punctures andflashovers here, such conductors are connected viaisolating spark gaps or with live conductors viasurge protective devices (see DEHN main cataloguefor Surge Protection) to the earth-termination sys-

U i R Ldi

dtE A= ⋅ + ⋅ ⋅ 1

2

dA

=⋅ 4

π

RdA

E=⋅

2

3

ρ

Rd

d

rAE=⋅

⋅⋅ρ

ππ

2

ln

Rl lA

E

flat strip eath rod

≈+

ρ

RR

pAA= '

www.dehn.de114 LIGHTNING PROTECTION GUIDE

Page 116: Lightning Protection Guide

tem as part of the lightning equipotential bond-ing.

In order to keep touch and step voltages as low aspossible, the magnitude of the earth electroderesistance must be limited.The earth-termination system can be designed as afoundation earth electrode, a ring earth electrodeand, for structures with large surface areas, as ameshed earth electrode and, in special cases, alsoas an individual earth electrode.In Germany foundation earth electrodes must bedesigned in accordance with DIN 18014.The foundation earth electrode must be designedas a closed ring and arranged in the foundations ofthe external walls of the structure, or in the foun-dation slab, in accordance with DIN 18014. Forlarger structures, the foundation earth electrodeshould contain interconnections to prevent anexceeding of the max. mesh size 20 m x 20 m.The foundation earth electrode must be arrangedto be enclosed by concrete on all sides. For steelstrips in non-reinforced concrete, the earth elec-trode must be installed on edge.In the service entrance room, a connection must beestablished between foundation earth electrodeand equipotential bonding bar. According to IEC62305-3 (EN 62305-3), a foundation earth elec-trode must be equipped with terminal lugs forconnection of the down-conductor systems of theexternal lightning protection system to the earth-termination system.Due to the risk of corrosion at the point where aterminal lug comes out of the concrete, supple-mentary corrosion protection should be consid-ered (with PVC sheath or by using stainless steelwith Material No. 1.4571).The reinforcement of plate and strip foundationscan be used as a foundation earth electrode if therequired terminal lugs are connected to the rein-forcement and the reinforcements are intercon-nected via the joints.Surface earth electrodes must be installed in adepth of at least 0.5 m.

The impulse earthing resistance of earth elec-trodes is a function of the maximum value of thelightning current and of the specific earth resist-ance. See also Figure 5.5.13. The effective lengthof the earth electrode for the lightning current iscalculated as an approximation as follows:

Surface earth electrode:

Earth rod:

Ieff Effective length of the earth electrode in m

î Peak value of the lightning current in kA

ρE Specific earth resistance Ωm

The impulse earth resistance Rst can be calculatedusing the formulae in (Table 5.5.1), where theeffective length of the earth electrode Ieff is usedfor the length I.

Surface earth electrodes are always advantageouswhen the upper soil layers have less specific resist-ance than the subsoil.If the ground is relatively homogeneous (i.e. if thespecific earth resistance at the surface is roughlythe same as it is deep down) then, for a given earthelectrode resistance, the construction costs of sur-face earth electrodes and earth rods are roughlythe same.

According to Figure 5.5.15, an earth rod must haveonly around half the length of a surface earth elec-trode.

l îeff E= ⋅0 2. ρ

l îeff E= ⋅0 28. ρ

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0 5 10 15 20 30 40 50 60 70 80 90 100

90

80

70

60

50

40

30

201510

50

Length of the earth electrode l (m)

surface earth electrode

earth rod

ρE = 400 Ωm

ρE = 100 Ωm

Eart

h el

ectr

ode

resi

stan

ce R

A(Ω

)

Fig. 5.5.15 Earth electrode resistance RA of surface and earth rodsas a function of the length of the earth electrode I

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If the conductivity of the ground is better deepdown than it is on the surface, e.g. because ofground water, then an earth rod is generally morecost-effective than the surface earth electrode.The issue of whether earth rods or surface earthelectrodes are more cost-effective in a particularcase, can often only be decided by measuring thespecific earth resistance as a function of the depth.Since earth rods are easy to assemble and achieveexcellent constant earth electrode resistanceswithout the need to dig a trench and withoutdamaging the ground, these earth electrodes arealso suitable for improving existing earth-termina-tion system.

5.5.1 Earth-termination systems in accor-dance with IEC 62305-3 (EN 62305-3)

Earth-termination systems are the continuation ofair-termination and down-conductor systems todischarge the lightning current into the earth. Fur-ther functions of the earth-termination system areto create equipotential bonding between thedown conductors and a potential control in thevicinity of the walls of the structure.It must be borne in mind that a common earth-ter-mination system for the various electrical systems(lightning protection, low voltage systems andtelecommunications systems) is preferable. Thisearth-termination system must be connected tothe equipotential bonding (MEBB – main equipo-tential bonding bar).Since IEC 62305-3 (EN 62305-3) assumes a systemat-ic lightning equipotential bonding, no particularvalue is required for the earth electrode resistance.

Generally, however, a low earth resistance (lessthan 10 Ω, measured with low frequency) is recom-mended.The standard classifies earth electrode arrange-ments into Type A and Type B.

For both Type A and B earth electrode arrange-ments, the minimum earth electrode length I1 ofthe earthing conductor is a function of the class oflightning protection system (Figure 5.5.1.1)The exact specific earth resistance can only bedetermined by on-site measurements using the“WENNER method“ (four-conductor measure-ment).

Earth electrode Type AEarth electrode arrangement Type A describesindividually arranged horizontal star-type earthelectrodes (surface earth electrodes) or verticalearth electrodes (earth rods), each of which mustbe connected to a down-conductor system.There must be at least 2 earth electrodes Type A.Lightning protection systems Class III and IVrequire a minimum length of 5 m for earth elec-trodes. For lightning protection systems, Class Iand II the length of the earth electrode is deter-mined as a function of the specific ground resist-ance. The minimum length for earth electrodes I1can be taken from Figure 5.5.1.1.

Minimum length of each earth electrode is:

I1 x 0.5 for vertical or slanted earth electrodes

I1 for star-type earth electrodes

The values determined apply to each individualearth electrode.

For combinations of the various earth electrodes(vertical and horizontal) the equivalent totallength should be taken into account.The minimum length for the earth electrode canbe disregarded if an earth electrode resistance ofless than 10 Ω is achieved.

Earth rods are generally driven vertically down togreater depths into natural soil which is generallyinitially encountered below the foundations. Earthelectrode lengths of 9 m have provided the advan-tage of lying at greater depths in soil layers whosespecific resistance is generally lower than in theareas closer to the surface.

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80

70

60

50

40

30

20

10

00 500 1000 1500 2000 2500 3000

l1 (m)

ρE (Ωm)

class of LPS III-IV

class of LP

S I

class of LPS II

Fig. 5.5.1.1 Minimum lengths of earth electrodes

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In frosty conditions, it is recommended to considerthe first 100 cm of a vertical earth electrode asineffective.

Earth electrodes Type A do not fulfill the equipo-tential bonding requirements between the downconductors and the potential control.Earth electrodes Type A must be interconnected tosplit the current equally. This is important for cal-culating the separation distance s. Earth electrodesType A can be interconnected underground or onsurface. When upgrading existing installations theinterconnection of the individual earth electrodescan also be realised by laying a conductor in thebuilding or structure.

Earth electrode Type BEarth electrodes of the Type B arrangement arering earth electrodes around the structure to beprotected, or foundation earth electrodes. In Ger-many the requirements on these earth electrodesare described in DIN 18014.If it is not possible to have a closed ring outsidearound the structure, the ring must be completedusing conductors inside the structure. Conduits orother metal components which are permanentlyelectrically conductive can also be used for thispurpose. At least 80 % of the length of the earthelectrode must be in contact with the earth toensure that, when calculating the separation dis-tance, the earth electrode Type B can be used asthe base.

The minimum lengths of the earth electrodes cor-responding to the Type B arrangement are a func-tion of the class of lightning protection system. Forlightning protection systems Class I and II, the min-imum length for earth electrodes is also deter-mined as a function of the specific ground resist-ance (see also Figure 5.5.4).For earth electrodes Type B, the average radius r ofthe area enclosed by the earth electrode must benot less than the given minimum length l1.To determine the average radius r, the area underconsideration is transferred into an equivalent cir-cular area and the radius is determined as shownin Figures 5.5.1.2 and 5.5.1.3.

Below a calculation example:

If the required value of l1 is greater than the valuer corresponding to the structure, supplementarystar-type earth electrodes or vertical earth elec-trodes (or slanted earth electrodes) must beadded, their respective lengths lr (radial/horizon-tal) and lv (vertical) being given by the followingequations:

ll r

v =−1

2

l l rr = −1

www.dehn.de LIGHTNING PROTECTION GUIDE 117

Fig. 5.5.1.2 Earth electrode Type B – Determination of the meanradius – example calculation

Fig. 5.5.1.3 Earth electrode Type B – Determination of the meanradius

r

area A1 to beconsidered

circular area A2,mean radius r

A = A1 = A2

r =

r l1

With respect to ring or foundationearth electrodes, the mean radiusr of the area enclosed by the earthelectrode must not be shorterthan l1.

12 m

12 m

5 m

5 m

7 m

7 m

r

area A1to be considered

Example: Residential building,LPS Class III, l1 = 5 m

A1 = 109 m2

r =

r = 5.89 m

109 m2

3.14

circular area A2mean radius r

A = A1 = A2

r =

r l1

No furtherearthelectrodesrequired!

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The number of supplementary earth electrodesmust not be less than the number of down conduc-tors, but a minimum of 2. These supplementaryearth electrodes shall be connected to the ringearth electrode so as to be equidistant around thecircumference.

If supplementary earth electrodes have to be con-nected to the foundation earth electrode, caremust be taken with the materials of the earth elec-trode and the connection to the foundation earthelectrode. It is preferable to use stainless steel withMaterial No. 1.4571 (Figure 5.5.2.1).

The following systems can make additionaldemands on the earth-termination system, forexample:

⇒ Electrical systems – conditions of disconnectionfrom supply with respect to the type of net-work (TN-, TT-, IT systems) in accordance withIEC 60364-4-41: 2005, mod and HD 60364-4-41:2007

⇒ Equipotential bonding in accordance with IEC60364-5-54: 2002 and HD 60364-5-54: 2007

⇒ Electronic systems – data information techno-logy

⇒ Antenna earthing installation in accordancewith VDE 0855 (German standard)

⇒ Electromagnetic compatibility

⇒ Substation in or near the structure in accor-dance with HD 637 S1 and En 50341-1

5.5.2 Earth-termination systems, foundationearth electrodes and foundation earthelectrodes for special structural mea-sures

Foundation earth electrodes – Earth electrodesType BDIN 18014 (German standard) specifies the re-quirements on foundation earth electrodes.Many national and international standards specifyfoundation earth electrodes as a preferred earthelectrode because, when professionally installed, itis enclosed in concrete on all sides and hence cor-rosion-resistant. The hygroscopic characteristics ofconcrete generally produce a sufficiently low earthearth electrode resistance.The foundation earth electrode must be installedas a closed ring in the strip foundation or the bed-plate (Figure 5.5.2.1) and thus also acts primarily asthe equipotential bonding. The division into mesh-es ≤ 20 m x 20 m and the terminal lugs to the out-side required to connect the down conductors ofthe external lightning protection system, and tothe inside for equipotential bonding, must be con-sidered (Figure 5.5.2.2).According to DIN 18014, the installation of thefoundation earth electrode is an electrical engi-neering measure to be carried out or monitored bya recognised specialist electrical engineer.The question of how to install the foundationearth electrode must be decided according to themeasure required to ensure that the foundation

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Terminal lugmin. 1.5 m long, noticeably marked− steel strip 30 mm x 3.5 mm− StSt round steel bar 10 mm− round steel bar 10 mm with PVC coating− fixed earthing point

Foundation earth electrode− steel strip 30 mm x 3.5 mm− round steel bar 10 mm

20 m

≤ 20

m

Recommendation:Several terminal lugs e.g. in every technical centre

terminal lug

additional terminal conductorfor forming meshes ≤ 20 m x 20 m

Fig. 5.5.2.1 Foundation earth electrode with terminal lug Fig. 5.5.2.2 Mesh of a foundation earth electrode

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earth electrode is enclosed on all sides as the con-crete is being poured in.

Installation in non-reinforced concreteNon-reinforced foundations, e.g. strip foundationsof residential structures (Figure 5.5.2.3), requirethe use of spacers.Only by using the spacers at distances of approx. 2 m, is it possible to ensure that the foundationearth electrode is “lifted up” and can be enclosedon all sides by concrete.

Installation in reinforced concreteWhen using steel mats, reinforcement cages orreinforcement irons in foundations, it is not onlypossible to connect the foundation earth electrodeto these natural iron components, but this shouldbe done. The function of the foundation earthelectrode is thus made even more favourable.There is no need to use spacers. The modern meth-ods of laying concrete and then vibrating it, ensurethat the concrete also “flows” under the founda-tion earth electrode enclosing it on all sides.Figure 5.5.2.4 illustrates one possible applicationfor the horizontal installation of a flat strip as afoundation earth electrode. The intersections ofthe foundation earth electrode must be connectedso as to be capable of carrying currents. Galvanisedsteel is sufficient as material of the foundationearth electrode.Terminal lugs to the outside into the ground musthave supplementary corrosion protection at theoutlet point. Suitable materials are, for example,plastic sheathed steel wire (owing to the risk offracture of the plastic sheath at low temperatures,special care must be taken during the installation),

high-alloy stainless steel, Material No. 1.4571, orfixed earthing terminals.If professionally installed, the earth electrode isenclosed on all sides by concrete and hence corro-sion-resistant.When designing the foundation earth electrode,meshes no bigger than 20 m x 20 m shall berealised. This mesh size bears no relation to theclass of lightning protection system of the externallightning protection system.Modern building techniques employ various typesof foundations in a wide variety of designs andsealing versions.The terminal insulation regulations have also influ-enced the design of the strip foundations andfoundation slabs. For foundation earth electrodesinstalled in new structures in accordance with DIN18014, the insulation affects their installation andarrangement.

Perimeter insulation/Base insulation“Perimeter” is the earth-touching area of the walland base of a structure. The perimeter insulation isthe external heat insulation around the structure.The perimeter insulation seated on the externalsealing layer encloses the structure so that there isno heat bridge and protects the sealing additional-ly against mechanical damage.

The magnitude of the specific resistance of theperimeter insulating plates is a decisive factorwhen considering the effect of perimeter insu-lation on the earth electrode resistance of foun-dation earth electrodes in conventional arrange-ments in the foundation (strip foundation, foun-dation slab). Thus, for a polyurethane rigid foam

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Fig. 5.5.2.3 Foundation earth electrode Fig. 5.5.2.4 Foundation earth electrode in use

Page 121: Lightning Protection Guide

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granular sub-grade course

foundation slab

concrete

basement floor

drainage

moisture barrier

insulation

soil

perimeter /base insulation

foundation earth electrode

terminal lug

Ref.: Acc. to DIN 18014: 2007-09; VDE series 35, Schmolke, H.; Vogt, D., “Der Fundamenterder”; HEA Elektro+: 2004

granular sub-grade course

foundation slab

concrete

basement floor

drainage

moisture barrier

insulation

soil

perimeter /base insulation

foundation earth electrode

terminal lug

insulating layer

Ref.: Acc. to DIN 18014: 2007-09; VDE series 35, Schmolke, H.; Vogt, D., “Der Fundamenterder”; HEA Elektro+: 2004

MV TerminalPart No. 390 050

Distance holderPart No. 290 001

Cross unitPart No. 318 201

Fixed earthing terminal for EBBPart No. 478 800

MV TerminalPart No. 390 050

Distance holderPart No. 290 001

Cross unitPart No. 318 201

Fixed earthing terminal for EBBPart No. 478 800

Fig. 5.5.2.5 Arrangement of a foundation earth electrode in a strip foundation (insulated basement wall)

Fig. 5.5.2.6 Arrangement of a foundation earth electrode in a strip foundation (insulated basement wall and foundation slab)

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with bulk density 30 kg/m2, for example, a specificresistance of 5.4 ⋅ 1012 Ωm is given. In contrast, thespecific resistance of concrete lies between 150 Ωmand 500 Ωm. This alone shows that, in the case ofcontinuous perimeter insulation, a conventionalfoundation earth electrode arranged in the foun-dations has practically no effect. The perimeterinsulation also acts as an electrical insulator.The diagrams below illustrate the various ways ofinsulating the foundations and walls for structureswith perimeter and base insulation.Figures 5.5.2.5 to 5.5.2.7 show the arrangement ofthe foundation earth electrodes at structures withperimeter and base insulation.The arrangement of the earth electrode in thestrip foundation with insulated sides towards theoutside and the bedplate is not regarded as critical(Figure 5.5.2.5 and 5.5.2.6).

If the foundation slab is completely insulated, theearth electrode must be installed below the bed-plate. Material V4A (Material No. 1.4571) shouldbe used (Figure 5.5.2.7).

It is efficient to install fixed earthing terminals,especially for reinforced structures. In such cases,care must be taken that the installation during theconstruction phase is carried out professionally(Figure 5.5.2.8).

www.dehn.de LIGHTNING PROTECTION GUIDE 121

concrete

basement floor

moisture barrier

insulation

soil

perimeter /base insulation

ring earth electrode Mat. No. 1.4571

terminal lugMat. No. 1.4571

foundation slab

reinforcement granular sub-grad course

Ref.: Acc. to DIN 18014: 2007-09; VDE series 35, Schmolke, H.; Vogt, D., “Der Fundamenterder”; HEA Elektro+: 2004

MV TerminalPart No. 390 050

Cross unitPart No. 318 209

Fixed earthing terminal for EBBPart No. 478 800

Fig. 5.5.2.7 Arrangement of a foundation earth electrode in case of a closed floor slab (fully insulated)

Fig. 5.5.2.8 Fixed earthing terminal

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Black tank, white tank

In structures erected in regions with a highgroundwater level, or in locations, e.g. on hillsides,with “pressing” water, the cellars are equippedwith special measures to prevent moisture pene-trating. The outer walls surrounded by earth, andthe foundation slab are sealed against the pene-tration of water to ensure that no troublesomemoisture can form on the inside of the wall.

Modern building techniques apply both abovementioned processes for sealing against penetrat-ing water.

One particular issue in this context is whether theefficiency of a foundation earth electrode is stillprovided for maintaining the measures to protectagainst life hazards in accordance with IEC 60364-4-41, and as a lightning protection earth electrodein accordance with IEC 62305-3 (EN 62305-3).

Foundation earth electrodes for structures withwhite tankThe name “white tank” is used to express theopposite of “black tank”: a “white tank” receivesno additional treatment on the side facing theearth, hence it is “white”.

The “white tank” is manufactured from a specialtype of concrete. Due to the aggregates used atmanufacturing of the concrete the concrete bodyis absolutely waterproof. In contrast to formeryears there is no risk of humidity penetrating a fewcentimeters into the tank. Therefore an earth elec-trode is laid outside of structures with white tank.

Figure 5.5.2.8 shows the designing of an earth con-nection by a fixed earthing terminal.

Figure 5.5.2.9 illustrates the arrangement of thefoundation earth electrode in a white tank.

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concrete

basement floor

drainage

moisture barrier

insulation

soil

terminal lug

foundation earth electrode

Ref.: Acc. to DIN 18014: 2007-09; VDE series 35, Schmolke, H.; Vogt, D., “Der Fundamenterder”; HEA Elektro+: 2004

foil

foundation plate

MEBB

granular sub-grade course

ring earth electrode corrossion-resistant e.g. StSt V4A (Material No. 1.4571) reinforcement

sealing tape

MV TerminalPart No. 390 050

Connecting clampPart No. 308 025

Cross unitPart No. 318 201

Fixed earthing terminal for EBBPart No. 478 200

Fig. 5.5.2.9 Arrangement of the foundation earth electrode in case of a closed tank “white tank”

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Earth electrodes for structures with black tankThe name “black tank” derives from the multi-lay-ered strip of black bitumen applied to the sectionsof the structure which are outside in the ground.The body of the structure is coated withbitumen/tar which is then covered by generally upto 3 layers of bitumen strips.A ring conductor set into the foundation slababove the seal can act as the potential control inthe structure. Due to the high-impedance insula-tion to the outside, however, the earth electrode isineffective.In order to comply with the earthing requirementsstipulated in the various standards, an earth elec-trode, e.g. a ring earth electrode, must be installedexternally around the structure or below all sealsin the granular sub-grade course.Wherever possible, the external earth electrodeshould be led into the structure above the seal ofthe structure (Figure 5.5.2.10), in order to ensurethe tightness of the tank also in the long term. Awaterproof penetration of the “black tank” is only

possible using a special bushing for the earth elec-trodes.

Fibre concrete foundation slabsFibre concrete is a type of concrete which forms aheavy-duty concrete slab with steel fibres added tothe liquid concrete before hardening.The steel fibres are approx. 6 cm long and have adiameter of 1 – 2 mm. The steel fibres are slightlywavy and are admixed equally to the liquid con-crete. The proportion of steel fibres is around 20 – 30 kg/m3 concrete.The admixture gives the concrete slab both a highcompression strength and also a high tensilestrength and, compared to a conventional con-crete slab with reinforcement, it also provides aconsiderably higher elasticity. The liquid concrete is poured on site. This allows tocreate large areas with a smooth surface and nojoints. It is used for bedplates in the foundations oflarge halls, for example.

www.dehn.de LIGHTNING PROTECTION GUIDE 123

Fig. 5.5.2.10 Arrangement of the earth electrode in case of a closed tank “black tank”

granular sub-grade course

concrete

soil

foundation plate

Max. ground water leveltank seal

terminal luge.g. StSt V4A(Mat. No. 1.4571)

MEBB

ring earth electrode corrosion-resistant e.g. StSt V4A (Material No. 1.4571)mesh size of the ring earth electrode max. 10 m x 10 m

Ref.: Acc. to DIN 18014: 2007-09; VDE series 35, Schmolke, H.; Vogt, D., “Der Fundamenterder”; HEA Elektro+: 2004

soilfoundation earth electrode

Cross unitPart No. 318 201

Connection clampPart No. 308 025

Bushing for walls and earth electrodesPart No. 478 320

Page 125: Lightning Protection Guide

Fibre concrete has no reinforcement. This requiresa supplementary ring conductor or a meshed net-work to be constructed for installing earthingmeasures. The earthing conductor can be set in theconcrete and, if it is made of galvanised material, itmust be enclosed on all sides. This is very difficultto do on site.It is therefore recommended to install a corrosion-resistant high-alloy stainless steel, Material No.1.4571, below the subsequent concrete bedplate.The corresponding terminal lugs have to be con-sidered.Note:A specialist must install the earthing conductorsand connecting components in concrete. If this isnot possible, the building contractor can under-take the work only if it is supervised by a specialist.

5.5.3 Ring earth electrode – Earth electrodeType B

In Germany the national standard DIN 18014 stipu-lates that all new structures must have foundationearth electrodes. The earth-termination system ofexisting structures can be designed in the form ofa ring earth electrode (Figure 5.5.3.1).This earth electrode must be installed in a closedring around the structure or, if this is not possible,a connection to close the ring must be made insidethe structure.

80 % of the conductors of the earth electrode shallbe installed so as to be in contact with the earth. Ifthis 80 % cannot be achieved, it has to be checkedif supplementary earth electrodes Type A arerequired.The requirements on the minimum length of earthelectrodes according to the class of lightning pro-tection system must be taken into account (seeChapter 5.5.1).When installing the ring earth electrode, care mustbe taken that it is installed at a depth > 0.5 m anda distance of 1 m from the structure.If the earth electrode is driven in as previouslydescribed, it reduces the step voltage and thus actsas a potential control around the structure.

This earth electrode should be installed in naturalsoil. Setting it in gravel or ground filled with con-struction waste worsens the earth electrode resist-ance.When choosing the material of the earth electrodewith regard to corrosion, the local conditions mustbe taken into consideration. It is advantageous touse stainless steel. This earth electrode materialdoes not corrode nor does it subsequently requirethe earth-termination system to be refurbishedwith time-consuming and expensive measures suchas removal of paving, tar coatings or even steps,for installing a new flat strip.In addition, the terminal lugs must be particularlyprotected against corrosion.

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EBB

Type S Type Z Type AZ

Fig. 5.5.3.1 Ring earth electrode around a residential building Fig. 5.5.4.1 Couplings of DEHN earth rods

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5.5.4 Earth rod – Earth electrode Type AThe sectional earth rods, System DEHN, are manu-factured from special steel and hot-dip galvanised,or they consist of high-alloy stainless steel withMaterial No. 1.4571 (the high-alloy stainless steelearth electrode is used in areas especially at riskfrom corrosion). The particular feature of theseearth rods is their coupling point, which allows theearth rods to be connected without increasingtheir diameter.Each rod has a bore at its lower end, while the oth-er end of the rod has a corresponding spigot (Fig-ure 5.5.4.1).

With DEHN earth electrode Type “S”, the soft metal insert deforms as it is driven into the bore,creating an excellent electrical and mechanicalconnection.With DEHN earth electrode Type “Z”, the high coupling quality is achieved with a multiplyknurled spigot.With DEHN earth electrode Type “AZ”, the highcoupling quality is achieved with a multiplyknurled and shouldered spigot.

The advantages of the DEHN earth rods are:.

⇒ Special coupling:

⇒ no increase in diameter so that the earth rod isin close contact with the ground along thewhole of its length

⇒ Self-closing when driving in the rods

⇒ Simple to drive in with vibration hammers (Fig-ure 5.5.4.2) or mallets

⇒ Constant resistance values are achieved sincethe earth rods penetrate through the soil lay-ers which are unaffected by seasonal changesin moisture and temperature

⇒ High corrosion resistance as a result of hot-dipgalvanising (zinc coating 70 μm thick)

⇒ Galvanised earth rods also provide hot-gal-vanised coupling points

⇒ Easy to store and transport since individualrods are 1.5 or 1 m long.

5.5.5 Earth electrodes in rocky groundIn bedrock or stony ground, surface earth elec-trodes such as ring earth electrodes or star-typeearth electrodes are often the only way of creatingan earth-termination system.When installing the earth electrodes, the flat stripor round material is laid on the stony ground or onthe rock. The earth electrode should be coveredwith gravel, wet-mix slag aggregate or similar.It is advantageous to use stainless steel MaterialNo. 1.4571 as earth electrode material. Theclamped points should be installed with particularcare and be protected against corrosion (anticorro-sive band).

5.5.6 Intermeshing of earth-termination sys-tems

An earth-termination system can serve a wide vari-ety of purposes.The purpose of protective earthing is to safely con-nect electrical installations and equipment toearth potential and to prevent life hazard andphysical damage to property in the event of anelectrical fault.The lightning protection earthing system takesover the current from the down conductors anddischarges it into the ground.

www.dehn.de LIGHTNING PROTECTION GUIDE 125

Fig. 5.5.4.2 Driving the earth rod in with a work scaffolding and avibrating hammer

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The functional earthing installation serves toensure that the electrical and electronic installa-tions operate safely and trouble-free.The earth-termination system of a structure mustbe used for all earthing tasks together, i.e. theearth-termination system deals with all earthingtasks. If this were not the case, potential differ-ences could arise between the installations earth-ed on different earth-termination systems.Previously, a “clean earth” was sometimes appliedin practice for functional earthing of the electronicequipment, separately from the lightning protec-tion and the protective earth. This is extremely disadvantageous and can even be dangerous. Inthe event of lightning effects, great potential dif-ferences up to a few 100 kV occur in the earth-ter-mination system. This can lead to destruction ofelectronic installations and also to life hazards.Therefore, IEC 62305-3 and -4 (EN 62305-3 and -4)require continuous equipotential bonding withina structure.The earthing of the electronic systems can be con-structed to have a radial, central or intermeshed 2-dimensional design within a structure, (Figure5.5.6.1). This depends both on the electromagnet-ic environment and also on the characteristics ofthe electronic installation. If a larger structure

comprises more than one building, and if these areconnected by electrical and electronic conductors,then combining the individual earthing systemscan reduce the (total) earth resistance. In addition,the potential differences between the structuresare also reduced considerably. This diminishesnoticeably the voltage load of the electrical andelectronic connecting cables. The interconnectionof the individual earth-termination systems of thestructure should produce a meshed network. Themeshed earthing network should be constructedto contact the earth-termination systems at thepoint where the vertical down conductors are alsoconnected. The smaller the mesh size of the net-work of the earthing installation, the smaller thepotential differences between the structures in theevent of a lightning strike. This depends on thetotal area of the structure. Mesh sizes from 20 m x 20 m up to 40 m x 40 m have proved to becost-effective. If, for example, high vent stacks(preferred points of strike) are existing, then theconnections around this part of the plant shouldbe made closer, and, if possible, radial with circularinterconnections (potential control) When choos-ing the material for the conductors of the meshedearthing network, the corrosion and material com-patibility must be taken into account.

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administrationworkshop stock

gate

production

production

production

power centre

Fig. 5.5.6.1 Intermeshed earth-termination system of an industrial facility

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5.5.7 Corrosion of earth electrodes

5.5.7.1 Earth-termination systems with par-ticular consideration of corrosion

Metals in immediate contact with soil or water(electrolytes) can be corroded by stray currents,corrosive soils and the formation of voltaic cells. Itis not possible to protect earth electrodes fromcorrosion by completely enclosing them, i.e. byseparating the metals from the soil, since all theusual sheaths employed until now have had a highelectrical resistance and therefore negate theeffect of the earth electrodes.Earth electrodes made of a uniform material canbe threatened by corrosion from corrosive soilsand the formation of concentration cells. The riskof corrosion depends on the material and the typeand composition of the soil.Corrosion damage due to the formation of voltaiccells is being increasingly observed. This cell forma-tion between different metals with widely differ-ent metal /electrolyte potentials has been knownfor many years. What is not widely realised, how-ever, is that the reinforcements of concrete foun-dations can also become the cathode of a cell andhence cause corrosion to other installations.With the changes to the way buildings are con-structed – larger reinforced concrete structuresand smaller free metal areas in the ground –anode / cathode surface ratio is becoming moreand more unfavourable, and the risk of corrosionof the more base metals is inevitably increasing.An electrical isolation of installations acting asanodes to prevent this cell formation is only pos-sible in exceptional cases. The aim nowadays is tointegrate all earth electrodes including thosemetal installations connected to the earth in orderto achieve equipotential bonding and hence maxi-mum safety against touch voltages at faults orlightning strikes.In high voltage installations, high voltage protec-tive earth electrodes are increasingly connected tolow voltage operating earth electrodes in accor-dance with HD 637 S1. Furthermore IEC 60364-4-41, mod and HD 60364-4-41 requires the integra-tion of conduits and other installations into theshock hazard protective measures. Thus, the onlyway of preventing or at least reducing the risk ofcorrosion for earth electrodes and other installa-tions in contact with them is choosing suitablematerials for the earth electrodes.

In Germany, the national standard DIN VDE 0151“Material and minimum dimensions of earth elec-trodes with respect to corrosion” has been avail-able since June 1986 as a white paper. Apart fromdecades of experience in the field of earthing tech-nology, the results of extensive preliminary exami-nations have also been embodied in this standard.Many interesting results are available which areimportant for the earth electrodes, including thoseof lightning protection systems.The fundamental processes leading to corrosionare explained below.Practical anticorrosion measures especially forlightning protection earth electrodes shall bederived from this and from the wealth of materialalready acquired by the VDE task force on “Earthelectrode materials”.

Terms used in corrosion protection and corrosionprotection measurements

Corrosionis the reaction of a metal material to its environ-ment which leads to impairment of the character-istics of the metal material and/or its environment.The reaction is usually of electrochemical charac-ter.

Electrochemical corrosionis corrosion during which electrochemical process-es occur. They take place exclusively in the pres-ence of an electrolyte.

Electrolyteis an ion-conducting corrosive medium (e.g. soil,water, fused salts).

Electrodeis an electron-conducting material in an elec-trolyte. The system of electrode and electrolyteforms a half-cell.

Anodeis an electrode from which a d.c. current enters theelectrolyte.

Cathodeis an electrode from which a d.c. current leaves theelectrolyte.

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Reference electrodeis a measuring electrode for determining thepotential of a metal in the electrolyte.

Copper sulphate electrodeis a reference electrode which can hardly bepolarised, made of copper in saturated copper sul-phate solution.The copper sulphate electrode is the most commonform of reference electrode for measuring thepotential of subterranean metal objects (Figure5.5.7.1.1).

Corrosion cellis a voltaic cell with different local partial currentdensities for dissolving the metal. Anodes andcathodes of the corrosion cell can be formed

⇒ on the materialdue to different metals (contact corrosion) ordifferent structural components (selective orintercrystalline corrosion).

⇒ on the electrolytecaused by different concentrations of certainmaterials having stimulatory or inhibitorycharacteristics for dissolving the metal.

PotentialsReference potentialPotential of a reference electrode with respect tothe standard hydrogen electrode.

Electropotentialis the electrical potential of a metal or an electron-conducting solid in an electrolyte.

5.5.7.2 Formation of voltaic cells, corrosionThe corrosion processes can be clearly explainedwith the help of a voltaic cell. If, for example, ametal rod is dipped into an electrolyte, positivelycharged ions pass into the electrolyte and con-versely, positive ions are absorbed from the elec-trolyte from the metal band. In this context onespeaks of the “solution pressure” of the metal andthe “osmotic pressure” of the solution. Dependingon the magnitude of these two pressures, eithermore of the metal ions from the rod pass into thesolution (the rod therefore becomes negative com-pared to the solution) or the ions of the electrolytecollect in large numbers on the rod (the rodbecomes positive compared to the electrolyte). Avoltage is thus created between two metal rods inthe electrolyte.In practice, the potentials of the metals in theground are measured with the help of a coppersulphate electrode. This consists of a copper roddipped into a saturated copper sulphate solution(the reference potential of this reference electroderemains constant).Consider the case of two rods made of differentmetals dipping into the same electrolyte. A volt-age of a certain magnitude is now created on eachrod in the electrolyte. A voltmeter can be used to

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i

i

electrolyte

electrode IICu

electrode IFe

i

i

electrolyte I

permeable to ions

electrode IIelectrode I

electrolyte II

12

34

5

6

1 Electrolyte copper bar with hole formeasurements

2 Rubber plug3 Ceramic cylinder with porous base4 Glaze5 Saturated Cu/CuSO4 solution6 Cu/CuSO4 crystals

Fig. 5.5.7.1.1 Application example of a non-polarisable measuringelectrode (copper /copper sulphate electrode) for tap-ping a potential within the electrolyte (cross-sectionalview)

Fig. 5.5.7.2.1 Galvanic cell: iron/copper

Fig. 5.5.7.2.2 Concentration cell

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measure the voltage between the rods (elec-trodes); this is the difference between the poten-tials of the individual electrodes compared withthe electrolyte.

How does it now come that current flows in theelectrolyte and hence that material is transported,i.e. corrosion occurs?If, as shown here, the copper and iron electrodesare connected via an ammeter outside the elec-trolyte, for example, the following (Figure5.5.7.2.1) is ascertained: in the outer circuit, thecurrent i flows from + to –, i.e. from the “nobler”copper electrode according to Table 5.5.7.2.1 tothe iron electrode.

In the electrolyte, on the other hand, the current imust therefore flow from the “more negative”iron electrode to the copper electrode to close thecircuit. As a generalisation, this means that themore negative pole passes positive ions to the elec-trolyte and hence becomes the anode of the volta-ic cell, i.e. it dissolves. The dissolution of the metaloccurs at those points where the current enters theelectrolyte.A corrosion current can also arise from a concen-tration cell (Figure 5.5.7.2.2). In this case, two elec-trodes made of the same metal dip into differentelectrolytes. The electrode in electrolyte II with thehigher concentration of metal ions becomes elec-trically more positive than the other. Connecting

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Km

I t=

Δ

Ws

tlin =Δ

ZincDefinition−0.9 to −1.15)

Free corrosion potential in the soil1) [V]

1Iron−0.5 to −0.83)

Tin−0.4 to −0.62)

Lead−0.5 to −0.6

Copper0 to −0.1

Symbol(s)UM-Cu/CuSO4

−1.25)Cathodic protective potential in the soil1) [V]

2 −0.854)−0.652)−0.65−0.2UM-Cu/CuSO4

10.7Electrochemical equivalent[kg/(A • year)]

3 9.119.433.910.4

0.15Linear corrosion rate [mm/year]at J = 1 mA/dm2

4 0.120.270.30.12

1) Measured to saturated copper/copper sulphate electrode (Cu/Cu So4).

2) Values are verified in presently performed tests. The potential of tin-coated copper depends on the thickness of the tin coating. Common tin coatings up to now have amounted up to a few μm and are thus between the values of tin and copper in the soil.

3) These values do also apply to lower alloyed types of iron. The potential of steel in concrete (reinforcing iron of foundations) depends considerably on external influences. Measured to a saturated copper/copper sulphate elctrode it generally amounts −0.1 to −0.4 V. In case of metal conductive connections with wide underground installations made of metal with more negative potential, it is cathodically polarised and thus reaches values up to approximately −0.5 V.

4) In anaerobic soils the protective potential should be −0.95 V.

5) Hot-dip galvanised steel, with a zinc coating according to the above mentioned table, has a closed external pure zinc layer. The potential of hot-dip galvanised steel in the soil corresponds therefore to approximately the stated value of zinc in the soil. In case of a loss of the zinc layer, the potential gets more positive. With its complete corresion it can reach the value of steel.

The potential of hot-dip galvanised steel in concrete has approximately the same initial values. In the course of time, the potential can get more positive. Values more positive than approx. −0.75 V, however, have not been found yet.

Heavily hot-dip galvanised copper with a zinc layer of min. 70 μm has also a closed external pure zinc layer. The potential of hot-dip galvanised copper in soil corresponds therefore to approx. the stated value of zinc in soil. In case of a thinner zinc layer or a corrosion of the zinc layer, the potential gets more positive. Limit values have still not been defined yet.

Table 5.5.7.2.1 Potential values and corrosion rates of common metal materials

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the two electrodes enables the current i to flowand the electrode, which is electrochemically morenegative, dissolves.A concentration cell of this type can be formed, forexample, by two iron electrodes, one of which isfixed in concrete while the other lies in the ground(Figure 5.5.7.2.3).Connecting these electrodes, the iron in the con-crete becomes the cathode of the concentrationcell and the one in the ground becomes the anode;the latter is therefore destroyed by ion loss.For electrochemical corrosion it is generally thecase that, the larger the ions and the lower theircharge, the greater the transport of metal associ-ated with the current flow i, (i.e. i is proportionalto the atomic mass of the metal).In practice, the calculations are carried out withcurrents flowing over a certain period of time, e.g.over one year. Table 5.5.7.2.1 gives values whichexpress the effect of the corrosion current (currentdensity) in terms of the quantity of metal dis-solved. Corrosion current measurements thusmake it possible to calculate in advance how manygrammes of a metal will be eroded over a specificperiod.Of more practical interest, however, is the predic-tion if, and over which period of time, corrosionwill cause holes or pitting in earth electrodes, steeltanks, pipes etc. So it is important whether theprospective current attack will take place in a dif-fuse or punctiform way.For the corrosive attack, it is not solely the magni-tude of the corrosion current which is decisive, butalso, in particular, its density, i.e. the current perunit of area of the discharge area.It is often not possible to determine this currentdensity directly. In such cases, this is managed withpotential measurements the extent of the avail-

able “polarisation” can be taken from. The polari-sation behaviour of electrodes is discussed onlybriefly here.Let us consider the case of a galvanised steel stripsituated in the ground and connected to the(black) steel reinforcement of a concrete founda-tion (Figure 5.5.7.2.4). According to our measure-ments, the following potential differences occurhere with respect to the copper sulphate elec-trode:steel, (bare) in concrete: – 200 mVsteel, galvanised, in sand: – 800 mV

Thus there is a potential difference of 600 mVbetween these two metals. If they are now con-nected above ground, a current i flows in the out-er circuit from reinforced concrete to the steel inthe sand, and in the ground from the steel in thesand to the steel in the reinforcement.The magnitude of the current i is now a functionof the voltage difference, the conductance of theground and the polarisation of the two metals.Generally, it is found that the current i in theground is generated by changes in the material.But a change to the material also means that thevoltage of the individual metals changes withrespect to the ground. This potential drift causedby the corrosion current i is called polarisation. Thestrength of the polarisation is directly proportion-al to the current density. Polarisation phenomenanow occur at the negative and positive electrodes.However, the current densities at both electrodesare mostly different.

For illustration, we consider the following exam-ple:A well-insulated steel gas pipe in the ground isconnected to copper earth electrodes.

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i

i

soil

electrode IISt

electrode ISt/tZn

concretesoil

i

electrode IIFe

electrode IFe

i

concrete

Fig. 5.5.7.2.3 Concentration cell: Iron in soil / iron in concrete Fig. 5.5.7.2.4 Concentration cell: Galvanised steel in soil / steel(black) in concrete

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If the insulated pipe has only a few small spotswhere material is missing, there is a higher currentdensity at these spots resulting in rapid corrosionof the steel.In contrast, the current density is low over themuch larger area of the copper earth electrodeswhere the current enters. Thus the polarisation is greater at the more nega-tive insulated steel conductor than at the positivecopper earth electrodes. The potential of the steelconductor is shifted to more positive values. Thus,the potential difference across the electrodesdecreases as well. The magnitude of the corrosioncurrent is therefore also a function of the polarisa-tion characteristics of the electrodes. The strength of the polarisation can be estimatedby measuring the electrode potentials for a splitcircuit. The circuit is split in order to avoid the volt-age drop in the electrolyte. Recording instrumentsare usually used for such measurements since thereis frequently a rapid depolarisation immediatelyafter the corrosion current is interrupted.If strong polarisation is now measured at theanode (the more negative electrode), i.e. if there isan obvious shift to more positive potentials, thenthere is a high risk that the anode will corrode.

Let us now return to our corrosion cell-steel (bare)in concrete / steel, galvanised in the sand (Figure5.5.7.2.4). With respect to a distant copper sulphate electrode, it is possible to measure apotential of the interconnected cells of between –200 mV and –800 mV. The exact value dependson the ratio of the anodic to cathodic area and thepolarisability of the electrodes. If, for example, the area of the reinforced concretefoundation is very large compared to the surfaceof the galvanised steel wire, then a high anodiccurrent density occurs at the latter, so that it ispolarised to almost the potential of the reinforce-ment steel and destroyed in a relatively short time.High positive polarisation thus always indicates anincreased risk of corrosion.In practice it is, of course, now important to knowthe limit above which a positive potential shiftingmeans an acute risk of corrosion. Unfortunately, itis not possible to give a definite value, whichapplies in every case; the effects of the soil condi-tions alone are too various. It is, however, possibleto stipulate fields of potential shifting for naturalsoils.

Summary:A polarisation below +20 mV is generally non-haz-ardous. Potential shifts exceeding +100 mV aredefinitely hazardous. Between 20 and 100 mVthere will always be cases where the polarisationcauses considerable corrosion phenomena.

To summarise, one can stipulate:The precondition for the formation of corrosioncells (voltaic cells) is always the presence of metaland electrolytic anodes and cathodes connected tobe conductive.

Anodes and cathodes are formed from:

⇒ Materials

• different metals or different surface condi-tions of a metal (contact corrosion),

• different structural components (selective orintercrystalline corrosion),

⇒ Electrolytes

• different concentration (e.g. salinity, ventila-tion).

In corrosion cells, the anodic fields always have amore negative metal /electrolyte potential thanthe cathodic fields.The metal /electrolyte potentials are measuredusing a saturated copper sulphate electrodemounted in the immediate vicinity of the metal inor on the ground. If there is a metal conductiveconnection between anode and cathode, then thepotential difference gives rise to a d.c. current inthe electrolyte which passes from the anode intothe electrolyte by dissolving metal before enteringagain the cathode.

The “area rule” is often applied to estimate theaverage anodic current density JA:

JA Average anodic current density

UA,UC Anode or cathode potentials in V

ϕC Specific polarisation resistance of the cathode in Ωm2

AA,AC Anode or cathode surface m2

JU U A

AAC A

C

C

A

=−

⋅ϕ

in A/m2

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The polarisation resistance is the ratio of the polar-isation voltage and the total current of a mixedelectrode (an electrode where more than one elec-trode reaction takes place).In practice, it is indeed possible to determine thedriving cell voltages UC – UA and the size of theareas AC and AA as an approximation for estimat-ing the rate of corrosion. The values for ϕA (speci-fic polarisation resistance of the anode) and ϕC ,however, are not available to a sufficient degree ofaccuracy. They depend on the electrode materials,the electrolytes and the anodic and cathodic cur-rent densities.The results of examinations available until nowallow the conclusion that ϕA is much smaller thanϕC .To ϕC applies:steel in the ground approx. 1 Ωm2

copper in the ground approx. 5 Ωm2

steel in concrete approx. 30 Ωm2

From the area rule, however, it is clear, that power-ful corrosion phenomena occur both on enclosedsteel conductors and tanks with small spots in thesheath where material is missing, connected tocopper earth electrodes, and also on earthing con-ductors made of galvanised steel connected toextended copper earth-termination systems orextremely large reinforced concrete foundations.By choosing suitable materials it is possible toavoid or reduce the risk of corrosion for earth elec-trodes. To achieve a satisfactory service life, mate-rial minimum dimensions must be maintained(Table 5.5.8.1).

5.5.7.3 Choice of earth electrode materialsTable 5.5.8.1 is a compilation of the earth elec-trode materials and minimum dimensions usuallyused today.

Hot-dip galvanised steelHot-dip galvanised steel is also suitable for embed-ding in concrete. Foundation earth electrodes,earth electrodes and equipotential bonding con-ductors made of galvanised steel in concrete maybe connected with reinforcement iron.

Steel with copper sheathIn the case of steel with copper sheath, the com-ments for bare copper apply to the sheath mater-

ial. Damage to the copper sheath, however, cre-ates a high risk of corrosion for the steel core,hence a complete closed copper layer must alwaysbe present.

Bare copperBare copper is very resistant due to its position inthe electrolytic insulation rating. Moreover, incombination with earth electrodes or other instal-lations in the ground made of more “base” mate-rials (e.g. steel), it has additional cathodic protec-tion, albeit at the expense of the more “base”metals.

Stainless steelsCertain high-alloy stainless steels according to EN 10088 are inert and corrosion-resistant in theground. The free corrosion potential of high-alloystainless steels in normally aerated soils is mostlyclose to the value of copper.The surface of stainless steel earth electrode mate-rials passivating within a few weeks, they are neu-tral to other (more inert and base) materials.Stainless steels shall contain at least 16 % chrome,5 % nickel and 2 % molybdenum.Extensive measurements have shown that only ahigh-alloy stainless steel with the Material No.1.4571, for example, is sufficiently corrosion-resist-ant in the ground.

Other materialsOther materials can be used if they are particularlycorrosion-resistant in certain environments or areat least equally as good as the materials listed inTable 5.5.8.1.

5.5.7.4 Combination of earth electrodesmade of different materials

The cell current density resulting from the combi-nation of two different metals installed in theearth to be electrically conductive, leads to the cor-rosion of the metal acting as the anode (Table5.5.7.4.1). This essentially depends on the ratio ofthe magnitude of the cathodic area AC to the mag-nitude of the anodic area AA.The “Corrosion behaviour of earth electrode mate-rials” research project has found the followingwith respect to the choice of earth electrode mate-rials, particularly regarding the combination of dif-ferent materials:

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A higher degree of corrosion is only to be expect-ed if the ratio of the areas is

Generally, it can be assumed that the material withthe more positive potential will become the cath-ode. The anode of a corrosion cell actually presentcan be recognised by the fact that it has the morenegative potential when opening the metal con-ductive connection.Connecting steel installations in the ground, thefollowing earth electrode materials always behaveas cathodes in (covering) soils:

– bare copper,

– tin-coated copper,

– high-alloy stainless steel.

Steel reinforcement of concrete foundationsThe steel reinforcement of concrete foundationscan have a very positive potential (similar to cop-per). Earth electrodes and earthing conductorsconnected directly to the reinforcement of largereinforced concrete foundations should thereforebe made of stainless steel or copper.This also applies particularly to short connectingcables in the immediate vicinity of the founda-tions.

Installation of isolating spark gapsAs already explained, it is possible to interrupt theconductive connection between systems with verydifferent potentials installed in the ground byintegrating isolating spark gaps. Normally, then it

is no longer possible for corrosion currents to flow.At upcoming surges, the isolating spark gap oper-ates and interconnects the installations for theduration of the surges. However, isolating sparkgaps must not be installed for protective and oper-ating earth electrodes, since these earth electrodesmust always be connected to the plant.

5.5.7.5 Other anticorrosion measures

Galvanised steel connecting cables from founda-tion earth electrodes to down conductorsGalvanised steel connecting cables from founda-tion earth electrodes to down conductors shall belaid in concrete or masonry up to above the sur-face of the earth.If the connecting cables are led through theground, galvanised steel must be equipped withconcrete or synthetic sheathing or, alternatively,terminal lugs with NYY cable, stainless steel orfixed earthing terminals must be used.Within the masonry, the earth conductors can alsobe led upwards without corrosion protection.

Earth entries made of galvanised steelEarth entries made of galvanised steel must beprotected against corrosion for a distance of atleast 0.3 m above and below the surface of theearth.Generally, bitumen coatings are not sufficient.Sheathing not absorbing moisture offers protec-tion, e.g. butyl rubber strips or heat-shrinkablesleeves.

Underground terminals and connectionsCut surfaces and connection points in the groundmust be designed to ensure that the corrosionresistance of the corrosion protection layer of theearth electrode material is the same for both. Con-nection points in the ground must therefore beequipped with a suitable coating, e.g. sheathedwith an anticorrosive band.

Corrosive wasteWhen filling ditches and pits to install earth elec-trodes, pieces of slag and coal must not come intoimmediate contact with the earth electrode mate-rial; the same applies to construction waste.

A

AC

A

> 100

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Material with great areaMaterial with Galvanised Steel Steel in Coppersmall area steel concrete

Galvanised steel + + − −

Steel + + − −

Steel in concrete + + + +

Steel with Cu coating + + + +

Copper/StSt + + + ++ combinable − not combinable

zinc removal

Table 5.5.7.4.1 Material combinations of earth-termination systems for different area ratios (AC > 100 x AA)

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NotesEarth rodØ mm

Material Configuration

Copper stranded3)

solid round material3)

solid flat material3)

solid round material

pipe

solid plate

grid-type plate

158)

20

min. diameterof each strand 1.7 mm

diameter 8 mm

min. thickness 2 mm

min. wall thickness 2 mm

min. thickness 2 mm

section 25 mm x 2 mm,min. length of gridconstruction: 4.8 m

1) The coating must be smooth, continuous and free of residual flux, mean value 50 μm for round and70 μm for flat material.

2) Threads must be tapped before galvanising.3) Can also be tin-coated.4) The copper must be connected unresolvably with the steel.5) Only permitted, if embedded completely in concrete.6) Only permitted for the part of the foundation in contact with the earth, if connected safely with the

reinforcement every 5 m.7) Chrome 16 %, nickel 5 %, molybdenum 2 %, carbon 0,08 %.8) In some countries 12 mm are permitted.9) Some countries require earth lead-in rods to connect down conductor and earth electrode.

Earthconductor50 mm2

50 mm2

50 mm2

Earth platemm

500 x 500

600 x 600

Steel galvanised solid roundmaterial1), 2)

galvanised pipe1), 2)

galvanised solid flatmaterial1)

galvanised solid plate1)

galvanised grid-type plate1)

copper-plated solid roundmaterial4)

bare solid roundmaterial5)

bare or galvanised solidflat material5), 6)

galvanised cable5), 6)

169)

25

14

min. wall thickness 2 mm

min. thickness 3 mm

min. thickness 3 mm

section 30 mm x 3 mm

min. 250 μmcoating with 99.9 %copper

min. thickness 3 mm

min. diameter of everywire 1.7 mm

diameter10 mm

90 mm2

diameter10 mm

75 mm2

70 mm2

500 x 500

600 x 600

Min. dimensions

StainlessSteel7)

solid round material

solid flat material

15

min. thickness 2 mm

diameter10 mm

100 mm2

Table 5.5.8.1 Material, configuration and min. dimensions of earth electrodes according to IEC 62305-3 (EN 62305-3) Table 7

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5.5.8 Materials and minimum dimensionsfor earth electrodes

Table 5.5.8.1 illustrates the minimum cross sec-tions, shape and material of earth electrodes.

5.6 Electrical isolation of the exter-nal lightning protection system– Separation distance

There is a risk of uncontrolled flashovers betweencomponents of the external lightning protectionsystem and metal and electrical installations with-in the structure, if there is insufficient distancebetween the air-termination or down-conductorsystem on one hand, and metal and electricalinstallations within the structure to be protected,on the other.

Metal installations such as water and air condition-ing pipes and electric power lines, produce induc-tion loops in the structure which are induced byimpulse voltages due to the rapidly changing mag-netic lightning field. These impulse voltages mustbe prevented from causing uncontrolled flash-overs which can also possibly cause a fire.Flashovers on electric power lines, for example,can cause enormous damage to the installationand the connected consumers. Figure 5.6.1 illus-trates the principle of separation distance.The formula for calculating the separation dis-tance is difficult for the practitioner to apply.

The formula is:

ki is a function of the class of lightning protec-tion system chosen (induction factor),

kc is a function of the geometric arrangement(current splitting coefficient),

km is a function of the material in the point ofproximity (material factor) and

l (m) is the length of the air-termination systemor down-conductor system from the pointat which the separation distance shall bedetermined to the next point of equipoten-tial bonding.

The coefficient ki (induction factor) of the corres-ponding class of lightning protection system repre-sents the threat from the steepness of the current.

Factor kc takes into consideration the splitting ofthe current in the down-conductor system of theexternal lightning protection system. The standardgives different formulae for determining kc. Inorder to achieve the separation distances whichstill can be realised in practice, particularly forhigher structures, it is recommended to install ringconductors, i.e. to intermesh the down conductors.This intermeshing balances the current flow, whichreduces the required separation distance.The material factor km takes into consideration theinsulating characteristics of the surroundings. Thiscalculation assumes the electrical insulating char-acteristics of air to be a factor of 1. All other solidmaterials used in the construction industry (e.g.masonry, wood, etc.) insulate only half as well asair.

Further material factors are not given. Deviatingvalues must be proved by technical tests. A factorof 0.7 is specified for the GRP material (glass-fibrereinforced plastic) used in the products of the iso-lated air-termination systems from DEHN + SÖHNE(DEHNiso distance holder, DEHNiso Combi). This

s kk

kl mi

c

m

= ⋅ ( )

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l

s

s

soil

EBB

MDB

foundation earth electrode

electrical installation

metal installation

downconductor

s separation distanceMDB Main Distribution Board

Fig. 5.6.1 Illustration – Separation distance

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factor can be used for calculation in the same wayas the other material factors.

Length l is the actual length along the air-termina-tion system or down-conductor system from thepoint at which the separation distance to the nextpoint of equipotential bonding or the next light-ning equipotential bonding level shall be deter-mined.

Each structure with lightning equipotential bond-ing has an equipotential surface of the foundationearth electrode or earth electrode near the surfaceof the earth. This surface is the reference plane fordetermining the distance l.

If a lightning equipotential bonding level is to becreated for high structures, then for a height of 20 m, for example, the lightning equipotentialbonding must be carried out for all electrical andelectronic conductors and all metal installations.The lightning equipotential bonding must berealised by using surge protective devices Type I.

Otherwise, even for high structures, the equipo-tential surface of the foundation earth elec-trode/earth electrode shall be used as referencepoint and basis for the length l. Higher structures

are making it more and more difficult to maintainthe required separation distances.

The potential difference between the structure’sinstallations and the down conductors is equal tozero near the earth’s surface. The potential differ-ence increases with increasing height. This can beimagined as a cone standing on its tip (Figure5.6.2).

Hence, the separation distance to be maintained isgreatest at the tip of the building or on the surfaceof the roof and becomes less towards the earth-termination system.This requires a multiple calculation of the distancefrom the down conductors with a different dis-tance l.

The calculation of the current splitting coefficientkc is often difficult because of the different struc-tures.If a single air-termination rod is erected next to thestructure, for example, the total lightning currentflows in this one air-termination conductor anddown conductor. Factor kc is therefore equal to 1.The lightning current cannot split here. Thereforeit is often difficult to maintain the separation dis-

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s

s

soil

down conductor

earth electrode

α

protective angle

s

I

Fig. 5.6.2 Potential difference with increasing height Fig. 5.6.3 Air-termination mast with kc = 1

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tance. In Figure 5.6.3, this can be achieved byerecting the mast further away from the structure.Almost the same situation occurs for air-termina-tion rods e.g. for roof-mounted structures. Until itreaches the next connection of the air-terminationrod to the air-termination or down conductor. Thisdefined path carries 100 % (kc = 1) of the lightningcurrent (Figure 5.6.4).

If two air-termination rods or air-terminationmasts have a cable spanned between them, thelightning current can split between two paths (Fig-ure 5.6.5). Owing to the different impedances,however, the splitting is not always 50 % to 50 %,since the lightning flash does not always strike theexact centre of the arrangement but can also strikealong the length of the air-termination system. The most unfavourable case is taken into accountby calculating the factor kc in the formula.This calculation assumes an earth-termination sys-tem Type B. If single earth electrodes Type A areexisting, these must be interconnected.

h length of the down conductor

c mutual distance of the air-termination rods orair-termination masts

The following example illustrates the calculationof the coefficient for a gable roof with two downconductors (Figure 5.6.6). An earth-terminationsystem Type B (ring or foundation earth electrode)is existing.

kc =+

⋅ +=

9 12

2 9 120 7

.

kh c

h cc =+

+2

www.dehn.de LIGHTNING PROTECTION GUIDE 137

s

soil

kc = 1

M

h

c

h

c

Fig. 5.6.4 Flat roof with air-termination rod and ventilation outlet

Fig. 5.6.5 Determination of kc with two masts with overspannedcable and an earth electrode Type B

Fig. 5.6.6 Determination of kc for a gable roof with 2 down conduc-tors

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The arrangement of the down-conductor systemshown in Figure 5.6.6 should no longer beinstalled, not even on a detached house either. Thecurrent splitting coefficient is significantlyimproved by using two further down conductors,i.e. a total of 4 (Figure 5.6.7). The following formu-la is used in the calculation:

h length of the down conductor up to the eavesgutter of the building as worst point for alightning input

c mutual distance of the down conductors

n is the total number of down conductors

Result: kc ≈ 0.51

For structures with flat roofs, the current splittingcoefficient is calculated as follows. In this case, anearth electrode arrangement Type B is a precondi-tion (Figure 5.6.8).

kc =⋅

+ +1

2 40 1 0 2

12

43

. .

kn

c

hc = + +1

20 1 0 2 3. .

h plumb distance, height of the building

c mutual distance of the down conductors

n the total number of down conductors

The distances of the down conductors are assumedto be equal. If not, c is the greatest distance.

If electrical structures or domelights are located onthe flat roof (Figure 5.6.9), then two current split-ting coefficients must be taken into account whencalculating the separation distance. For the air-ter-mination rod, kc = 1 to the next air-termina-tion/down conductor.The calculation of the current splitting coefficientkc for the subsequent course of the air-terminationsystem and down conductors is performed asexplained above. For illustration, the separationdistance s for a flat roof with roof-mounted struc-tures is determined below.

Example:Domelights were installed on a structure with alightning protection system Class III. They are con-trolled electrically.

Structure data:

⇒ Length 40 mWidth 30 m

Height 14 m

⇒ Earth-termination system, foundation earthelectrode Type B

⇒ Number of down conductors: 12

⇒ Distance of the down conductors: min. 10 mmax. 15 m

⇒ Height of the electrically controlled dome-lights: 1.5 m

The calculation of the current splitting coefficientkc for the structure is:

Result: kc ≈ 0.35

kc =⋅

+ +1

2 120 1 0 2

15

143. .

kn

c

hc = + +1

20 1 0 2 3. .

www.dehn.de138 LIGHTNING PROTECTION GUIDE

l

c

h

Fig. 5.6.7 Gable roof with 4 down conductors

Page 140: Lightning Protection Guide

It is not necessary to calculate the factor kc for theair-termination rod kc = 1.

For the calculation of the current splitting the air-termination rod is assumed to be positioned at theedge of the roof and not within the mesh of theair-termination system. If the air-termination rod iswithin the mesh, the current splitting and theshortest length in the mesh has to be consideredadditionally.

Calculation of the separation distance for the topedge of the roof of the structure:

The material factor km is set as for solid buildingmaterial km = 0.5.

Result: s ≈ 0.39 m

Calculation of the separation distance for the air-termination rod:

The material factor is km = 0.5 because of the posi-tion of the air-termination rod on the flat roof.

Result: s = 0.12 m

This calculated separation distance would be cor-rect if the air-termination rod were erected on thesurface of the earth (lightning equipotential bond-ing level).In order to obtain the separation distance com-pletely and correctly, the separation distance ofthe structure must be added.

Stot = sstructure + sair-termination rod

= 0.39 m + 0.12 m

Stot = 0.51 m

This calculation states that a separation distance of0.51 m must be maintained at the uppermost pointof the domelight. This separation distance wasdetermined using the material factor 0.5 for solidmaterials.Erecting the air-termination rod with a concretebase, the “full insulating characteristics” of the airare not available at the foot of the air-terminationrod (Figure 5.6.9). At the foot of the concrete basea separation distance of sstructure = 0.39 (solid mate-rial) is sufficient.

If lightning equipotential bonding levels are creat-ed for high structures at different heights by inte-grating all metal installations and all electrical andelectronic conductors by means of lightning cur-rent arresters (SPD Type I), then the following cal-culation can be carried out. This involves calculat-ing distances to conductors installed on only onelightning equipotential bonding level, and also tothose installed over several levels.

s m= 0 041

0 5.

.( ) 1.5

s m= 0 040 35

0 5.

.

.( ) 14

www.dehn.de LIGHTNING PROTECTION GUIDE 139

c

h

s

km = 0.5

km = 1

Fig. 5.6.8 Value of coefficient kc in case of a meshed network of air-termination conductors and an earthing Type B

Fig. 5.6.9 Material factors of an air-termination rod on a flat roof

Page 141: Lightning Protection Guide

This assumes an earth-termination system in formof a foundation or ring earth electrode (Type B) ora meshed network (Figure 5.6.10).

As previously explained, supplementary ring con-ductors can be installed around the structure(truss) to balance the lightning current. This has apositive effect on the separation distance. Figure5.6.10 illustrates the principle of ring conductorsaround the structure, without installing a light-ning equipotential bonding level by using light-ning current arresters at the height of the ringconductors.

The individual segments are assigned differentcurrent splitting coefficients kc. If the separationdistance for a roof-mounted structure shall now bedetermined, the total length from the equipoten-tial surface of the earth electrode to the upper-most tip of the roof-mounted structure must beused as the base (sum of the partial lengths). If the

total separation distance stot is to be determined,the following formula must be used for the calcu-lation:

With this design of supplementary ring conductorsaround the structure, it is still the case that no par-tial lightning currents whatsoever are conductedinto the structure.Even if the numerous down conductors and sup-plementary ring conductors do not allow a main-taining of the separation distance for the com-plete installation, it is possible to define the upperedge of the structure as the lightning equipoten-tial bonding surface (+/–0). This roof-level light-ning equipotential bonding surface is generallyimplemented for extremely high structures whereit is physically impossible to maintain the separa-tion distance.

This requires the integration of all metal installa-tions and all electrical and electronic conductorsinto the equipotential bonding by means of light-ning current arresters (SPD Type I). This equipoten-tial bonding is also directly connected to the exter-nal lightning protection system. These previouslydescribed measures allow to set the separation dis-tances on the upper edge of the structure to 0. Thedisadvantage of this type of design is that all con-ductors, metal installations, e.g. reinforcements,lift rails and the down conductors as well, carrylightning currents. The effect of these currents onelectrical and electronic systems must be takeninto account when designing the internal light-ning protection system (surge protection).It is advantageous to split the lightning currentover a large area.

5.7 Step and touch voltagesIEC 62305-3 (EN 62305-3) draws attention to thefact that, in special cases, touch or step voltagesoutside a structure in the vicinity of the down con-ductors can present a life hazard even though thelightning protection system was designed accord-ing to the latest standards.Special cases are, for example, the entrances orcanopies of structures frequented by large num-

sk

kk l k l k ltot

i

ml tot c c= ⋅ + ⋅ + ⋅( ) 3 3 4 4

www.dehn.de140 LIGHTNING PROTECTION GUIDE

h 1h 2

h 3h 4

h n

I a

I gI f

I bI c

I d

c c

sa

sb

sc

sd

sf

sg

(A)

Fig. 5.6.10 Value of coefficient kc in case of an intermeshed net-work of air-termination, ring conductors interconnectingthe down conductors and an earthing Type B

Page 142: Lightning Protection Guide

bers of people such as theatres, cinemas, shoppingcentres, where bare down conductors and earthelectrodes are present in the immediate vicinity.

Structures which are particularly exposed (at riskof lightning strikes) and freely accessible to mem-bers of the public may also be required to havemeasures preventing intolerably high step andtouch voltages.These measures (e.g. potential control) are prima-rily applied to steeples, observation towers, moun-tain huts, floodlight masts in sports grounds andbridges.

Gatherings of people can vary from place to place(e.g. in shopping centre entrances or in the stair-case of observation towers). Measures to reducestep and touch voltages are therefore only re-quired in the areas particularly at risk.Possible measures are potential control, isolationof the site or the additional measures describedbelow. The individual measures can also be com-bined with each other.

Definition of touch voltageTouch voltage is a voltage acting upon a personbetween his position on the earth and whentouching the down conductor.The current path leads from the handvia the body to the feet (Figure 5.7.1).

For a structure built with a steel skele-ton or reinforced concrete, there is norisk of intolerably high touch voltagesprovided that the reinforcement is safe-ly interconnected or the down conduc-tors are installed in concrete. Moreover, the touch voltage can be dis-regarded for metal facades if they areintegrated into the equipotential bond-ing and/or used as natural componentsof the down conductor.

If there is a reinforced concrete with asafe tying of the reinforcement to thefoundation earth electrode under thesurface of the earth in the areas outsidethe structure which is at risk, then thismeasure already improves the curve ofthe gradient area and acts as a poten-tial control. Hence step voltage can beleft out of the considerations.

The following measures can reduce the risk ofsomeone being injured by touching the down con-ductor:

⇒ The down conductor is sheathed in insulatingmaterial (min. 3 mm crosslinked polyethylenewith an impulse withstand voltage of 100 kV1.2/50 μs).

⇒ The position of the down conductors can bechanged, e.g. not in the entrance of the struc-ture.

⇒ The probability of people accumulating can bereduced with information or prohibition signs;barriers can also be used.

⇒ The specific resistance of the surface layer of the earth at a distance of up to 3 m aroundthe down conductor must be not less than 5000 Ωm.

A layer of asphalt with a thickness of 5 cm,generally meets this requirement.

⇒ Compression of the meshed network of theearth-termination system by means of poten-tial control.

NoteA downpipe, even if it is not defined as a downconductor, can present a hazard to persons touch-

www.dehn.de LIGHTNING PROTECTION GUIDE 141

Fig. 5.7.1 Illustration of touch voltage and step voltage

1 m

ϕFE

US

FE

ϕ

UE

Ut

UE Earth potentialUt Touch voltageUS Step voltageϕ Potential of earth surfaceFE Foundation earth electrode

reference earth

Page 143: Lightning Protection Guide

ing it. In such a case, one possibility is to replacethe metal pipe with a PVC one (height: 3 m).

Definition of step voltageStep voltage is a part of the earthing potentialwhich can be bridged by a person taking a stepover 1 m. The current path runs via the humanbody from one foot to the other (Figure 5.7.1).

The step voltage is a function of the form of thegradient area.As is evident from the illustration, the step voltagedecreases as the distance from the structureincreases. The risk to persons therefore decreasesthe more they are away from the structure.

The following measures can be taken to reducethe step voltage:

⇒ Persons can be prevented from accessing thehazardous areas (e.g. by barriers of fences)

⇒ Reducing the mesh size of the earthing instal-lation network – potential control

⇒ The specific resistance of the surface layer ofthe earth at a distance of up to 3 m around thedown-conductor system must be not less than5000 Ωm.

A layer of asphalt with a thickness of 5 cm, ora 15 cm thick bed of gravel generally meetsthis requirement

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symbolic course

refe

renc

e e

arth

0.5

m

1 m

1.5

m

1 m 3 m 3 m2

m3 m

Fig. 5.7.2 Potential control – Illustration and symbolic course of the gradient area

Page 144: Lightning Protection Guide

If a large number of people frequently congregatein a hazardous area near to the structure to beprotected, then a potential control must be pro-vided to protect them.

The potential control is sufficient if the resistancegradient on the surface of the earth in the field tobe protected does not exceed 1 Ω/m.To achieve this, an existing foundation earth elec-trode should be supplemented by a ring earthelectrode installed at a distance of 1 m and a depthof 0.5 m. If the structure already has an earth-ter-mination system in form of a ring earth electrode,this is already “the first ring” of the potential con-trol.

Additional ring earth electrodes should beinstalled at a distance of 3 m from the first one and

the subsequent ones. The depth of the ring earthelectrode shall be increased (in steps of 0.5 m) themore it is away from the structure (see Table 5.7.1).

If a potential control is implemented for a struc-ture, it must be installed as follows (Figure 5.7.2and 5.7.3):The down conductors must be connected to all therings of the potential control. The individual rings must be connected at leasttwice, however (Figure 5.7.4).

If ring earth electrodes (control earth electrodes)cannot be designed to be circular, their ends mustbe connected to the other ends of the ring earthelectrodes. There should be at least two connec-tions within the individual rings (Figure 5.7.5).

When choosing the materials for the ring earthelectrodes, attention must be paid to the possiblecorrosion load (Chapter 5.5.7). Stainless steel V4A (Material No. 1.4571) hasproved to be a good choice for taking the forma-tion of voltaic cells between foundation and ringearth electrodes into account.Cables Ø 10 mm or flat strips 30 mm x 3.5 mm canbe installed as ring earth electrodes.

www.dehn.de LIGHTNING PROTECTION GUIDE 143

1m 3m 3m 3m

mast

clamped points

1m3m 3m 3m

conn

ectio

n to

e.g.

exi

stin

g fo

unda

tion

(reifo

rced

con

cret

e)

mast

Distance fromthe building

Depth

1st ring

2nd ring

3rd ring

4th ring

1 m

4 m

7 m

10 m

0.5 m

1.0 m

1.5 m

2.0 m

Table 5.7.1 Ring distances and depths of the potential control

Fig. 5.7.3 Possible potentialcontrol in entrancearea of the building

Fig. 5.7.4 Potential control performance for a flood light orcell site mast

Fig. 5.7.5 Connection control at the ring/ foun-dation earth electrode

Page 145: Lightning Protection Guide

5.7.1 Control of the touch voltage at downconductors of lightning protection sys-tems

The hazardous area of touch and step voltages forpersons outside of a building is within the distanceof 3 m to the building and up to a height of 3 m.This height of the area to be protected corres-ponds to the level which a person can reach withhis hand plus an additional separation distance s(Figure 5.7.1.1).

Special measures of protection are required, forexample, for the entrances or canopies of struc-tures highly frequented such as theatres, cinemas,shopping centres, kindergartens where non-insu-lated down conductors and earth electrodes arenearby.

Structures which are particularly exposed (at riskof lightning strikes) and freely accessible to mem-bers of the public, for example mountain huts,may also be required to have measures preventingintolerably high touch voltages. Moreover life haz-ard is considered as parameter L1 (injury or deathof persons) in the risk analyse of a structureaccording to IEC 62305-2 (EN 62305-2).

The following measures can reduce the risk oftouch voltage:

⇒ The down conductor is sheathed in insulatingmaterial (min. 3 mm polymerised polyethylene

with an impulse withstand voltage of 100 kV(1.2/50 μs).

⇒ The position of the down conductors ischanged, (e.g. down conductors are notinstalled in the entrance of the structure).

⇒ The specific resistance of the surface layer ofthe earth at a distance of up to 3 m around thedown conductor is at least 5 kΩm.

⇒ The probability of people accumulating can bereduced by information or prohibition signs;barriers can also be used.

The measures of protection against touch voltagemay be insufficient with regard to an effective pro-tection of people. The required high-voltageresistant coating of an exposed down conductor,for example is not enough if there are no addition-al measures of protection against creep-flashoversat the surface of the insulation. This is particularlyimportant if environmental influences such as rain(humidity) are to be considered.Just like at a bare down conductor, high voltagesoccurs at an insulated down conductor in case of alightning strike. This voltage, however, is separat-ed from people by the insulation. The human bodybeing a very good conductor compared with theinsulator, the insulating layer is stressed by almostthe whole touch voltage. If the insulation does notcope with the voltage, part of the lightning cur-rent might flow to the earth via the human bodyas in case of the bare down conductor. Safe protec-tion against life hazard due to touch voltagerequires to prevent from flashover through theinsulation and from creep-flashovers along theinsulation.A balanced system solution as provided by the CUIconductor meets these requirements of electric

www.dehn.de144 LIGHTNING PROTECTION GUIDE

s

2.50 m

copper conductor

PEX insulation

PE coating

Fig. 5.7.1.1 Area to be protected for a person Fig. 5.7.1.2 Structure of the CUI conductor

Page 146: Lightning Protection Guide

strength and creep-flashover insulation to protectagainst touch voltage.

Structure of the CUI conductorA copper conductor with a cross section of 50 mm2

is coated with an insulating layer of surge proofcross-linked polyethylene (PEX) of approx. 6 mmthickness (Figure 5.7.1.2).

The insulated conductor has an additional thinpolyethylene (PE) layer for protection againstexternal influences. The insulated down conductorCUI is installed vertically in the whole hazard area,

i.e. from the earth surface level up to a height of 3 m. The upper end of the conductor is connectedto the down conductor coming from the air-termi-nation system, the lower end to the earth-termina-tion system.Not only the electric strength of the insulation butalso the risk of creep-flashovers between the ter-minal point at the bare down conductor and thehand of the touching person has to be considered.This problem of creeping discharges, well-knownin high voltage engineering, is getting worse incase of rain, for example. Tests have shown thatunder sprinkling the flashover distance can bemore than 1 m at an insulated down conductorwithout additional measures. A suitable shield onthe insulated down conductor keeps the CUI con-ductor dry enough to avoid a creep-flashoveralong the insulating surface. The operating safetyof the CUI conductor with regard to the electricstrength and the resistance against creep-flash-overs at impulse voltages up to 100 kV (1.2/50 μs)has been tried and tested in withstand voltagetests under sprinkling conditions according to IEC60060-1. At these sprinkling tests water of a cer-tain conductivity and quantity is sprinkled on theconductor in an angle of approx. 45 ° (Figure5.7.1.3).

The CUI conductor is prefabricated with connec-tion element to be connected to the down conduc-tor (inspection joint) and can be shortened on siteif necessary for being connected to the earth-ter-mination system. The product is available inlengths of 3.5 m or 5 m and with the necessaryplastic or metal conductor holders (Figure 5.7.1.4).By the special CUI conductor the touch voltage atdown conductors can be controlled with easymeasures and little installation work. Hence thedamage risk for persons in special areas will beconsiderably reduced.

Inductive coupling at a very great steepness ofcurrentRegarding the damage risk for persons also themagnetic field of the arrangement with its influ-ence on the closer surrounding of the down con-ductor has to be considered. In extended installa-tion loops, for example, voltages of several 100 kVcan occur near the down conductor which canresult in high economic losses. Also the humanbody, due to its conductivity, together with thedown conductor and the conductive earth, forms a

www.dehn.de LIGHTNING PROTECTION GUIDE 145

connectionelement

shield

conductorholder

Fig. 5.7.1.4 CUI conductor

Fig. 5.7.1.3 Withstand voltage test under sprinkling

Page 147: Lightning Protection Guide

loop having a mutual inductanceof M where high voltages Ui canbe induced (Figures 5.7.1.5a and5.7.1.5b). In this case the systemarrester-person has the effect of atransformer.

This coupled voltage arises at theinsulation, the human body andthe earth being primarily consid-ered as conductive. The voltageload becoming too high it resultsin a puncture or creeping flash-over. The induced voltage thendrives a current through this loop,the magnitude of which dependson the resistances and the self-inductance of the loop and meanslife hazard for the person con-cerned. Hence the insulation mustwithstand this voltage load. Thenormative specification of 100 kVat 1.2/50 μs includes the high butvery short voltage impulses whichare only applied as long as the cur-rent rises (0.25 μs in case of a neg-ative subsequent lightning strike).The deeper the insulated downconductors are buried, the greateris the loop and thus the mutualinductance. Hence the inducedvoltage and the loading of theinsulation increases correspond-ingly which also has to be takeninto account with regard to theinductive coupling.

www.dehn.de146 LIGHTNING PROTECTION GUIDE

h

a

∆i/∆t

a)

∆i/∆t

b)

M

Ui

U Mi

ti = ⋅ΔΔ

M ha

rconductor= ⋅ ⋅

⎝⎜

⎠⎟0 2. ln

Fig. 5.7.1.5 (a) Loop formed by conductor and person (b) Mutual inductance M and induced voltage Ui

Page 148: Lightning Protection Guide

6.1 Equipotential bonding for metalinstallations

Equipotential bonding according to IEC 60364-4-41 and IEC 60364-5-54

Equipotential bonding is required for all newlyinstalled electrical power consumer’s installations.Equipotential bonding according to IEC 60364series removes potential differences, i.e. preventshazardous touch voltages between the protectiveconductor of the low voltage electrical power con-sumer’s installations and metal, water, gas andheating pipes, for example.

According to IEC 60364-4-41, equipotential bond-ing consists of themain equipotential bonding (in future: protectiveequipotential bonding)and the supplementary equipotential bonding (in future:supplementary protective equipotential bonding)Every building must be given a main equipotentialbonding in accordance with the standards statedabove (Figure 6.1.1).The supplementary equipotential bonding isintended for those cases where the conditions fordisconnection from supply cannot be met, or forspecial areas which conform to the IEC 60364 seriesPart 7.

www.dehn.de LIGHTNING PROTECTION GUIDE 147

6. Internal lightning protection

kWh

burie

d in

stal

latio

n, o

pera

tion-

ally

isol

ated

(e.g

. cat

hodi

cpr

otec

ted

tank

inst

alla

tion)

met

al e

lem

ent g

oing

thro

ugh

the

build

ing

(e.g

. lift

rails

)

ante

nna

rem

ote

sign

allin

g sy

stem

equi

pote

ntia

l bon

ding

of b

athr

oom

230/

400

V

insu

latin

g el

emen

t

Z

SEB

to PEN

dist

ribut

ion

netw

ork

IT s

yste

m

terminal lug for externallightning protection

Z

water wastewatergas

heating

Equipotential bonding bar(main equipotential bonding,in future: main earthingterminal)

Foundation earth electrode

Connector

Lightning current arrester

Terminal

Pipe clamp

Terminal lug

Isolating spark gap

foundation earth electrode/lightning protection earth electrode

6

8

5

1

6

4

4

32

7

6 6

1

2

3

3

4

5

6

7

8

Fig. 6.1.1 Principle of lightning equipotential bonding consisting of lightning and main equipotential bonding (in future: protective equipoten-tial bonding)

Page 149: Lightning Protection Guide

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Main equipotential bondingThe following extraneous conductive parts have tobe directly integrated into the main equipotentialbonding:

⇒ main equipotential bonding conductor inaccordance with IEC 60364-4-41 (in future:earthing conductor)

⇒ foundation earth electrodes or lightning pro-tection earth electrodes

⇒ central heating system

⇒ metal water supply pipe

⇒ conductive parts of the building structure (e.g.lift rails, steel skeleton, ventilation and air con-ditioning ducting)

⇒ metal drain pipe

⇒ internal gas pipe

⇒ earthing conductor for antennas (in Germanyin DIN VDE 0855-300)

⇒ earthing conductor for telecommunicationsystems (in Germany in DIN VDE 0800-2)

⇒ protective conductors of the electrical installa-tion in accordance with IEC 60364 series (PENconductor for TN systems and PE conductorsfor TT systems or IT systems)

⇒ metal shields of electrical and electronic con-ductors

⇒ metal cable sheaths of high-voltage currentcables up to 1000 V

⇒ earth termination systems for high-voltagecurrent installations above 1 kV according toHD 637 S1, if no intolerably high earthing volt-age can be dragged.

Normative definition in IEC 60050-826 of an extra-neous conductive component:A conductive unit not forming part of the electri-cal installation, but being able to introduce electricpotential including the earth potential.Note: Extraneous conductive components alsoinclude conductive floors and walls, if an electricpotential including the earth potential can beintroduced via them.The following installation components have to beintegrated indirectly into the main equipotentialbonding via isolating spark gaps:

⇒ installations with cathodic corrosion protec-tion and stray current protection measures inaccordance with EN 50162

⇒ earth-termination systems of high-voltage cur-rent installations above 1 kV in accordancewith HD 637 S1, if intolerably high earthingpotentials can be transferred

⇒ railway earth for electric a.c. and d.c. railwaysin accordance with EN 50122-1 (railway lines ofthe Deutsche Bahn may only be connectedupon written approval)

⇒ measuring earth for laboratories, if they areseparate from the protective conductors

Figure 6.1.1 shows the terminals and the respectivecomponents of the main equipotential bonding.

Design of the earth-termination system forequipotential bondingThe electrical low-voltage consumer’s installationrequiring certain earthing resistances (disconnec-tion conditions of the protective elements) and thefoundation earth electrode providing good earth-ing resistances at cost-effective installation, thefoundation earth electrode is an optimal andeffective complement of the equipotential bond-ing. The design of a foundation earth electrode isgoverned in Germany by DIN 18014, which, forexample requires terminal lugs for the earthingbusbar. More exact descriptions and designs of thefoundation earth electrode can be found in Chap-ter 5.5.

If a foundation earth electrode is used as lightningprotection earth electrode, additional require-ments may have to be considered; they can be tak-en from Chapter 5.5.

Equipotential bonding conductors (in future: pro-tective bonding conductors)Equipotential bonding conductors should, as longas they fulfil a protective function, be labelled thesame as protective conductors, i.e. green/yellow.Equipotential bonding conductors do not carryoperating currents and can therefore be eitherbare or insulated.The decisive factor for the design of the mainequipotential bonding conductors in accordancewith IEC 60364-5-54 and HD 60364-5-54 is the crosssection of the main protective conductor. The mainprotective conductor is the one coming from thesource of current or from the service entrance boxor the main distribution board.

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www.dehn.de LIGHTNING PROTECTION GUIDE 149

In any case, the minimum cross section of the mainequipotential bonding conductor is at least 6 mm2

Cu. 25 mm2 Cu has been defined as a possible max-imum.The supplementary equipotential bonding (Table6.1.1) must have a minimum cross section of 2.5mm2 Cu for a protected installation, and 4 mm2 Cufor an unprotected installation.

For earth conductors of antennas (according to IEC60728-11 (EN 60728-11)), the minimum cross sec-tion is 16 mm2 Cu, 25 mm2 Al or 50 mm2 steel.

Equipotential bonding barsEquipotential bonding bars are a central compo-nent of equipotential bonding which must clampall the connecting conductors and cross sectionsoccurring in practice to have high contact stability;it must be able to carry current safely and have suf-ficient corrosion resistance.DIN VDE 0618-1: 1989-08 (German standard) con-tains details of the requirements on equipotentialbonding bars for the main equipotential bonding.It defines the following connection possibilities asa minimum:

⇒ 1 x flat conductor 4 x 30 mm or round conduc-tor Ø 10 mm

⇒ 1 x 50 mm2

⇒ 6 x 6 mm2 to 25 mm2

⇒ 1 x 2.5 mm2 to 6 mm2

These requirements on an equipotential bondingbar are met by K12 (Figure 6.1.2).

This standard also includes the requirements forthe inspection of clamping units of cross sectionsabove 16 mm2 with regard to the lightning currentampacity. Reference is made therein to the testingof the lightning protection units in accordancewith EN 50164-1.If the requirements in the previously mentionedstandard are met, then this component can also beused for lightning equipotential bonding in accor-dance with IEC 62305-1 to 4 (EN 62305-1 to 4).

Terminals for equipotential bondingTerminals for equipotential bonding must providea good and permanent contact.

Main equipotential bonding Supplementary equipotential bonding

Normal 0.5 x cross section of thelargest protective conduc-tor of the installation

between two bodies 1xcross section of the small-er protective conductor

between a body and anextraneous conductivepart

0.5 x cross section of theprotective conductor

Minimum 6 mm2 with mechanicalprotection

2.5 mm2 Cu or equivalentconductivity

without mechanicalprotection

4 mm2 Cu or equivalentconductivity

Possible limit 25 mm2 Cu or equivalentconductivity

− −

Table 6.1.1 Cross sections for equipotential bonding conductors

Fig. 6.1.2 K12 Equipotential bonding bar, Part No. 563 200

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Integrating pipes into the equipotential bondingIn order to integrate pipes into the equipotentialbonding, earthing pipe clamps corresponding tothe diameters of the pipes are used (Figures 6.1.3and 6.1.4).Pipe earthing clamps made of stainless steel, whichcan be universally adapted to the diameter of thepipe, offer enormous advantages for mounting(Figure 6.1.5).These pipe earthing clamps can be used to clamppipes that are made of different materials (e.g.steel, copper and stainless steel). These compo-nents allow also a straight-through connection.Figure 6.1.6 shows equipotential bonding of heat-ing pipes with straight-through connection.

Test and inspection of the equipotential bondingBefore commissioning the electrical consumer’sinstallation, the connections must be inspected toensure their faultless condition and effectiveness.A low-impedance conductance to the various partsof the installation and to the equipotential bond-ing is recommended. A guide value of < 1 Ω for theconnections at equipotential bonding is consid-ered to be sufficient.

Supplementary equipotential bonding

If the disconnection conditions of the respectivesystem configuration can not be met for an instal-lation or a part of it, a supplementary local equipo-tential bonding is required. The reason behind isto interconnect all simultaneously accessible partsas well as the stationary operating equipment andalso extraneous conductive parts. The aim is tokeep any touch voltage which may occur as low aspossible.

Moreover, the supplementary equipotential bond-ing must be used for installations or parts of instal-lations of IT systems with insulation monitoring.

The supplementary equipotential bonding is alsorequired if the environmental conditions in specialinstallations or parts of installations mean a partic-ular risk.

The IEC 60364 series Part 7 draws attention to thesupplementary equipotential bonding for opera-tional facilities, rooms and installations of a partic-ular type.

These are , for example,

⇒ IEC 60364-7-701 Rooms with bathtub or show-er

⇒ IEC 60364-7-702 Swimming pools and otherbasins

⇒ IEC 60364-7-705 For agricultural and horticul-tural premises

The difference to the main equipotential bondingis the fact that the cross sections of the conductorscan be chosen to be smaller (Table 6.1.1), and alsothis supplementary equipotential bonding can belimited to a particular location.

Fig. 6.1.3 Pipe earthing clamp,Part No. 408 014

Fig. 6.1.4 Pipe earthing clamp,Part No. 407 114

Fig. 6.1.5 Pipe earthing clamp,Part No. 540 910

Fig. 6.1.6 Equipotential bonding with straight-through connection

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6.2 Equipotential bonding for lowvoltage consumer’s installations

Equipotential bonding for low voltage consumer’sinstallations as part of the internal lightning pro-tection, represents an extension of the main equi-potential bonding (in future: protective equipo-tential bonding) according to IEC 60364-4-41 (Fig-ure 6.1.1).In addition to all conductive systems, this also inte-grates the supply conductors of the low voltageconsumer’s installation into the equipotentialbonding. The special feature of this equipotentialbonding is the fact that a tie-up to the equipoten-tial bonding is only possible via suitable surge pro-tective devices. The demands on such surge protec-tive devices are described more detailed in AnnexE subclause 6.2.1.2 of IEC 62305-3 (EN 62305-3) aswell as in subclause 7 and Annexes C and D of IEC62305-4 (EN 62305-4).Analogous to the equipotential bonding with met-al installations (see Chapter 6.1), the equipotentialbonding for the low voltage consumer’s installa-tion shall also be carried out immediately at thepoint of entry into the object. The requirementsgoverning the installation of the surge protectivedevices in the unmetered area of the low voltageconsumer’s installation (main distribution system)are described in the directive of the VDN (Associa-tion of German Network Operators) “Surge pro-tective devices Type 1. Directive for the use ofsurge protective equipment Type 1 (up to nowClass B) in main distribution systems” (see sub-clauses 7.5.2 and 8.1) (Figures 6.2.1 and 6.2.2).

6.3 Equipotential bonding for infor-mation technology installations

Lightning equipotential bonding requires that allmetal conductive components such as cable linesand shields at the entrance to the building shall beincorporated into the equipotential bonding so asto cause as little impedance as possible. Examplesof such components include antenna lines, (Figure6.3.1) telecommunication lines with metal conduc-tors, and also fibre optic systems with metal ele-ments. The lines are connected with the help ofelements capable of carrying lightning current(arresters and shielding terminals). A convenientinstallation site is the point where cabling going

Fig. 6.2.1 DEHNbloc NH lightning current arrester installed in a bus-bar terminal field of a meter installation (refer to Fig. 6.2.2)

Fig. 6.2.2 DEHNventil ZP combined arrester directly snapped on thebusbars in the terminal field of the meter cabinet

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outside the building transfers to cabling inside thebuilding. Both the arresters and the shielding ter-minals must be chosen to be appropriate to thelightning current parameters to be expected.In order to minimise induction loops within build-ings, the following additional steps are recom-mended:

⇒ cables and metal pipes shall enter the buildingat the same point

⇒ power lines and data lines shall be laid spatial-ly close but shielded

⇒ avoiding of unnecessarily long cables by layinglines directly

Antenna installations:For reasons connected with radio engineering,antenna installations are generally mounted in anexposed location. Therefore they are more affect-ed by surges, especially in the event of a directlightning strike. In Germany they must be integrat-

ed into the equipotential bonding in accordancewith DIN VDE 0855 Part 300 (German standard)and must reduce the risk of being affectedthrough their design, (cable structure, connectorsand fittings) or suitable additional measures.Antenna elements that are connected to an anten-na feeder and cannot be connected directly to theequipotential bonding, as this would affect theirfunctioning, should be protected by arresters.

Expressed simply, it can be assumed that 50 % ofthe direct lightning current flows away via theshields of all antenna lines. If an antenna installa-tion is dimensioned for lightning currents up to100 kA (10/350 μs) (Lightning Protection Level III(LPL III)), the lightning current splits so that 50 kAflow through the earth conductor and 50 kA viathe shields of all antenna cables. Antenna installa-tions not capable of carrying lightning currentsmust therefore be equipped with air-terminationsystems in whose protection area the antennas are

αα

earth-terminationsystem

equipotential bondingto BTS

connectionequipotential bonding

antenna

insulating pipe

air termination tip

feeding point

isolated down conductor(HVI-conductor)

s = 0.75 m in airs = 1.5 m in brickworks = separation distance

seal

ing

unit

rang

e

Fig. 6.3.2 Isolated construction of a lightning protection system at acell site

α α

isolated air-termination system(DEHNconductor)

230 V~

230 V~

DATA

Fig. 6.3.1 Lightning equipotential bonding with isolated air-termina-tion system, type DEHNconductor, for professional anten-na systems according to IEC 62305-3 (EN 62305-3)

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located. Choosing a suitable cable, the respectivepartial lightning current share must be determinedfor each antenna line involved in down conduct-ing. The required cable dielectric strength can bedetermined from the coupling resistance, thelength of the antenna line and the amplitude ofthe lightning current.

According to the current standard IEC 62305-3 (EN62305-3), antenna installations mounted on build-ings can be protected by means of

⇒ air-termination rods

⇒ elevated wires

⇒ or spanned cables

In each case the separation distance s must bemaintained in the areas protected against light-ning strikes.The electrical isolation of the lightning protectionsystem from conductive components of the build-ing structure (metal structural parts, reinforce-ment etc.), and the isolation from electric lines inthe building, prevent partial lightning currentsfrom penetrating into control and supply lines andhence protect sensitive electrical and electronicdevices from being affected or destroyed (Figure6.3.1 and Figure 6.3.2).

Fibre optic installations:Fibre optic installations with metal elements cannormally be divided into the following types:

⇒ cables with metal-free core but with metalsheath (e.g. metal vapour barrier) or metalsupporting elements

⇒ cables with metal elements in the core andwith metal sheath or metal supporting ele-ments

⇒ cables with metal elements in the core, butwithout metal sheath.

For all types of cable with metal elements, the min-imum peak value of the lightning current, whichadversely affects the transmission characteristics ofthe optical fibre, must be determined. Cables capa-ble of carrying lightning currents must be chosen,and the metal elements must be connected to theequipotential bonding bar either directly or via anSPD.

⇒ Metal sheath: termination by means of shieldterminals e.g. SAK, at the entrance of thebuilding

⇒ Metal core: termination by means of earthingclamp e.g. SLK, near splice box

⇒ Prevention of potential equalising currents:connect indirectly via spark gap e.g. DEHNgapCS, base part BLITZDUCTOR CT, rather thandirectly

Telecommunication lines:Telecommunication lines with metal conductorsnormally consist of cables with balanced or coaxialcabling elements of the following types:

⇒ cables with no additional metal elements

⇒ cables with metal sheath (e.g. metal damp-proofing) and/or metal supporting elements

⇒ cables with metal sheath and additional light-ning protection reinforcement

The splitting of the partial lightning currentbetween IT lines can be determined using the pro-cedures in Annex E of IEC 62305-1 (EN 62305-1).The individual cables must be integrated into theequipotential bonding as follows:

a) Unshielded cables must be connected by SPDswhich are capable of carrying partial lightningcurrents. Partial lightning current of the linedivided by the number of individual wires =partial lightning current per wire.

b) If the cable shield is capable of carrying light-ning currents, the lightning current flows viathe shield. However, capacitive/inductive inter-ferences can reach the wires and make it nec-essary to use surge arresters. Requirements:

⇒ The shield at both ends must be connected tothe main equipotential bonding to be capableof carrying lightning currents (Figure 6.3.3).

Fig. 6.3.3 SAK shield connection system capable of carrying light-ning currents

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⇒ In both buildings where the cable ends, thelightning protection zone concept must beapplied, and the active wires must be connect-ed in the same lightning protection zone (usu-ally LPZ 1)

⇒ If an unshielded cable is laid in a metal pipe,this must be treated like a cable with a cableshield which is capable of carrying lightningcurrents.

c) If the cable shield is not capable of carryinglightning currents, then:

⇒ for the terminal connected at both ends, theprocedure is the same as for a signal wire in anunshielded cable. Partial lightning current ofthe cable divided by the number of individualwires + 1 shield = partial lightning current perwire

⇒ if the shield is not connected at both ends, ithas to be treated as if it were not there; partiallightning current of the line divided by thenumber of individual wires = partial lightningcurrent per wire

If it is not possible to determine the exact wireload, it is recommendable to take the threatparameters from IEC 61643-22. For a telecommuni-cations line hence results a maximum load per wireof 2.5 kA (10/350 μs).

Of course not only the used SPD must be capableof withstanding the expected lightning currentload, but also the discharge path to the equipoten-tial bonding.By means of a multi-core telecommunications linefor example this can be demonstrated:

⇒ A telecommunications cable with 100 doublewires coming from LPZ 0A is connected in anLSA building distribution case and shall be pro-tected by arresters.

⇒ The lightning current load of the cable wasassumed to be 30 kA (10/350 μs)

⇒ The resulting symmetrical splitting of light-ning current to the individual wire is 30 kA/200 wires = 150 A/wire.

At first this means no special requirements to thedischarge capacity of the protective elements to beused. After the discharge elements have flownthrough, the partial currents of all wires add up to30 kA again to load in the downstream dischargepath, for example clamping frames, earthingclamps or equipotential conductors. To be safefrom any damage in the discharge path lightningcurrent tested enclosure systems can be used (Fig-ure 6.3.5).

3 OUT 4

1 IN 2

BLI

TZD

UC

TOR

BC

T M

LC B

D 1

10N

o.9

19 3

47

BLITZDUCTOR CTBCT MLC BD 1105 kA (10/350 μs)

APL

TAE

Telekom customer

IT installation

Fig. 6.3.4 Lightning equipotential bonding for connection of atelecommunications device BLITZDUCTOR CT (applicationpermitted by Deutsche Telekom)

Fig. 6.3.5 DEHN equipotential bonding enclosures (DPG LSA) forLSA-2/10 technology, capable to carry lightning current

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7.1 Lightning protection zones con-cept

A lightning protection system (LEMP ProtectionMeasures System (LPMS)) according to IEC 62305-3(EN 62305-3) protects persons and material assetsof value in the buildings, but it does not protectthe electrical and electronic systems in the build-ings which are sensitive to transient high-energysurges resulting from the lightning discharge. It isprecisely such systems – in the form of buildingmanagement, telecommunications, control andsecurity systems – which are rapidly becomingcommon in practically all areas of residential andfunctional buildings. The owner /operator placesvery high demands on the permanent availabilityand reliability of such systems.

The protection of electrical and electronic systemsin buildings and structures against surges resultingfrom the lightning electromagnetic pulse (LEMP) isbased on the principle of Lightning ProtectionZones (LPZ). According to this principle, the build-

ing or structure to be protected must be dividedinto internal lightning protection zones accordingto the level of threat posed by LEMP (Figure 7.1.1).This enables areas with different LEMP risk levelsto be adjusted to the immunity of the electronicsystem.With this flexible concept, suitable LPZs can bedefined according to the number, type and sensi-tivity of the electronic devices /systems. From smalllocal zones to large integral zones which canencompass the whole building. Depending on thetype of threat posed by lightning, the followinglightning protection zones are defined:

External zones

⇒ LPZ 0A – at risk from direct lightning strikes,from impulse currents up to the whole light-ning current and from the whole electromag-netic field of the flash of lightning.

⇒ LPZ 0B – protected against direct lightningstrikes, at risk from the whole electromagnetic

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7. Protection of electrical and electronic systems againstLEMP

ventilation

down-conductor

system

spatial shield

terminal device

steel reinforcement

IT system

foundation earth electrode

air-termination system

l.v. powersupply system

Lightning equipotential bondingLightning current arrester (SPD Type 1)

Local equipotential bondingSurge arrester (SPD Type 2, SPD Type 3)

Lightning equipotential bondingLightning current arrester

Local equipotential bondingSurge arrester

Lightning electro-magnetic pulse

Switching electro-magnetic pulse

Lightningprotection zone

Fig. 7.1.1 Lightning protection zones concept according to IEC 62305-4 (EN 62305-4)

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field of the flash of lightning. Internal systemscan be exposed to (partial) lightning currents.

Internal zones

⇒ LPZ 1 – impulse currents limited by the split-ting of the current and by surge protectivedevices (SPDs) at the zones boundaries. Theelectromagnetic field of the lightning flashcan be attenuated by spatial shielding.

⇒ LPZ 2 ... n – impulse currents further limited bythe splitting of the current and by surge pro-tective devices (SPDs) at the zone boundaries.The electromagnetic field of the lightningflash is usually attenuated by spatial shielding.

The requirements on the internal zones must bedefined according to the immunity of the electricaland electronic systems to be protected.At the boundary of each internal zone, theequipotential bonding must be carried out for allmetal components and utility lines entering thebuilding or structure. This is done directly or withsuitable SPDs. The zone boundary is formed by theshielding measures.

Figure 7.1.2 illustrates an example of how torealise the measures described for the lightningprotection zones concept.

7.2 LEMP protection management

For new buildings and structures, optimum protec-tion of electronic systems can only be achievedwith a minimum of expense if the electronic sys-tems are designed together with the building andbefore its construction. In this way, building com-ponents such as the reinforcement, the metal gird-ers and metal buttresses can be integrated into theLEMP protection management.For existing buildings and structures, the cost ofthe LEMP protection is usually higher than for newbuildings and structures. If, however, the LPZs arechosen appropriately and existing installations areused or upgraded, the costs can be reduced.

If the risk analysis in accordance with IEC 62305-2(EN 62305-2) shows that LEMP protection is re-quired, this can only be achieved if:

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Fig. 7.1.2 Example for realisation of the lightning protection zones concept

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⇒ the measures are designed by a lightning protec-tion specialist having profound knowledge of EMC,

⇒ there is close coordination on all aspects of thework between the building experts (e.g. civil andelectrical engineers) and those experts in LEMPprotection and

⇒ the management plan according to Table 7.2.1(IEC 62305-4 (EN 62305-4) Subclause 8.1) isadhered to.

A concluding risk analysis must prove that theresidual risk is less than the tolerable risk.

www.dehn.de LIGHTNING PROTECTION GUIDE 157

Step Aim Measure must be taken by(if relevant)

Initial risk analysis a Assessing of the necessity of an LEMPprotection.

If necessary an appropriate LEMP Pro-tection Measures System (LPMS) basedon a risk assessment has to be chosen.

Lightning protection specialist b

Owner

Design of LEMPProtection MeasuresSystem (LPMS)

Definition of the LPMS:

• Measures of spatial shielding

• Equipotential bonding networks

• Earth-termination systems

• Leading and shielding of conductors

• Surge protective devices system

Lightning protection specialist b

Owner

Architect

Designer of the electronic systems

Designer of the importantinstallations

Design of the LPMS General drawings and descriptions

Preparation of the tenderdocumentation

Detailed drawings and schedules forthe installation

Engineering office or equivalent

Installation andinspection of the LPMS

Quality of the installation

Documentation

Possible revision of detailed drawings

Lightning protection specialist b

Installer of the LPMS

Engineering office

Inspection representativeAcceptance of theLPMS

Inspection and documentation of thesystem

• Independent lightning protection expert b

•Authorised inspectorRepeat inspections Ensuring of an appropriate LPMS Lightning protection specialist b

•Authorised inspectora see IEC 62305-2 (EN 62305-2)b with profound knowledge of EMC and installation practice

Final risk analysis a The cost/benefit ratio of the chosenprotection measures should be optimisedagain by a risk assessment. Accordinglyto be determined:

• Lightning protection level (LPL) and the lightning parameters

• LPZ and their boundaries

Lightning protection specialist b

Owner

Table 7.2.1 LEMP protection management for new buildings and for comprehensive modifications of the construction or the utilisation ofbuilding according to IEC 62305-4 (EN 62305-4)

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7.3 Calculation of the magneticshield attenuation of building/room shielding

Lightning current and the associated electromag-netic field represent the primary source of interfer-ence for devices and installations requiring protec-tion in a property. Figure 7.3.1 shows the principleof how lattice structures work. The fundamentalsof the calculation are described in the IEC 62305-4(EN 62305-4) standard.The fundamentals of the calculation are based onassumptions and estimates. The complex distribu-tion of the magnetic field inside lattice-shapedshields is determined with a first approximation.The formulae for the determination of the mag-netic field are based on numerical calculations ofthe magnetic field. The calculation takes intoaccount the magnetic field coupling of each rod inthe lattice-shaped shield with all other rods,including the simulated lightning channel.To consider whether it is the effect of the electro-magnetic field of the first partial lightning strikeor the subsequent lightning strike which is themore critical interference variable for the electricinstallation requiring protection, the calculationsmust be done with the maximum value of the cur-rent of the short strike (if/max) and the maximumvalue of the current of the long strike (is/max) corre-sponding to the lightning protection level derivedfrom Table 5, IEC 62305-1 (EN 62305-1).

The shielding effect of lattice-shaped shields in theevent of direct lightning strikes can be calculatedusing the formula shown in Figure 7.3.2. This viewis based on the fact that the lightning strike canhappen at any point on the roof.The values calculated for the magnetic field applyto the safety volume Vs inside lattice-shapedshields, which are defined by the separation dis-tance ds/... (Figure 7.3.3).

This safety volume takes into account maximumvalues of the magnetic field strength directly atthe lattice structure, a factor which the approxima-tion formula does not sufficiently take intoaccount. IT devices may only be installed inside ofvolume Vs.

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High field strength, great magneticfields / induced voltages close to thedown conductor

Lower partial currents, reducedmagnetic fields / induced voltagesin the building

w

dr

dw

i

H1 = kH ⋅ io ⋅ wdw ⋅√dr [A/m]

direct lightning strikeinto a shielded building

io = lightning current in LPZ 0A

ds/1

w

volume Vsfor electro-nic devices

shield for LPZ 0A – LPZ 1

separationdistancedirect lightningstrike: ds/1 = w

Fig. 7.3.1 Reduction of the magnetic field by means of lattice shields

Fig. 7.3.3 Volume for electronic devices within LPZ 1

Fig. 7.3.2 Magnetic field at a lightning strike(LEMP) IEC 62305-4 (EN 62305-4)

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located within the lightning protection zone witha separation distance ds/1 from the shielding.

The separation distance ds/1 (for SF < 10) results in:

w corresponds to the mesh size of the lattice-shaped shield in metres

Implementation of the magnetic shield-attenua-tion of building/room shieldingParticularly important when shielding againstmagnetic fields, and hence for the installation of

lightning protection zones, areextended metal components,e.g. metal roofs and facades,steel reinforcements in con-crete, expanded metals inwalls, lattices, metal support-ing structures and pipe systemsexisting in the building. Themeshed connection creates an effective electromagneticshield.

Figure 7.3.6 shows the princi-ple how a steel reinforcementcan be developed into an elec-tromagnetic cage (hole shield).In practice, however, it will notbe possible to weld or clamptogether every junction inlarge buildings and structures.The usual practice is to install ameshed system of conductorsinto the reinforcement, saidsystem typically having a sizeof a ≤ 5 m. This meshed net-work is connected in an electri-cally safe way at the cross-points, e.g. by means ofclamps. The reinforcement is“electrically hitched” onto themeshed network at a typicaldistance of b ≤ 1 m. This isdone on the building side, forexample by means of tie con-nections.Mats made of constructionsteel in concrete are suitable

d w ms / ]1 = [

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The fundamentals of the calculation of the shield-ing effect of lattice-shaped shields for nearbylightning strikes are explained more in detail byFigures 7.3.4 and 7.3.5.Figure 7.3.4 shows the formation of the electro-magnetic field whose reduction in field strength isindirectly proportional to the distance sa. Themagnitude of the magnetic field inside a protect-ed volume, e.g. lightning protection zone LPZ 1(Figure 7.3.5), can be described by the quality ofthe shielding.The shielding factor SF can be calculated as shownin Table 7.3.1.The results of this calculation of the magnetic fieldare valid for a safety volume Vs (Figure 7.3.3),

Material25 kHz (first short strike) 1Mhz (subsequent strike)

w = mesh size (m)

(w ≤ 5 m)

r = rod radius (m)

μr ≈ 200 (permeability)

Shielding factor SF (dB)

CopperAluminium 20 • log (8.5/w) 20 • log (8.5/w)

Steel 20 • log (8.5/w)

Example: Steel lattice

w (m)

0.012

0.100

0.200

0.400

r (m)

0.0010

0.0060

0.0090

0.0125

dB at 25 kHz

44

37

32

26

dB at 1 MHz

57

39

33

27

208 5

1 18 10 6 2⋅

+ ⋅ −log

( . /

/

w)

r

sa

field of thelightningchannel

H0 = i2πSa [A/m]

H0

sa

field of thelightningchannel

H0 = i2πSa

H0 H1

without shield

H1 =

with shieldH0

10 SF1/20

Fig. 7.3.4 Magnetic field at a lightning strike(LEMP) IEC 62305-4 (EN 62305-4)

Table 7.3.1 Magnetic attenuation of lattices at a nearby lightning strike acc. to IEC 62305-4 (EN 62305-4)

Fig. 7.3.5 Magnetic field at a distant lightningstrike (LEMP) IEC 62305-4 (EN62305-4)

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for shielding purposes. When upgrading existinginstallations, such steel mats are also laid later. Forthis type of design, the steel mats must be gal-vanised to protect them from corrosion.

These galvanised steel mats are then laid on roofs,for example, so that they overlap, or applied eitherexternally or internally to the exterior wall to pro-vide shielding for the building.

Figures 7.3.7a and 7.3.7b show the subsequentinstallation of galvanised steel mats on the roof ofa building.

To bridge expansion joints, connect the reinforce-ment of precast concrete components, and for ter-minals on the external earth-termination system orthe internal equipotential bonding system, thebuilding must already be equipped with sufficientfixed earthing points.

Figure 7.3.8 shows an installation of this type,which must be taken into consideration for design-ing the preliminary building works.

The magnetic field inside the building or structureis reduced over a wide frequency range by meansof reduction loops, which arise as a result of themeshed equipotential bonding network. Typicalmesh sizes are a 5 m. The interconnection of allmetal components both inside, as well as on thebuildings and structures results in a three-dimen-sional meshed equipotential bonding network.

Figure 7.3.9 shows a meshed equipotential bond-ing network with appropriate terminals.

If an equipotential bonding network is installed inthe lightning protection zones, the magnetic fieldcalculated according to the formulae stated aboveis typically further reduced by a factor of 2 (corre-sponds to 6 dB).

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a

ba

4 1 4

2

3

6

7

89

5

1 Metal cover of the attic2 Steel reinforcing rods3 Intermeshed conductors, superimposed of the reinforcement4 Connection of the air-termination system5 Internal equipotential bonding bar6 Connection capable of carrying lightning currents7 Connection, e.g. tie connection8 Ring earth electrode (if existing)9 Foundation earth electrode

(Typical dimension: a ≤ 5 m, b ≤ 1 m)

Fig. 7.3.6 Use of reinforcing rods of a building or structure forshielding and equipotential bonding

Fig. 7.3.7b Use of galvanised construction steel mats for shielding,e.g. in case of planted roofs

Fig. 7.3.7a Galvanised construction steel mats for shielding thebuilding

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base plate

fixed earthing point

concrete supportconcretefacade

earthing ring conductor

tape conductor holder

steel support

min. 50 mm2

earthing bus

reinforcement

connection tothe earthing bus

Fig. 7.3.8 Shielding of a structure or building

Fig. 7.3.9 Earthing bus according to DIN VDE 0800-2 (German standard)

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7.3.1 Cable shieldingCable shields are used to reduce the effect of theinterference on the active lines, and the interfer-ence emitted from the active lines to neighbouringsystems. From the point of view of lightning andsurge protection, attention must be paid to thefollowing applications of shielded lines:

⇒ No shield earthingSome installation systems recommend a shieldedcable but, at the same time, forbid shield earthing,(e.g. KNX). If there is no shielding terminal, theshield is not effective against interferences andmust therefore be considered as non-existing (Fig-ure 7.3.1.1).

⇒ Double-ended shield earthingA cable shield must be continuously connectedalong the whole of its length for good conductingperformance, and earthed at least at both ends.Only a shield used at both ends can reduce induc-tive and capacitive inputs. Cable shields entering abuilding or structure must have a certain minimumcross section to avoid the risk of sparking. Other-wise the shields are not considered being capableof carrying lightning current. The minimum crosssection of a cable shield (Scmin) laid isolated fromearth or air, depends on its specific shield resist-ance (ρc) (Table 7.3.1.1) on the lightning currentflowing (lf), on the impulse withstand voltage ofthe system (Uw), and on the cable length (Lc).

If can be calculated in accordance with IEC 62305-1(EN 62305-1). The shield connection technologyusually being tested up to 10 kA (10/350 μs), thisvalue, as a first approximation, can be drawn on asmaximum value.Uw can be interpreted quite differently. If the cableshield away from the internal system is interruptedat the building entry then the electric strength ofthe cable is decisive. The cable shield, however,being uninterrupted up to the terminal device, theelectric strength of the terminal device is theimportant (Table 7.3.1.2).Two examples shall illustrate the difference:TC cable shield up to the building entry, Al, loadedwith 10 kA, length 100 m : Scmin ≈ 6 mm2. It also hasto be minded, that the shield terminals at theMEBB must be capable of carrying lightning current.

S I L U mmcmin f c c w= ⋅ ⋅ ⋅( / )[ ]ρ 106 2

Bus conductor shield up to the terminal device, Cu,loaded with 5 kA, length 100 m : Scmin ≈ 17 mm2.Such cable shields for bus conductors, however,being not convenient for the practice thedescribed conductor has to be considered as notcapable of carrying lightning current.

⇒ Single-ended and indirect shield earthingFor operational reasons, cable shields are some-times earthed at only one end. In fact, a certainattenuation of capacitive interference fields is giv-en. Protection against the electromagnetic induc-tion arising with lightning strikes, however, is notprovided. The reason for the single-ended shieldearthing is the fear of low frequency equalisingcurrents. In extended installations, a bus cable, forexample, can often stretch many hundreds ofmetres between buildings. Especially with olderinstallations, it can happen that one part of theearth-termination systems is no longer in opera-tion, or that no meshed equipotential bonding isexisting. In such cases, interferences can occur as aresult of multiple shield earthing. Potential differ-ences of the different building earthing systemscan allow low frequency equalising currents (n x 50 Hz), and the transients superimposed there-on, to flow. At the same time, currents measuringup to a few amperes are possible which, inextreme cases, can cause cable fires. In addition,crosstalk can cause signal interference if the signalfrequency is in a similar frequency range to theinterference signal.The aim, however, must be to virtually implementthe requirements of EMC and prevent equalising

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Shielding material ρc in Ωm

Copper

Aluminium

Lead

Steel

17.241 . 10-9

28.264 . 10-9

214 . 10-9

138 . 10-9

Examples Electric strength

15 kV

5 kV

1.5 kV

0.5 – 1 kV

LV cable

TC cable

TC subscriber’s side

Measuring and control equipment

Table 7.3.1.1 Specific shield resistance ρc for different materials

Table 7.3.1.2 Electric strength

Page 164: Lightning Protection Guide

currents. This can beachieved by combiningsingle-ended and indirectshield earthing. All shieldsare directly connectedwith the local equipoten-tial bonding at a centralpoint such as the controlroom. At the far ends ofthe cable, the shields areindirectly connected tothe earth potential viaisolating spark gaps. Sincethe resistance of a sparkgap is around 10 GΩ,equalising currents areprevented in surge-freeoperation. Should EMCinterferences such aslightning strikes occur,the spark gap ignites anddischarges the interfer-ence pulse without conse-quential damage to theequipment. This reducesthe residual impulse onthe active lines and theterminal devices are sub-ject to even less stress.The BLITZDUCTOR CTarrester is equipped withan insert which can take a gas discharge tube, if necessary. This switchesbetween the cable shieldand the local earth. Thegas discharge tube can beinserted or removed dur-ing upgrading or mainte-nance work in order tochange between directand indirect shield earth-ing (Figure 7.3.1.3).

⇒ Low impedance shieldearthing

Cable shields can conductimpulse currents of up toseveral kA. During the dis-charge, the impulse cur-rents flow through theshield and the shield ter-

www.dehn.de LIGHTNING PROTECTION GUIDE 163

EBB 1 EBB 2

direct earthing

indirect earthing viagas discharge tube

EBB 1 EBB 2the impulse transfer

impedance of theshield has to be

considered!

C

EBB 1 EBB 2

Fig. 7.3.1.1 No shield connection – No shielding from capacitive/ inductive couplings

Fig. 7.3.1.2 Shield connection at both ends – Shielding from capacitive/inductive couplings

Fig. 7.3.1.3 Shield connection at both ends – Solution: Direct and indirect shield earthing

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minals to earth. The impedance of the cable shieldand the shielding terminal creates voltage differ-ences between shield potential and earth. In sucha case, voltages of up to some kV can develop anddestroy the insulation of conductors or connecteddevices. Coarse-meshed shields and the twisting ofthe cable shield (pig tail) to the terminal in a railclamp are particularly critical. The quality of thecable shield used affects the number of shieldearthings required. Under certain circumstances,an earthing is required every 10 metres in order toachieve an efficient shielding effect. Suitable largecontacting clamps with slipping spring elementsare recommended for the shielding terminal. Thisis important to compensate for the yield of thesynthetic insulation of the conductor (Figure7.3.1.4).

⇒ Maximum length of shielded cables

Cable shields have a so-called coupling resistancewhich roughly corresponds to the d.c. resistanceprovided by the cable manufacturer. An interfer-ence pulse flowing through the resistance createsa potential drop on the cable shield. The permissi-ble coupling resistance for the cable shield can bedetermined as a function of the dielectric strengthof the terminal device and the cable, as well as thecable length. It is crucial that the potential drop isless than the insulation strength of the system. Ifthis is not the case, arresters must be used (Figure7.3.1.5).

⇒ Extension of LPZs with the help of shieldedcables

IEC 62305-4 (EN 62305-4) states that using a shield-ed cable between two equal LPZs obviates theneed for arresters. This statement applies to inter-ferences to be expected from the spatial surround-ings of the shielded cable (e.g. electromagneticfields) and for meshed equipotential bonding con-forming to the standard. But beware. Dependingon the conditions the installation is set up in, haz-ards can still arise and make the use of arrestersnecessary. Typical potential hazards are: the feed-ing of the terminal devices from different low volt-age main distribution boards (MDB), TN-C systems,high coupling resistances of the cable shields orinsufficient earthing of the shield. Further cautionmust be exercised with cables with poor shield cov-er, which are often used for economic reasons. Theresult is residual interferences on the signal lines.Interferences of this type can be controlled byusing a high-quality shielded cable or surge pro-tective devices.

7.4 Equipotential bonding network

The main function of the equipotential bondingnetwork is to prevent hazardous potential dropsbetween all devices / installations in the inner LPZs,and to reduce the magnetic field of the lightning.

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RKh = = = 0.4 ΩUiso

I2000 V5000 A

l = 200 m: RKh = = 20.4 Ω

200 m 10-3 Ω

m

U = 2 kVdielectric strength

l = 200 m

I = 5 kA

iso

to be calculated: max. permissible coupling impedance RKh of the cable shielding

shield terminal

cable

cable shield

anchor bar

Fig. 7.3.1.4 Shield connection Fig. 7.3.1.5 Shield connection at both ends – Shielding from capacitive/ inductive coupling

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The low inductance equipotential bonding net-work required is achieved by means of intercon-nections between all metal components aided byequipotential bonding conductors inside the LPZof the building or structure. This creates a three-dimensional meshed network (Figure 7.4.1). Typi-cal components of the network are:

⇒ all metal installations (e.g. pipes, boilers),

⇒ reinforcements in the concrete (in floors, wallsand ceilings),

⇒ gratings (e.g. intermediate floors),

⇒ metal staircases, metal doors, metal frames,

⇒ cable ducts,

⇒ ventilation ducts,

⇒ lift rails,

⇒ metal floors,

⇒ supply lines.

Ideally, a lattice structure of the equipotentialbonding network would be around 5 m x 5 m. Thiswould typically reduce the electromagnetic light-ning field inside an LPZ by a factor of 2 (correspon-ding to 6 dB).

Enclosures and racks of electronic devices and sys-tems should be integrated into the equipotentialbonding network with short connections. Thisrequires sufficient numbers of equipotential bond-ing bars and/or ring equipotential bonding bars(Figure 7.4.2) in the building or structure. The bus-bars, in turn, must be connected to the equipoten-tial bonding network (Figure 7.4.3).

Protective conductors (PE) and cable shields of thedata links of electronic devices and systems mustbe integrated into the equipotential bonding net-work in accordance with the instructions of thesystem manufacturer. The connections can bemade as a mesh or in the shape of a star (Figure7.4.4).When using a star point arrangement S, all metalcomponents of the electronic system must be suit-ably insulated against the equipotential bondingnetwork. A star-shaped arrangement is thereforeusually limited to applications in small, locally con-fined systems. In such cases, all lines must enter thebuilding or structure, or a room within the build-ing or structure, at a single point. The star pointarrangement S must be connected to the equipo-

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Fig. 7.4.1 Equipotential bonding network in a structure or building

Fig. 7.4.2 Ring equipotential bonding bar in a computer facility

Fig. 7.4.3 Connection of the ring equipotential bonding bar with theequipotential bonding network via fixed earthing point

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tential bonding network at one single earthingreference point (ERP) only. This produces thearrangement SS.When using the meshed arrangement M, all metalcomponents of the electronic system do not haveto be insulated against the equipotential bondingnetwork. All metal components shall be integratedinto the equipotential bonding network at asmany equipotential bonding points as possible.The resulting arrangement Mm is used for extend-ed and open systems with many lines between the

individual devices. A further advantage of thisarrangement is the fact that the lines of the systemcan enter a building, structure or room at differentpoints.Complex electronic systems, also allow combina-tions of star point and meshed arrangements (Fig-ure 7.4.5) in order to combine the advantages ofboth arrangements.

7.5 Equipotential bonding on theboundary of LPZ 0A and LPZ 1

7.5.1 Equipotential bonding for metalinstallations

At the boundaries of the EMC lightning protectionzones, measures to reduce the radiated electro-magnetic field must be realised, and all metal andelectrical lines / systems passing through the sec-tional area must be integrated into the equipoten-tial bonding without exception.This requirement on the equipotential bondingbasically corresponds to that on the main equipo-tential bonding bar in accordance with IEC 60364-4-41 and IEC 60364-5-54, HD 60364-5-54.Further towards the main equipotential bondingbar, the lightning equipotential bonding must alsobe implemented for cables of electrical and elec-tronic systems (see also Chapter 7.5.2) at thisboundary of the zones.

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ERP

Ss

Mm

Ms

Ss

S M

Mm

ERP

Star shape arrangement S Mesh shape arrangement M

Basicarrangement

Integrationinto theequipotentialbondingnetwork

Legend to 7.4.4 and 7.4.5

Equipotential bonding network

Equipotential bonding conductor

Device

Termination point to theequipotential bonding network

Earthing reference point

Star shape arrangementintegrated via a neutral point

Mesh shape arrangementintegrated via a meshed lattice

Mesh shape arrangementintegrated via a neutral point

Combination 1 Combination 2

Ss

ERP

Mm

Ms

Mm

ERP

Fig. 7.4.4 Integration of electronic systems into the equipotential bonding network

Fig. 7.4.5 Combination of the integration methods according to Figure 7.4.4

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This equipotential bonding must be installed asclose as possible to the location where the linesand metal installations enter the building or struc-ture. The equipotential bonding conductor shouldbe designed to be as short (low impedance) as pos-sible.

For equipotential bonding, the following mini-mum cross sections for tying in the equipotentialbonding bar to the earth-termination system,interconnecting the different equipotential bond-ing bars, and tying in the metal installations to theequipotential bonding bar, must be taken intoaccount:

The following metal installations have to be incor-porated into the equipotential bonding:

⇒ Metal cable ducts

⇒ Shielded cables and lines

⇒ Building reinforcement

⇒ Metal water supply pipes

⇒ Metal conduits for lines

⇒ Other metal pipe systems or conductive com-ponents (e.g. compressed air)

A corrosion-free earth connection can be easilyconstructed by using fixed earthing points. Duringthis process, the reinforcement can be connectedto the equipotential bonding at the same time(Figure 7.5.1.1).

The procedure of tying in the equipotential bond-ing bar to the fixed earthing point, and connectingthe conduits to the equipotential bonding, isshown below (Figure 7.5.1.1).

Chapter 7.3 illustrates the tying in of cable shieldsto the equipotential bonding.

7.5.2 Equipotential bonding for power supply installations

In analogy to metal installations, all electrical pow-er lines and data links at the entrance of the build-ing (lightning protection zone boundary LPZ 0A toLPZ 1) must be integrated into the equipotentialbonding. Whereas the design of data links isdescribed in Section 7.5.3, the following sectionwill look at the design of equipotential bondingwith electrical power lines in more detail. Theintersections for the equipotential bonding at theLPZ boundary LPZ 0A to LPZ 1 are defined with thehelp of the specific design of the property whichrequires protection. For installations fed by lowvoltage systems, the LPZ boundary LPZ 0A/ LPZ 1 isusually taken to be the boundary of the building(Figure 7.5.2.1).

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Fig. 7.5.1.1 Connection of EBB with fixed earthing point Fig. 7.5.2.1 Transformer outside the structure or building

Material

Cu

Al

Fe

Cross section

14 mm2

22 mm2

50 mm2

SPD

0/1

Page 169: Lightning Protection Guide

ing or structure centrally at one point. If local cir-cumstances do not permit this, the use of a ringequipotential bonding bar (Figures 7.5.2.3 and7.5.2.4) is recommended.

The ability of the lightning current arrester used(SPD, Class 1) to discharge the current must corre-spond to the loads at the location where it isemployed, based on the lightning protection sys-tem level used for the property. The lightning pro-tection system level appropriate for the buildingor structure under consideration must be chosenon the basis of a risk assessment. If no risk assess-ment is available, or if it is not possible to makedetailed statements about the splitting of thelightning current at the LPZ boundary LPZ 0A toLPZ 1, it is recommended to use the class of light-ning protection system with the highest require-ments (lightning protection level I) as a basis. Theresulting lightning current load of the individualdischarge paths is shown in Table 7.5.2.1.

When installing lightning current arresters on theLPZ boundary LPZ 0A to LPZ 1, it must still be bornein mind that, if the recommended installation siteis directly at the service entrance box, this can fre-quently only be done with the agreement of thepower supplier (new: distribution network opera-tor). The requirements on lightning currentarresters in main distribution systems are laiddown in the directive of the Association of the

For properties fed directly from the medium volt-age network, the lightning protection zone LPZ 0Ais extended up to the secondary side of the trans-former. The equipotential bonding is carried outon the 230/400 V side of the transformer (Figure7.5.2.2).

To avoid damage at the transformer the addition-al use of surge protective devices on the high volt-age side of the transformer isrecommended.

To prevent the flow of partiallightning currents in LPZ 0from affecting parts of theinstallation/systems in LPZ 1,additional shielding meas-ures are required for themedium voltage line enter-ing the building or structure.

To prevent equalising cur-rents from occurring bet-ween the various equipoten-tial bonding points in an elec-trical installation, it is recom-mended to carry out thelightning equipotential bon-ding of all metal lines andelectrical power lines anddata links entering the build-

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SPD

0/1

2

31

84 10

5

7

9

6

Reinforcement of the outer walls and thefoundation

Other earth electrodes, e.g. intermeshingto neighbouring buildings

Connection to the reinforcement

Internal (potential) ring conductor

Connection to external conductive parts,e.g. water pipeline

Earth electrode Type B, ring earth electrode

Surge protective device

Equipotential bonding bar

Electrical power or telecommunicationsline

Connection to supplementary earthelectrodes, earth electrode Type A

1

2

3

4

5

6

7

8

9

10

Fig. 7.5.2.2 Transformer inside the structure or building (LPZ 0 inte-grated in LPZ 1)

Fig. 7.5.2.3 Example for equipotential bonding in a structure or building with several entries or theexternal conductive parts and with an internal ring conductor as a connection betweenthe equipotential bonding bars

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German network operators (VDN) 2004-08: “Surgeprotective devices Type 1. Directive for the use ofsurge protective equipment Type 1 (up to nowClass B) in main distribution systems” and IEC60364-5-53/A2 (IEC 64/1168/CDV: 2001). Whenchoosing lightning current arresters for the LPZboundary LPZ 0A to LPZ 1 then, besides the ratingof the discharge capability, the prospective shortcircuit current to be expected at the installationsite must also be taken into account. According toIEC 62305-3 (EN 62305-3) Annex E, Subclause

6.2.1.2, lightning current arresters based on sparkgaps should have a high self-quenching capacityand a good ability to limit follow currents, in orderto ensure that follow currents at the mains fre-quency are switched off automatically, and to pre-vent overcurrent protective devices, e.g. fuses,from false tripping (Figures 7.5.2.5 – 7.5.2.7).The special issues relating to the choice, installa-tion and assembly of lightning current arresters(SPD Type 1) are described in more detail in Chap-ter 8.1.

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meter

serviceentrance box

meter

foundation earth electrode

antenna line

electronic equipment

EBB

consumer's circuits

water meter

water

heating

gas

power

Fig. 7.5.2.4 Internal lightning protection with a common entry of all supply lines

Table 7.5.2.1 Required lightning impulse current carrying capability of surge protective devices SPDs Type 1 according to the lightning protec-tion level LPL and the type of low voltage consumer’s installation

Lightning protection levelLPL

(former: Type of LPS)in TN systems in TT systems

(L – N)in TT systems

(N – PE)

Lightning impulse current carrying capability

I

II

III / IV

100 kA / m

75 kA / m

50 kA / m

100 kA / m

75 kA / m

50 kA / m

100 kA

75 kA

50 kA

m: Quantity of conductors, e.g. for L1, L2, L3, N and PE; m = 5

Page 171: Lightning Protection Guide

7.5.3 Equipotential bonding for informationtechnology installations

LPZ 0 – LPZ 1

The lightning equipotential bonding from LPZ 0 toLPZ 1 must be carried out for all metal systemsentering a building. IT lines must be connected asclose as possible to the point where they enter thebuilding or structure with lightning current

arresters providing a suitable discharge capacity.For IT lines a general discharge capability of 2.5 kA(10/350 μs) each wire is required for the boundaryfrom LPZ 0A to LPZ 1. The generalised approach isnot used, however, when designing the dischargecapability for installations with a large number ofIT lines. After calculating the partial lightning cur-rent to be expected for an IT cable (see IEC 62305-3(EN 62305-3)), the lightning current must then be

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Fig. 7.5.2.5 DEHNventil combined lightning current and surgearrester

Fig. 7.5.2.7 Lightning current arrester at LPZ boundary LPZ 0A – LPZ 1

Fig. 7.5.2.6 Lightning equipotential bonding for power supply andinformation technology systems situated centrally atone point

Page 172: Lightning Protection Guide

⇒ they have no inductance as a decoupling ele-ment

⇒ the specified nominal discharge current is(8/20 μs) > 25 x the required discharge current(10/350 μs) per core (Figure 7.5.3.1).

If the equipotential bonding is carried out for lineson the LPZ boundary 0B to LPZ 1, it is sufficient touse surge protective devices with a dischargecapacity of 20 kA (8/20 μs) since no electrically cou-pled partial lightning currents flow.

7.6 Equipotential bonding on theboundary of LPZ 0A and LPZ 2

7.6.1 Equipotential bonding for metalinstallations

See Chapter 7.5.1.

7.6.2 Equipotential bonding for power sup-ply installations

LPZ 0A – LPZ 2Depending on the design of the building or struc-ture, it is often unavoidable to realise a LPZ bound-ary from LPZ 0A to LPZ 2, especially with compactinstallations (Figure 7.6.2.1).

Putting such an LPZ transition into practice makeshigh demands on the surge protective devicesemployed, and the surroundings of the installa-tion. Besides the parameters previously describedin Section 7.5.2, a protection level must beachieved which ensures the safe operation ofequipment and systems of LPZ 2. A low voltageprotection level and high limiting of the inter-ference energy still transmitted by the arrester,form the basis here for a safe energy coordinationto surge protective devices in LPZ 2, or to surgesuppressing components in the input circuits of the equipment to be protected. The combinedlightning current and surge arresters of the DEHNventil M family are designed for such appli-cations and enable the user to combine lightningequipotential bonding and coordinated terminaldevice protection in a single device (Figure 7.6.2.2).

Since, for the LPZ boundary from LPZ 0 to LPZ 2, itis inevitable for both lightning protection zones to

divided by the number of individual cores in thecable actually used, in order to arrive at theimpulse current per core. The partial lightning cur-rent load is lower for multi-core cables than it is forcables with fewer individual cores. For furtherinformation please see Chapter 6.3.

The following surge protective devices can there-fore be used:

1. Arresters designed for a discharge current of(10/350 μs)

2. Arresters designed for a discharge current of(8/20 μs) if

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0

5

10

15

20

25

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Impu

lse

curr

ent (

8/20

μs)

in k

A

Testing lightning current (10/350 μs) in kA

SPD

0/1/2

Fig. 7.5.3.1 Comparison of the amplitudes of test currents waveform 10/350 μs and 8/20 μs, each at equal loads

Fig. 7.6.2.1 Only one SPD (0/1/2) required (LPZ 2 integrated in LPZ 1)

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border directly on each other, a high degree ofshielding at the zone boundaries is absolutelyimperative. As a matter of principle, it is recom-mended to design the area of the lightning protec-tion zones LPZ 0 and LPZ 2, which border directlyon each other, to be as small as possible. Providedthat the building or structure will permit it, LPZ 2should be equipped with an additional zone shieldwhich is constructed at the zone boundary LPZ 0,

separately from the zone shield flown through bya lightning current, so that, as can be seen in Fig-ure 7.6.2.1, LPZ 1 is assembled for a further area ofthe installation. The attenuation of the electro-magnetic field in LPZ 2 this measure brings about,obviates the need for systematic shielding of alllines and systems within LPZ 2, which would other-wise be necessary.

7.6.3 Equipotential bonding for informationtechnology installations

LPZ 0A – LPZ 2Generally, a lightning current arrester from LPZ 0to LPZ 1 acts like a kind of of wave breaker. It con-ducts a large part of the interference energy away,thus protecting the installation in the buildingfrom damage. However, it is frequently the casethat the level of residual interference is still toohigh to protect the terminal devices. In a furtherstep, additional surge protective devices are theninstalled at the LPZ boundary from LPZ 1 to LPZ 2to make available a low level of residual interfer-

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?

lightning current arrester surge arrester

?

combined lightning current and surge arrester

shielded cable

externallightningprotectionsystem

terminal device(severity 1)

terminal device(severity 1)

Y/L SPD classH QY/L SPD class

MY/L SPD class

Fig. 7.6.2.2 DEHNventil M TT 255

Fig. 7.6.3.1 Combination aid for Yellow/Line SPD classes (see also Figure 7.8.2.2)

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ence adjusted to the immunity of the terminaldevice.

When the equipotential bonding from LPZ 0 to LPZ 2 is carried out, the first thing is to choose theinstallation site, and determine the partial light-ning current of the individual lines and shields,precisely as described in Chapter 6.3.

However, the requirements on an SPD to beinstalled changes at the LPZ boundary, as do therequirements on the wiring after this boundary.The protective device must be designed as a com-bined lightning current and surge arrester and itsenergy must be coordinated with that of the ter-minal device (Figure 7.6.3.1). Combined lightningcurrent and surge arresters have, on the one hand,an extremely high discharge capacity and, on theother, a low level of residual interference to pro-tect the terminal devices. Furthermore, care mustbe taken that the outgoing line from the protec-tive device to the terminal device is shielded, andthat both ends of the cable shield are integratedinto the equipotential bonding.

Combined lightning current and surge arrestersare recommended

⇒ if the terminal devices are near to the locationwhere the cables enter the building

⇒ if low impedance equipotential bonding fromprotective device to terminal device can becreated

⇒ if the line from the protective device to theterminal device is continuously shielded andearthed at both ends

⇒ if a particularly cost-effective solution issought.

The use of lightning current arresters and surgearresters is recommended

⇒ if there are long cable distances from the pro-tective device to the terminal device

⇒ if the SPDs for power systems and IT surge pro-tective devices are earthed via differentequipotential bonding bars

⇒ if unshielded lines are used

⇒ if large interferences can occur inside LPZ 1.

7.7 Equipotential bonding on theboundary of LPZ 1 and LPZ 2and higher

7.7.1 Equipotential bonding for metalinstallations

This equipotential bonding must be done as closeas possible to the location where the lines andmetal installations enter the zone.

All systems and conductive components must alsobe connected as described in Chapter 7.5.1.

The equipotential bonding conductors should bedesigned to be as short (low impedance) as possi-ble.

Ring equipotential bonding in these zones facili-tates a low impedance tie-in of the systems intothe equipotential bonding.Figure 7.7.1.1 illustrates the preparation for tying-in a cable trough to the ring equipotential bond-ing at the zone transition.

The following metal installations have to be inte-grated into the equipotential bonding:

⇒ metal cable ducts

⇒ shielded cables and lines

⇒ building reinforcement

⇒ metal water supply pipes

⇒ metal conduits for lines

⇒ other metal pipe systems or conductive com-ponents (e.g. compressed air)

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Fig. 7.7.1.1 Ring equipotential bonding and fixed earthing point forconnection of metal installations

Page 175: Lightning Protection Guide

The cross sections described in Chapter 7.5.1 mustagain be used for equipotential bonding conduc-tors combining the equipotential bonding bar andthe earth-termination systems as well as otherequipotential bonding bars.

For the tie-ins of the metal installations to theequipotential bonding, reduced cross sections canbe used for these zone boundaries:

7.7.2 Equipotential bonding for power sup-ply installations

LPZ 1 – LPZ 2 and higherFor LPZ boundaries LPZ 1 to LPZ 2 and higher, aswell, surge limitation and field attenuation isachieved by systematical integration of the electri-cal power lines and data links, also, into theequipotential bonding at each LPZ boundary, as isdone with all metal systems (Figure 7.7.2.1). Shield-ing the rooms and devices leads to the attenuationof the electromagnetic effect.

The function of the surge protective devicesemployed at the LPZ boundaries LPZ 1 to LPZ 2, orat the higher LPZ boundaries, is to minimise theresidual values of upstream surge protectivedevices yet further. They must reduce inducedsurges affecting the lines laid in the LPZ, andsurges generated in the LPZ itself. Depending onthe location where the protective measures aretaken, they can be either assigned to a device(device protection) (Figure 7.7.2.2) or representthe infrastructural basis for the functioning of adevice or system in the installation (Figure 7.7.2.3).

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U2, I2 U1, I1 partiallightningcurrent

H2

H1

H01

2

primary source of interferenceI0, H0

electronic system(susceptible device)

shield

shield

shield (enclosure)

1 Primary source of interference definedaccording to the chosen lightning protectionlevel by

IEC 62305-1 (EN 62305-1):I0 and H0: impulse 10/350 μs and 0.25/100 μs

Electronic system (susceptible device) definedby the immunity against conducted (U, I) andradiated (H) lightning effects:

IEC 61000-4-5: U: impulse 1.2/50 μsI: impulse 8/20 μs

IEC 61000-4-9H: impulse 8/20 μs, (attenuated wave 25 kHz),

Tp = 10 μs

IEC 61000-4-10:H: (impulse 0.2/5 μs), attenuated wave 1 MHz,

Tp = 0.25 μs

2

Material

Cu

Al

Fe

Cross section

5 mm2

8 mm2

16 mm2

Fig. 7.7.2.1 Electromagnetic compatibility in case of a lightning strike

Fig. 7.7.2.2 Surge protective device for terminal circuits DEHNflex M

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The embodiments of the surge protection at theLPZ boundaries LPZ 1 to LPZ 2 and higher can thusbe designed in very different ways.

7.7.3 Equipotential bonding for informationtechnology installations

LPZ 1 – LPZ 2 and higherAt the LPZ boundaries inside buildings, furthermeasures must be taken to reduce the level ofinterference (Figure 7.7.3.1). Since, as a rule, termi-nal devices are installed in LPZ 2 or higher, the pro-tective measures must ensure that the level ofresidual interference, lies below values the termi-nal devices can cope with.

⇒ Use of surge protective devices in the vicinityof terminal devices

⇒ Integration of the cable shields into theequipotential bonding

⇒ Low impedance equipotential bonding of theSPD for IT installations to terminal device andSPD for power installations

⇒ Paying attention to the energy coordinationof SPD and terminal device

⇒ Telecommunications lines and gas dischargelamps must be installed at least 130 mm apart

⇒ The distribution boards of electrical installa-tions and data should be located in differentcabinets

⇒ Low voltage lines and telecommunicationslines must cross at an angle of 90 °

⇒ Cable intersection must be carried out usingthe shortest route

7.8 Coordination of the protectivemeasures at various LPZ bound-aries

7.8.1 Power supply installationsWhereas surge protection in the terminal device,or immediately upstream of it, expressly fulfils thefunction of protecting the device, the function ofsurge protective devices in the surrounding instal-lation is twofold. On the one hand, they protectthe installation, and, on the other, they form theprotective link between the threat parameters ofthe complete system and the immunity of thedevice of the equipment and systems requiringprotection. The threat parameters of the system,and the immunity of the device to be protected,are thus dimensioning factors for the protectivecascade to be installed. To ensure that this protec-tive cascade, beginning with the lightning currentarrester and ending with the terminal device pro-tection, is able to function, one must ensure thatindividual protective devices are selectively effec-tive, i.e. each protection stage only takes on theamount of interference energy which it isdesigned for. The synchronisation between theprotective stages is generally termed coordinationand is explained more detailed in IEC 62305-4 (EN 62305-4) Chapter 7. In order to achieve thedescribed selectivity as the protective device oper-ates, the parameters of the individual arresterstages must be coordinated in such a way that, ifone protection stage is faced with the threat of anenergy overload, the upstream more powerfularrester “responds“ and thus takes over the dis-charge of the interference energy. When design-ing the coordination, one must be aware that the

www.dehn.de LIGHTNING PROTECTION GUIDE 175

Fig. 7.7.2.3 Multi-pole surge arrester DEHNguard M TT Fig. 7.7.3.1 Protection of industrial electronic equipment (e.g. anSPC) by BLITZDUCTOR CT and SPS Protector

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pulse waveform with the greatest pulse lengthmust be assumed to be a threat for the completearrester chain. Even though surge protectivedevices, by definition, are only tested with pulsewaveforms of 8/20 μs, for the coordinationbetween surge arrester and lightning currentarrester, and also for the surge protective device, itis imperative to determine the ability of the deviceto carry an impulse current of the partial lightningcurrents with the waveform 10/350 μs. TheRed/Line family of energy-coordinated products,was created to avert the dangers arising fromdefective coordination and the resulting overload-ing of low-energy protective stages . These surgeprotective devices, which are coordinated bothwith each other and also with the device to be pro-tected, provide the user with high safety. Bydesigning them as lightning current arresters,surge arresters and combined lightning currentand surge arresters, they are ideally matched tothe requirements of the corresponding LPZ bound-aries (Figures 7.8.1.1 – 7.8.1.3).

7.8.2 IT installations

When implementing measures to protect againstdisturbance variables from nearby, distant anddirect lightning strikes within buildings, it is re-commended to apply a concept of protectivedevices with several protective stages. This reducesthe high energy interference (partial lightning cur-rent) in stages because an initial energy absorbingstage prevents the main part of the interferencefrom reaching the downstream system. The subse-quent stages serve to reduce the interference tovalues which the system can cope with. Dependingon the conditions of the installation, several pro-tective stages can also be integrated into onesurge protective device using a combined protec-tive circuit.

The relevant interfaces where the protectivedevices are employed as part of a cascade are, forexample, the zone boundaries (LPZ) of a lightningprotection zone concept which conforms to IEC62305-4 (EN 62305-4).

A cascading of the surge protective devices mustbe carried out with due regard to the coordinationcriteria.

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Fig. 7.8.1.1 DEHNbloc 3-pole – Lightning current arrester andDEHNventil ZP – Combined arrester

Fig. 7.8.1.2 DEHNguard TT H LI – Multi-pole surge arrester withservice life indication

Fig. 7.8.1.3 DEHNventil M TNS – Modular combined arrester

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www.dehn.de LIGHTNING PROTECTION GUIDE 177

Fig. 7.8.2.1 Coordination according to let-through method of 2 SPDs and one terminal device (according to IEC 61643-21)

Fig. 7.8.2.2 Examples for the energy coordinated use of arresters according to the Yellow/Line TYPE of arresters and structure of the Yellow/Line-TYPE of arresters symbol

SPD 1 SPD 2 ITE

IP1

UP1 UIN

2

IIN2 IP2

UP2 UIN

ITE

IIN ITE UIN Surge immunity againstimpulse voltages

IIN Surge immunity againstimpulse currents

UP Voltage protection levelimpulse voltage

IP Let-through impulsecurrent

M

H Q

HQ

H Q

terminaldevice

1

lightning currentimmunity severity

acc. to EN 61000-4-5

Use of a combined lightning current and surge arrester

terminaldevice

1

surge

Cascaded use of SPDs

lightning current

Energy coordination of Yellow/Lineis independent of conductor length

discharge capacity

+decoupling for

coordination witha further arrester ( )

SPD suitable for coordinationwith an other arrester

( +)

specific protectionof terminal equipment

EN 61000-4-5

immunity severityacc. to EN 61000-4-5

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To determine the coordination conditions acc. toIEC 61643-22, various methods are available (IEC60364-5-53/A2 (IEC 64/1168/CDV: 2001)), some ofwhich require certain knowledge about the struc-ture of the protective devices. A “black box”method is the so-called “Let-Through-EnergyMethod”, which is based on standard pulse param-

eters and hence can be understood from both amathematical and a practical point of view.

All parts of the cascade are considered to be coor-dinated if the residual values Ip for a short-circuit-ed output, and Up for an open-circuit output, aresmaller than the input values Iin/Uin.

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Cabling SPD

to LPZ 1 to LPZ 2 to LPZ 3

Exemplified assignment of SPD classes to LPZboundaries

From LPZ 0A

From LPZ 0B

From LPZ 1

From LPZ 2

Combined SPD

Cascading

Same solution as from LPZ 0A

Surge arrester

Cascading

Combined arrester

Surge arrester

Same solution as from LPZ 1

Surge arrester

M

H

G

s. a.

T or Q

F

Q

O

J

M

T or Q

s. a.

T

W

[

Discharge capacity ofan SPD (acc. to categoriesof IEC 61643-21)

Protective effect of an SPD(limitation below the testlevels acc. to EN 61000-4-5)

Energy coordination (withanother Yellow/Line arrester)

Characteristic Symbol Legend

A

B

C

D

M

L

K

K

k

Q

Impulse D1 (10/350 μs), lightning impulse current ≥ 2.5 kA / line or ≥ 5 kA / total• exceeds the discharge capacity of B – D

Impulse C2 (8/20 μs), increased impulse load ≥ 2.5 kA / line or ≥ 5 kA / total• exceeds the discharge capacity of C – D

Impulse C1 (8/20 μs), impulse load ≥ 0.25 kA / line or ≥ 0.5 kA / total• exceeds the discharge capacity of D

Load < C

Test level required for the terminal device: 1 or higher

Test level required for the terminal device: 2 or higher

Test level required for the terminal device: 3 or higher

Test level required for the terminal device: 4

SPD has a decoupling impedance and is suitable for coordination withan arrester labeled Q

SPD suitable for coordination with an arrester having a decouplingimpedance k

Table 7.8.2.1 Symbol of the SPD class

Table 7.8.2.2 Assignment of the Yellow/Line class of the SPDs at the LPZ boundaries

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These methods are, however, difficult for the userto carry out because they are very time-consuming.In order to save time and work, the standard per-mits the use of information supplied by the manu-facturers for the coordination (Figure 7.8.2.1).

Lightning current arresters at LPZ 0 /1 or higherare, as a rule, specified with a discharge capacity ofwaveform 10/350 μs. Surge arresters, by contrast,are only specified with a waveform of 8/20 μs. Thisoriginates from the fact that surge arresters weredeveloped primarily for interferences of inductiveand capacitive inputs. If, however, a line passingout of the building is connected to a cascade com-prising lightning current arrester and surgearrester, it follows from the coordination condi-tions that

⇒ the most sensitive element responds first – thesurge arrester

⇒ the surge arrester must also be able to carrypart of the partial lightning current with thewaveform 10/350 μs, albeit a small one

⇒ before the surge arrester is overloaded, thelightning current arrester must trip and takeover the discharge process.

The surge protective devices of the Yellow/Linefamily are coordinated sequentially and safelywith each other and with the terminal devices.Therefore they provide markings indicating thesymbol of their SPD class (Figure 7.8.2.2, Tables7.8.2.1 and 7.8.2.2).

7.9 Inspection and maintenance ofthe LEMP protection

The fundamentals and pre-conditions governingthe inspection and maintenance of the LEMP pro-tection are the same as those governing theinspection and maintenance of lightning protec-tion systems, as previously described in Chapter3.4.The inspections carried out during the construc-tion phase are particularly important for theinspection of the LEMP protection, since manycomponents of the LEMP protection are no longeraccessible when the building work has been com-pleted. The necessary measures (e.g. connectingthe reinforcement) must be documented photo-graphically and included with the inspectionreport.

Inspections shall be carried out:

⇒ during the installation of the LEMP protection,

⇒ after the installation of the LEMP protection,

⇒ periodically,

⇒ after each modification to components whichare relevant for the LEMP protection,

⇒ after a lightning strike to the building or struc-ture, if necessary.

After completion of the inspection, all defectsfound must be corrected forthwith. The technicaldocumentation must be updated as and wherenecessary.A comprehensive inspection of the LEMP protec-tion should be carried out at least every four yearsas part of the inspection of the electrical installa-tion in accordance with workplace regulations.

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8.1 Power supply systems (withinthe scope of the lightning pro-tection zones concept accordingto IEC 62305-4 (EN 62305-4))

The installation of a lightning and surge protec-tion system for electrical installations representsthe latest state of the art and is an indispensableinfrastructural condition for the trouble-free oper-ation of complex electrical and electronic systemswithout consequential damage. The requirementson SPDs needed for the installation of this type oflightning and surge protection system as part ofthe lightning protection zones concept accordingto IEC 62305-4 (EN 62305-4) for power supply sys-tems are stipulated in IEC 60364-5-53/A2 (IEC64/1168/CDV: 2001).

SPDs employed as part of the structure’s fixedinstallation are classified according to the require-ments and loads on the installation sites as surgeprotective devices Type 1, 2 and 3 and testedaccording to IEC 61643-1 (EN 61643-11).The highest requirements with respect to the dis-charge capacity are made on SPDs Type 1. Theseare employed within the scope of the lightning

and surge protection system at the boundary oflightning protection zone LPZ 0A to LPZ 1 andhigher, as shown in Figure 8.1.1. These protectivedevices must be capable of carrying partial light-ning currents, waveform 10/350 μs, many timeswithout consequential damage to the equipment.These SPDs Type 1 are called lightning currentarresters. The function of these protective devicesis to prevent destructive partial lightning currentsfrom penetrating the electrical installation of astructure.

At the boundary of lightning protection zone LPZ 0B to LPZ 1 and higher, or lightning protectionzone LPZ 1 to LPZ 2 and higher, SPDs Type 2 areemployed to protect against surges. Their dis-charge capacity is around some 10 kA (8/20 μs).

The last link in the lightning and surge protectionsystem for power supply installations is the protec-tion of terminal devices (boundary from lightningprotection zone LPZ 2 to LPZ 3 and higher). Themain function of a protective device Type 3 used atthis point is to protect against surges arisingbetween L and N in the electrical system. These areparticularly switching surges.The different func-tions, arrangements and requirements of arrestersis given in Table 8.1.1.

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8. Selection, installation and assembly of surge protectivedevices (SPDs)

terminal equipment

L1L2L3NPE

subdistribution board

surge arrester

F3

local EBB

main distribution board

lightning current arrester

F2

WhSEBPEN

meterF1

MEBB

exte

rnal

ligh

tnin

gpr

otec

tion

syst

em

Fig. 8.1.1 Use of SPDs in power supply systems (schematic diagram)

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8.1.1 Technical characteristics of SPDsMaximum continuous voltage UcThe maximum continuous voltage (equal to: ratedvoltage) is the root mean square (rms) value of themax. voltage which may be applied to the corre-spondingly marked terminals of the surge protec-tive device during operation. It is the maximumvoltage on the arrester in the defined non-conduc-tive state which ensures that this state is regainedafter it has responded and discharged.The value of Uc shall be selected in accordancewith the nominal voltage of the system to be pro-tected and the requirements of the installationprovisions (IEC 60364-5-53/A2 (IEC 64/1168/CDV:2001)). Taking into account a 10 % voltage toler-ance for TN and TT systems, the maximum contin-uous voltage Uc is 253 V for 230/400 V systems.

Lightning impulse current IimpThis is a standardised impulse current curve with a10/350 μs waveform. Its parameters (peak value,charge, specific energy) simulate the load causedby natural lightning currents.Lightning impulse currents (10/350 μs) apply toSPDs Type 1. They must be able to discharge suchlightning impulse currents several times withoutconsequential damage to the equipment.

Nominal discharge current InThe nominal discharge current In is the peak valueof the current flowing through the surge protec-tive device (SPD). It has an 8/20 μs impulse currentwaveform and is rated for classifying the test ofSPDs Type 2 and also for conditioning the SPDs forType 1 and 2 tests.

Voltage protection level UpThe voltage protection level of an SPD denotes themaximum instantaneous value of the voltage onthe terminals of an SPD while at the same time

characterising their capacity to limit surges to aresidual level.

Depending on the type of SPD, the voltage protec-tion level is determined by means of the followingindividual tests:

⇒ Lightning impulse sparkover voltage

1.2/50 μs (100 %)

⇒ Residual voltage for nominal discharge current(in accordance with EN 61643-11: Ures)

The surge protective device appropriate to theinstallation site is chosen in accordance with theovervoltage categories described in IEC 60664-1(EN 60664-1). It must be noted that the requiredminimum value of 2.5 kV for a 230/400 V three-phase system only applies to equipment belongingto the fixed electrical installation. Equipment inthe terminal circuits supplied by the installationrequire a voltage protection level which is muchlower than 2.5 kV.IEC 60364-5-53/A2 (IEC 64/1168/CDV: 2001) alsorequires a minimum voltage protection level of 2.5 kV for a 230/400 V low-voltage consumers‘installation. This minimum voltage protection level can be realised by means of a coordinatedsystem of SPDs Type 1 and SPDs Type 2, or byemploying a Type 1 combined lightning currentand surge arrester.

Short-circuit withstand capabilityThis is the value of the prospective power-frequen-cy short circuit current controlled by the surge pro-tective device in case it is furnished with anupstream backup fuse (backup protection).

Follow current extinguishing capability Uc (Ifi)The follow current extinguishing capability, alsotermed breaking capacity, is the unaffected

www.dehn.de LIGHTNING PROTECTION GUIDE 181

E DIN VDE 0675-6 with A1, A2(already withdrawn)

IEC 61643-1:2005

EN 61643-11:2002

Lightning current arrester; Combinedlightning current and surge arrester

Class B SPD class I SPD Type 1

Surge arrester for distribution boards,subdistribution boards, fixed installations

Class C SPD class II SPD Type 2

Surge arrester for socket outlets/terminal units

Class D SPD class III SPD Type 3

StandardType/Description

Table 8.1.1 Classification of SPDs according to VDE, IEC and EN

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(prospective) rms value of the mains follow currentwhich can automatically be extinguished by thesurge protective device when Uc is applied.According to IEC 62305-3 (EN 62305-3) and IEC60364-5-53/A2 (IEC 64/1168/CDV: 2001) the followcurrent extinguishing capability of the SPDs shouldcorrespond to the maximum prospective short cir-cuit current at the SPD’s installation site. For distri-butions in industrial plants with very high short cir-cuit currents a corresponding backup fuse has tobe chosen for the protective device which inter-rupts the mains follow current through the protec-tive device.According to both IEC 60364-5-53/A2 (IEC 64/1168/CDV: 2001) and EN 61643-11, SPDs connected bet-ween neutral conductors and PE conductors,where a follow current with mains frequency canarise after the SPD has responded (e.g. spark gaps),must have a follow current extinguishing capabili-ty of Ifi ≥ 100 Arms.

Follow current limiting (for spark-gap based SPDsType 1)Follow current limiting is the capability of a spark-gap based SPD to limit any mains follow currentsarising to such a degree that the current actuallyflowing is noticeably smaller than the possibleshort circuit current at the installation site.A high degree of follow current limiting preventsupstream protective elements (e.g. fuses) fromtripping because of a too high mains follow cur-rent.The follow current limiting is an important para-meter for the availability of the electrical installa-tion, particularly for spark-gap based SPDs with alow voltage protection level.

CoordinationIn order to ensure a selective functioning of thevarious SPDs, an energy coordination among theindividual SPDs is absolutely essential. The basicprinciple of energy coordination is characterisedby the fact that each protective stage must onlydischarge the amount of interference energy theSPD is designed for. If higher interference energiesoccur, the protective stage upstream of the SPD,e.g. SPD Type 1, must take over the discharge ofthe impulse current and relieve the downstreamprotective devices. This type of coordination must take into account all possible incidences of interference such as switching surges, partiallightning currents, etc.. According to IEC 62305-4

(EN 62305-4) the manufacturer must prove theenergy coordination of its SPDs.The devices in the Red/Line family are coordinatedwith each other and tested with reference to theirenergy coordination.

TOVTOV (Temporary OverVoltage) is the term used todescribe temporary surges which can arise as aresult of faults within the medium and low-volt-age networks.To TN systems as well as the L-N path in TT systemsand for a measuring time of 5 seconds applies:UTOV = 1.45 x U0 , where U0 represents the nominala.c. voltage of the line to earth. At 230/400 V systems the TOV to be taken into consideration for the SPDs between L and N is Utov = 333.5 V. For TOVs arising in low-voltage sys-tems as a result of earth faults in the high-voltagesystem, UTOV = 1200 V for the N-PE path in TT sys-tems has to be taken into consideration for 200 ms.IEC 60364-5-53/A2 (IEC 64/1168/CDV: 2001) requiresa TOV withstand capability for SPDs installed inlow voltage consumer’s installations.The devices of the Red/Line family of productsmust be rated for TOVs according to EN 61643-11and meet th requirements of IEC 60364-5-53/A2(IEC 64/1168/CDV: 2001).

8.1.2 Use of SPDs in various systemsMeasures to ensure protection against life hazardsalways take priority over surge protective meas-ures. Since both measures are directly linked to thetype of power supply systems and hence also withthe use of surge protective devices (SPDs), the fol-lowing describes TN, TT and IT systems and thevariety of ways in which SPDs can be used. Electriccurrents flowing through the human body canhave hazardous consequences. Every electricalinstallation is therefore required to incorporateprotective measures to prevent hazardous currentsflowing through the human body. Componentsbeing energised during normal operation must beinsulated, covered, sheathed or arranged to pre-vent from being touched if this could result in haz-ardous currents flowing through the body. Thisprotective measure is termed “protection againstelectric shock under normal conditions”. More-over, it goes without saying, of course, that a haz-ard must not be caused either by current flowing

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through the body if, as the result of a fault, e.g. afaulty insulation, the voltage is transferred to themetal enclosure (body of a piece of electricalequipment). This protection against hazardswhich, in the event of a fault, can result fromtouching bodies or extraneous conductive compo-nents, is termed “protection against electric shockunder fault conditions”.Generally, the limit of the permanently permissibletouch voltage UL for a.c. voltages is 50 V and ford.c. 120 V.In electrical circuits containing socket outlets andin electrical circuits containing Class I mobileequipment normally held permanently in the handduring operation, higher touch voltages, whichcan arise in the event of a fault, must be discon-nected automatically within 0.4 s. In all other elec-trical circuits, higher touch voltages must be auto-matically disconnected within 5 s.IEC 60364-4-41: 2005-12 describes protective meas-ures against indirect shock hazard with protectiveconductors. These protective measures operate inthe event of a fault by means of automatic discon-nection or message. When setting up the measuresfor the “protection against electric shock underfault conditions”, they must be assigned accordingto the system configuration and the protectivedevice.According to IEC 60364-4-41: 2005-12, a low volt-age distribution system in its entirety, from thepower source of the electrical installation to thelast piece of equipment, is essentially characterisedby:

⇒ earthing conditions at the power source of theelectrical installation (e.g. low voltage side ofthe local network transformer)

and

⇒ earthing conditions of the body of the equip-ment in the electrical consumer´s installations.

Hence, essentially, three basic types are defined asdistribution systems:TN system, TT system and IT system.

The letters used have the following significance:

The FIRST LETTER describes the earthing condi-tions of the supplying power source of the electri-cal installation:

T direct earthing of one point of the powersource (generally the neutral point of thetransformer),

I Insulation of all active components from theearth or connection of one point of the powersource to earth via an impedance.

The SECOND LETTER describes the earthing condi-tions of the bodies of the equipment of the electri-cal installation:

T Body of the equipment is earthed directly,regardless of any possible existing earthing ofone point of the power supply,

N Body of the electrical equipment is directlyconnected to the power system earthing(earthing of the power source of the electricalinstallation).

SUBSEQUENT LETTERS describe the arrangementof the neutral conductor and the protective con-ductor:

S Neutral conductor and protective conductorare separate from each other,

C Neutral conductor and protective conductorare combined (in one conductor).

There are therefore three possible options for theTN system:TN-S system, TN-C system and TN-C-S system.

The protective devices which can be installed inthe various systems are:

⇒ overcurrent protective device,

⇒ residual current device,

⇒ insulation monitoring device,

⇒ fault-voltage-operated protection device (spe-cial cases).

As previously mentioned, the system configurationmust be assigned to the protective device. Thisresults in the following assignments:TN system

⇒ Overcurrent protective device,

⇒ Residual current device.

TT system

⇒ Overcurrent protective device,

⇒ Residual current device,

⇒ Fault-voltage-operated protective device (spe-cial cases).

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IT system

⇒ Overcurrent protective device,

⇒ Residual current device,

⇒ Insulation monitoring device,

These measures to protect against life hazardshave top priority when installing power supply sys-tems. All other protective measures such as light-ning and surge protection of electrical systems andinstallations are secondary to the protective meas-ures taken against indirect contact with protectiveconductors under consideration of the system con-figuration and the protective device. The lattermust not be overridden by the use of protectivedevices for lightning and surge protection. Theoccurrence of a fault in an SPD, unlikely as it maybe, shall also be taken into account. This has partic-ular significance because the surge protectivedevices are always used to the protective conduc-tor.In the following sections we therefore describe theuse of SPDs in various system configurations. Thesecircuit proposals are taken from IEC 60364-5-53/A2(IEC 64/1168/CDV: 2001).

The concepts shown illustrate the use of lightningcurrent arresters mainly in the area of the serviceentrance box, i.e. upstream of the meter. IEC60364-5-53/A2 (IEC 64/1168/CDV: 2001) defines theinstallation site of lightning current arresters as“close to the origin of the installation”.

In Germany the use of lightning current arrestersupstream the meter is regulated by the VDN-Richtlinie 2004-08 [engl.: Directive of the Asso-ciation of the German Network Operators]:“Überspannungs-Schutzeinrichtungen Typ 1. Richt-linie für den Einsatz von Überspannungs-Schutzeinrichtungen (ÜSE) Typ 1 (bisher Anfor-derungsklasse B) in Hauptstromversorgungssyste-men.“ [engl: “Surge protective devices Type 1.Directive for the use of surge protective equip-ment Type 1 (up to now Class B) in main distribu-tion systems”This directive, compiled by the VDN defines basicrequirements which, depending on the Distribu-tion Network Operator (DNO) can lead to differenttechnical designs.The preferred kind of supply (network configura-tion) must be ascertained from the responsibleoperator of the distribution network

8.1.3 Use of SPDs in TN Systems

For “protection against electric shock under faultconditions“ in TN systems, overcurrent and resi-dual current devices have been approved. For theuse of SPDs this means that these protectivedevices may only be arranged downstream of thedevices for “protection against electric shockunder fault conditions” in order to ensure that themeasure to protect against life hazards also oper-ates in the event of a failure of an SPD.If an SPD Type 1 or 2 is installed downstream of aresidual current device, it has to be expected that,because of the discharged impulse current to PE,this process will be interpreted as residual currentby a residual current device (RCD), and it interruptsthe circuit.Moreover, if an SPD Type 1 is loaded with partiallightning currents it must be assumed that thehigh dynamics of the lightning current will causemechanical damage on the residual current device(Figure 8.1.3.1). This would override the protectivemeasure “protection against electric shock underfault conditions”.

Of course, this must be avoided. Therefore bothlightning current arresters Type 1 and SPDs Type 2should be used upstream of the residual currentdevice. Hence, for SPDs Type 1 and 2, the only pos-sible measure for “protection against electricshock under fault conditions” is using overcurrentprotective devices. The use of SPDs must thereforealways be considered in conjunction with a fuse asthe overcurrent protective device. Whether or nota supplementary separate backup fuse must bedesignated for the arrester branch, depends onthe size of the next upstream supply fuse and thebackup fuse approved for the SPD. The followingmaximum continuous voltages apply to SPDs Type1, 2 and 3 when used in TN systems (Figures.8.1.3.2and 8.1.3.3a to b):Figure 8.1.3.4 illustrates an example of the connec-tions for use of lightning current arresters andsurge protective devices in TN-C-S systems. It canbe seen that SPDs Type 3 are used downstream ofthe residual current device (RCD). In this context,please note the following:As a result of the frequency of switching surges inthe terminal circuits, SPDs Type 3 are primarilyemployed to protect against differential modevoltages. These surges generally arise between Land N. A surge limitation between L and N means

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that no impulse current is dischargedto PE. Thus, this process can also notbe interpreted as residual current bythe RCD. In all other cases, SPDs Type 3are designed for a nominal dischargecapacity of 1.5 kA. These values aresufficient in the sense that upstreamprotective stages of SPDs Type 1 and 2take over the discharge of high ener-gy impulses. When using an RCD capa-ble of withstanding impulse currents,these impulse currents are not able totrip the RCD or cause mechanical dam-age. The Figures 8.1.3.5 to 8.1.3.9 illus-trate the use of SPDs as part of thelightning protection zones concept,and the required lightning and surgeprotective measures for a TN-C-S sys-tem.

8.1.4 Use of SPDs in TT systems

For “protection against electric shockunder fault conditions“ in TT systems,the overcurrent protective devices,residual current devices (RCD) and, inspecial cases, fault-voltage-operated

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U0 = Nominal a.c. voltage of thephase conductors to earth

L1L2L3

PEN

U0 = 230 V a.c.Uc 1.1 x 230 V = 255 V a.c.

=> 3 x SPD with Uc 255 V a.c.

1.1 U0

RA

U0 = 230 V a.c.Phase conductor to PE:Uc 1.1 x 230 V = 255 V a.c.Neutral conductor to PE:Uc 230 V a.c.

3 x SPD with Uc 255 V a.c.1 x SPD with Uc 230 V a.c.

The values of U0 between neutralconductor and PE already refer tomost unfavourable operating con-ditions. A tolerance of 10 % wastherefore not considered

1.1 U0 U0

L1L2L3NPE

U0 = Nominal a.c. voltage of the phase conductors to earth

RA

U0 = 230 V a.c.Phase conductor to PE:Uc 1.1 x 230 V = 255 V a.c.Neutral conductor to PE:Uc 230 V a.c.

3 x SPD with Uc 255 V a.c.1 x SPD with Uc 230 V a.c.

The values of U0 between neutralconductor and PE already refer tomost unfavourable operating con-ditions. A tolerance of 10 % wastherefore not considered.

1.1 U0

U0

L1L2L3NPE

U0 = Nominal a.c. voltage of thephase conductors to earthRA

Fig. 8.1.3.1 RCD destroyed by lightning impulsecurrent

Fig. 8.1.3.2 “3-0” circuit in TN-C systems

Fig. 8.1.3.3a “4-0” circuit in TN-S systems

Fig. 8.1.3.3b “3+1” circuit in TN-S systems

Page 187: Lightning Protection Guide

www.dehn.de186 LIGHTNING PROTECTION GUIDE

terminal equipment

L1L2L3NPE

subdistribution board

surge arrester

F3

local EBB

main distribution board

lightning current arrester

F2

Wh

F1

SEBPEN

exte

rnal

ligh

tnin

gpr

otec

tion

syst

em

MEBB

RCD

protection acc. to IEC 60364-4-443

protection acc. to IEC 62305 (EN 62305)

terminal equipment

L1L2L3NPE

subdistribution board

surge arrester

F3

local EBB

main distribution board

lightning current arrester

Wh

exte

rnal

ligh

tnin

gpr

otec

tion

syst

em

MEBB

F2

SEB

F1protection acc. to IEC 60364-4-443

protection acc. to IEC 62305 (EN 62305)

Fig. 8.1.3.4 Use of SPDs in TN-C-S systems

Fig. 8.1.3.5 Use of SPDs in TN-S systems

Page 188: Lightning Protection Guide

www.dehn.de LIGHTNING PROTECTION GUIDE 187

Fig. 8.1.3.6 SPDs used in TN systems – Example: Office Building – Separation of the PEN in the main distribution board

DEH

Ngu

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DG

MO

D 2

75

DEH

Ngu

ard®

DG

MO

D 2

75

L1 L2

PE

DEH

Ngu

ard®

DG

MO

D 2

75

L3

DEH

Ngu

ard®

DG

MO

D 2

75

N

DEH

Ngu

ard®

DG

MO

D 2

75

DEH

Ngu

ard®

DG

MO

D 2

75

L1 L2

PE

DEH

Ngu

ard®

DG

MO

D 2

75

L3

DEH

Ngu

ard®

DG

MO

D 2

75

N

DEHNflex

ÜS-Schutz

L1 L1' L2 L2' L3 L3'

N´/PEN N/PEN

DEHNbloc® DB 3 255 H

L1 L1´ L2 L2´

PEN

L3 L3´

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L1 L2 L3 N PE

Cable length ≥ 5 m

16 A

Sock

et O

utle

t

faul

t sig

nal

1 x DSA 230 LA Part No. 924 370for cable ducts

1 x STC 230 Part No. 924 350for existing socket outlets

or with remote signalling contact:1 x DG M TNS 275 FM Part No. 952 405

1 x DV M TNC 255 Part No. 951 300alt. 1 x DV M TNC 255 FM Part No. 951 305also available as

1 x DV M TNS 255 Part No. 951 400alt. 1 x DV M TNS 255FM Part No. 951 405

1125 A

SPD Type 2(Surge arrester)

1125 A

SPD Type 2(Surge arrester)

1 x DG M TNS 275 Part No. 952 400

Cable length ≥ 15 m

SPD Type 1(Lightning current arrester)

1 x DB 3 255 H Part No. 900 120alt. 3 x DB 1 255 H Part No. 900 222

1 x MVS 1 8 Part No. 900 611

1315 A

SPD Type 1(Coordinated lightning

current arrester)

DEHNbloc® MaxiCoordinated to DEHNguard®

without additional cable length.

3 x DBM 1 255 L Part No. 900 0261 x MVS 1 8 Part No. 900 611

alt. 3 x DBM 1 255 Part No. 900 0251 x MVS 1 8 Part No. 900 611

1315 A

Mai

n D

istr

ibut

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Boar

dSu

bdis

trib

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ard

SPD Type 1(Combined lightning current

and surge arrester)

DEHNventil®

Directly coordinated toRed/Line SPDs Type 2 and 3

without additional cable length.

1315 A

SPD Type 3(Surge arrester)

1 x DFL M 255 Part No. 924 396for flush-mounted systems

SPD Type 3(Surge arrester)

SPD Type 3(Surge arrester)

EBB

1) Only required, if a fuse of the same or a lower nominal value is not already provided in the upstream power supply.

Page 189: Lightning Protection Guide

www.dehn.de188 LIGHTNING PROTECTION GUIDE

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

S-PROTECTOR

230V~ Defect

Überspannungsschutz

SFL-Protector

0 1

DEH

Ngu

ard®

DG

MO

D 2

75

DEH

Ngu

ard®

DG

MO

D 2

75

L1 L2

PEN

DEH

Ngu

ard®

DG

MO

D 2

75

L3

DEH

Ngu

ard®

DG

MO

D 2

75

DEH

Ngu

ard®

DG

MO

D 2

75

L1 L2

PEN

DEH

Ngu

ard®

DG

MO

D 2

75

L3

L1 L1' L2 L2' L3 L3'

N´/PEN N/PEN

DEHNbloc® DB 3 255 H

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

L1 L1´ L2 L2´

PEN

L3 L3´

L1 L2 L3 N PE

Cable length ≥ 5 m

16 A

Sock

et O

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tM

ain

Dis

trib

utio

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ard

Subd

istr

ibut

ion

Boar

d

SPD Type 2(Surge arrester)

Cable length ≥ 15 m

SPD Type 1(Lightning current arrester)

SPD Type 1(Coordinated lightning

current arrester)

SPD Type 1(Combined lightning current

and surge arrester)

DEHNbloc® MaxiCoordinated to DEHNguard®

without additional cable length.

faul

t sig

nal

1 x NSM PRO EW Part No. 924 3421 x SF PRO Part No. 909 8201 x S PRO Part No. 909 821 1 x SFL PRO Part No. 912 260

1 x DG M TNC 275 Part No. 952 300or with remote signalling contact:1 x DG M TNC 275 FM Part No. 952 305

1 x DB 3 255 H Part No. 900 120alt. 3 x DB 1 255 H Part No. 900 222

1 x MVS 1 8 Part No. 900 611

3 x DBM 1 255 L Part No. 900 0261 x MVS 1 8 Part No. 900 611

alt. 3 x DBM 1 255 Part No. 900 0251 x MVS 1 8 Part No. 900 611

1 x DV M TNC 255 Part No. 951 300alt. 1 x DV M TNC 255 FM Part No. 951 305

1) Only required, if a fuse of the same or a lower nominal value is not already provided in the upstream power supply.

DEHNventil®

Directly coordinated toRed/Line SPDs Type 2 and 3

without additional cable length.

1125 A 1125 A

SPD Type 2(Surge arrester)

1315 A 1315 A 1315 A

SPD Type 3(Surge arrester)

SPD Type 3(Surge arrester)

SPD Type 3(Surge arrester)

EBB

Fig. 8.1.3.7 SPDs used in TN systems – Example: Office Building – Separation of the PEN in the subdistribution board

Page 190: Lightning Protection Guide

www.dehn.de LIGHTNING PROTECTION GUIDE 189

DEHN SPDSPS PRO

/ IN function

OUT / FM

DEH

Nrail

DR

MO

D 255

4 3

2 1

NETZFILTER

L' L' N' N'OUT

L L N NIN

N L1

N L1

L2 L3

L2 L3

DEHNrail 230/3N FMLDR 230 3N FML

DEH

Ngu

ard

DG

MO

D 2

75

DEH

Ngu

ard

DG

MO

D 2

75

L1 L2

PEN

DEH

Ngu

ard

DG

MO

D 2

75

L3

DEHNbloc®

NHDB NH00 255

DEHNbloc®

NHDB NH00 255

DEHNbloc®

NHDB NH00 255

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

1 2 3

14 11 12

DEHNsignalDSI DBM

DEH

Nve

ntil

DV

MO

D 2

55

DEH

Nve

ntil

DV

MO

D 2

55

DEH

Nve

ntil

DV

MO

D 2

55

L1 L1´ L2 L2´

PEN

L3 L3´

VNHV NH 00 280

VNHV NH 00 280

VNHV NH 00 280

3 x V NH00 280 Part No. 900 261

3 x DB NH00 255 H Part No. 900 273alt. 3 x DB 1 255 H Part No. 900 222

1 x MVS 1 8 Part No. 900 611

1315 A

3 x DBM 1 255 L Part No. 900 0261 x MVS 1 8 Part No. 900 611

alt. 3 x DBM 1 255 S Part No. 900 220

1315 A

faul

t sig

nal

1 x DV M TNC 255 FM Part No. 951 305alt. 1 x DV M TNC 255 Part No. 951 300

1315 A

faul

t sig

nal

1 x DG M TNC 275 Part No. 952 300or with remote signalling contact:1 x DG M TNC 275 FM Part No. 952 305

1125 A

13 A

1 x SPS PRO Part No. 912 253 1 x DR 230 3N FML Part No. 901 130

116 A

electronicequipment

25 A alsopermissiblewithout NF 10

1 x DR M 2P 255 FM Part No. 953 2051 x NF 10 Part No. 912 254

110 A

L1 L2 L3 N PE

Cable length ≥ 5 m

16 A

Swit

chge

ar/M

achi

ne

SPD Type 2(Surge arrester)

SPD Type 2(Surge arrester)

Cable length ≥ 15 m

SPD Type 1(Lightning current arrester)

SPD Type 1(Coordinated lightning

current arrester)

DEHNbloc® MaxiCoordinated to DEHNguard®

without additional cable length.

Mai

n D

istr

ibut

ion

Boar

dSu

bdis

trib

utio

n Bo

ard

SPD Type 1(Combined lightning current

and surge arrester)

SPD Type 3(Surge arrester)

SPD Type 3(Surge arrester)

SPD Type 3(Surge arrester)

DEHNventil®

Directly coordinated toRed/Line SPDs Type 2 and 3

without additional cable length.

2

EBB

PLC PLC

1) Only required, if a fuse of the same or a lower nominal value is not already provided in the upstream power supply.2) Without separate backup fuse in case of earth-fault- and short-circuit-proof installation.

Fig. 8.1.3.8 SPDs used in TN systems – Example: Industry – Separation of the PEN in the subdistribution board

Page 191: Lightning Protection Guide

protective devices havebeen approved. This meansthat, in TT systems, light-ning current and surgearresters may only be ar-ranged downstream of the above described pro-tective devices in order to ensure the “protectionagainst electric shock un-der fault conditions” inthe event of an SPD fail-ure.

As previously described inSection 8.1.3, in case of anarrangement of an SPDType 1 or 2 downstream ofan RCD, it has to beexpected that, because ofthe impulse current dis-charged to PE, this dis-charge process will be

www.dehn.de190 LIGHTNING PROTECTION GUIDE

DEH

Nra

il

DR

MO

D 2

55

43

21

S-PROTECTOR

230V~ Defect

DEHNventil® ZPDV ZP TNC 255

PEN

PEN

L3

L2

L1

L1 L2 L3 N PE

16 A

Sock

et O

utle

t

EBB

Hea

ting

Con

trol

SPD Type 1(Combined lightning current

and surge arrester)

1 x DV ZP TNC 255 Part No. 900 390also available for 5-wire systems1 x DV ZP TT 255 Part No. 900 391

Note:As an alternative, surge arresters can also be used(e.g. DG M TNC 275 Part No. 952 300),if no- lightning protection system,- electrical power supply by the service entry mast,- antenna on the roofis available.

Cent

ral M

ain

and

Subd

istr

ibut

ion

Boar

d

1 x S PRO Part No. 909 8211 x SF PRO Part No. 909 8201 x SFL PRO Part No. 912 260

SPD Type 3(Surge arrester)

1 x DR M 2P 255 Part No. 953 200

SPD Type 3(Surge arrester)

KW h

L1L2L3

PEN

heating

315 A gL/gG

Fig. 8.1.3.9 SPDs used in TN systems – Example: Residential building

Fig. 8.1.4.1 TT system (230/400 V); “3+1” circuit

U0 = 230 V a.c.

Phase conductor to neutral conductorUc 1.1 x 230 V = 255 V a.c.

Neutral conductor to PE:Uc 230 V a.c.

3 x SPD with Uc 255 V a.c.

1 x N-PE arrester with Uc 230 V a.c.

The values of U0 between neutral con-ductor and PE already refer to the mostunfavourable operating conditions.A tolerance of 10 % has therefore notbeen considered.

1.1 U0

U0

L1L2L3NPE

U0 = Nominal a.c. voltage of thephase conductors to earthRA

Page 192: Lightning Protection Guide

interpreted by the RCD as residual current, andthen the circuit is interrupted by the same. If SPDsType 1 are used, it must further be assumed thatthe dynamics of the discharged partial lightningcurrent would cause mechanical damage to theRCD as the SPD Type 1 responds as is the case withTN systems. This would damage the protectivedevice for “protection against electric shock underfault conditions” and override the protectivemeasure. This type of state, which can result in lifehazard, must of course be avoided. Hence, bothSPDs Type 1 and SPDs Type 2 must always beinstalled upstream of the residual current device inTT systems. SPDs Type 1 and 2 must be arranged inTT systems to meet the conditions for the use ofovercurrent protective devices for “protectionagainst electric shock under fault conditions”.

In the event of a failure, i.e. a faulty SPD, short cir-cuit currents must flow to initiate an automaticdisconnection of the overcurrent protectivedevices within 5 s. If the arresters in the TT systemwere arranged as shown in Figures 8.1.3.4 and8.1.3.5 for TN systems then, in the event of a fault,only earth fault currents would arise instead of

short circuit currents. In certain circumstances,however, these earth fault currents do not trip anupstream overcurrent protective device within thetime required.

SPDs Type 1 and 2 in TT systems are thereforearranged between L and N. This arrangement shallensure that, in the event of a faulty protectivedevice in the TT system, a short circuit current candevelop and cause the next upstream overcurrentprotective device to respond. However, since light-ning currents always occur to earth, i.e. PE, a sup-plementary discharge path between N and PEmust be provided.

These so-called “N-PE arresters” must meet specialrequirements since here, on the one hand, the sumof the partial discharge currents from L1, L2, L3and N must be carried and, on the other, theremust be a follow current extinguishing capabilityof 100 Arms because of a possible shifting of theneutral point.

The following maximum continuous voltagesapply to the use of SPDs in TT systems between Land N (Figure 8.1.4.1):

www.dehn.de LIGHTNING PROTECTION GUIDE 191

Fig. 8.1.4.2 Use of SPDs in TT systems

surge arrester

terminal equipment

L1L2L3NPE

subdistribution board

F3

local EBB

main distribution board

lightning current arrester

F2

Wh

F1

SEB

exte

rnal

ligh

tnin

gpr

otec

tion

syst

em

MEBB

RCD

protection acc. to IEC 60364-4-443

lightning current and surge protection acc. to IEC 62305 (EN 62305)

Page 193: Lightning Protection Guide

The lightning current carrying capability of theSPDs Type 1 must be designed to conform to light-ning protection levels I, II, III/IV, as per IEC 62305-1(EN 62305-1).For the lightning current carrying capability of theSPDs between N and PE, the following values mustbe maintained:

Lightning protection level:I Iimp ≥ 100 kA (10/350 μs)II Iimp ≥ 75 kA (10/350 μs)III/IV Iimp ≥ 50 kA (10/350 μs).

The SPDs Type 2 are also connected between L andN and between N and PE. For the SPD between Nand PE, in combination with SPDs Type 2, the dis-charge capacity must be at least In ≥ 20 kA (8/20 μs)for three-phase systems and In ≥ 10 kA (8/20 μs) forsingle-phase systems.Since coordination is always performed on thebasis of the worst-case conditions (10/350 μs wave-form), the N-PE Type 2 arrester from the Red/Linefamily is based on a value of 12 kA (10/350 μs).

Figure 8.1.4.2 to 8.1.4.6 shows examples of theconnections for use of SPDs in TT systems. As is thecase in TN systems, surge protective devices Type 3are installed downstream of the RCD. Generally,the impulse current discharged by this SPD is solow that the RCD does not recognise this process asa residual current.

However, it is still important to use an RCD capableof withstanding impulse currents.

8.1.5 Use of SPDs in IT systemsFor “protection against electric shock under faultconditions“ in IT systems, overcurrent protectivedevices, residual current devices (RCD) and insula-tion monitoring devices have been approved.

Whereas in TN or TT systems, the “protectionagainst electric shock under fault conditions” inthe event of the first fault is ensured by the appro-priate automatic disconnection from supply

www.dehn.de192 LIGHTNING PROTECTION GUIDE

DEH

Nra

il

DR

MO

D 2

55

43

21

DEH

Nve

ntil

DV

MO

D 2

55

DEH

Nve

ntil

DV

MO

D 2

55

DEH

Nve

ntil

DV

MO

D 2

55

DEH

Nve

ntil

DV

MO

D N

PE50

L1 L1´ L2 L2´

PE

L3 L3´ N N´

DEHNflex

L1 L2 L3 N PE

16 A

Sock

et O

utle

t

Hea

ting

Con

trol

SPD Type 1(Combined lightning current

and surge arrester)

1 x DV M TT 255 Part No. 951 310

Note:As an alternative, surge arresters can also be used(e.g. DG M TT 275 Part No. 952 310),if no- lightning protection system,- electrical power supply by the service entry mast,- antenna on the roofis available.

Cent

ral M

ain

and

Subd

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ibut

ion

Boar

d

1 x DR M 2P 255 Part No. 953 200

SPD Type 3(Surge arrester)

125 A

1 x DFL M 255 Part No. 924 396

SPD Type 3(Surge arrester)

heating

EBB

Fig. 8.1.4.3 SPDs used in TT systems – Example: Residential Building

Page 194: Lightning Protection Guide

www.dehn.de LIGHTNING PROTECTION GUIDE 193

Fig. 8.1.4.4 SPDs used in TT systems – Example: Office building

DEH

Ngu

ard®

DG

MO

D 2

75

DEH

Ngu

ard®

DG

MO

D 2

75

L1 L2

PE

DEH

Ngu

ard®

DG

MO

D 2

75

L3 N

DEH

Ngu

ard®

DG

MO

D N

PE

DEH

Ngu

ard®

DG

MO

D 2

75

DEH

Ngu

ard®

DG

MO

D 2

75

L1 L2

PE

DEH

Ngu

ard®

DG

MO

D 2

75

L3 N

DEH

Ngu

ard®

DG

MO

D N

PE

DEHNflex

ÜS-Schutz

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D N

PE50

L1 L1´ L2 L2´

PE

L3 L3´ N N´

DEHNgap MaxiDGP M255

DSI!

N N'

N

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L1 L1' L2 L2' L3 L3'

N´/PEN N/PEN

DEHNbloc® DB 3 255 HDurchgangsklemme

DK 35DEHNgap B/nDGP BN 255

1 x DB 3 255 H Part No. 900 120alt. 3 x DB 1 255 H Part No. 900 222

1 x DGP BN 255 Part No. 900 1321 x DK 35 Part No. 900 6991 x MVS 1 4 Part No. 900 610

1315 A

3 x DBM 1 255 L Part No. 900 026alt. 3 x DBM 1 255 Part No. 900 025

1 x DGPM 255 Part No. 900 0551 x MVS 1 8 Part No. 900 611

1315 A

1 x DV M TT 255 FM Part No. 951 315alt. 1 x DV M TT 255 Part No. 951 310

1315 A

fault signal

L1 L2 L3 N PE

Cable length ≥ 5 m

16 A

Sock

et O

utle

t

faul

t sig

nal

1 x DSA 230 LA Part No. 924 370for cable ducts

1 x STC 230 Part No. 924 350for existing socket outlets

or with remote signalling contact:1 x DG M TT 275 FM Part No. 952 315

1125 A

SPD Type 2(Surge arrester)

1125 A

SPD Type 2(Surge arrester)

1 x DG M TT 275 Part No. 952 310

Cable length ≥ 15 m

SPD Type 1(Lightning current arrester)

SPD Type 1(Coordinated lightning

current arrester)

DEHNbloc® MaxiCoordinated to DEHNguard®

without additional cable length.

Mai

n D

istr

ibut

ion

Boar

dSu

bdis

trib

utio

n Bo

ard

SPD Type 1(Combined lightning current

and surge arrester)

SPD Type 3(Surge arrester)

1 x DFL M 255 Part No. 924 396for flush-mounted systems

SPD Type 3(Surge arrester)

SPD Type 3(Surge arrester)

DEHNventil®

Directly coordinated toRed/Line SPDs Type 2 and 3

without additional cable length.

RCD

EBB

1) Only required, if a fuse of the same or a lower nominal value is not already provided in the upstream power supply.

Page 195: Lightning Protection Guide

www.dehn.de194 LIGHTNING PROTECTION GUIDE

DEH

Ngu

ard®

DG

MO

D 2

75

DEH

Ngu

ard®

DG

MO

D 2

75

L1 L2

PE

DEH

Ngu

ard®

DG

MO

D 2

75

L3 N

DEH

Ngu

ard®

DG

MO

D N

PE

DEH

Ngu

ard®

DG

MO

D 2

75

DEH

Ngu

ard®

DG

MO

D 2

75

L1 L2

PE

DEH

Ngu

ard®

DG

MO

D 2

75

L3 N

DEH

Ngu

ard®

DG

MO

D N

PE

DEHN SPDSPS PRO

/ IN function

OUT / FM

DEH

Nrail

DR

MO

D 255

4 3

2 1

NETZFILTER

L' L' N' N'OUT

L L N NIN

N L1

N L1

L2 L3

L2 L3

DEHNrail 230/3N FMLDR 230 3N FML

DEHNgap MaxiDGP M255

DSI!

N N'

N

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N’/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

1 2 3 4

14 11 12

DEHNsignalDSI DV

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D N

PE50

L1 L1´ L2 L2´

PE

L3 L3´ N N´

DEHNbloc®

NHDB NH00 255

DEHNbloc®

NHDB NH00 255

DEHNbloc®

NHDB NH00 255

DEHNbloc®

NHDB NH00 255

RCD

13 A

1 x SPS PRO Part No. 912 253

3 x DB NH00 255 H Part No. 900 2731 x DGP B NH00 N 255 Part No. 900 269

1315 A

1 x DV M TT 255 FM Part No. 951 315alt. 1 x DV M TT 255 Part No. 951 310

1315 A

fault signal

1 x DR 230 3N FML Part No. 901 130

116 A

electronicequipment

3 x DBM 1 255 L Part No. 900 026alt. 3 x DBM 1 255 Part No. 900 025

1 x DGPM 255 Part No. 900 0551 x MVS 1 8 Part No. 900 611

1315 A

indi

catio

n of

inte

rfere

nce

25 A alsopermissiblewithout NF 10

1 x DR M 2P 255 FM Part No. 953 2051 x NF 10 Part No. 912 254

110 A

L1 L2 L3 N PE

Cable length ≥ 5 m

16 A

Swit

chge

ar/M

achi

ne

faul

t sig

nal

or with remote signalling contact:1 x DG M TT 275 FM Part No. 952 315

1125 A

SPD Type 2(Surge arrester)

1125 A

SPD Type 2(Surge arrester)

1 x DG M TT 275 Part No. 952 310

Cable length ≥ 15 m

SPD Type 1(Lightning current arrester)

SPD Type 1(Coordinated lightning

current arrester)

DEHNbloc® MaxiCoordinated to DEHNguard®

without additional cable length.

Mai

n D

istr

ibut

ion

Boar

dSu

bdis

trib

utio

n Bo

ard

SPD Type 1(Combined lightning current

and surge arrester)

SPD Type 3(Surge arrester)

SPD Type 3(Surge arrester)

SPD Type 3(Surge arrester)

DEHNventil®

Directly coordinated toRed/Line SPDs Type 2 and 3

without additional cable length.

EBB

PLC PLC

1) Only required, if a fuse of the same or a lower nominal value is not already provided in the upstream power supply.

Fig. 8.1.4.5 SPDs used in TT systems – Example: Industry

Page 196: Lightning Protection Guide

through the overcurrent protective devices orRCDs, the first fault in an IT system only creates analarm. An excessive shock hazard voltage cannotoccur because the first fault in the IT system simplycreates an earth connection of the system. Theoperating state of the IT system then becomes a TNor TT system. Hence, an IT system can be furtheroperated at no risk after the first fault. Thus, workor production processes already begun (e.g. chem-ical industry) can still be completed. For the firstfault, the protective conductor adopts the poten-tial of the faulty external conductor, which, how-ever, does not create a risk, because all bodies andmetal components which persons can come intocontact with, adopt this potential via the protec-tive conductor. Hence, no hazardous potential dif-ferences can be bridged either. When the first faultoccurs, however, it must be noted, that the voltageof the IT system of the intact conductors to earthcorresponds to the voltage between the externalconductors. Hence, in a 230/400 V IT system, in theevent of a faulty SPD there is a voltage of 400 Vacross the non-faulty SPD. This possible operatingstate must be taken into account when choosingthe SPDs with respect to their maximum continu-ous voltage.

When considering IT systems, a distinction is madebetween IT systems with neutral conductors enter-ing the building with the others, and IT systemswithout such neutral conductors. For IT systemswith the latter configuration, the SPDs in the so-called “3-0” circuit must be installed between eachexternal conductor and the PE conductor. For ITsystems with neutral conductors entering thebuilding with the others, both the “4-0” and the“3+1” circuit can be used. When using the “3+1”circuit, it must be noted that, in the N-PE path, anSPD must be employed with a follow current extin-guishing capability appropriate to the system con-ditions.

The following maximum continuous operatingvoltages apply to the use of SPDs Type 1, 2 and 3 inIT systems with and without neutral conductorsentering the building with the others (Figures8.1.5.1a – c).

A second fault in an IT system must then cause atripping of a protective device. The statementsabout TN and TT systems made in Sections 8.1 and8.2 apply to the use of SPDs in IT systems in connec-

www.dehn.de LIGHTNING PROTECTION GUIDE 195

L1L2L3PE

UL-L

RA

UL-L 500 V a.c.

Phase conductor to PE:Uc 500 V a.c.

3 x SPD with Uc 500 V a.c.

The values of Uc between neutralconductor and PE already refer tothe most unfavourable operatingconditions. A tolerance of 10 %has therefore not been considered.

√3 U0

L1L2L3NPE

RA

U0

U0 = 230 V a.c.

Phase conductor to neutral conductor:Uc 3 x 230 V = 398 V a.c.

Neutral conductor to PE:Uc 230 V a.c.

3 x SPD with Uc 398 V a.c.1 x SPD with Uc 230 V a.c.

The values of Uc between neutralconductor and PE already refer tothe most unfavourable operatingconditions. A tolerance of 10 %has therefore not been considered.

U0 = Nominal a.c. voltage of thephase conductors to earth

1,1 U0

L1L2L3NPE

U0

RA

U0 = 230 V a.c.

Phase conductor to neutral conductor:Uc 1.1 x 230 V = 255 V a.c.

Neutral conductor to PE:Uc 230 V a.c.

3 x SPD with Uc 255 V a.c.1 x SPD with Uc 230 V a.c.

The values of Uc between neutralconductor and PE already refer tothe most unfavourable operatingconditions. A tolerance of 10 %has therefore not been considered.

1.1 U0

L1L2L3NPE

U0 = Nominal a.c. voltage of thephase conductors to earth

U0

RA

Fig. 8.1.5.1a IT system without neutral conductor; “3-0” circuit

Fig. 8.1.5.1b IT system with neutral conductor; “4-0” conductor

Fig. 8.1.5.1c IT system with neutral conductor; “3+1” circuit

Page 197: Lightning Protection Guide

tion with a protec-tive device for "pro-tection against electricshock under fault con-ditions".The use of SPDs Type 1and 2 upstream of theRCD is therefore alsorecommended for ITsystems. A connectionexample for the use of SPDs in IT systemswithout neutral con-ductors entering thebuilding with the oth-ers is shown in Figure8.1.5.2 and 8.1.5.3.

Figure 8.1.5.4 showsthe use of SPDs in ITsystems with neutralconductor.

www.dehn.de196 LIGHTNING PROTECTION GUIDE

surge arrester

terminal equipment

L1L2L3

PE

subdistribution board

F3

local EBB

main distribution board

lightning current arrester

F2

Wh

F1exte

rnal

ligh

tnin

gpr

otec

tion

syst

em

MEB

protection acc. to IEC 60364-4-443

protection acc. to IEC 62305 (EN 62305)

SEB

DEH

Ngu

ard

DG

MO

D 4

40

DEH

Ngu

ard

DG

MO

D 4

40

DEH

Ngu

ard

DG

MO

D 4

40

125 A1

250 A1

L L' PE PE'

DEHNbloc® MAXI DBM 440

L L' PE PE'

DEHNbloc® MAXI DBM 440

L L' PE PE'

DEHNbloc® MAXI DBM 440

DEH

Ngu

ard

DG

MO

D 4

40

DEH

Ngu

ard

DG

MO

D 4

40

DEH

Ngu

ard

DG

MO

D 4

40

125 A1

Mai

n D

istr

ibut

ion

Boar

dSu

bdis

trib

utio

n Bo

ard

1) Only required, if a fuse of the same or a lower nominal valueis not already provided in the upstream power supply.

faul

t sig

nal

or with remote signalling contact:3 x DG S 440 FM Part No. 952 0951 x MVS 1 4 Part No. 900 610

3 x DG S 440 Part No. 952 0751 x MVS 1 4 Part No. 900 610

Coordinated lightning current arrester Type 1DEHNbloc® Maxi

SPD Type 2(Surge arrester)

SPD Type 2(Surge arrester)

L1 L2 L3PE

3 x DBM 440 Part No. 900 044

Fig. 8.1.5.2 Use of SPDs in IT systems without neutral conductor

Fig. 8.1.5.3 Use of SPDs in 400 V IT systems – Example without neutral conductor

Page 198: Lightning Protection Guide

8.1.6 Rating the lengths of the connectingleads for SPDs

Rating the lengths of connecting leads of surgeprotective devices is a significant part of the IEC60364-5-53/A2 (IEC 64/1168/CDV: 2001) installationregulations.The aspects stated below are also frequently thereason for complaints through experts, membersof technical inspectorates, etc. inspecting thestructure.

Series connection (V-shape) in accordance with IEC60364-5-53/A2 (IEC 64/1168/CDV: 2001)Crucial for the protection of systems, equipmentand consumers is the actual level of impulse volt-age across the installations to be protected. Theoptimum protective effect is then achieved whenthe impulse level across the installation to be pro-tected matches the voltage protection level pro-

vided by the surge pro-tective device. Therefore, IEC 60364-5-53/A2 (IEC64/1168/CDV: 2001) sug-gests a series connectionsystem (V-shape) as shownin Figure 8.1.6.1 to beused for connecting surgeprotective devices. Thisrequires no separate con-ductor branches for con-necting the surge protec-tive devices.

Parallel connection sys-tem in accordance withIEC 60364-5-53/A2 (IEC64/1168/CDV: 2001)The optimum series con-nection system cannot beused under all system con-ditions.Nominal currents carriedvia the double terminalson the surge protectivedevice as part of the serieswiring are limited by thethermal loadability of thedouble terminals. For thisreason, the manufacturerof the surge protectivedevice prescribes a certain

max. permissible value of the backup fuse which,in turn, means that series wiring can sometimesnot be used for systems with higher nominal oper-ating currents.Meanwhile, the industry provides so-called two-conductor terminals to solve this problem. Thus,the cable lengths can still be kept short, even if thenominal operating current is increased. Whenusing the two-conductor terminals, however, itmust be ensured that the value of the backup fusestated by the manufacturer for this particularapplication is always observed (Figures 8.1.6.2 and8.1.6.3).If series connection is definitely no option, surgeprotective devices must be integrated into a sepa-rate branch circuit. If the nominal value of the nextupstream installation fuse exceeds the nominalcurrent of the max. permissible backup fuse of thesurge protective device, the branch must beequipped with a backup fuse for the surge protec-

www.dehn.de LIGHTNING PROTECTION GUIDE 197

Fig. 8.1.5.4 Use of SPDs in 230/400 V IT systems – Example with neutral conductor

DEH

Ngu

ard

DG

MO

D 2

75

Durchgangsklemme

DK 35

DEH

Ngu

ard

DG

MO

D 2

75

DEH

Ngu

ard

DG

MO

D 2

75

DEH

Ngu

ard

DG

MO

D 2

75

125 A1

315 A1

Durchgangsklemme

DK 35

L L'

N/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

L L'

N/PEN N/PENDSI!

DEHNbloc® MaxiDBM 1 255 L

Mai

n D

istr

ibut

ion

Boar

dSu

bdis

trib

utio

n Bo

ard

EBB1) Only required, if a fuse of the same or a lower nominal value

is not already provided in the upstream power supply.

SPD Type 2(Surge arrester)

4 x DG S 275 Part No. 952 0701x MVS 1 8 Part No. 900 6111x DK 35 Part No. 900 699

Coordinated lightning current arrester Type 1DEHNbloc®

4x DBM 1 255 Part No. 900 0251x MVS 1 8 Part No. 900 6111x DK 35 Part No. 900 699

L1 L2 L3 N PE

Page 199: Lightning Protection Guide

tive device (Figure 8.1.6.4), or SPDs with integratedbackup fuse are used (Figures 8.1.6.5 and 8.1.6.6).

When the surge protective device in the conductorbranch responds, the discharge current flowsthrough further elements (conductors, fuses) caus-ing additional dynamic voltage drops across theseimpedances.

It can be stated here that the ohmic component isnegligible compared to the inductive component.

Taking into account the relation

and the rate of current change (di/dt) for transientprocesses of a few 10 kA/μs, the dynamic voltagedrop Udyn is considerably determined by the induc-tive component.In order to keep this dynamic voltage drop low,the electrician carrying out the work must keepthe inductance of the connecting cable and henceits length as low as possible. IEC 60364-5-53/A2 (IEC 64/1168/CDV: 2001) therefore recommends todesign the total cable length of surge protectivedevices in branch circuits to be not longer than 0.5 m (Figure 8.1.6.7).

Design of the connecting lead on the earth sideThis requirement, which is seemingly difficult torealise, shall be explained with the help of the

u i Rdi

dtLdyn = ⋅ +

⎛⎝⎜

⎞⎠⎟

www.dehn.de198 LIGHTNING PROTECTION GUIDE

iimp Discharged impulse currentuSPD Limiting SPD voltageUtotal Limiting voltage on the terminal

equipment

Utotal = uSPD

UtotaluSPDiimp

iimp Discharged impulse current

uSPD Limiting SPD voltage

Utotal Limiting voltage on the terminal equip-ment

udyn 1 Dynamic voltage drop on the phase-side connection of the SPD

udyn 2 Dynamic voltage drop at the earth-sideconnection of the SPD

Utotal = udyn 1 + uSPD + udyn 2

L/N

PE

UtotaluSPDiimp

udyn 1

udyn 2

Fig. 8.1.6.1 Surge protective devices in V-shape series connection

Fig. 8.1.6.2 Principle of “two-conductor ter-minals (TCT)“ – Illustration of asingle-pole unit

Fig. 8.1.6.3 Pin connection terminal (PCT)2x16

Fig. 8.1.6.4 Connection of surge protectivedevices in cable branches

Fig. 8.1.6.5 DEHNbloc Maxi S: coordinatedlightning current arrester for thebusbar with integrated backup fuse

Fig. 8.1.6.6 Surge protective device Type2 V NH for use in NH fusebases

Page 200: Lightning Protection Guide

example shown in Figures 8.1.6.8a and b. Theseshow the main equipotential bonding (in future:protective equipotential bonding) of a low voltageconsumer’s installation in accordance with IEC60364-4-41 and IEC 60364-5-54. Here, the use ofsurge protective devices Type 1 extends theequipotential bonding to become a lightningequipotential bonding.In Figure 8.1.6.8a, both measures are installed sep-arately. In this case, the PEN was connected to theequipotential bonding bar and the earthing con-nection of the surge protective devices was per-formed via a separate equipotential bonding con-ductor.

Thus, the effective cable length(la) for the surge protectivedevices corresponds to the dis-tance between the installationsite of the surge protectivedevices (e.g. service entrancebox, main distribution board) tothe equipotential bonding bar. Aconnection configuration of thistype mostly achieves minimumeffective protection of the instal-lation. Without great expenses,however, it is possible to use a conductor leading as shown in Figure 8.1.6.8b to reduce the effective cable length of the surge protective devices (lb < 0.5 m).This is achieved by using a“bypass” conductor (y) from theterminal of the earth side of thearrester to the PEN. The connec-tion from the terminal of theearth side of the arrester to theequipotential bonding bar (x)remains as it was.

According to the VDN-Richt-linie 2004-08 [engl.: Directive ofthe Association of the GermanNetwork Operators]: “Überspan-nungs-Schutzeinrichtungen Typ 1.Richtlinie für den Einsatz vonÜberspannungs - Schutzeinrich-tungen (ÜSE) Typ 1 (bisher An-forderungsklasse B) in Haupt-stromversorgungssystemen.“[engl: “Surge protective devices

Type 1. Directive for the use of surge protectiveequipment Type 1 (up to now Class B) in main dis-tribution systems.“], the bypass conductor (y) mayonly be omitted if the surge protective device isinstalled in the immediate vicinity (≤ 0.5 m) of theservice entrance box and hence also in the immedi-ate vicinity of the equipotential bonding.

When installing the connection y, the distancebetween service entrance box or main distributionboard and equipotential bonding bar is thusinsignificant. The solution for this problemreferred only to the design of the connecting cableon the earth side of the surge protective devices.

www.dehn.de LIGHTNING PROTECTION GUIDE 199

Fig. 8.1.6.7 Recommended max. cable lengths of surge protective devices in branch circuits

Fig. 8.1.6.8a Unfavourable conductor rout-ing from the “consumer’s pointof view”

Fig. 8.1.6.8b Favourable conductor routingfrom the “consumer’s point ofview”

l a

L1L2L3

PEN

EBB

x

unfavourable

l b

L1L2L3

PEN

EBB

x

favourable

y

ab

b1

b2

SPD

TEI

a+b ≤ 0.50 m

EBB

SPD

TEI

(b1 + b2) < 0.50 m

EBB

TEI = Terminal Equipment Interface

Page 201: Lightning Protection Guide

Design of the phase-side connecting cableThe cable length on the phase side must also betaken into consideration. The following case studyshall illustrate this:In expanded control systems, surge protectionmust be provided for the busbar system and thecircuits attached thereto (A to D) with their con-sumers (Figure 8.1.6.9).For the use of the surge protective devices in thiscase, installation sites 1 and 2 are taken as alterna-tives. Installation site 1 is located directly at thesupply of the busbar system. This ensures the samelevel of protection against surges for all con-sumers. The effective cable length of the surgeprotective device at installation site 1 is l1 for allconsumers. If there is not enough space, the instal-lation site of the surge protectivedevices is sometimes chosen at aposition along the busbar system. Inextreme cases, installation site 2 canbe chosen for the arrangementshown in Figure 8.1.6.9. For circuit Aresults the effective cable length l2.Busbar systems in fact have a lowerinductance compared to cables andconductors (approx. 1/4) and hencea lower inductive voltage drop.However, the length of the busbarsmust not be disregarded.

The design of the connecting cableshas considerable influence on the

effectiveness of surge protective devices and musttherefore be taken into consideration at thedesign stage of the installation!

The contents of IEC 60364-5-53/A2 (IEC 64/1168/CDV: 2001) described above were important guide-lines for the development of the new DEHNventilcombined lightning current and surge arresterwhich was supposed to combine the requirementson lightning current and surge arresters in ac-cordance with the IEC 62305 Part 1 – 4 (EN 62305 Part 1 – 4) standard series in a single device.This allows to realise a series connection directlyvia the device. Figure 8.1.6.10 shows such a seriesconnection in form of an operating circuit dia-gram.

www.dehn.de200 LIGHTNING PROTECTION GUIDE

l1

l2

A B C D inst

alla

tion

site

2in

stal

latio

n si

te 1

l1: Total cable length at installation site 1l2: Total cable length at installation site 2

EBB

L1'L2'L3'PEN

L1 L2 L3PENnew connecting cable

F4 F5 F6

F1-F3

SEBF1 – F3

> 125 A gL/gG

F4 – F6= 125 A gL/gG

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

L1 L1´ L2 L2´

PEN

L3 L3´

Fig. 8.1.6.9 Arrangement of surge protectivedevices in a system and the resultingeffective cable length

Fig. 8.1.6.10 Series connection V-shape

Fig. 8.1.6.11 V-shape series connection of the DEHNventil M TNC combined lightning cur-rent and surge protective device by means of a busbar

Page 202: Lightning Protection Guide

From Figure 8.1.6.11 it can be taken how advanta-geous it is to implement a series connection withthe aid of a busbar.

Because of the thermal loading capacity of thedouble terminals employed, a v-shape series con-nection (also called through-wiring) can be usedup to 125 A.

For load currents > 125 A, the surge protectivedevices are connected in the conductor branch (so-called parallel wiring). The maximum cable lengthsaccording to IEC 60364-5-53/A2 (IEC 64/1168/CDV:2001) must be observed. The parallel wiring can beimplemented as shown in Figure 8.1.6.12.

In this context, it should be ensured that the con-necting cable on the earth side still benefits fromthe double terminal for the earth connection. Asshown in Figure 8.1.6.12, it is often possible, with-out great effort, to achieve an effective cablelength of the order of magnitude l < 0.5 m with aconductor leading from terminal component “PE”of the earth-side double terminal to PEN.

At the installation of surge protective devices indistributions it must generally be considered thatconductors loaded by impulse currents and thosenot loaded by impulse currents are routed as sepa-rately as possible. In any case, a parallel routing ofboth conductors has to be avoided (Figure8.1.6.13).

8.1.7 Rating of the terminal cross-sectionsand the backup protection of surgeprotective devices

Connecting leads of arresters can be subjected toloads from impulse currents, operating currentsand short circuit currents. The individual loadsdepend on various factors:

⇒ Type of protective circuit: one-port (Figure8.1.7.1) / two-port (Figure 8.1.7.2)

⇒ Type of arrester: lightning current arrester,combined lightning current and surge arrester,surge protective devices

www.dehn.de LIGHTNING PROTECTION GUIDE 201

Fig. 8.1.6.12 Parallel wiringFig. 8.1.6.13 Cable routing

Fig. 8.1.7.1 One-port protective circuit

Fig. 8.1.7.2 Two-port protective circuit

EBB

L1'L2'L3'PEN

L1 L2 L3PEN

F4 F5 F6

F1-F3

SEBF1 – F3

> 315 A gL/gG

F4 – F6= 315 A gL/gG

s s s

Connection cabel

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

L1 L1´ L2 L2´

PEN

L3 L3´ IN (OUT)

OUT (IN)

okIN (OUT)

OUT (IN)

1

2

S2

S3

3

4

1

2

Page 203: Lightning Protection Guide

⇒ Performance of the arrester on follow cur-rents: follow current extinction/follow currentlimitation

If surge protective devices are installed as shown inFigure 8.1.7.1, the S2 and S3 connecting cablesmust only be rated upon the criteria of short circuitprotection according to IEC 60364-4-43 and theimpulse current carrying capability. The data sheetof the protective device provides the maximumpermissible overcurrent protection which can beused in this application as backup protection forthe arrester.When installing the devices, it must be ensuredthat the short circuit current actually flowing isable to trip the backup protection. The rating ofthe cross-sectional area or of the conductor is thengiven by the following equation:

www.dehn.de202 LIGHTNING PROTECTION GUIDE

L1 L1' L2 L2' L3 L3'

H1 H2 H3

PEN- only for DEHNsignal -

- nur für DEHNsignal -

DEHNventil® DV TNC 255

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

DEH

Nve

ntil®

DV

MO

D 2

55

L1 L1´ L2 L2´

PEN

L3 L3´

F2

L1L2L3

PEN

L1'L2'L3'PEN

S3

F1

S2

DEHNventil DV M TNC 255

F1

F2

F1 > 315 A gL / gG

F2 ≤ 315 A gL / gG

F1 ≤ 315 A gL / gG

F2

Fuse F1 S2 / mm2 S3 / mm2 Fuse F2A gL / gG A gL / gG

25 10 16 ---35 10 16 ---40 10 16 ---50 10 16 ---63 10 16 ---80 10 16 ---100 16 16 ---125 16 16 ---160 25 25 ---200 35 35 ---250 35 35 ---315 50 50 ---

> 315 50 50 ≤ 315

MEBB

Conductormaterial RubberPVC EPR / XLPE

Insulating material

Cu

Al

141

93

115

76

143

94

DEHNguard M TNC 275DEHNguard M TNS 275DEHNguard M TT 275

F1

F1 > 125 A gL / gG

F2 ≤ 125 A gL / gG

Fuse F1 S2 / mm2 S3 / mm2 Fuse F2A gL / gG A gL / gG

35 4 6 ---40 4 6 ---50 6 6 ---63 10 10 ---80 10 10 ---100 16 16 ---125 16 16 125160 25 16 125200 35 16 125250 35 16 125315 50 16 125400 70 16 125

F2

F1 ≤ 125 A gL / gG

F2

A

F2

L1'L2'L3'

L1L2L3N

PE

F1

S2

S3

DEH

Ngu

ard®

DG

MO

D 2

75

DEH

Ngu

ard®

DG

MO

D 2

75

L1 L2

PE

DEH

Ngu

ard®

DG

MO

D 2

75

L3 N

DEH

Ngu

ard®

DG

MO

D N

PE

current carryingcapability of theDINrail to beconsidered

local EBB

Table 8.1.7.1 Material coefficient k for copper and aluminium con-ductors with different insulating material

Fig. 8.1.7.3 SPD with through-wiring

Fig. 8.1.7.4 Example: DEHNventil, DV TNC 255 Fig. 8.1.7.5 Example: DEHNguard (M) TNC/TNS/TT

Page 204: Lightning Protection Guide

t Permissible time for disconnection in the eventof a short circuit in s

S Conductor cross section in mm2

I Current at complete short circuit in A

k Material coefficient in A ⋅ s /mm2 according toTable 8.1.7.1

Furthermore, it must be ensured that the informa-tion concerning the maximum permissible overcur-rent protection circuits in the data sheet of thesurge protective device is only valid up to the val-ue of the stated short-circuit withstand capabilityof the protective device. If the short circuit currentat the installation site is greater than the statedshort-circuit withstand capability of the protectivedevice, a backup fuse must be chosen which issmaller than the maximum backup fuse stated inthe data sheet of the arrester by a ratio of 1:1.6.For surge protective devices installed as shown inFigure 8.1.7.2, the maximum operating currentmust not exceed the nominal load current statedfor the protective device. To protective deviceswhich can be connected in series, applies the max-imum current for through-wiring (Figure 8.1.7.3).

Figure 8.1.7.4 shows examples of cross-sectionalareas and backup protection for lightning currentarresters and combined lightning current and surge

arresters Type 1. Figure 8.1.7.5 shows examples ofcross-sectional areas and backupprotection for surge protectivedevices Type 2. Figure 8.1.7.6 showsthe same for surge protectivedevices Type 3.

The behaviour of the impulse cur-rent must be taken into considera-tion when rating the backup fusesfor surge protective devices. There isa noticeable difference in the wayfuses disconnect short circuit cur-rents compared to the way they dis-connect loads with impulse currents,particularly with lightning impulsecurrents, waveform 10/350 μs.The performance of fuses wasdetermined as a function of the rat-ed current of the lightning impulsecurrent (Figure 8.1.7.7).

k S I t2 2 2⋅ = ⋅

www.dehn.de LIGHTNING PROTECTION GUIDE 203

DEH

Nra

il

DR

MO

D 2

55

43

21

DEH

Nra

il

DR

MO

D 2

55

43

21

F1

F1 ≤ 25 A gL / gG

F1

F2 ≤ 25 A

F2

LN

PE

LN

PE

electronicdevice

electronicdevice

0 10 20 30 40 50 60 70 80 90 100

250 A/1

200 A/1

160 A/00

100 A/C00

63 A/C00

35 A/C00

20 A/C00

I (kA)

25 kA 75 kA

22 kA 70 kA

20 kA 50 kA

25 kA

20 kA

4 kA 15 kA

8 kA

Nominal currentsand design

explosion

melting explosion

9.5 kA

5.5 kA

1.7 kA

Fig. 8.1.7.6 Example: DEHNrail

Fig. 8.1.7.7 Performance of NH fuses bearing impulse current loads

Page 205: Lightning Protection Guide

Field 1: No meltingThe energy brought into the fuse by the lightningimpulse current is too low to cause a melting ofthe fuse.

Field 2: MeltingThe energy of the lightning impulse current is suf-ficient to melt the fuse and hence interrupt thecurrent path through the fuse (Figure 8.1.7.8).It is characteristical for the performance of thefuse that the lightning impulse current, since it isinjected, continues to flow, unaffected by the per-formance of the fuse. The fuse disconnects onlyafter the lightning impulse current has decayed.The fuses are therefore not selective with respectto the disconnection of lightning impulse currents.Therefore it must be ensured that, because of thebehaviour of the impulse current, the maximumpermissible backup fuse as per the data sheetand/or installation instructions of the protectivedevice is always used.

From Figure 8.1.7.8 it can also be seen that, duringthe melting process, a voltage drop builds upacross the fuse which in part can be significantlyabove 1 kV. For applications as illustrated in Figure8.1.7.9, a melting of the fuse can also result in thevoltage protection level of the installation beingsignificantly higher than the voltage protectionlevel of the surge protective device employed.

Field 3: Explosion

If the energy of the lightning impulse current is sohigh to be much higher than the pre-arcing of thefuse, then the fuse strip can vaporise explosively.This often results in a bursting fuse box. Apartfrom the mechanical consequences, it must be not-ed that the lightning impulse current continues toflow through the bursting fuse in the form of anelectric arc; the lightning impulse current can thusnot be interrupted nor, linked to this, can therequired impulse current carrying capability of theemployed arrester be reduced.

Selectivity to the protection of the installation

When using spark-gap based surge protectivedevices, care must be taken that any starting mainsfollow current is limited to the extent that overcur-rent protective devices such as fuses and /orarrester backup fuses cannot trip. This characteris-tic of the protective devices is called follow currentlimitation or follow current suppression. Only byusing technologies such as the RADAX Flow tech-nology allows to develop arresters and combina-tions of arresters which, even for installations withhigh short circuit currents, are able to reduce andextinguish the current to such a degree thatupstream fuses for lower rated currents do not trip(Figure 8.1.7.10).

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F1... F3 > max.permissiblebackup fuse ofthe SPD

F4 F5 F6

F4... F6 = max.permissiblebackup fuse ofthe SPD

L1L2L3N

F1F2F3

PE

US

UP

8

7

6

5

4

3

2

1

0

-200 0 200 400 600 800 1000 1200 1400 1600 1800

kA

I

t μs

kV

U

8

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6

5

4

3

2

1

0

0 200 400 600 800 1000 1200 1400 1600 1800

kA

I

t μs

kV

U

-200

impulse current

fuse voltage

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

Fig. 8.1.7.8 Current and voltage of a blowing 25 A NH fuse being charged with lightningimpulse currents (10/350 μs)

Fig. 8.1.7.9 Use of a separate backup fuse forsurge protective devices

Page 206: Lightning Protection Guide

The system availability required by EN 60439-1,even in the event of responding surge protectivedevices, can be fulfilled by the aforementioned“follow current suppression” characteristic of thedevice. For surge protective devices with lowsparkover voltage, in particular, designed to not

only take on the function of the lightning equipo-tential bonding but also that of surge protectionin the installation, the performance of the followcurrent limitation is more important than ever forthe availability of the electrical installation (Figure8.1.7.11).

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100 000

10 000

1 000

100

prearcing I2 tof the fuse in A2 s

0.1 1 10 100

prospectiveshort-circuit current [kArms]

let-through I2 • t of theRADAX Flow spark gap,e.g. in DEHNventil® modularno follow current

25A32A

63A

100A

250A

NH-gGfuse linknominal current

20A

= minimum prearcing I2tvalues of the fuse link

I2 t of a sinusoidialhalf-wave (10 ms)

50

16A

400

200

0

-200

-400

U0

U (V)

70

35

0

0 5 10 15 20 25 t (ms)

I (kA)

0.5

0

0 10 15 t (ms)

I (kA)

mainsvoltage

arc voltage U

prospectiveshort circuitcurrent Ikpros

flowingfollow current If

Fig. 8.1.7.10 Reduction of the follow current with the patented RADAX Flow principle

Fig. 8.1.7.11 Disconnection selectivity of DEHNventil to NH fuse holders with different rated currents

Page 207: Lightning Protection Guide

8.2 Information technology systemsThe primary function of arresters is to protectdownstream terminal devices. They also reducethe risk of cables from being damaged.The choice of arresters depends, among otherthings, on the following considerations:

⇒ Lightning protection zones of the installationsite, if existing

⇒ Energies to be discharged

⇒ Arrangement of the protective devices

⇒ Immunity of the terminal devices

⇒ Protection against differential-mode and/orcommon-mode interferences

⇒ System requirements, e.g. transmission param-eters

⇒ Compliance with product or user-specific stan-dards, where required

⇒ Adaption to the environmental conditions /installation conditions

Protective devices for antenna cables are classifiedaccording to their suitability for coaxial, balanced

or hollow conductor systems, depending on thephysical design of the antenna cable.

In the case of coaxial and hollow conductor sys-tems, the outer conductor can generally be con-nected directly to the equipotential bonding.Earthing couplings specially adapted to the respec-tive cables are suitable for this purpose.

Procedure for selection and installation of arres-ters: Example BLITZDUCTOR CT

Opposite to choosing surge protective devices forpower supply systems (see Chapter 8.1), where uni-form conditions can be expected with respect tovoltage and frequency in 230/400 V systems, thetypes of signals to be transmitted in automationsystems differ with respect to their

⇒ voltage (e.g. 0 – 10 V)

⇒ current (e.g. 0 – 20 mA, 4 – 20 mA)

⇒ signal reference (balanced, unbalanced)

⇒ frequency (DC, NF, HF)

⇒ type of signal (analogue, digital).

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U in V500

400

300

200

100

100

200

300

400

500

600

700

800

t in μs

U in V500

400

300

200

100

100

200

300

400

500

600

700

800

t in μs

U in V500

400

300

200

100

100

200

300

400

500

600

700

800

t in μs

l in kA10

8

6

4

2

100

200

300

400

500

600

700

800

t in μs

l in kA10

8

6

4

2

100

200

300

400

500

600

700

800

t in μs

l in kA10

8

6

4

2

100

200

300

400

500

600

700

800

t in μs

SPD classification

B = Lightning current arresterIimp = 2.5 kA (10/350 μs)per line

B_ = Combined lightning currentand surge arresterIimp = 2.5 kA (10/350 μs)per line.However: voltage protectionlevel like surge arrester

M_ = Surge arresterIsn = 10 kA (8/20 μs)per line

BCT MLC _ _ _ _ _BCT MOD _ _ _ _ _

Voltage protection levelDischarge capacity

MLC = Arrester module with integrated LifeCheck (LC)MOD = Standard arrester module

Fig. 8.2.1 SPD classification

Page 208: Lightning Protection Guide

Each of these electrical characteristics for the sig-nal to be transmitted can contain the actual infor-mation to be transferred.Therefore, the signal must not be influenced intol-erably by the use of lightning current and surgearresters in measuring and control installations.Several points must be taken into account whenchoosing protective devices for measuring andcontrol systems. They are described below for ouruniversal BLITZDUCTOR CT protective devices andillustrated by means of application examples (Fig-ures 8.2.1 – 8.2.4 and Table 8.2.1).

Type designation of the protective modules

C Supplementary limiting of differential-modeinterferences and supplementary decouplingresistors in the BLITZDUCTOR CT output fordecoupling the BLITZDUCTOR protectivediodes from any diodes possibly present at theinput of the device to be protected (e.g.clamping diodes, optocoupler diodes)

HF Design for protection of high frequency trans-mission paths (use of a diode matrix for finelimiting of surges), limiting of common-modeand differential-mode interferences

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Up

Up

Up

E = Fine limiting ofsurgesline ⇒ earth(limiting ofcommon-modeinterferences)

D = Fine limitingof surgesline ⇒ line(limiting ofdifferential-modeinterferences)

SPD classification

MLC = Arrester module with integrated LifeCheck (LC)MOD = Standard arrester module

BCT MLC _ _ _ _ _BCT MOD _ _ _ _ _

1

2

3

4

1

2

3

4

_E = Voltage between line-earth

The indication of the nominal voltage characterises the range of atypical signal voltage which has no limiting effect on the protectivedevice under nominal conditions. The value of nominal voltage isindicated as d.c. value. Transmitting a.c. voltages, the peak value ofthe a.c. voltage must not exceed the nominal voltage value.

The nominal voltages for the individual types are indicated as follows:

_D = Voltage between line-line

_E C = Voltage between line-lineas well as line-earth

_D HF = Voltage between line-line

_D HFD = Voltage between line-line

_D EX = Voltage between line-line

SPD classification

BLITZDUCTOR CT

Uline-earth

BLITZDUCTOR CT

Uline-line

Type Nominal voltage UN

BCT MLC _ _ _ _ _BCT MOD _ _ _ _ _

C = Additional limiting of differenti-al-mode interferences and addi-tional decoupling resistors in theBLITZDUCTOR CT output for de-coupling the BLITZDUCTOR pro-tective diodes from eventuallyexisting diodes in the input ofthe device to be protected(e.g. clamping diodes, optocoup-ler diodes)

HF = Design for protection of high-frequency transmission lengths(use of a diode matrix for finelimiting of surges), limiting ofcommon-mode and differential-mode interferences

EX = Protective device for use inintrinsically safe circuits(a.c. voltage resistance toearth 500 V a.c.)

SPD classification

BCT MLC _ _ _ _ _BCT MOD _ _ _ _ _

Fig. 8.2.2 Limiting performance Fig. 8.2.3 Note on special applications

Fig. 8.2.4 Nominal voltage

Page 209: Lightning Protection Guide

EX Protective device for use in intrinsically safecircuits approved by, ATEX and FISCO (a.c. volt-age resistance to earth 500 V a.c.)

Technical Data:Voltage protection level UpThe voltage protection level is a parameter thatcharacterises the performance of a surge protec-tive device in limiting the voltage at its terminals.The voltage protection level must be higher thanthe maximum limiting voltage measured.The measured limiting voltage is the maximumvoltage measured at the terminals of the surgeprotective device when exposed to a surge currentand/or surge voltage of a certain waveform andamplitude.

Measured limiting voltage with a steepness of theapplied test voltage waveform of 1 kV/μsThis test is to determine the response characteris-tics of gas discharge tubes (GDT). These protectiveelements have a “switching characteristic”. Themode of functioning of a GTD can be compared toa switch whose resistance can “automatically“

switch from > 10 GΩ (in non-ignited state) to val-ues < 0.1 Ω (in ignited state) when a certain volt-age value is exceeded and the surge applied isnearly short circuited. The response voltage of theGDT depends on the steepness of the incomingvoltage (du/dt).

Generally applies:

The higher the steepness du/dt, the higher is theresponse voltage of the gas discharge tube. The

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Voltagedu/dt = 1 kV/μs

1

2

3

4

limiting voltage

rate of voltage risedu/dt = 1 kV/μs

U in V

1000900800700600500400300200100

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

t in μs

MLC B 110MLC BE 5MLC BE 12MLC BE 15MLC BE 24MLC BE 30MLC BE 48MLC BE 60MLC BE 110MLC BD 5MLC BD 12MLC BD 15MLC BD 24MLC BD 30MLC BD 48MLC BD 60MLC BD 110MLC BD 250MLC BE C 5MLC BE C 12MLC BE C 24MLC BE C 30MLC BD HF 5MLC BD HFD 5MLC BD HFD 24

MOD B 110MOD ME 5MOD ME 12MOD ME 15MOD ME 24MOD ME 30MOD ME 48MOD ME 60MOD ME 110MOD MD 5MOD MD 12MOD MD 15MOD MD 24MOD MD 30MOD MD 48MOD MD 60MOD MD 110MOD MD 250MOD ME C 5MOD ME C 12MOD ME C 24MOD ME C 30MOD MD HF 5MOD MD HFD 5MOD MD HFD 24

MOD MD EX 24MOD MD EX 30MOD MD EX HFD 6

B 1 ABE 1 ABD 1 ABE C 0.1 ABD HF 0.1 ABD HFD 0.1 A

ME 1 AMD 1 AME C 0.1 AMD HF 0.1 AMD HFD 0.1 AMD EX 0.5 AMD EX HFD 4.8 A

Table 8.2.1 Type designation of the protection modules

Fig. 8.2.5 Test arrangement for determining the limiting voltage at arate of voltage rise of du/dt = 1kV/μs

Fig. 8.2.6 Sparkover performance of an SPD at du/dt = 1kV/μs

Table 8.2.2 Nominal currents of the protection modules BCT

Page 210: Lightning Protection Guide

To the different types of protec-tion modules of BLITZDUCTORCT apply the nominal currentsaccording to Table 8.2.2:

Cut-off frequency fG

The cut-off frequency describesthe performance of an SPDdepending on the frequency. Itis that frequency which gives aninsertion loss (aE) of 3 dB undercertain test conditions (see EN61643-21)

If there is no other indication inthe catalogue, this frequencystated applies to a 50 Ohm sys-tem (Figure 8.2.10).

Selection features (SF)

1. Which discharge capacity isrequired?

The rating of the dischargecapacity of BLITZDUCTOR CT isdetermined by the protectivetask to be fulfilled. For easyselection, the following cases ato d are explained.

www.dehn.de LIGHTNING PROTECTION GUIDE 209

comparability of different gas discharge tubes ismade possible by applying a voltage rise of 1 kV/μsat the gas discharge tube for determination of thedynamic response voltage (Figures 8.2.5 and 8.2.6).

Measured limiting voltage at nominal dischargecurrentThis test is carried out to determine the limitingbehaviour of protective elements with constantlimiting characteristics (Figures 8.2.7 and 8.2.8).

Nominal current ILThe nominal current of BLITZDUCTOR CT charac-terises the permissible continuous operating cur-rent. The nominal current of BLITZDUCTOR CT isdetermined by the current carrying capability andthe insertion loss of the impedances used fordecoupling of gas discharge tubes and fine protec-tion elements as well as by the follow currentextinguishing capability. The value is stated as d.c.value (Figure 8.2.9).

Case a: In this case the terminal equipment to beprotected is located in a building structure with anexternal lightning protection system or the roof ofthe building is equipped with metal roof structuresexposed to lightning (e.g. antenna masts, air-con-ditioning systems). The measuring and control ortelecommunications cable connecting the terminalequipment (Figure 8.2.11) to the transformer ismounted outside the building structure. Due tothe fact that the building structure is fitted with anexternal lightning protection, the installation of alightning current arrester TYPE 1 is necessary. Themodules BCT MLC B... or B... of the BLITZDUCTORCT family can be used for this purpose.

Case b: Case b is similar to case a, only the buildingstructure, where the terminal equipment to beprotected is located, has no external lightning pro-tection system: The arising of lightning currents orpartial lightning currents is not assumed here. Theinstallation of a lightning current carrying capable

U in V

60

40

20

0

−20

−40

−60

0 10 20 30 40 50 60 70 80 90 100

t in μs

limiting voltage

1

2

3

4

BLITZDUCTOR CTIL

aE in dB

f in Hz

3 dB

fG

1

2

3

4

current isn

Fig. 8.2.7 Test arrangement for determiningthe limiting voltage at nominaldischarge current

Fig. 8.2.8 Limiting voltage at nominal dis-charge current

Fig. 8.2.9 Nominal current of BLITZDUCTORCT

Fig. 8.2.10 Typical frequency response of aBLITZDUCTOR CT

Page 211: Lightning Protection Guide

Type 1 arresters is only necessary if the measuringand control cable can be influenced by lightningstriking adjacent building structures. If this can beexcluded, BLITZDUCTOR CT module BCT MOD M...as surge protective device TYPE 2 is used (Figure8.2.12).

Case c: In case c, no cable of the data and telecom-munications system is mounted outside the build-ing. Although the building structure is fitted withan external lightning protection system, directlightning currents cannot be injected into this partof the telecommunications system. Therefore,

surge protective devices BCT MOD M... of theBLITZDUCTOR CT family are installed here (Figure8.2.13).

Case d: The difference between case d and case c isthat the building structure concerned has neitheran external lightning protection system nor arecables of the data and telecommunications systemmounted outside the building structure. Thereforeonly the installation of surge arresters is necessaryfor protection of the equipment. As in cases b andc, protection modules BCT MOD M... of the BLITZ-DUCTOR CT family are installed (Figure 8.2.14).

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SPD

terminal device

Case b:

measuring/control cabletelecommunications cable

external lightning protection system

terminal deviceSPD

transducer

Case c:

terminal deviceSPD

transducer

Case d:

measuring/control cabletelecommunications cable

terminal device

SPD

external lightning protection systemCase a:

Fig. 8.2.11 Building with external lightning protection system andcables installed between buildings

Fig. 8.2.12 Building without external lightning protection systemand cables installed between buildings

Fig. 8.2.13 Building with external lightning protection system andcables installed inside of the building

Fig. 8.2.14 Building without external lightning protection systemand cables installed inside of the building

Page 212: Lightning Protection Guide

2. Which kinds of interferences have to be con-trolled?

Basically, interferences are classified into common-mode and differential-mode interferences. Com-mon-mode interferences always arise between thesignal line and earth whereas differential-modeinterferences only arise between two signal lines.The majority of interferences arising in communi-cation/signalling systems are common-mode inter-ferences. Therefore protective surges devices limit-ing between signal line and earth (Type ...E) shouldnormally be chosen. Some input modules ofdevices, as e.g. isolating transformers, do not needfine protection of the line-to-earth connectionagainst surges. Only gas discharge tubes protectthem against common-mode interferences. Due to their different response characteristics, theresponse of gas discharge tubes might cause acommon-mode interference to change to a differ-ential-mode interference. Therefore, fine protec-tion elements are integrated between the signallines (Type ...D).

3. Are there special requirements to adopt theprotection circuit to the input circuit of theequipment to be protected?

In some cases it is necessary to protect the equip-ment against common-mode and differential-mode interferences. The input modules of suchelectronic equipment are normally fitted withtheir own protection circuit or contain optocou-pler inputs for control-to-load isolation of sig-nalling circuit and internal circuit of the automa-tion equipment. Therefore additional measuresare required for decoupling BLITZDUCTOR CT andinput circuit of the equipment to be protected.This decoupling is realised with additional decou-pling elements between the fine protection ele-ments and output terminals of BLITZDUCTOR CT.

4. How high is the signal frequency/data trans-mission rate to be transmitted?

As every transmission system, the protection circuitof BLITZDUCTOR CT has certain low-pass character-istics. The cut-off frequency indicates the frequen-cy value from which the frequency to be transmit-ted is attenuated in its amplitude (above 3 dB). Inorder to keep the feedback effects of BLITZDUC-TOR CT on the communication/signalling system inthe limits, the signal frequency of the signallingcircuit must be below the cut-off frequency ofBLITZDUCTOR CT. The cut-off frequency is indicat-

ed for sinusoids. However, sinusoid signals are notvery common in data transmissions. With respectto this fact, a BLITZDUCTOR is to be chosen with ahigher cut-off frequency than the nominal fre-quency of the signalling circuit. When transmittingwaveshape signals evaluating the rising or sinkingpulse edge, it must be considered that this edgechanges from L to H or from H to L within theappropriate interval. This time interval is impor-tant for the identification of an edge and for passing “restricted areas“. This signal thereforerequires a frequency bandwidth which is consider-ably higher than the fundamental of this wave.That is why the frequency of the protective devicemust be rated that high. As a general rule appliesthat the cut-off frequency must not be lower thanfive times the fundamental wave.

5. How high is the operating current of theinstallation to be protected?

Due to the electrical features of the componentsused in the protection circuit of BLITZDUCTOR CT,the signal current which can be transmitted by theprotective device is limited. For practical applica-tions this means that the operating current of asignalling system has to be lower than or equal tothe nominal current of the protective device.

6. Which maximum continuous operating volt-age can arise in the installation to be protect-ed?

The maximum continuous operating voltage in sig-nalling systems must be lower than or equal to thenominal voltage of BLITZDUCTOR CT, so that theprotective device has no limiting effects with nor-mal operating conditions. The maximum continuous operating voltage in sig-nalling systems is normally the nominal voltage ofa transmission system regarding also tolerances.When current loops (e.g. 0 – 20 mA) are used, theopen circuit voltage of the installation is to beapplied to the maximum continuous operatingvoltage.

7. Which reference has the maximum continuousoperating voltage?

Different signal current circuits have different sig-nal references (balanced /unbalanced). On onehand, the continuous operating voltage of theinstallation can be stated as line/ line voltage, onthe other hand, as line/earth voltage. This is to be

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Page 213: Lightning Protection Guide

considered when choosing the protective devices:Different nominal voltages are stated on the basisof the different circuit of the fine protection ele-ments in the protection module of BLITZDUCTORCT. These are shown in Figure 8.2.4 and Table 8.2.1.

8. Do the integrated decoupling elements ofBLITZDUCTOR CT affect the signal transmis-sion?

Decoupling elements are used inside of BLITZDUC-TOR CT in order to coordinate the energy load of the integrated protection elements. They aremounted directly in the signalling circuit and may influence it. Especially with current loops (0 ... 20 mA, 4 ... 20 mA), the operation of a BLITZ-DUCTOR CT can cause the overrange of the permis-sible load of the signalling circuit when it is alreadyoperated with its maximum load. This has to beconsidered before use!

9. Which protection level is required?Basically it is possible to dimension the protectivelevel of a surge protective device to be lower thanthe immunity level of an automation/telecommu-nications equipment. However, the problem is thatthis level is often unknown. Therefore it is neces-sary to use other means of comparison. In the testsfor electromagnetic compatibility (EMC), electricaland electronic equipment must have a certainimmunity level against line-conducted interfer-ences. The requirements for testing and test set-upare stipulated in IEC 61000-4-5: 2005. Different testlevels are determined with respect to the immuni-ty to pulse-shaped interferences for the variousdevices used under varying electromagnetic envi-ronmental conditions. These test levels bear thedesignation 1 to 4, whereby test level 1 containsthe lowest immunity requirements (on the devicesto be protected) and test level 4 ensures the high-est immunity requirements of a device.

With regard to the protection provided by thesurge protective devices this means that the “let-through energy“ must be below the immunity lev-el of the equipment to be protected. Therefore theYellow/Line devices were classified according tocertain characteristics allowing a coordinatedinstallation of the SPDs for protection of automa-tion engineering equipment. The surge immunitytest of this equipment was taken as a basis of

determining Yellow/Line SPD class symbols (Table7.8.2.1). If, for example, automation engineeringequipment is tested according to test level 1, theequipment may only have a let-through energycorresponding to this test level. In practice thismeans that an equipment tested with level 4 canonly discharge overvoltages without damagingthe equipment if the output of the surge protec-tive device corresponds to a let-through energy of1, 2, 3, or 4. This makes it very easy for the user tochoose suitable protective devices.

10. Shall there be one or two stages ofprotection?

Depending on the building structure and the pro-tection requirements stipulated by the LightningProtection Zones Concept it may be necessary toinstall lightning current and surge arresters locallyseparated from each other or at one point of theinstallation. In the first case, the protection mod-ule Type BCT MLC B of BLITZDUCTOR CT is installedas lightning current arrester and the protectionmodule Type BCT MOD M... as surge arrester. Iflightning and surge protective measures arerequired at one point of the installation, the use ofa combined lightning current and surge arresterBLITZDUCTOR CT, Type B... is required.

Remark:The following examples show the choice of surgeprotective devices of the BLITZDUCTOR CT familyin accordance with the 10 selection featuresdescribed in Table 8.2.3. The result of each singlestage is indicated in the column “intermediateresult“.The column “final result” shows the influence ofthe intermediate result on the total result.

Surge protection for electrical temperature controlsystemsThe electrical temperature control of media intechnological processes is applied in all branchesof industry. The branches differ a lot from eachother: They stretch from food industry via chemicalprocesses up to ventilation systems of buildingstructures and building services control systems.However, they have something in common: thedistance between measuring sensor and indicatoror measured-value processing is long. Due to thelong connection cables, overvoltages can be cou-pled which are not only caused by atmospheric dis-charges. Therefore a possible protection concept

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SF Application Intermediate result Final result

1

2

3

4

5

6

7

8

9

10

The measuring sensor is situated at a process framework in a production hall andthe measuring transducer is installed in a control room inside of the productionbuilding. The building has no external lightning protection system. The measuringlines are inside the building. This example corresponds to case d (Figure 8.2.14).

BLITZDUCTOR CTBCT MOD M...

BLITZDUCTOR CTBCT MOD M...

The threat to the measuring sensor Pt 100 as well as the measuring transducer Pt 100 by surges arises between signal line and earth. This requires a finelimiting of common-mode interferences.

BLITZDUCTOR CTBCT MOD ME

BLITZDUCTOR CTBCT MOD ME

There are no special requirements on the adjustment of the protective circuit to theinput circuit of the devices to be protected (Pt 100, Pt 100 measuring transducer). no influence

BLITZDUCTOR CTBCT MOD ME

The temperature measuring equipment is a system supplied by d.c. current. Thetemperature-related measuring voltage is also a d.c. voltage variable.Thus no signal frequencies have to be considered.

no influenceBLITZDUCTOR CTBCT MOD ME

The operating current of the supply circuit is limited to 1 mA due to the physicalmeasuring principle of Pt 100. The operating current of the measuring signal amountsto some μA due to the very high impedance measurement tapping.

IL type ME = 1 A1 mA < 1 A ⇒ okμA < 1 A ⇒ ok

BLITZDUCTOR CTBCT MOD ME

The maximum arising operating voltage in this system results from the followingconsideration:According to IEC 60751, Pt 100 measuring resistors are designed for a maximumtemperature of up to 850 °C. The respective resistance is 340 Ω. Considering theload-independent measuring current of 1 mA, results a measuring voltage of approx.340 mV.

BLITZDUCTOR CTBCT MOD ... 5 V

BLITZDUCTOR CTBCT MOD ME 5

The operating voltage of the system arises from line to line. BCT MOD ME 5 Vhas nominal voltage 5 V d.c.line ⇒ earth, this allows line ⇒line 10 V d.c. ⇒ no influence onthe measuring signal

BLITZDUCTOR CTBCT MOD ME 5

Using the four-wire circuit for measuring the temperature with Pt 100, the influenceof the cable resistance and its temperature-related fluctuations on the measuringresult are completely eliminated. This also applies to the increasing of the cableresistance by the decoupling impedances of BLITZDUCTOR CT.

no influenceBLITZDUCTOR CTBCT MOD ME 5

The Pt 100 measuring transducer has an immunity against conducted interferencesaccording to test level 2 according to IEC 61000-4-5: 2005. The “transmitted energy”being related to the voltage protection level of the surge protective device maycorrepond to max. test level 2 of IEC 61000-4-5: 2005.

BLITZDUCTOR CTBCT MOD ME 5Q

“transmitted energy” correspondsto level 1

“transmitted energy” of the pro-tective device is less than immunityof the terminal device

⇒ Q is okBLITZDUCTOR CTBCT MOD ME 5

The surge protection shall be performed in one stage. BLITZDUCTOR CTBCT MOD ME 5⇒ surge arrester

BLITZDUCTOR CTBCT MOD ME 5

Result of selection: BLITZDUCTOR CTBCT MOD ME 5

Table 8.2.3 Selection features for an electrical temperature measuring equipment

Page 215: Lightning Protection Guide

of temperature measurements against surges by astandard type Pt 100 shall be worked out in thefollowing. The building structure where the meas-uring instrument is located has no external light-ning protection system.

The temperature is controlled indirectly by meas-uring the electrical resistance. The resistance ther-mometer Pt 100 has a resistance of 100 Ω at 0 °C.This value varies by around 0.4 Ω/K depending onthe temperature. The temperature is controlled byinjecting a constant current causing a voltage dropproportional to the temperature rise at the resist-ance thermometer. In order to prevent the the self-heating of the resistance thermometer, the currentis limited to 1 mA. In this case, a voltage drop of100 mV appears at the Pt 100 at 0 °C. This meas-ured voltage must now be transmitted to the indi-cator or receiver (Figure 8.2.15). Out of many vari-ous connections of Pt 100 measuring sensors to themeasuring transformer, the four-wire configura-tion is chosen. It represents the best connection forresistance thermometers. By this configuration,the interfering effects of the conductor resistanceand its temperature sensitivity on the measuredresult are excluded. The Pt 100 sensor is suppliedwith an injected current. Alternations of the con-ductor resistance are compensated by automaticadjustment of the supply voltage. If the conductorresistance does not alter, the measured voltage Umremains unchanged. This measured voltage is onlyinfluenced by the alternation of the measuringresistance depending on the temperature. It ismeasured at the transformer using a high-resist-ance voltage detector. Line compensation is there-fore not necessary with this configuration. (Table8.2.3)

Remark:For ease of assembly, power supply and measuringlines of the temperature control system are fittedwith the same type of surge protective device. Inpractice it has proved that the balanced lines forsupply, compensation and measurement are allo-cated to one protected device each (Table 8.2.3).Surge protection of the 230 V power supply of thePt 100 receiver as well as the 4 ... 20 mA currentloop coming from the receiver is also necessary butnot shown here in order to retain clearness.

8.2.1 Measuring and control systems

The large separations between the measuring sen-sor and the evaluation unit in measuring and con-trol systems allow a coupling of surges. The conse-quential destruction of components and thebreakdown of complete control units can severelyinterfere with a process technology procedure.The extent of a surge damage caused by a light-ning strike often becomes apparent only someweeks later because more and more electroniccomponents have to be replaced because they nolonger operate safely. Such kind of damage canhave serious consequences for the operator whouses a so-called field bus system because all intelli-gent field bus components together in one seg-ment can break down simultaneously.The situation can be improved by installing light-ning and surge protective devices (SPDs) whichhave to be chosen to suit the specific interface.Typical interfaces and the protective devicesappropriate to the system can be found in our“Surge Protection” product catalogue or atwww.dehn.de.

www.dehn.de214 LIGHTNING PROTECTION GUIDE

feed-in (l = const.)

measuring signal (Um / ϑ)

measuring sensorPt 100

connecting line Pt 100 measuring transducer

ϑ

Pt 100

4 ... 20 mA

4 ... 20 mA

230 V supply

Fig. 8.2.15 Block diagram of temperature measuring

Page 216: Lightning Protection Guide

Electrical isolation using optocouplers:

Optoelectronic components (Figure 8.2.1.1), whichtypically produce a dielectric strength between theinput and output of a few 100 V to 10 kV, are fre-quently installed to transmit signals in processtechnology systems in order to isolate the fieldside electrically from the process side. Thus theirfunction is similar to that of transmitters and theycan primarily be installed to block low common-mode interferences. However, they cannot providesufficient protection against arising common-mode and differential-mode interferences. Whenbeing affected by a lightning strike (> 10 kV)above their transmitter / receiver surge withstandcapability.

Many designers and operators of such installationsmisleadingly assume that this also realises light-ning and surge protection. At this point it isexpressly emphasised that this voltage only pro-vides the insulating resistance between input andoutput (common-mode interference). This meansthat, when installed in transmission systems atten-tion must be paid not only to the limitation ofcommon-mode interferences but also to sufficientlimitation of differential-mode interferences. Fur-thermore, the integration of supplementarydecoupling resistors at the output of the SPDachieves an energy coordination with the opto-coupler diode.

Hence, in this case, common-mode and differen-tial-mode interference limiting SPDs, e.g. BLITZ-DUCTOR XT Type BXT ML BE C 24, must be in-stalled.Detailed designs for the application-specific choiceof protective devices for measuring and controlsystems can be found in Chapter 9.

8.2.2 Technical property managementThe pressure of rising costs is forcing the ownersand operators of buildings in both the public andthe private sector to look more and more for costsaving opportunities for building services manage-ment. Technical property management can help toreduce costs on a permanent basis. Technical prop-erty management is a comprehensive instrumentto make technical equipment in buildings continu-ously available, to keep it operative and to adapt itto changing organisational requirements. Thisfacilitates optimum management which increasesthe profitability of a property.

Building automation (BA) has grown out of meas-uring and control systems on the one hand, andcentral control systems on the other. The functionof building automation is to automate the techni-cal processes within the building in their entirety.This involves networking the complete installationcomprising room automation, the M-bus measur-ing system and the heating-ventilation-air-condi-tioning and alarm systems via powerful computerson the management level (Figure 8.2.2.1), wherealso data archiving takes place. Long term datastorage allows evaluations concerning the energyconsumption and the adjustment of the installa-tions in the building to be obtained.

The actual control devices are at the automationlevel. DDC stations (Direct Digital Control) areincreasingly being installed. They implement thecomplete control and switching functions from asoftware point of view. All operating modes, con-trol parameters, nominal values, switching timesand alarm trigger levels and the correspondingsoftware is filed at the automation level.Process field devices such as actuators and sensorsare located at the lowest level, the field level. Theyrepresent the interface between the electrical con-trol and the process. Actuators transform an elec-trical signal into another physical value (engines,valves, etc.). Sensors transform a physical value

www.dehn.de LIGHTNING PROTECTION GUIDE 215

Fig. 8.2.1.1 Optocoupler – Schematic diagram

1

2

3

4

input current IF output current IC

radiation

transmitter

receiver

optical fibresubstrate

sheathing

connections3, 4

connections 1, 2

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into an electrical signal (temperature sensor, limitswitch, etc.).

It is precisely the diffuse branched network of DDCstations and the consequential integration intobuilding control systems which offer a large con-tact area for interferences caused by lightning cur-rents and surges. If this causes a breakdown of thecomplete lighting, air-conditioning or heatingcontrol, this not only incurs primary costs for theequipment, it is also precisely the consequences ofthis system breakdown which make a difference.They can significantly increase the energy costsbecause peak loads can no longer be analysed andoptimised due to the fault in the control electron-ics. If production processes are integrated into theBA, damage to the BA can lead to breakdowns inproduction and hence quite possibly to large eco-nomic losses. To ensure permanent availability,protective measures are required, whose exactnature depends on the risk to be controlled.

8.2.3 Generic cabling systems (EDP net-works, TC installations)

The European standard EN 50173 “Informationtechnology – Generic cabling systems” defines auniversal cabling system which can be used in sitesof one or more buildings. It deals with cable sys-tems with balanced copper cables and optical fibrecables (OF cables). This universal cabling supports awide range of services including voice, data, textand images.

It provides:

⇒ users with an application independent genericcabling system and an open market for (activeas well as passive) cabling components;

⇒ users with a flexible cabling scheme thatallows to carry out modifications in a botheasy and economical way;

⇒ building professionals (for example, architects)with guidance allowing the accommodation

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management level

automation level

field level

Fig. 8.2.2.1 Levels of building automation

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of cabling before specific requirements areknown; i.e. in the initial design stage either forconstruction or refurbishment,

⇒ industry and standardisation bodies for appli-cations with a cabling system which supportscurrent products and provides a basis forfuture product development.

The universal cabling system comprises the follow-ing functional elements:

⇒ Campus distributors (CD),

⇒ Campus backbone cables,

⇒ Building distributors (BD),

⇒ Building backbone cables,

⇒ Floor distributors (FD),

⇒ Horizontal cables,

⇒ Transition points (optional),

⇒ Telecommunication outlet (TO).

Groups of these functional elements are connect-ed together to form cabling subsystems.Generic cabling schemes contain three cabling sub-systems: campus backbone, building backbone andhorizontal cabling. The cabling subsystems areconnected together to create a generic cablingstructure as shown in Figure 8.2.3.1. The distribu-tors provide the means to configure the cabling tosupport different topologies like bus, star andring.The campus backbone cabling subsystem extendsfrom the campus distributor to the building dis-tributor(s) usually located in separate buildings.When present, it includes the campus backbonecables, the mechanical termination of the campusbackbone cables (at both the campus and building

distributors) and the cross-connections at the cam-pus distributor.

A building backbone cabling subsystem extendsfrom building distributor(s) to the floor distribu-tor(s). The subsystem includes the building back-bone cables, the mechanical termination of thebuilding backbone cables (at both the buildingand floor distributors) and the cross connections atthe building distributor.

The horizontal cabling subsystem extends from thefloor distributor to the telecommunications out-let(s) connected to it. The subsystem includes thehorizontal cables, the mechanical termination ofthe horizontal cables at the floor distributor, thecross connections at the floor distributor and thetelecommunications outlets.

Optical fibre cables are usually used as data con-nection between the CD and the BD. This meansthat no surge arrester (SPD) is required for thefield side. If, however, the OF cables have a metalrodent protection, this must be integrated into thelightning protection system. The active OF compo-nents for the distribution of the optical fibrecables, however, are supplied with 230 V on thepower side. In this case, SPDs can be used for thepower supply system.

Nowadays, building backbone cables (BD to FD)are equipped almost exclusively with OF cables forthe transmission of data. Balanced copper cables(so-called master cables), however, are still used totransmit voice (telephone).With a few exceptions, balanced copper cables areused today for the horizontal cables (FD to TO).

www.dehn.de LIGHTNING PROTECTION GUIDE 217

Fig. 8.2.3.1 Universal cabling structure

CD BD FD TP(optionally)

TO

terminaldevice

universal cabling system

campus backbonecabling subsystem

building backbonecabling subsystem

horizontalcabling subsystem terminal cabling subsystem

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For cable lengths of around 500 m (building back-bone cables) or 100 m (horizontal cables) directlightning strikes to the structure (Figure 8.2.3.2)can induce common-mode interferences whichwould overload the insulation capacity of a routeror an ISDN card in the PC. Both the building/floordistributors (hub, switch, router) and the terminalequipment must be equipped with protectivemeasures in this case.

The protective devices required here must be cho-sen according to the network application. Com-mon network applications are:

⇒ Token Ring,

⇒ Ethernet 10 Base T,

⇒ Fast Ethernet 100 Base TX,

⇒ Gigabit Ethernet 1000 Base TX.

An appropriate protection concept for choosingthe appropriate protective devices can be found inChapter 9.11 “Surge protection for ETHERNET net-works”.

8.2.4 Intrinsically safe circuitsIn all fields of industry where combustible materi-als are processed or transported gases, vapors, mistor dust will be produced. These, when mixed withair, can form a potentially explosive atmosphere ofhazardous proportions. Therefore special meas-ures must be taken to protect against explosions.

Depending on the possibility and the duration ofthe occurrence of a potentially explosive atmos-phere, sections of the installation are divided intohazardous areas – so-called Ex-zones.

Hazardous areas:Areas where hazardous potentially explosiveatmospheres arise due to gases, vapors and mist,for example, are divided into zones 0 to 2. Thosewhere hazardous potentially explosive atmos-pheres can arise due to dust are divided into zones20, 21 or 22.Explosion groups I, IIA, IIB and IIC provide a systemof classification according to the explosiveness ofthe combustible materials used in the respective

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IT cabling 100 Ω (Cat. 3, 5, 6, ...)

Horizontal cabling system– Connecting lead between FD and TO– Transmission characteristics up to

250 MHz, (Category 6)

TO Telecommunication outletFD Floor distributorBD Building distributor

Building backbone cabling subsystem– Connecting lead between BD and FD

optical fibre cabling (data)

copper cabling (telecommunications)

OF cabling

externallightningprotection

TO

FD

FD

TOTO FD

FD

FD

BD SD

Fig. 8.2.3.2 Influence of lightning on IT cabling subsystems

Page 220: Lightning Protection Guide

field of application. Classification criteria are the“Maximum Experimental Safe Gap (MESG)“ andthe “Minimum Ignition Current (MIC)”. The MESGand MIC are determined for the various gases andvapors according to a stipulated testing arrange-ment.Explosion group IIC contains the most highly com-bustible materials such as hydrogen and acetylene.When heated, these materials have different igni-tion temperatures classified into temperatureclasses (T1 ... T6).To avoid electrical equipment from being sourcesof ignition in explosive atmospheres, these aredesigned with different types of protection. Onetype of protection used all over the world, particu-larly in measuring and control systems, is the typeof protection “Intrinsic safety” Ex(i).

Ignition protection type – intrinsic safety:Intrinsic safety being a type of protection is basedon the principle of current and voltage limitationin an electric circuit. With this system, the energyof the circuit or a part of the circuit, which is in aposition to ignite potentially explosive atmos-pheres, is kept so low to ensure that neither sparksnor intolerable surface heating of the electricalcomponents can cause an ignition of the surround-ing potentially explosive atmosphere. Apart fromvoltages and currents of the electrical equipment,the inductances and capacitances in the completecircuit acting as energy storage devices must belimited to safe maximum values.For the safe operation of a measuring and controlsystem circuit, for example, this means that neitherthe sparks arising during the operational openingand closing of the circuit (e.g. at a make-or-breakcontact in an intrinsically safe circuit), nor thosearising in the event of a fault (e.g. a short circuit orearth fault) must be capable of causing an igni-tion. Moreover, both for normal operation andalso in the event of a fault, heat ignition as a resultof overheating of the equipment and cables in theintrinsically safe circuit, must also be excluded.This basically limits intrinsic safety as a type of pro-tection to circuits requiring relatively little power.These are circuits of measuring and control systemsand also data systems. Intrinsic safety which can beachieved by limiting the energies available in thecircuit does not relate to individual devices – as isthe case with other types of protection – but to thecomplete circuit. This produces a number of con-

siderable advantages compared to other types ofprotection.

Firstly, no expensive special constructions arerequired for the electrical equipment used in thefield, for example flame-proof encapsulation orembedding in cast resin, which results mainly inmore cost-effective solutions. Another advantageis that the intrinsic safety is the only type of protec-tion which allows the user to work freely at all liveintrinsically safe installations in a hazardous areawithout having an adverse effect on the protec-tion against explosion.

The economic advantage of using intrinsically safecircuits lies in the fact that, even in the hazardousareas, conventional non-certified passive equip-ment can be used. Thus this type of protection isalso one of the simplest types of installation.

Intrinsic safety has therefore considerable signifi-cance, particularly in measuring and control sys-tems, not least because of the increased use ofelectronic automation systems. However, intrinsicsafety demands more from the designer or con-structor of an installation than other types of pro-tection. The intrinsic safety of a circuit not onlydepends on compliance with the design provisionsfor the individual pieces of equipment, but also onthe correct connection of all equipment in theintrinsically safe circuit and the correct installation.

Transient surges in hazardous areas:

Intrinsic safety as type of protection considers allelectrical energy storage devices present in the sys-tem but not energy from outside, such as coupledsurges resulting from atmospheric discharges.

Coupled surges come up in expanded industrialinstallations mainly as a result of close and distantlightning strikes. In the event of a direct lightningstrike, the voltage drop across the earth-termina-tion system causes a potential rise between some10 and 100 kV. This potential rise acts as a poten-tial difference on all equipment connected viacables to distant equipment. These potential dif-ferences are considerably greater than the insula-tion resistance of the equipment and can easily besparked over. For distant lightning strikes it ismainly the coupled surges in conductors that candestroy the inputs of electronic equipment by act-ing as differential-mode interferences (differentialvoltage between the lines).

www.dehn.de LIGHTNING PROTECTION GUIDE 219

Page 221: Lightning Protection Guide

Classification of electrical equipment into catego-ry ia or ibAn important aspect of intrinsic safety for explo-sion protection is the issue of the reliability withrespect to maintaining of voltage and current lim-its, even assuming certain faults. There are twocategories of reliability.Category ib specifies that the intrinsic safety mustbe maintained if a fault occurs in the intrinsicallysafe circuit.Category ia requires that the intrinsic safety mustbe maintained if two independent faults occur.

The classification of the BLITZDUCTOR CT or DEHN-connect DCO as category ia is the classification inthe highest category. This means that the BLITZ-DUCTOR may also be used with other equipmentlocated in zones 0 and 20. Extra attention must bepaid to the special conditions of zones 0 and 20and clarified in each individual case.

Figure 8.2.4.1 shows the principle use of SPDs inmeasuring and control circuits

Maximum values of current I0 , voltage U0 ,inductance L0 and capacitance C0At the interface between hazardous area and safearea, safety barriers or transmitters with Ex(i) out-put circuit are used to separate these two differentzones.The safety-related maximum values of a safety bar-rier or a measuring transformer with Ex(i) outputcircuit are defined by the test certificates of anauthorised testing laboratory:

⇒ Maximum output voltage U0

⇒ Maximum output current I0⇒ Maximum external inductance L0

⇒ Maximum external capacitance C0

The designer/constructor must test whether thesesafety-related permissible maximum values of theequipment connected and located in the intrinsi-cally safe circuit (i.e. process field devices, conduc-tors and SPD) are maintained for each individualcase. The corresponding values have to be takenfrom the rating plate of the pertinent equipmentor the type examination certificate.

Classification in explosion groupsExplosive gases, vapors and mist are classifiedaccording to the spark energy required to ignitethe most explosive mixture with air. Equipment is classified according to the gaseswhich it can be used with.Group II C applies to all fields of application, e.g.chemical industry, coal and grain processing, withexception of underground mining.Group II has the highest risk of explosion, since thisgroup considers a mixture with the lowest ignitionenergy.The certification of BLITZDUCTOR for explosiongroup II C means that it fulfils the highest, i.e. mostsensitive, requirements for a mixture of hydrogenin air.

Classification into temperature classesWhen a potentially explosive atmosphere is ignit-ed as a result of the hot surface of a piece of equip-

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1’

2’

1

2

1

2

1’

2’

1’

2’

1

2

1

2

1’

2’

measuring transfor-mer with Ex(i) input(max. perm. Lo , Co)

BLITZDUCTOR® BLITZDUCTOR®

MT

transmitter

EB/PE EB/PE

non-hazardous area hazardous area MC circuit Ex(i)

signal line

Lo LBXT + LLtg + LBD + LGe Co CBXT + CLtg + CBXT + CGe + C

BLITZDUCTOR® XT BLITZDUCTOR® XT

LBXT

CBXT

LLtg

C

LBXT

CBXTCLtg

LGe

CGe

C

Fig. 8.2.4.1 Calculating of L0 and C0

Page 222: Lightning Protection Guide

ment, a minimum temperature specific to thematerial is required to cause the explosion. Theignition temperature is a characteristic of thematerial characterising the ignition behaviour ofthe gases, vapors or dust on a hot surface. For eco-nomic reasons, gases and vapors are therefore clas-sified into certain temperature classes. Tempera-ture class T6 specifies that the maximum surfacetemperature of the component must not exceed85 °C either in operation or in the event of a fault,and that the ignition temperature of the gases andvapors must be higher than 85 °C. With its T6 classification, BLITZDUCTOR CT also ful-fils the highest stipulated requirements in thisaspect.

In accordance with the certificate of conformityissued by KEMA, the following electrical parame-ters must also be taken into consideration.

Selection criteria for SPD – BLITZDUCTOR XTUsing the example of BLITZDUCTOR XT, BXT ML4BD EX 24, the specific selection criteria for thiscomponent are explained below (Figures 8.2.4.2aand 8.2.4.2b).This component has already a certificate of con-formity issued by KEMA.

The SPD has the following classification:

II 2(1) G EEx ia IIC T4 ,T5, T6

This classification states the:

II Group of devices – the SPD may be used inall fields apart from mining.

2(1) G Device category – the SPD may be installedin potentially explosive gas atmospheres in

zone 1 and also in conductors from zone 0(to protect terminal devices in zone 0)

EEx Testing laboratory certifies that this electri-cal equipment conforms to the harmonisedEuropean standards.

EN 50014: General Principles

EN 50020: Intrinsic safety “i”

BLITZDUCTOR CT equipment has passed atype examination successfully.

ia Type of protection – the SPD controls even acombination of two arbitrary faults in anintrinsically safe circuit without causingignition itself.

IIC Explosion group – the SPD fulfils therequirements of explosion group IIC andmay also be used with ignitable gases suchas hydrogen or acetylene.

T4 between -40 °C and +80 °C

T4 between -40 °C and +75 °C

T6 between -40 °C and +60 °C

Further important electrical data:

⇒ Maximum external inductance L0 and maxi-mum external capacitance (C0):

The special choice of components in BLITZ-DUCTOR XT means that the values of the inter-nal inductance and capacitance of the variousindividual components are negligibly small.

⇒ Maximum input current (Ii):

The maximum permissible current which maybe supplied via the connections is 500 mA,without overriding the intrinsic safety.

www.dehn.de LIGHTNING PROTECTION GUIDE 221

1

2

3

4

1’

2’

3’

4’

BLITZDUCTOR®XT

1

2

3 3´

4 4´

protected

circuit application example

protectedintrinsically safeequipment

KEMA 06 ATEX 0274 XII 2(1) G EEx ia IICT4 / T5 / T6

Fig. 8.2.4.2a Intrinsically safe SPD Fig. 8.2.4.2b Schematic diagram of BXT ML4 BD EX 24

Page 223: Lightning Protection Guide

⇒ Maximum input voltage (Ui):

The maximum voltage which may be appliedto BLITZDUCTOR XT is 30 V, without overridingthe intrinsic safety.

Insulation resistanceThe insulation between an intrinsically safe circuitand the frame of the electrical equipment or othercomponents which can be earthed must usually beable to withstand the root mean square value ofan a.c. test voltage which is twice as high as thevoltage of the intrin-sically safe circuit, or500 V, whichever val-ue is higher.

Equipment with aninsulation resistance < 500 V a.c. is consid-ered to be earthed. Intrinsically safe equip-ment (e.g. cables, sen-sors, transmitters) ge-nerally have an insu-lating strength > 500 Va.c. (Figure 8.2.4.3).

Intrinsically safe circuits must be earthed if this isrequired for safety reasons. They may be earthed ifthis is required for functional reasons. This earth-ing must be carried out at only one point by con-nection with the equipotential bonding. SPDs witha d.c. sparkover voltage to earth < 500 V d.c. repre-sent an earthing of the intrinsically safe circuit.

If the d.c. sparkover voltage of the SPD is > 500 Vd.c., the intrinsically safe circuit is considered to benon-earthed. This requirement corresponds toBLITZDUCTOR XT, BXT ML4 BD EX 24.

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1

2

1 2

3

3 3

3

4

4 4 4

protected

protected

protected

Segment 1

Segment 2

Power supply (Fisco); Segment 1 / 2

Blitzductor BXT ML4 BD EX 24

Field device (Fisco)

Terminator

prot

ecte

d

Fieldbus FISCOPower supplyUo ≤ 17.5 V,Io ≤ 380 mA

Field deviceUi ≤ 17.5 V, Ii ≤ 380 mA,Pi ≤ 5.32 W, Ci ≤ 5 nF,Li ≤ 10 mH

1

2

3

4

1’

2’

3’

4’

BLITZDUCTOR®XT

1

2

3 3´

4 4´

protected

circuit application example

Fig. 8.2.4.3 SPD in hazardous location – Insulation resistance > 500 V a.c.

Fig. 8.2.4.4 Application – Insulation resistance < 500 V a.c.

Page 224: Lightning Protection Guide

In order to coordinate the dielectric strength ofthe devices to be protected (transmitter and sen-sor) with the voltage protection level of the SPDs,it must be ensured that the insulation resistance ofthe devices to be protected is considerably higherthan the requirements for an a.c. test voltage 500 V a.c..In order to avoid that the voltage drop of theinterference current to be discharged in the earthconnection does not degrade the voltage protec-tion level, it must be ensured that the equipoten-tial bonding between the device to be protectedand the SPD is consistent.

Figure 8.2.4.4 illustrates a special type of applica-tion. This particular application arises if the termi-nal device to be protected has an insulation resist-ance < 500 V a.c.. In this case, the intrinsically safemeasuring circuit is not floating.

A BLITZDUCTOR XT, BXT ML4 BE, which is not cer-tified for use in hazardous areas, is used as the SPDin the hazardous area and realises a voltage pro-tection level between lines to earth/equipotentialbonding which is considerably less than 500 V. Thisis necessary in this particular application since theinsulating strength of the transmitter correspondsto < 500 V a.c..

This example illustrates particularly the impor-tance of a common consideration of the conditionsof intrinsic safety and the EMC /surge protectionto be brought into line with each other in systemsengineering.

Earthing/Equipotential bondingA consistent equipotential bonding and an inter-meshing of the earth-termination system in thehazardous area of the installation must beensured.The cross section of the earth conductor from theSPD to the equipotential bonding must be at least4 mm2 Cu.

Installation of SPD BLITZDUCTOR CT in Ex(i)-cir-cuitsThe normative stipulations for Ex(i)-circuits fromthe point of view of the protection against explo-sion and of electromagnetic compatibility (EMC)correspond to different positions, a situationwhich occasionally causes consternation amongdesigners and building constructors.

Chapter 9.15 “Installation of surge protectivedevices in intrinsically safe circuits”, lists the mostimportant selection criteria for both intrinsic safe-ty and EMC/ surge protection in installations inorder to detect the interaction on the otherrequirement profile in each case.

8.2.5 Special features of the installation ofSPDs

The protective effect of an SPD for a device to beprotected is provided if a source of interference isreduced to a specified value below the interfer-ence or destruction limit and above the maximumoperating voltage of a device to be protected.Generally, the protective effect of an arrester isindicated by the manufacturer in form of the voltage protection level Up (see IEC 61643-21, EN 61643-21). The effectiveness of a surge pro-tective device, however, depends on additionalparameters, which are determined by the instal-lation. During the discharge, the current flowthrough the installation (e.g. L and R of theequipotential bonding conductor) can cause avoltage drop UL + UR which must be added to Upand results in the residual voltage at the terminaldevice Ur.

Optimal surge protection is possible under the fol-lowing conditions:

⇒ The maximum operating voltage Uc of the SPDis just above the open circuit voltage of thesystem

⇒ Up of the SPD should be as low as possible,since additional voltage drops through theinstallation have less effect

⇒ The equipotential bonding should be de-signed to have the lowest impedance possi-ble

⇒ Installing the SPD as close as possible to theterminal device has a favourable effect on theresidual voltage

U U U Ur p L R= + +

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Page 225: Lightning Protection Guide

Installation examples:

Example 1: Correct installation (Figure 8.2.5.1)

The terminal device is only earthed directly via theearth connection point of the arrester. The conse-quence is that the Up of the SPD is in fact availableat the terminal device. This form of installationillustrates the most favourable application of theSPD for protection of the terminal device.

UL + UR have no effect

Example 2: Most common installation(Figure 8.2.5.2)

The terminal device is earthed directly via theearth connection point of the arrester and is alsoconnected via the protective conductor. The conse-quence is that a part of the discharge current,depending on the impedance ratio, flows away viathe connection to the terminal device. To preventa coupling of the interference from the connectingequipotential bonding conductor to the protectedlines, and to keep the residual voltage low, this

equipotential bonding conductor must be in-stalled separately, if possible, and/or be designedto have extremely low impedance (e.g. metalmounting plate). This form of installation illus-trates current installation practice for terminaldevices protection class I.

Example 3: Wrong method of equipotential bond-ing (Figure 8.2.5.3)

The terminal device is only earthed directly via theprotective conductor terminal, for example. Thereis no low impedance equipotential bonding to thesurge protective device. The path of the equipo-tential bonding conductor from protective deviceto where it meets the protective conductor termi-nal of the terminal device (e.g. equipotentialbonding bar) has considerable effect on the resid-ual voltage. Depending on the length of the con-ductor, voltage drops up to a few kV can arisewhich add up to Up and can lead to the destructionof the terminal device during the discharge ofsurges.

U U U Ur p L R= + +

U U Ur p v= +

U Ur p=

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3OUT

4

1IN

2

BLITZDUCTOR

BCT MLC BD 110No.919 347

disc

harg

e cu

rren

t

L of line

R of line

L and R of the line have no effect on Ur out of Ur = Up

Up = voltage protection levelUr = residual voltage

Up

Ur

3OUT

4

1IN

2

BLITZDUCTOR

BCT MLC BD 110No.919 347

Up

Ur

Uv

L and R of the line have a little effect on Ur , if the connectionhas a low impedance: Ur = Up + Uv

e.g. connection of protective conductor of power supply

disc

harg

e cu

rren

t

L of line

R of line

Uv = voltage drop connection; BCT > terminal device

Fig. 8.2.5.1 Correct installation Fig. 8.2.5.2 Most frequent installation

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Example 4: Wrong conductor leading (Figure 8.2.5.4)

Even if the equipotential bonding is carried outcorrectly, a wrong conductor leading can interferewith the protective effect or even result in damageto the terminal device. If strict spatial separation orshielding of an unprotected conductor upstreamof the SPD, and protected conductor downstreamof the SPD, is not maintained, then the electro-magnetic interference field can cause coupling ofinterference impulses on the protected conductor.

Shielding

The shielding of cables is described under 7.3.1.

Recommendations for installation:The use of metal shields or cable ducts reduces theinteraction between line pair and surroundings.For shielded cables, please note the following:

⇒ Shield earthing at one end reduces the irradia-tion of electric fields

⇒ Shield earthing at both ends reduces the irra-diation of electromagnetic fields

www.dehn.de LIGHTNING PROTECTION GUIDE 225

Fig. 8.2.5.3 Wrong method of equipotential bonding

Table 8.2.5.1 Separation of telecommunications and low voltage supply lines (based on EN 50174-2)

Fig. 8.2.5.4 Wrong conductor leading

3OUT

4

1IN

2

BLITZDUCTOR

BCT MLC BD 110No.919 347

no direct equipotentialbonding connection betweenBLITZDUCTOR and terminal device

disc

harg

e cu

rren

t

L and R of the line impair Ur: Ur = Up + UL + UR

Up

UrUL

UR

3OUT

4

1IN

2

BLITZDUCTOR

BCT MLC BD 110No.919 347

Due to wrong conductor leading interferences are coupledfrom the unprotected to the protected line

1

2

3

4

Ur

Unshielded l.v. supply lines andunshielded telecommunications lines 200 mm 100 mm 50 mm

Type of installation

Without divideror non-metallic

divider

Aluminiumdivider

Steeldivider

Distance

Unshielded l.v. supply lines andshielded telecommunications lines 50 mm 20 mm 5 mm

Shielded l.v. supply lines andunshielded telecommunications lines 30 mm 10 mm 2 mm

Shielded l.v. supply lines andshielded telecommunications lines 0 mm 0 mm 0 mm

Page 227: Lightning Protection Guide

⇒ Conventional shields offer no significant pro-tection against low frequency magnetic fields.

Recommendations:Shields should run continuously between IT instal-lations, have a low coupling resistance and be con-ducted around the complete circumference, if pos-sible. The shield must enclose the conductors com-pletely, if possible. Interruptions in the shield andhigh impedance earth connections and “pig tails“of cables should be avoided.The extent to which low voltage lines can affecttelecommunication lines depends on a multitude

of factors. The recommended guide values for thespatial distances to low voltage lines are describedin EN 50174-2. For a cable length less than 35 m nodistance is generally required. In all other cases,Table 8.2.5.1 gives the distances applying.It is recommended to install telecommunicationlines in metal ducts which are electrically connect-ed and completely enclosed. The metal cable ductsystems should be connected with low impedanceto earth as frequently as possible, at least at thebeginning and the end (Figure 8.2.5.5).

www.dehn.de226 LIGHTNING PROTECTION GUIDE

not recommended

right

metal cable trays

Low voltage cables

Auxiliary cables(e.g. fire alarm systems, door openers)

Telecommunication cables

Cables for sensitive applications

Recommended

l.v. cables

auxiliary cables

telecommunica-tion cables

sensitiveapplications

Fig. 8.2.5.5 Separation of cables in cable duct systems

Page 228: Lightning Protection Guide

In principle a frequency converter consists of a rec-tifier, a d.c. link converter, an inverter and of thecontrol electronics (Fig. 9.1.1).At the input of the inverter the single phase orinterlinked, three-phase a.c. voltage is changedinto a pulsating d.c. voltage and is pushed into thed.c. link converter that also serves as energy store(buffer).Capacitors in the d.c. link converter and the LC net-works connected to earth in the a.c. line filter, cancause problems with the residual current devices(RCD) connected in series. The reason for this isoften wrongly seen in the application of surgearresters.

The problems, however, result from the short-terminduction of fault currents by the frequency con-verter. These are sufficient to activate sensitiveearth leakage circuit breakers (RCDs). A surge-proof RCD circuit breaker available for a trippingcurrent IΔn = 30 mA and a min. discharge capabilityof 3 kA (8/20 μs) provides a remedy.

By the control electronics, the inverter delivers aclocked output voltage. The higher the clock fre-quency of the control electronics for the pulse-width-modulation, the more sinusoidal is the out-put voltage. With each cycle, a peak voltage is cre-ated that is superimposed on the curve of the fun-

www.dehn.de LIGHTNING PROTECTION GUIDE 227

9. Application proposals9.1 Surge protection for frequency converters

line-sideconverter rectifier

d.c. linkbank of capacitors

load-sideconverter inverter

+

C

V1 V3 V5

V4 V6 V2

+

U1V1W1

M3~

motor load

control electronicscontrol / regulation / monitoring / communication

L1

L2

L3

data

INPUT OUTPUT

Fig. 9.1.1 Schematic diagram of a frequency converter

shielded motor supply lineshield is earthed on bothsides over a wide area

motor

connection to FC filter

frequencyconverter

compact filterkept as shortas possible

power supply line

metal mounting plate connected to earthgeneral: all cables should be kept as short as possible

1

Type Part No.No.

1 919 031 - 919 038Constant force spring SA KRF ...

1

Fig. 9.1.2 EMC conforming shield connection of the motor supply line

Page 229: Lightning Protection Guide

damental frequency. This peak voltage reaches values of 1200 V and higher (according to the fre-quency converter). The better the simulation ofthe sine curve at the output, the better is the per-formance and control response of the motor. Thismeans, however, that the voltage peaks appear at

the output of the frequency converter more fre-quently.

For choosing of surge arresters, the maximum con-tinuous operating voltage Uc has to be taken intoaccount. It specifies the maximum permissible

www.dehn.de228 LIGHTNING PROTECTION GUIDE

1

3

1

3

2

2DE

HNgu

ard®

T

3OU

T4

1IN

2

Blitzductor CTBCT MOD ...

DEHNguard

DG MOD 275

P1 + PX PR −

L1L2L3

L11L21

PCSTFSTR

STOPRHRMRLRT

JOGMRSAUCSSDRES

10E102541

SERUNSUOLIPFFU

FMSD

AM5

ABC

UVW

L1L2L3

Hz

M3~

PU/DU

Processor/DSP

Software

Functions:PID controller

Basic functions:Voltage/frequency

functionvector control

powersupply

protectivecircuits

LCD/LED display PU/DU

charge

alarm

reset

operator’s station

inputsignal circuit

faultindicator

analogueoutput

operatingstateandfaultindicator

d.c. link

3x 400V/50Hz

Type Part No.No.

952 070DEHNguard S DG S 275

BLITZDUCTOR XTBXT ML4 BE 24 + BXT BAS

920 324 +920 320

DEHNguard S DG S 600 952 076

4-20 mA

INPUT OUTPUT

Fig. 9.1.3 Structure of a frequency converter with SPD

Page 230: Lightning Protection Guide

operating voltage a surge protective device maybe connected to. This means that surge protectivedevices with a correspondingly higher Uc are usedat the output side of the frequency converter. Thisavoids faster ageing due to gradually heating ofthe surge protective device under normal operat-ing conditions and the consequential voltagepeaks. This heating of the arrester leads to a short-er service life and consequently to a disconnectionof the surge protective device from the system tobe protected.

The voltage at the output of the frequency con-verter is variable and adjusted a little bit higherthan the nominal voltage at the input. Often it isapprox. + 5 % during continuous operation, inorder to compensate the voltage drop at the con-nected line, for example. Otherwise, one can sim-ply say that the maximum voltage at the input ofthe frequency converter is equal to the maximumvoltage at the output of the frequency converter.

The high clock frequency at the output of the fre-quency converter generates fieldborne interfer-ences and therefore, requires necessarily a shield-

ed cabling so that adjacent systems are not dis-turbed.For shielding the motor power supply line, a bila-teral shield earthing at the frequency converterand the drive motor has to be ensured. The large-surface contacting of the shield results from theEMC requirements. Advantageous is here the useof constant force springs (Fig. 9.1.2). By means ofintermeshed earth-termination systems, i.e. theearth-termination system the frequency convertersand the drive motor are connected to, potentialdifferences are reduced between the parts of theinstallation and thus equalising currents via theshield are avoided.

Figure 9.1.3 shows the use of surge protectivedevices Type DEHNguard on the power supply sideand Type BLITZDUCTOR for 0 – 20 mA signals. Theprotective devices have to be individually adaptedaccording to the interface.

For the integration of the frequency converter intothe building automation it is absolutely essentialthat all evaluation and communication interfacesare connected with surge protective devices inorder to avoid system failures.

www.dehn.de LIGHTNING PROTECTION GUIDE 229

Page 231: Lightning Protection Guide

Outdoor lighting can be installed at the outerwalls of buildings as well as on open site. In anycase it has to be considered whether the outdoorlighting is located in lightning protection zone LPZ0A or in lightning protection zone LPZ 0B. Outdoorlighting in LPZ 0A is at risk of direct lightningstrikes, impulse currents up to the whole lightningcurrent and of the whole field of the lightningflash. In LPZ 0B they are protected against directlightning strikes, however, at risk of impulse cur-rents up to partial lightning currents and thewhole field of lightning.

Lamp poles in lightning protection zone LPZ 0Ahave to be interconnected underground and theyhave to be connected with the earth electrodes ofthe buildings or structures via permissible earthingconductors. The recommended materials, dimen-sions and cross sections are indicated in Table 7 of

IEC 62305-3 (EN 62305-3). Table 9.2.1 shows anexcerpt of it for practical use. The material to beused always has to be selected with regard toprobable corrosion.

Measures to reduce the risk of electric shock haz-ard due to touch and/or step voltage are subjectto individual examination.Analogously to IEC 62305-3 (EN 62305-3) therequired measure to reduce the touch voltages is,for example, an asphalt layer of at least 5 cm thick-ness or 15 cm gravel, 3 m around the lamp pole(Figure 9.2.1).

In IEC 62305-3 (EN 62305-3) also the potential con-trol, for example, is mentioned as measure toreduce step voltages. In this case four rings areinstalled in the distances 1.0 m, 4.0 m, 7.0 m, and10.0 m, and in the corresponding depths of 0.5 m,

1.0 m, 1.5 m, and2.0 m around thelamp pole. Theserings are inter-connected by fourconnecting leadswhich are stag-gered by 90 ° andalso with thelamp pole (Fig-ure 9.2.2).

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9.2 Lightning and surge protection for outdoor lightingsystems

Material Form Earthing conductor Notes

Copper cableroundstrip

50 mm2

50 mm2

50 mm2

min. wire thickness 1.7 mmØ 8 mmmin. thickness 2 mm

Steel round galvanised 50 μmstrip galvanised 70 μm

Ø 10 mm90 mm2

-min. thickness 3 mm

StainlessSteel

roundstrip

Ø 10 mm100 mm2

-min. thickness 2 mm

3 m 3 m

asphalt layer≥ 5 cm

Fig. 9.2.1 Insulation of the place around the lamp pole to reduce the risk of touch voltage in case of lightning strike

Table 9.2.1 Min. dimensions of earthing conductors for interconnecting lamp poles in LPZ 0A and for connecting tothe earth-termination system of the building or structure

Page 232: Lightning Protection Guide

The following types of lightning current and surgeprotective devices are installed at the boundary of the lightning protection zone LPZ 0A – LPZ 1 or LPZ 0B – LPZ 1.All outdoor lightings in lightning protection zoneLPZ 0A shall be protected by lightning currentarresters Type 1 to be installed at the entrance tothe building or structure. This lightning protectionzone to be determined, requires “to approach”the corresponding rolling sphere from all possibledirections to the outdoor lighting. If it is touched

by the rolling sphere, the outdoor lighting is inlightning protection zone LPZ 0A (Figure 9.2.3 andFigure 9.2.4).

Before installing lightning current arresters Type 1,it has to be checked, whether the circuits of theoutdoor lighting are already protected by an ener-gy coordinated SPD Type 2 in the current distribu-tion board, if not, combined lightning current andsurge arresters are recommended to be installed atthe lightning protection zone boundary.

www.dehn.de LIGHTNING PROTECTION GUIDE 231

Fig. 9.2.2 Potential control to reduce the arising step voltage at lightning strikes into a lamp pole

Fig. 9.2.3 230 V wall lamp as outdoor lighting in lightning protection zone LPZ 0A

-0.5 m

1 m

4 m

± 0

-1.0 m-1.5 m

-2.0 m

7 m10 m

Lightning current arresters

Combined lightning currentand surge arresters

TN systemDB 1 255 H (2x), Part No. 900 222

TT systemDB 1 255 H, Part No. 900 222DGP BN 255, Part No. 900 132

TN systemDV M TN 255, Part No. 951 200TT systemDV M TT 2P 255, Part No. 951 110

radius of therolling sphere

Page 233: Lightning Protection Guide

www.dehn.de232 LIGHTNING PROTECTION GUIDE

Lightning current arresters

Combined lightning currentand surge arresters

TNC systemDB 3 255 H, Part No. 900 120TNS systemDB 3 255 H, Part No. 900 120DB 1 255 H, Part No. 900 222

TNC systemDV M TNC 255, Part No. 951 300TNS systemDV M TNS 255, Part No. 951 400

TT systemDB 3 255 H, Part No. 900 120DK 35, Part No. 900 699DGP BN 255, Part No. 900 132

TT systemDV M TT 255, Part No. 951 310

radius of therolling sphere

TN systemDG M TN 275, Part No. 952 200

TT systemDG M TT 2P 275, Part No. 952 110

radius of the

rolling sphere

TNC systemDG M TNC 275, Part No. 952 300TNS systemDG M TNS 275, Part No. 952 400TT systemDG M TT 275, Part No. 952 310

radius of the

rolling sphere

Fig. 9.2.4 Lamp pole with 3 x 230/400 V outdoor lighting in lightning protection zone LPZ 0A

Fig. 9.2.5 230 V wall lamp as outdoor lighting in lightning protec-tion zone LPZ 0B

Fig. 9.2.6 Lamp pole with 3 x 230/400 V outdoor lighting in light-ning protection zone LPZ 0B

Page 234: Lightning Protection Guide

All outdoor lightings in lightning protection zoneLPZ 0B shall be protected by surge protectivedevices Type 2, to be installed at the entrance tothe building or structure. This lightning protectionzone to be determined, requires “to approach”

the corresponding rolling sphere from all possibledirections to the outdoor lighting, which in thiscase, may not be touched by the rolling sphere(Figures 9.2.5 and 9.2.6).

www.dehn.de LIGHTNING PROTECTION GUIDE 233

Page 235: Lightning Protection Guide

In modern biogas plants biodegradable organicsubstrates such as liquid manure, dung, grass,straw, biowaste, residues of sugar, wine, beer pro-duction, leftovers, and fats, are fermented in anair-tight container (fermenter /fermentation tank).In this atmosphere without oxygen, bacteria pro-duce biogas of the fermentable, organic biomasscomponents. This biogas is used to generate heatand current.

Figure 9.3.1 shows the system layout of a typicalbiogas plant usually consisting of a slurry store(collecting basin), a sanitation system, one or moreheatable fermenters, a repository tank, probably arefermenter, a gasholder and a gas conditioner.Grain, for example, is preserved in the ligavator(liquids tank) shown in Figure 9.3.1. The gas motorwith heat exchanger and connected generator is acombined heat and power unit (CHP). Dependingon the energy content of biogas, the CHP gener-ates electrical current with an efficiency degree ofapprox. 30 % and heat with an efficiency degreeof approx. 60 %. Partly the heat is used for the fer-menter while the surplus of it, for example, is used

for the heating of residential and agriculturalbuildings.

Necessity of a lightning protection systemUntil January 2003, the ElexV “Verordnung überelektrische Anlagen in explosionsgefährdetenBereichen“ (Directive for electrical installations inexplosion hazard areas) had to be applied and isnow replaced by the German Health and Safety atWork Regulations (BetrSichV). These regulationsare applicable for the provision of work equip-ment by employers as well as for the use of workequipment by employees (compare § 1 Subclause 1BetrSichV). It is also applied for systems whichrequire monitoring in the sense of § 2 Subclause 2aof the Device Safety Act (German: Gerätesicher-heitsgesetz). According to the Device Safety Act,systems with hazard of explosion are rated to bemonitored. As, for example, the vicinity of gas-holders and gas tanks of a biogas plant is at risk ofan explosive gas /air mixture, biogas plants are cat-egorised as explosion endangered systems.According to the German Health and Safety atWork Regulations (BetrSichV § 12) biogas plants

www.dehn.de234 LIGHTNING PROTECTION GUIDE

9.3 Lightning and surge protection for biogas plants

repository tank

fermenter

cooling tank

sanitationweighing vessel

collecting basin

liquids tank

grain silo

flare system

gas analyser

E-technologybuilding

mixerpump

mixer

pumpvalve

valve

pump

pump

circulatingpump

millmixer

valve valve

mixer

valve

gas pipeCHPCHP

controlcabinet

weigher

condensor

electricpower

heat

Fig. 9.3.1 System layout of a biogas plant

Page 236: Lightning Protection Guide

have to be mounted, installed, and operatedaccording to the state of the art. Hence also thelightning protection systems have to meet therequirements of the BetrSichV.

In the German safety regulations for agriculturalbiogas plants BGR 104 Section E 2 it is pointed outthat in areas with hazard of explosion “measuresto avoid the ignition of hazardous explosiveatmosphere” have to be carried out.

According to EN 1127-1 Subclause 5.3.1 there arethirteen different sources of ignition. In subclause5.3.8 of EN 1127-1 and in the German safety regu-lations BGR 104 lightning is defined as source ofignition: “Lightning striking potentially explosiveatmosphere will always cause ignition. Moreover,there is also a possibility of ignition due to thehigh temperature reached by lightning conduc-tors. Large currents flow from where the lightningstrikes and these currents can produce sparks inthe vicinity of the point of impact. Even in theabsence of lightning strikes, thunderstorms cancause high induced voltages in equipment, protec-tive systems and components.”The rules of explosion protection require to takeappropriate protection measures against lightninghazard.The BetrSichV clearly obligates the employer tomake a comprehensive determination and assess-ment of the risk factors for operation facilitieswith hazard of explosion. According to § 5 of theBetrSichV the employer have to subdivide explo-sion endangered areas into zones taking intoregard the results of the risk assessment. The zonesof protection against explosion have to be definedin a document of protection against explosion.“Further information for lightning protection sys-tems for buildings and installations with explosiveareas” is given in the lightning protection stan-dard IEC 62305-3 Annex D which requires a light-ning protection system class II for such systems. In special cases the requirement of additionalmeasures, however, has to be checked according toIEC 62305-2. A risk analysis can be made by meansof the calculation method specified in IEC 62305-2.For this risk analysis (acc. to IEC 62305-2) the soft-ware DEHNsupport can be used. So it is possible todetermine the risk of damage for a building orstructure and the persons and equipment thereinfrom direct and indirect lightning strikes. The riskof damage being higher than an tolerable risk, it is

necessary to minimize the damage risk due tolightning strike by lightning protection measuresso that the tolerable risk is no longer exceeded.

The German national Supplement 2 of DIN EN62305-3 gives additional information for specialbuildings or structures and a closer specification ofthe requirements for the lightning protection ofbiogas plants. Thus biogas plants shall be protect-ed by isolated air-termination and down conduc-tors systems if the risk of ignition by sparks at join-ings and connecting points can not be excluded.

External lightning protectionThe fermenter is the core of every biogas plant.There is a wide spectrum of fermenters and fer-menting systems on the market with differentdesigns. The required lightning protection systemmust always be adapted to the structural condi-tions of the plant. Different solutions can be foundfor one protective aim. As already mentioned, alightning protection system class II meets the gen-eral requirements for systems with explosive areasand hence those for biogas plants.The lightning protection system comprises anexternal and an internal lightning protection.The functions of the external lightning protectionare to intercept all lightning strikes, including sidestrikes into the building or structure, to conductthe lightning current from the striking point to theearth and to distribute it in the earth without hav-ing any damage at the building or structure to beprotected due to the thermal, mechanical, or elec-tric effects.

Fermenter with film domeIn biogas plants often fermenters with film domeare used which can be damaged by lightningstrike. The melting and spraying effect at the strik-ing point causes the risk of fire and explosion. Thelightning protection measures have to be designedin a way that there will be no direct lightningstrike into the film dome of the fermenter (Figure9.3.2).In the safety regulations for agricultural biogasplants, the Ex zone 2 is determined to be in thearea of 3 m around the film dome of the fer-menter. In Ex zone 2 explosive atmosphere isunusual and only temporary. This means, in zone 2explosive atmosphere has to be taken into consid-eration only at seldom, unforeseen operationalconditions (in case of failure and service/mainte-

www.dehn.de LIGHTNING PROTECTION GUIDE 235

Page 237: Lightning Protection Guide

nance work). According to IEC 62305-3 thereforethe positioning of air-termination systems in Exzone 2 is permitted.

The rolling sphere method is used to determineheight and number of air-termination installa-tions. The sag of the rolling sphere is decisive forthe dimensioning of the air-termination system,which can be determined according to IEC 62305-3.The corresponding class II for systems with explo-sive areas requires a rolling sphere radius of 30 m(Figure 9.3.2).

Depending on the gas volume, the inner mem-brane in the gasholder of the fermenter is pressedmore or less tightly against the metal inner wall ofthe fermenter. An isolated down conductor system

has to be installed to avoid uncontrolled flashoverfrom the down conductor to the metal wall of thefermenter. The isolated leading of the down con-ductors on distance holders out of GRP (glass-fibrereinforced plastic) ensures an electric isolation ofthe lightning protection system from conductiveparts of the fermenter. The length of the distanceholders being a function of the separation dis-tance determined according to IEC 62305-3. The DEHNiso-Combi Set according to Table 9.3.1 isused in a case as illustrated in Figure 9.3.2.

Another possibility to avoid the film dome of thefermenter being at hazard of direct lightningstrike is the use of steel telescopic lightning protec-tion masts (Figure 9.3.3). These masts are installedin natural soil or in a concrete foundation. Freeheights of 21 m above ground level can beachieved, even higher, if custom-made ones areused. The standard lengths of the steel telescopiclightning protection masts are supplied in sectionsof 3.5 m, offering enormous advantages for trans-portation. Further information about the use ofsteel telescopic lightning protection masts can befound in installation instructions No. 1574.

A third possibility to protect the fermenter withfilm dome against direct lightning strike is to use

www.dehn.de236 LIGHTNING PROTECTION GUIDE

rolling sphere radius r rolling sphere radius r

DEHNiso-Combi Set (Part No. 105 455)

1-part unit, total length 5700 mm consisting of:1x air-termination tip Al, L = 1000 mm(Part No. 105 071)1x insulating pipe, L = 4700 mm(Part No. 105 301)3x wall mounting bracket StSt (V2A)(Part No. 105 340)2x distance holder GRP/Al, L = 1030 mm(Part No. 106 331)

Fig. 9.3.2 Use of the DEHNiso-Combi system to protect a fermenterwith film dome

Fig. 9.3.3 Protection of a fermenter with film dome by steel tele-scopic lightning protection masts

Table 9.3.1 DEHNiso-Combi Set

Page 238: Lightning Protection Guide

the DEHNconductor system. The DEHNconductorsystem is a programme comprising the HVI conduc-tor and the specially adapted connecting and fix-ing elements. The HVI conductor is a high voltage-resistant, insulating down conductor with a specialouter coating. It is typically used as isolated downconductor in lightning protection to handle theseparation distance according to IEC 62305-3. Theseparation distance has to be calculated accordingto IEC 62305-3. Subsequently it has to be exam-ined if this calculated separation distance can berealised with the equivalent separation distance ofthe HVI conductor. The DEHNconductor systemoffers two variants of solution:

Variant 1: Air-termination masts with one HVI con-ductor (Figure 9.3.4). The maximum total length ofthe air-termination system from the equipotentialbonding level (earth-termination system) to theair-termination tip here is 12.5 m, the maximumfree length above the top edge of the fermentermust not exceed 8.5 m (for mechanical reasons).

Variant 2: Air-termination masts with two HVI con-ductors (Figure 9.3.5). The maximum total lengthof the air-termination system from the equipoten-tial bonding level (earth-termination system) tothe air-termination tip here is 16 m, the maximumfree length above the top edge of the fermenteralso 8.5 m.

Note: The distance between the two HVI conduc-tors, to be installed in parallel, has to be more than20 cm.

Further information about the DEHNconductorsystem can be found in the following installationinstructions under www.dehn.de:

⇒ Installation instructions 1565: Air-terminationmast with inner HVI conductor for biogasplants

⇒ Installation instructions 1501: HVI conductor inthe Ex area

Designing serviceIsolated air-termination systems being rathercomplex and extensive systems. DEHN + SÖHNEwould be pleased to assist you in designing of iso-lated air-termination systems on the basis of theDEHNconductor system, DEHNiso-Combi system orsteel telescopic lightning protection masts. Thisdesigning service offered against payment com-prises

⇒ the compiling of drawings of the lightningprotection (general layout drawings),

⇒ detail drawings for an isolated air-terminationsystem (partly as explosion drawings),

www.dehn.de LIGHTNING PROTECTION GUIDE 237

≤ 12

.5 m

≤ 10

.0 m

≤ 8.

5 m

rolling sphere radius r

≤ 16

.0 m

≤ 13

.5 m

≤ 8.

5 m

> 0.2 m

rolling sphere radius r

Fig. 9.3.4 Fermenter protected with air-termination masts isolatedby 1 HVI conductor

Fig. 9.3.5 Fermenter protected with air-termination masts isolatedby 2 HVI conductors

Page 239: Lightning Protection Guide

⇒ comprehensive parts list of the necessary com-ponents for the isolated air-termination sys-tem,

⇒ a quotation based on this parts list.

If you are interested please contact your local con-sultant or the head office in Neu-markt (www.dehn.de).

Fermenters out of sheet metalFermenters out of sheet metal usu-ally have a wall thickness between0.7 and 1.2 mm. The individualplates being screwed together(Figure 9.3.6)

If sheet metal shall be used as nat-ural air-termination system Table 3of IEC 62305-3 is applicable for thethickness. In case the required val-ues of plate thickness are not com-plied with, a lightning strike mightcause through-melting or intolera-ble heating-up at the point ofstrike with risk of fire and explo-sion. These fermenters then mustbe protected by supplementary air-termination systems to avoid melt-ing-out at the point of strike. Inthis case an isolated lightning pro-tection system will be installed. Itslocation be to determined by therolling sphere method. The down-conductor system has to be in-stalled on distance holders accord-ing to the determined separationdistance at the metal plates (Figure9.3.7).

Steel tankFigure 9.3.8 shows completelywelded biogas tank with a sheetsteel enclosure of at least 4 mmthickness. The requirements ofTable 3 of IEC 62305-3 with regardto the material are met. For thelightning protection system hencethe requirement according to IEC 62305-3 Annex D “Additionalinformation for LPS in case ofstructures with risk of explosion” isapplicable. The Ex zones of ex-

hausting vents being in the protected area of met-al enclosure parts capable of carrying lightningcurrents, supplementary air-termination systemsare not necessary. Otherwise supplementary air-termination systems have to be installed to protectthe exhausting vents from direct strike.

www.dehn.de238 LIGHTNING PROTECTION GUIDE

Fig. 9.3.6 Fermenter out of screwed sheet metal

Fig. 9.3.7 Isolated air-termination system toprotect a fermenter out of sheetmetal (Ref.: Büro für Technik,Hösbach)

Fig. 9.3.8 Welded steel tank (Ref.: EisenbauHeilbronn GmbH)

Page 240: Lightning Protection Guide

Earthing conceptConnecting the individual earth-termination sys-tems with an overall earth-termination system pre-vents the arising of high potential differences (Fig-ure 9.3.9 and Table 9.3.2). Intermeshing the indi-vidual building and system earth-termination sys-

tems, the mesh sizes varying between 20 m x 20 mup to 40 m x 40 m, is an economically and techni-cally reasonable method. Potential differencesbetween the various parts of the installation areclearly reduced, by intermeshing all earth-termina-tion systems. Also the voltage loading of the cables

going outside of the building will belower in case of lightning effects.

Power feed-inBy the biogas produced, usually pilotinjection gas engines generate cur-rent and heat. In this context suchengines are called combined heat andpower units (CHP). These CHPs areinstalled in a separate operationbuilding, with the switching and con-trol cabinets in the same or a separateroom. The electric power generated

www.dehn.de LIGHTNING PROTECTION GUIDE 239

No.Strip steel StSt (V4A) 30 mm x 3.5 mm

Alternative: Round-bar StSt (V4A), Ø 10 mm

Cross unit StSt (V4A)Alternative: SV Terminal StSt (V4A)Note: Anticorrosive band

Equipotential bonding bar StStAlternative: Earthing busbar

Terminal lugs directional strip steel StSt (V4A)Alternative: Terminal lugs directional round-bar StSt (V4A)

Part No.860 335860 010

319 209308 229556 125

472 209472 139

860 215860 115

1

2

3

4

fermenter

repository

refermenter

liquid container

grain silo

collectingbasin

operation room

controlsystem

referencemeasuring

EBB EBB MG∼

ϑ

3 x 20 kV

M∼

measuring of thedifference in limits

power feed-in

1

2

3

4

Fig. 9.3.9 Intermeshed earth-termination system for a biogas plant

Table 9.3.2 Material recommendation for earthing and equipotential bonding

Page 241: Lightning Protection Guide

by the CHP is feed into the public power supply sys-tem (see Figure 9.3.10).

An essential part of a lightning protection systemis the lightning equipotential bonding to be car-ried out for all conductive systems entering thebuilding or structure from outside. Lightningequipotential bonding requires that all metal sys-

tems shall be incorporated into theequipotential bonding so as tocause as little impedance as possibleand that all live systems shall be con-nected indirectly via surge protec-tive devices Type 1. The lightningequipotential bonding should beperformed preferably near theentrance of the structure in order toprevent a penetration of partiallightning currents into the building.The 230/400 a.c. power input of thelow-voltage main distribution of theconsumer system (Figure 9.3.10)shall be protected by surge protec-tive devices SPDs Type 1. Such asurge protective device SPD Type 1on RADAX Flow spark gap basis forpower supply systems is DEHNbloc.This lightning current arrester has adischarge capability up to 50 kA(10/350 μs) each pole. By the pa-tented RADAX Flow principle theamplitude of system short-circuitcurrents up to 50 kArms is reduced to approx. 500 A and extinguishedafter approx. 5 ms. Hence a discon-nection selectivity of the surge pro-tective device is possible also in caseof too weak system fuses. An inter-ruption of supply by tripping of themain fuse thus is avoided. Surgeprotective devices Type 2, for exam-ple DG TNS H230 400 LI, will beinstalled in downstream subdistribu-tions (Table 9.3.3). This surge protec-tive device has a three-stage visualservice life indication with remotesignalling link informing any timeabout the function standby of surgeprotection.

The DEHNventil, a multipole modu-lar combined lightning current and

surge arrester with high follow current limitationis installed in the CHP distribution (Figure 9.3.10).This combined lightning current and surge arresteris wired ready for connection, comprising a basepart and plug-in protective modules. The DEHN-ventil ensures utmost system availability and a dis-connection selectivity to 20 A gl/gG fuses up to 50kArms short-circuit current.

www.dehn.de240 LIGHTNING PROTECTION GUIDE

3

3

20 kV; 3 50 Hz

3

3

3 3

4

4

3

3

3

4

4

3

3

3

3G

M

3 125 A 3 3 3 3

5

1

2

3

CHPdistribution

generating systemconsumer system

Z

Z

Fig. 9.3.10 Sectional view of an overall circuit diagram of a biogas plant

Page 242: Lightning Protection Guide

At little distances between the DEHNventil and theconsumers (≤ 5 m) also the terminal equipment isprotected.

Remote monitoring

By the remote monitoring system the performancedata of the biogas plant are always available. Thesystem specific measured data can be directly readat the acquisition unit. The data acquisition unithas RS 232 or RS 485 interfaces to connect a PCand/or modems for remote enquiry and mainte-nance. The remote monitoring, for example permodem, allows the service staff to log on an exist-ing system and to provide direct assistance to theoperator in case of failure. The modem is connect-ed to the network termination unit (NTBA) of anISDN basic access. The forwarding of the measureddata via the telecommunication network per ISDNmodem must be provided as well, in order to pro-vide a continuous control and optimisation of theperformance of the installation. For this purpose

the Uk0 interface upstream of the NTBA which theISDN modem is connected to, is protected by asurge protective adapter NT PRO (Figure 9.3.11).This adapter ensures additional protection of the230 V power supply of the NTBA. The recommend-ed protection of telecommunication terminaldevices and telecommunication system with RJsocket outlet and plug is the surge arrester TypeBLITZDUCTOR VT ISDN (Table 9.3.4).

Figure 9.3.11 shows the protection of a surveil-lance camera. The shielded surge arrester UKGFBNC protects the coaxial cable of the video trans-mission system (Table 9.3.4). More about the pro-tection of video surveillance systems is provided inthe protection proposal “Surge protection forvideo surveillance systems” in Chapter 9.

Process controlOne of the most important components of operat-ing a biogas plant is the process control. All pumps

www.dehn.de LIGHTNING PROTECTION GUIDE 241

Lightning current arrester Type 1

1

Alternative

1

Surge arrester Type 2

2

Combined lightning current and surge arrester

3

Protection for:

TN-C system

TN-S system

TT system

TN-C system

TN-S system

TT system

TN-C system

TN-S system

TT system

TN-C system

TN-S system

TT system

Part No.

900 222

900 222

900 222+ 900 132

900 220

900 220

900 220+ 900 050

950 160

950 170

950 150

951 300

951 400

951 310

SPDs

3 x DB 1 255 H

4 x DB 1 255 H

3 x DB 1 255 H+ 1 x DGP BN 255

3 x DBM 1 255 S

4 x DBM 1 255 S

3 x DBM 1 255 S+ 1 x DGPM 1 255 S

DG TNC H230 400 LI

DG TNS H230 400 LI

DG TT H230 400 LI

1 x DV M TNC 255

1 x DV M TNS 255

1 x DV M TT 255

Note

Modular combined lightningcurrent and surge arrester withhigh follow current limiting anda protection level ≤ 1.5 kV

1-pole lightning current arresterwith high follow current limiting

Coordinated lightning currentarrester with integrated backupfuse for industrial busbar systems

Multi-pole surge arrester withSPD control „Pro-Active-Thermo-Control“ and 3-stage visual servicelife indicator

No.

Table 9.3.3 Surge protection for the power supply

Page 243: Lightning Protection Guide

www.dehn.de242 LIGHTNING PROTECTION GUIDE

1

2

3

4 5

6

operation building

switchgear cabinet

PROFIBUS DP

PROFIBUS PA

ISDNsystem

NTBA

NT 1

NT

EBB

Protection for...Power and data input of an NTBA

Telcommunications terminal devices and telephone system with RJ-plug-in connector

Coaxial line (frame transfer)

Part No.909 958

918 410

929 010

1

2

3

SPDsNT PRO

BLITZDUCTOR BVT ISDN

UGKF BNC

No.

DEHNpipe Type Part No.Application/ApprovalNo. Thread

M20 x 1,5; Internal / External thread4 – 20 mA, Profibus PA, Fieldbus Foundadtion; Ex (i) 929 960DPI MD EX 24 M 26

Protection for...4 – 20 mA

0 – 10 V

Profibus DP/FMS

Temperature measuring PT 100, PT 1000, Ni 1000

Profibus PA; Ex (i)

Part No.920 324 + 920 300

920 322 + 920 300

920 371 + 920 300

920 320 + 920 300

920 381 + 920 301

4

5

BLITZDUCTOR XT TypeBXT ML4 BE 24 + BXT BAS

BXT ML4 BE 12 + BXT BAS

BXT ML4 BD HF 5 + BXT BAS

BXT ML4 BE 5 + BXT BAS

BXT ML4 BD EX 24 + BXT BAS EX

No.

Fig. 9.3.11 Surge protection for information technology systems

Table 9.3.4 Surge protection for information technology systems

Table 9.3.5 Surge arresters for the measuring and control technology

Table 9.3.6 Surge arresters for field devices

Page 244: Lightning Protection Guide

and agitators shall be operated centrally, processdata such as gas volume and gas quality shall berecorded, temperature and all input materials shallbe acquired, all data shall be visualised and docu-mented.

A failure of the process control due to surgesresults in procedural disturbances and interrup-tions of the biogas generation. These processesbeing very complex anyway, unscheduled placingout of operation can lead to additional difficulties,and the period of standstill might be extended toseveral weeks.

The control unit is installed in a control cabinet. Inaddition to digital inputs and outputs, T 1000 sig-nals, 20 mA signals are evaluated. To ensure anundisturbed and continuous transmission of themeasured data to the control unit in the controlcabinet, the control and signal lines entering thebuilding, for example from frequency invertersand actuators have to be protected as close as pos-sible to the point where they enter the building bylightning current arresters, Type BLITZDUCTOR XT(Figure 9.3.12).

A non-contact and quick arrester check, calledLifeCheck, is integrated in this surge protectivedevice. An extreme thermal or electrical loading issafely detected and can be read out in a second bythe DEHNrecord DRC LC, a hand-held reader withnon-contact RFID technology. The protectivedevices for IT systems are selected according to themaximum operating voltage, the nominal current,

the type of signal (d.c., LF, HF) and the signal sup-ply (balanced, unbalanced).Table 9.3.5 exemplifies protective devices for signaland control lines.In order to protect 2-wire process field devices suchas pressure or fill level sensors, valves, pressuretransmitters, flow meters, the installation of thesurge arrester DEHNpipe (Figure 9.3.13, Table9.3.6) is recommended. This arrester offers anenergy coordinated surge protection for processfield devices in the outside area at a minimumneed of space. The German safety regulations foragricultural biogas plants BGR 104 and EuropeanStandard EN 1127 are applicable for biogas plants,being a system with risk of explosion.In BGR 104 and EN 1127 lightning is described assource of ignition. If the risk of lightning strike isstipulated, the BGR 104 requires all zones to beprotected by suitable lightning protection meas-ures.

The lightning protection standard IEC 62305-3requires to implement at least a lightning protec-tion system Class II for systems with hazard ofexplosion. The external lightning protection to bedesigned in such a way that no partial lightningcurrents can flow into the explosive area. This tar-get of protection can be achieved by an isolatedair-termination system. In order to increase theavailability of sensitive electronic equipment sup-plementary measures as the use of surge protec-tive devices shall be taken.

www.dehn.de LIGHTNING PROTECTION GUIDE 243

Fig. 9.3.12 Combined lightning current and surge arrester modules with LifeCheck Fig. 9.3.13 Surge arrester DEHNpipe for outdoorareas for screwing into 2-wire processfield devices

Page 245: Lightning Protection Guide

Resources of drinking water running short requirea more efficient treatment. Therefore, sewageplants play a central role in the circle of drinkingwater. The necessary high efficiency of sewageplants (Figure 9.4.1) requires the optimisation ofthe operating procedure at a simultaneous reduc-tion of the running operating costs. For this pur-pose, considerable financial efforts were made forelectronic measuring equipment and decentralisedelectronic control and automation systems inrecent years. Compared to conventional technolo-gy, however, the new electronic systems provideonly a low resistance against transient surges. Thestructural conditions of the spacious open-airplants with wastewater treatment technology andthe spread measuring devices and controlsincrease additionally the risk of interferences dueto lightning discharges or surges. Thus, a failure ofthe complete process control system or parts of it,is highly probable to expect, if no protective meas-ures are taken. The consequences of such a failurecan be far-reaching. They can reach from the costsfor the recovery of the system function to the

undefinable costs for the removal of ground watercontamination. In order to come up to this threateffectively and increase the availability of the sys-tems, external and internal lightning protectionmust be provided.

Lightning protection zones conceptIn order to obtain the best technical and economi-cal protection, the sewage plant control is dividedinto lightning protection zones (LPZ). Subsequent-ly, a risk analysis is carried out for each LPZ and forthe relevant types of damage. For the risk analysisacc. to IEC 62305-2 the software tool DEHNsupportcan be used. Lastly, the mutual dependences of theLPZs are examined and the finally required protec-tion measures are defined in order to reach thenecessary protection aim in all lightning protec-tion zones. The following areas were assignedlightning protection zone LPZ 1 and lightning pro-tection zone LPZ 2:

⇒ Electronic evaluation system in the controlroom (LPZ 2)

www.dehn.de244 LIGHTNING PROTECTION GUIDE

9.4 Lightning and surge protection retrofitting forsewage plants

rain overflow basin

pumping draw worksrough/ fine rake

black water basin

sewage plant control

ventilation/sand/fat catcher

primary sedimentation tank

precipitant tank

activated sludge basinnitrification – denitrification

sedimentation tank

outlet

Fig. 9.4.1 Schematic structure of a sewage plant

Page 246: Lightning Protection Guide

⇒ Oxygen measurement in the aeration tank(LPZ 1)

⇒ Interior of the control room (LPZ 1)According to the lightning protection zones con-cept of IEC 62305-4 (EN 62305-4), all conductors atthe LPZ boundaries must be provided with appro-priate protective measures against surges, (Figure9.4.2).

Risk assessment for the sewage plant controlThe following example was calculated by using IEC62305-2 (EN 62305-2). It should be pointed outthat the procedure is only described as an exam-ple. The solution presented is in no way bindingand can be replaced by any other equivalent solu-tions. The following states only the essential char-acteristics of the example.First, a questionnaire with relevant questions onthe structure and its utilisation was discussed withthe operator and fixed in writing. This proceedingensures the elaboration of a lightning protectionconcept that is comprehensible for all partiesinvolved. This concept represents then the mini-mum requirements, which, however, can still betechnically improved anytime.

Site descriptionThe complete process control of the sewage plantis situated centrally in the sewage plant control.Characterised by the extended cable connectionsto the measuring stations as well as substations,considerable partial lightning currents and surgesare imported by these lines into the control roomsat a lightning strike. In the past, this resulted againand again in destruction of the installation andsystem failures.The same applies to the power supply line and thetelephone line (Figure 9.4.3).The sewage plant control itself shall be protectedagainst damage by fire (direct lightning strike),and the electric and electronic systems (controland automation system, telecontrol) against theeffects of lightning electromagnetic pulses (LEMP).

Additional conditions

⇒ Protective measures against effects of light-ning actually are already existing (externallightning protection, surge protective devices(SPD), (previously class B), type VGA 280/4 atthe service entrance of the 230/400 V powersupply line, SPD, (previously class C) type

www.dehn.de LIGHTNING PROTECTION GUIDE 245

2 4

2’ 4’

BLI

TZD

UC

TOR

BX

T M

L4 B

E 24

1’ 3’

protected

1 3

2 4

2’ 4’

BLI

TZD

UC

TOR

BX

T M

L4 B

E 24

1’ 3’

protected

1 3

2 4

2’ 4’

BLI

TZD

UC

TOR

BX

T M

L4 B

E 24

1’ 3’

protected

1 3

2 4

2’ 4’

BLI

TZD

UC

TOR

BX

T M

L4 B

DEX

24

1’ 3’

protected

1 3

2 4

2’ 4’

BLI

TZD

UC

TOR

BX

T M

L4 B

E 24

1’ 3’

protected

1 3

L N

PE

DEH

Ngu

ard

DG

MO

D 2

75

DEH

Ngu

ard

DG

MO

D 2

75

230 V

MCS

sewage plant control

O2-value

measuring point

Fig. 9.4.2 Division of a sewage plant control into lightning protection zones

Page 247: Lightning Protection Guide

VM 280 in the switchgear cabinets of the mea-suring and control system).

⇒ The following types of damage are relevant:L2 for loss of services (water supply and waterdisposal) and L4 for economic losses (buildingsor structures and their contents). Type of dam-age L1 (loss of human life) was excluded, sincethe installation should run fully automaticallyin future operation.

The result after calculating the actual state is thatthe calculated risk R for L2 for loss of service is stillwell above the tolerable risk RT.

Now, possible protective measures are initiated inorder to obtain R < RT whereas with respect to L4loss of economic values the most cost effectivesolution has to be selected:

⇒ Installation of a lightning protection systemClass III according to IEC 62305-3 (EN 62305-3)

(this is the same result as stated in VdS publica-tion 2010)

⇒ Installation of SPDs Type 1 according to EN61643-11 (power supply) and SPDs, categoryD1 according to IEC 61643-21 for the data pro-cessing lines (data lines of the measuring andcontrol system and telecommunication lines)

⇒ SPD Type 2 according to EN 61643-11 (powersupply) and surge protective devices, categoryC2 according to IEC 61643-21 for the data pro-cessing lines (data lines of the measuring andcontrol system and telecommunication lines)

Lightning protection systemThe existing lightning protection system of thesewage plant control was upgraded in accordancewith the requirements of lightning protection sys-tems Class III (Figure 9.4.4). The existing, indirectconnection of the structures mounted on the roof(air conditioning systems) via isolating spark gaps

www.dehn.de246 LIGHTNING PROTECTION GUIDE

DEH

Ngu

ard

DG

MO

D 2

75

DEH

Ngu

ard

DG

MO

D 2

75

L N

PE

BLI

TZD

UC

TOR

BX

T M

L4 B

E 24

2’ 4’

1’ 3’

protected

2 4

1 3

sewage plant control

230 V supply

4 - 20 mA

fixed telecommunication network

230 / 400 V power supply

O2 value

measuring point

Fig. 9.4.3 Electrical lines going into the sewage plant control

Page 248: Lightning Protection Guide

was removed. The protection against direct light-ning strikes was realised by means of air-termina-tion rods in compliance with requested separationdistances and protective angles. Consequently, inthe case of a direct lightning strike into the control

room, no more partial light-ning current can flow intothe structure and cause da-mage. Due to the size of thecontrol room (15 m x 12 m),the number of down con-ductors (4) did not have tobe changed. The local earth-ing system of the sewageplant control was checkedat all measuring points andthe values were recorded.Also, no upgrades had to bemade here.

Lightning equipotential bon-ding for all cables enteringfrom the outside

In principle, all conductive systems entering thesewage plant from the outside must be integratedinto the lightning equipotential bonding (Figure9.4.5) The requirements of lightning equipotentialbonding are fulfilled by direct connection of all

www.dehn.de LIGHTNING PROTECTION GUIDE 247

Z

EBB

lightning equipotential bonding

cathodic protected tank pipe

exte

rnal

ligh

tnin

g pr

otec

tion

syst

em

gas

water

powersupply

foundation earth electrode

αϒ

I II III

80

70

60

50

40

30

20

10

00 2 10 20 30 40 50 60

IVI II III IV

h[m]

Class of LPS

Fig. 9.4.5 Lightning equipotential bonding according to IEC 62305-3 (EN 62305-3)

Fig. 9.4.4 Protective angle method according to IEC 62305-3 (EN 62305-3)

Page 249: Lightning Protection Guide

metal systems and indirect connection of live sys-tems via surge protective devices. The SPD Type 1(power supply system) and the SPD Type D1 (infor-mation technology) must have a lightning currentdischarge capability of test waveform 10/350 μs.The lightning equipotential bonding shall prefer-ably be installed near the entrance into the build-ing or structure in order to prevent a penetrationof lightning currents into the inside of the build-ing.

Equipotential bondingIn the entire sewage plant control, a consistentequipotential bonding is carried out according toIEC 60364-4-41 and IEC 60364-5-54. The alreadyexisting equipotential bonding is tested to avoidpotential differences between different as well asextraneous conductive parts. Also, supportingparts of the building and parts of the construction,pipelines, containers, etc., are included in theequipotential bonding, so that voltage differences

do not have to be expected, even at a failure. Forthe application of surge protective devices, thecross section of the earth conductor for equipoten-tial bonding must be minimum 6 mm2 Cu for SPDsfor power supply systems, and minimum 4 mm2 Cufor SPDs for information technology. Moreover, inareas with potentially explosive atmospheres theconnections of the equipotential bonding conduc-tors must be secured at e.g. equipotential bondingbars against self-loosening (e.g. by means of springwashers).

Surge protection for the low-voltage powersupplyIn the described application, the SPD type VGA280/4 installed at the service entrance of the build-ing is replaced by an SPD Type 1 DEHNventil M TNS255 (Figure 9.4.6), since the “old” SPD does nomore comply with the requirements for lightningprotection systems according to IEC 62305-3 (EN 62305-3). The SPDs Type 2, (previously class C),Type VM 280, were tested with an arrester testunit, type PM 10. Since the test values were stillwithin the tolerances, there was no reason toremove the SPDs. If further SPDs are installed forprotection of the terminal equipment as in thepresent case, they must be coordinated amongeach other and with the terminal equipment to beprotected. The corresponding instructions given inthe enclosed installation instructions must beobserved.Otherwise, the use of surge protective devices inlow voltage consumer's installations shows nopeculiarities compared to other applications andhas already been described many times (for moreinformation, please also see publication DS649 E“Surge Protection – Easy Choice”).

Surge protection in data processing systemsFrom the protection point of view, the transferinterface of all data processing lines to the sewageplant is the service entrance. At this point SPDs(category D1) type DRL 10B 180 FSD are used,which are capable of carrying lightning currents.From the transfer interface, the cables are leddirectly to the switchgear cabinets and are con-nected there. In accordance with the performedrisk analysis, the incoming cables must be led viaSPDs, types DCO RK ME 24 (20 mA signal) or DCORK MD 110 (telecontrol). These are suitable for usein the lightning protection zones concept (catego-

www.dehn.de248 LIGHTNING PROTECTION GUIDE

Fig. 9.4.6 DEHNventil installed into a switchgear cabinet for protec-tion of the power supply system

Page 250: Lightning Protection Guide

ry C2), and are system compatible (Figures 9.4.7and 9.4.8).This ensures a complete surge protection conceptfor the data processing cabling.

Additional applications for protection of sewageplants can be found in publication DS107 E.This can be downloaded from our website:www.dehn.de.

www.dehn.de LIGHTNING PROTECTION GUIDE 249

Fig. 9.4.7 DCO ME 24 surge protective device installed into aswitchgear cabinet for protection of the completemeasuring and control system

Fig. 9.4.8 DCO ME 24 surge protection device installed into aswitchgear cabinet, incoming lines from double bottom

Page 251: Lightning Protection Guide

IEC 60728-11: 2005 complies with the state of theart and offers easy, standardised and effective pro-tective mechanisms against the effects of lightningstrikes into antennas.

Antennas installed according to this standard donot increase the probability of lightnings to strikethe object under consideration. Nor is an antennasystem installed according to this standard a sub-stitute for a lightning protection system of a build-ing or structure. This standard deals with the safe-ty requirements for stationary systems and devicesand is, if applicable, also valid for mobile and tem-porary systems (e.g. campers, recreational vehi-cles). The range of validity comprises cable TV net-works (CATV networks) and satellite communityantenna television systems as well as individualreceiving networks.

Outside antennas which are installed at a level ofmore than 2 m below the roofing or the roof-edgeand at distance of less than 1.5 m from the build-ing (Figure 9.5.1) as well as antenna systems insidea building are excepted from the following meas-ures. However, at least the connection of the coax-ial cable shields to an equipotential bonding con-ductor is urgently recommended. All interconnect-

ed, conductive and touchable components of theinstallation should be integrated into the equipo-tential bonding as well.

Antennas must not be installed on buildings witheasily inflammable roofing (e.g. thatch or similarmaterials). Antenna cables and earthing conduc-tors must not lead through those sections of roomswhere easily inflammable materials like hay, strawor alike are stored, or in which there is a potentialrisk of explosive atmosphere to arise.

An equipotential bonding conductor has to bemechanically solid with a copper cross section ofminimum 4 mm2. The shields of the coaxial cablesgoing in or out of the building have to be connect-ed with an equipotential bonding conductor andby the shortest route with a common equipoten-tial bonding bar.An earthing conductor being capable of carryinglightning current can be a single solid wire havinga minimum cross section of 16 mm2 of insulated orbare copper, or of insulated 25 mm2 aluminium orof 50 mm2 aluminium wrought alloy (not to bedirectly installed on or in plaster nor on or in con-crete), or of steel 50 mm2, preferably for externalinstallation.

Natural components which can be used, are forexample,

⇒ the metal frame of the building or structure,

⇒ the interconnected reinforcement steel of thebuilding or structure,

⇒ facades, railings and substructures of metalfacades,

provided that

⇒ their dimensions meet the requirements ofdown-conductor systems and their thickness isnot less than 0.5 mm,

⇒ their electrical conductivity in vertical direc-tion is ensured (these permanent connectionshave to be carried out by brazing, welding,pressing, screwing or riveting), or that the distance between metal structures does not exceed 1 mm and the overlapping of two structural elements is at least 100 cm2.

IEC 62305-3 does no longer stipulate this possi-bility of overlapping sheet metal, except thesubstructure is continuously conductive in ver-tical direction. If not, the overlapping sheet

www.dehn.de250 LIGHTNING PROTECTION GUIDE

9.5 Lightning and surge protection for cable networks andantennas for TV, sound signals and interactive services

equipotential bonding conductor

max. 1.5 m

4 mm2 Cu

min. 2 m

Fig. 9.5.1 Horizontal and vertical distances of antenna arrange-ments requiring no earthing connection

Page 252: Lightning Protection Guide

metals have to be safely interconnected ac-cording to the requirements of IEC 62305-3.

Attention: Forming of loops has to be avoided.

The earth-termination system has to be designedaccording to one of the following manners (Figure9.5.2):

⇒ Connection with the external lightning protec-tion system of the building or structure.

⇒ Connection with the earth-termination systemof the building or structure.

⇒ Connection with at least two horizontal earthelectrodes having a minimum length of 2.5 m,being installed in an angle > 60 °, at least 0.5 mdeep and not closer than 1 m to the founda-tion, or connected with one vertical or slanted

earth electrode not shorter than 2.5 m or twovertical earth electrodes not shorter than 1.5 m, installed at a distance of 3 m from eachother and not closer than 1 m to the founda-tion.

Minimum cross section of each earth electrode tobe 50 mm2 copper or 80 mm2 steel.

Natural components such as interconnected rein-forcement of concrete or other suitable under-ground metal constructions embedded into thefoundation of the building the dimensions ofwhich complying with the above limit values, canbe used as well.

Other earth-termination system according to IEC 62305-3 are also permitted. If a supplementaryearth electrode is installed adjacent to the earth-

www.dehn.de LIGHTNING PROTECTION GUIDE 251

αα > 60°

1.5 mearth rod

2.5 mflat shaped earth electrode

0.5 m

2.5 m

earthing connection

steel skeleton, reinforced concrete buildings

1 m

2.5 m

earth rod1 m

1.5 m

3 m

building foundation

foundation earth electrode

1 m

Fig. 9.5.2 Examples of permitted earthelectrodes

Page 253: Lightning Protection Guide

termination system of the building, the earth elec-trodes have to be interconnected.

In case of buildings without lightning protectionsystem (LPS), the mast with an earthing conductorhas to be connected by the shortest route with theearth electrode. The earthing conductor has to beinstalled straightly and vertically. The coaxial cableshields have to be connected with the mast byequipotential bonding conductors (Figure 9.5.3).In case of buildings with lightning protection system (LPS), the antennas preferably shall beinstalled within the protective range of an air-ter-mination system, which means in the range of

existing protective zones or by isolated air-termi-nation systems. Only if this is not possible, a directconnection with the external lightning protectionsystem shall be implemented. In this case the aris-

www.dehn.de252 LIGHTNING PROTECTION GUIDE

EBB

equipotentialbonding bar

equipotentialbonding bar

earthconnection

multiswitchwithout mains

connection

equipotentialbonding conductor

earthing conductor

4 mm2 Cu

16 mm2 Cu

s

protective anglePotentialausgleichsleiter

equipotential bondingconductor 4 mm2 Cu

Air-termination rod, e.g. 1500 mmPart No. 104 150Concrete base, e.g. 17 kgPart No. 102 010

highly insulatingdistance holder

protectiveangle

DEHNiso Distance Holdere.g. with pipe clampPart No. 106 225

equipotential bonding conductor

EBB

equipotentialbonding bar

earthconnection

EB terminal

metalDIN rail

multiswitch

DEHNgate DGA FF TVPart No. 909 703

DEHNflex DFL M 255Part No. 924 396

connection of isolated air-termination system to exter-nal lightning protection system

equipotentialbonding conductor

surge arrester

4 mm2 Cu

1

12

1 2

Fig. 9.5.3 Earthing and equipotential bonding of antennas on buildings without external lightning protection system

Fig. 9.5.4 Antenna with air-termination rod on a flat roof of buildings with external lightning protection system

Fig. 9.5.5 Antenna with air-termination rod and highly insulatingdistance holder on pitched roofs with external lightningprotection system

Fig. 9.5.6 Surge protective devices downstream the equipotentialbonding bar for the coaxial cable shields in case of anten-na systems with external lightning protection system andisolated air-termination system

Page 254: Lightning Protection Guide

ing partial lightning currents via the coaxial con-ductors have to be taken into account individually.Lightning equipotential bonding has to be per-formed for the conductors going into the building.

If an antenna is protected by isolated air-termina-tion systems it means

⇒ that in the area of flat roofs an air-terminationrod will be installed with the required separa-tion distance s, putting the whole antennaarrangement (mast and antennas) in the pro-tective zone of the protective angle (Figure9.5.4). Now the antenna arrangement is nolonger in lightning protection zone LPZ 0A (riskof direct lightning currents) but lightning pro-tection zone LPZ 0B (risk of indirect impulsecurrents and of the unattenuated electromag-netic field of lightning.

⇒ that in the area of pitched roofs an air-termi-nation rod will be installed with the requiredseparation distance s using highly insulatingdistance holders (DEHNiso distance holders) tofix it at the antenna mast, putting the wholeantenna arrangement (mast and antenna) into

the protective zone of the protective angle(according to the applicable class of LPS) (Fig-ure 9.5.5). Also here the antenna arrangementis no longer in lightning protection zone LPZ 0A (risk of direct lightning currents), but inlightning protection zone LPZ 0B (risk of indi-rect impulse currents and of the unattenuatedelectromagnetic field of lightning).

Protection against surges, irrespective of aninstalled isolated air-termination system, has to beprovided for the coaxial cable shields by surge pro-tective devices, to be installed downstream theequipotential bonding bar (Figure 9.5.6). Thesesurge protective devices to be used both as singledevices and for rail mounting protect the down-stream devices against inductive and/or capacitiveinputs of waveform 8/20 μs, arising from cloud/cloud flashes, distant strikes or direct strikes intothe isolated air-termination system.

Surge protective devices Type 3 have to be provid-ed for any electrical equipment with 230/50 Hzdownstream the equipotential bonding bar, which

www.dehn.de LIGHTNING PROTECTION GUIDE 253

EBB

equipotentialbonding bar

earthconnection

EB terminal

metalDIN rail

multiswitch

1 DEHNgate DGA FF TVPart No. 909 703

2 DEHNflex DFL M 255Part No. 924 396

2

1

1

equipotentialbonding conductor

earthing conductor

surge arrester

4 mm2 Cu

16 mm2 Cu

Fig. 9.5.7 Surge protective devices downstream the equipotentialbonding bar for the coaxial cable shields in case of anten-na systems without external lightning protection systemand with isolated air-termination system

EBB

equipotentialbonding bar

earthconnection

EB terminal

metalDIN rail

multiswitch

1

2

3

equipotentialbonding conductor

earthing conductor

surge arrester

combined lightning currentand surge arrester

4 mm2 Cu

16 mm2 Cu

DEHNgate DGA GFF TVPart No. 909 705

1

DEHNgate DGA FF TVPart No. 909 703

2

DEHNflex DFL M 255Part No. 924 396

3

Fig. 9.5.8 Combined lightning current and surge arresters down-stream the equipotential bonding bar for the coaxial cableshields in case of antenna systems without external light-ning protection system

Page 255: Lightning Protection Guide

is installed for the coaxial cable shields. Care has tobe taken that the lightning equipotential bondingis carried out for all systems leading into the build-ing.

A lightning protection system not being installed,the following is recommended:

⇒ An air-termination rod mounted with insulat-ed distance holders prevents from a directstrike to the antenna. For this the air-termina-tion rod has to be connected with the earthelectrode by a separately installed earthingconductor (Figure 9.5.7) to be guided prefer-ably on the outside of the building and to beconnected with the earth electrode at groundlevel. Antenna mast and equipotential bond-

ing bar have to be connected with the earthelectrode via an equipotential bonding con-ductor.

⇒ If the antenna mast is earthed directly, com-bined lightning current and surge arrestershave to be provided (Figure 9.5.8), becausepartial lightning currents, which the surgearresters are not able to control, will be con-ducted in this case through the coaxial cables.The antenna mast has to be connected withthe earth electrode by an earthing conductor.

Underground utility lines of systems require com-bined lightning current and surge arresters beingable to carry lightning currents. They also have tobe mounted near the point of entrance into thebuilding (Figure 9.5.9).

www.dehn.de254 LIGHTNING PROTECTION GUIDE

amplifier

...

3

junction box

equiptentialbonding bar

1

2

terminalblock

DEHNgate DGA GFF TVPart No. 909 705

1

DEHNgate DGA FF TVPart No. 909 703

2

DEHNflex DFL M 255Part No. 924 396

3

equipotentialbonding conductor

combined lightning currentand surge arrester

surge arrester

4 mm2 Cu

Fig. 9.5.9 Combined lightning current and surge arresters downstream the equipotential bonding bar for the coaxial cable shields in case ofunderground cable networks

Page 256: Lightning Protection Guide

www.dehn.de LIGHTNING PROTECTION GUIDE 255

9.6 Lightning and surge protection in modern agriculture

Complex electrical and data processing systemscharacterise the picture of modern agriculture.Many processes are automated, and controlledand monitored by computers. Today, an intact datanetwork is an important survival factor on themarket not only for industry but also for agricul-ture.For protecting the installations and systemsagainst the destruction by powerful transientsurges, the use of surge protective devices isrequired. An external lightning protection alone isby far no longer sufficient there.

StructureAn example for the high degree of automation inagriculture is the keeping of cattle. Ultramodernelectrical and electronic installations like automat-ic milking systems (Figure 9.6.1), automatic feeders(Figure 9.6.2), ventilation systems, flushing plants(Figure 9.6.3), and heating systems with heatrecovery and industrial water supply (Figure 9.6.4)ensure a trouble-free operation.

The milking system (Figure 9.6.5), for example,runs almost fully automatically in a modern farm.

DEH

Nfle

x

DEHNflexDFL M 255Part No. 924 396

Fig. 9.6.1 Modern automatic milking system

Fig. 9.6.2 Automatic feeding system

Fig. 9.6.3 Ventilation and flushing system

Fig. 9.6.4 Heating system with heat recovery and service water supply

DEH

Ngu

ard

DG

MO

D 2

75

DEHNguard SDG S 275Part No. 952 070

3 OUT 4

1 IN 2

BLI

TZD

UC

TOR

BC

T M

LC B

E 24

No

. 919

323

BLITZDUCTOR CTBCT BASPart No. 919 506 +

BCT MLC BE 24Part No. 919 323

DEH

Nra

il

DR

MO

D 2

55

43

21

DEHNrailDR M 2P 255 FMPart No. 953 205

Page 257: Lightning Protection Guide

Following to a natural rhythm, the dairy cowsenter the milking carousel once in the early morn-ing and once in the evening – always at the sametime – to deliver their milk. The quantity deliveredis immediately acquired by the electronic operat-ing control system of this installation, saved andtransmitted online to an existing computer net-work for administration.

Each animal has a collar with a registration chip(Figure 9.6.6) for identification. Beside the milkquantity, inter alia the name, date of birth,descent, diseases, feed quantity, pregnancy dura-tion, etc. of the animal is acquired and stored. Thefarmer can immediately intervene, when e.g. themilk quantity changes, by modifying the feedquantity accordingly, and compensate for losses asquickly as possible.

The failure of even only one plant component dueto surges leads to non-foreseeable consequencesfor operators and animals. For example to

⇒ an impairment of the animals’ health,

⇒ downtimes of the systems,

⇒ production losses,

⇒ additional costs of medical care for the ani-mals,

⇒ high expenditure on data reconstruction and

⇒ expenses for the replacing of the faulty de-vices and the time required for it.

Reports on such damage in the following:

[ Donaukurier Online ] 29.06.2001

Lightning killed cow in the barnPower failed: Pigs suffocated

Munich. During the thunderstorms in the nighttowards Thursday, a flash of lightning set a barnon fire in the rural district of Roth. In a barn in Höt-tingen (rural district of Weißenburg-Gunzen-hausen), a cow was killed by lightning. Thestrongest cloudburst happened in Kempten,where more than 21 litres of rain per square metrefell in one hour. In Weißenburg, it was 20 litres.

Around 450 pigs suffocated in a fattening shed inKitzingen and died of panic attacks. A power fail-ure, apparently caused by a thunderstorm, has putthe ventilation of the stable out of operation inthe night towards Thursday, said the police. Thefarmer could still open a window of the barn butcould not prevent the perishing of the animals.

[ Oberpfalznet ] 16.06.2003

60 cows burn in the stable

Lightning discharge sets farm on fire in Kainsricht– 500,000 Euro damage

Kainsricht. A flash of lightning struck a farm onearly Saturday evening and set a stable with twooutbuildings on fire. 60 cows died in the flames.The owner of the farm, a 70 year old farmer, suf-fered a shock. The caused damage amounts to atleast 500,000 Euro.

www.dehn.de256 LIGHTNING PROTECTION GUIDE

Fig. 9.6.5 Electrical milking system with control box Fig. 9.6.6 Cow with collar and registration chip

DEH

Nra

il

DR

MO

D 2

55

43

21

DEHNrailDR M 2P 255 FMPart No. 953 205

Page 258: Lightning Protection Guide

[ Stuttgarter Nachrichten Online ] 09.05.2003Many fires and full cellarsThe fire brigade of Fribourg moved out for morethan 60 deployments. Within two hours, the policereceived 150 emergency calls in the city. In Ober-

wolfach (district of Ortenau), a flash of lightningset a farm on fire and caused a damage of approx-imately 150,000 Euro. The almost 100 year oldbuilding burned down to the foundation walls.Nobody was injured.

www.dehn.de LIGHTNING PROTECTION GUIDE 257

Type Part No.No.

1

2

3

4

951 400TN-S systemDEHNventil M TNSDV M TNS 255

TT systemDEHNventil M TTDV M TT 255

951 310

ISDN ProtectorISDN PRO

909 954

BLITZDUCTOR CTBCT MLC BD HF 5 + BCT BAS

BLITZDUCTOR CTBCT MLC BD 110 + BCT BAS

kWhHUB

NTBA

telecommu-nicationsupply line

powersupply line

lines to stabling

telephone

1

2

3

4

919 370 +919 506

919 347 +919 506

M M

milking carousel

lines to residentialbuilding

feeding trough

4–20 mA

potential control closeto the standing animals(IEC 60364-7-705)

230 V

feeding system control

milkingsystem control

feeding trough

Type Part No.No.

1

2

3

4

5

1

4

2 43

4

2

5

5 5

5

951 400TN-S-SystemDEHNventil M TNSDV M TNS 255

TT-SystemDEHNventil M TTDV M TT 255

951 310

DEHNrail DR M 2P 255 FM 953 205

S-ProtectorS PRO

909 821

BLITZDUCTOR CTBCT MLC BD HF 5 + BCT BAS

919 370 +919 506

BLITZDUCTOR CTBCT MLC BE 24 + BCT BAS

919 323 +919 506

Fig. 9.6.7 Lightning and surge protection for agricultural installations, residential building and office

Fig. 9.6.8 Lightning and surge protection for agricultural installations, stabling

Page 259: Lightning Protection Guide

These examples obviously show the importance oflightning and surge protection in agricultural sys-tems. An extensive protection requires the use ofcomponents for electrical engineering as well asfor information technology (telecommunicationsnetwork, computer network, measuring and con-trol line). Companies located at network spurs ofdistribution networks are especially at risk.

The Figures 9.6.7 and 9.6.8 show the implementa-tion of lightning and surge protection in agricul-tural buildings or structures. Here, the design ofthe lightning and surge protection on the powersupply side using protective devices arranged in adecentralised manner by means of combined light-ning current and surge arresters.

www.dehn.de258 LIGHTNING PROTECTION GUIDE

Page 260: Lightning Protection Guide

In the industry as well as in the private sector,video surveillance systems are used more and morefrequently for entrance monitoring and propertysupervision.The following describes protective measuresagainst surges that meet the availability require-ments on video surveillance systems.A video surveillance system consists at least of onecamera, one monitor and one suitable video trans-mission line. Remotely controllable camera sta-tions are normally equipped with an inclinationand swivel support so that position and viewingangle of the station can be individually adapted byan operator.As shown in Figure 9.7.1, video transmission andpower supply of the camera are implemented viaan interface cable between terminal box and cam-era.The communication line between terminal boxand monitor can be a coaxial cable or a balancedtwo-wire cable. The transfer of the video signalsthrough coaxial cables is certainly the most com-mon type in video technology. In this case, anunbalanced transfer is used, i.e. the video signal istransferred through the core of the coaxial cable

(inner conductor). The shielding (earth) is the ref-erence point for the signal transmission. The two-wire transmission is, beside the coaxial cable trans-mission, a common possibility. If there is already aglobal telecommunication infrastructure for theobject to be monitored, a free twin wire (two-wirecable) in the telecommunication cables is used totransfer the video signal

Video surveillance systems are partially powereddirectly from the distribution panels, but also viainserted UPS.

Choice of surge protective devices

Building with external lightning protection systemIn Figure 9.7.1, the camera is installed on a pole. Adirect lightning strike into the camera can be pre-vented by an air-termination rod mounted at thetop end of the pole. With reference to the cameraas well as to its connection cable, a sufficient sepa-ration distance (IEC 62305-3 (EN 62305-3)) must bemaintained from parts of the external lightningprotection system.

www.dehn.de LIGHTNING PROTECTION GUIDE 259

9.7 Lightning and surge protection for video surveillancesystems

camera

inclination andswivel head

junction box

junction box

coax or two-wire cable

control cable 230 V power cable

electrical distributor

camera

inclination andswivel head

control cable

monitor

control board

system cableair-termination rod

1

3 2

32

4

LV supply

MEBB

meshed earth termination system

BLITZDUCTOR XT ML4 BE HF5for two-wire cables orUGKF BNC for coax cable

2 BLITZDUCTOR XT ML4 BE...(e.g. 24 V)

3 Combined lightningcurrent and surge arresterDEHNventil modular

41 Surge arresterDEHNguard modular

Fig. 9.7.1 Video surveillance system – Lightning and surge protection

Page 261: Lightning Protection Guide

Usually, the connecting cable between terminalbox and camera is laid inside the metal pole.If this is not possible, the camera cable has to belaid in a metal pipe, which must be electrically con-nected with the pole. For cable lengths of a fewmeters, a protective circuit in the terminal box isnot necessary in these cases.For the coaxial cable or the two-wire cable as wellas for the control cable leading from the terminalbox at the pole into a building with an externallightning protection system, lightning equipoten-tial bonding must be implemented (Table 9.7.1).This includes connecting the lightning protectionsystem with pipings, metal installations within thebuilding and the earth-termination system. Addi-tionally, all earthed parts of the power supply anddata processing systems must be integrated intothe lightning equipotential bonding. All live wiresof power supply and data processing cables and

www.dehn.de260 LIGHTNING PROTECTION GUIDE

air-termination rod

No. in Figure9.7.1 and 9.7.3

Protection for ... SPDs Part No.

2-wire cable(video transmission)

Coax cable(video transmission)

Control cable(e.g. 24 V DC)

BLITZDUCTOR XT, BXT ML4 BE HF 5+ BXT BAS

UGKF BNC

BLITZDUCTOR XT, BXT ML4 BD 24+ BXT BAS

920 370920 300

929 010

920 324920 300

2

2

3

Protection for ... SPDs Part No.

3-phase TN-C system

3-phase TN-S system

3-phase TT system

Single-phase TN system

Single-phase TT system

DEHNventil DV M TNC 255

DEHNventil DV M TNS 255

DEHNventil DV M TT 255

DEHNventil DV M TN 255

DEHNventil DV M TT 2P 255

951 300

951 400

951 310

951 200

951 110

4

Combined SPDs (lightning current and surge arresters)

No. in Figure9.7.1 and 9.7.3 Protection for ... SPDs Part No.

3-phase TN-C system

3-phase TN-S system

3-phase TT system

Single-phase TN system

Single-phase TT system

DEHNguard DG M TNC 275

DEHNguard DG M TNS 275

DEHNguard DG M TT 275

DEHNguard DG M TN 275

DEHNguard DG M TT 2P 275

952 300

952 400

952 310

952 200

952 110

1

Surge arresters

No. in Figure9.7.1

Fig. 9.7.2 Camera for video surveillance in the protective area of theair-termination rod

Table 9.7.1 Lightning and surge protection for signal lines

Table 9.7.2 Lightning and surge protection for power supply lines

Page 262: Lightning Protection Guide

lines leading in and coming out of the structureare connected indirectly with the lightningequipotential bonding via lightning currentarresters (SPD Type 1). If no lightning currentarresters (SPD Type 1) are installed in the low volt-age main distribution board, the operator must beinformed that these need to be upgraded.Tables 9.7.1 and 9.7.2 show the surge protectivedevices to be used for signal and power supplylines according to consecutive numbers in Figure9.7.1.Figure 9.7.1 (No. 4) shows the application of a com-bined lightning current and surge arrester DEHN-ventil modular (Table 9.7.2). This combined SPDunites lightning current arrester and surge arrester(SPD Type 1 + 2) in one device, requires no decou-pling coil and is available as complete prewiredunit for each type of low voltage system (TN-C, TN-S, TT).Up to cable lengths of ≤ 5 m between DEHNventiland terminal equipment, there is sufficient protec-tion without additional protective devices. In caseof greater cable lengths, additional surge protec-tive devices are required for the terminal equip-ment, e.g. DEHNrail modular.

When mounting the camera at an external build-ing facade it should be ensured that the camera isfixed below the outer edge of the roof, in the pro-tection zone. If this is not possible, an area must becreated that is protected against lightning strikesby means of additional external lightning protec-tion measures. This can be done with an air-termi-nation system, as shown in Figure 9.7.2, to safe-guard the camera against direct lightning strikes.

Buildings without external lightning protectionsystemFor buildings without external lightning protec-tion system, it is assumed that the risk of damagecaused by a direct or close lightning strike into thebuilding, is low and therefore accepted.If this risk is also accepted for a subsequentlymounted video transmission equipment, this canbe sufficiently protected by installing SPDs.The surge protective devices to be used for thepower supply line in Figure 9.7.3 can be takenfrom Table 9.7.2.The surge arresters for protection of the signallines in Figure 9.7.3 are listed in Table 9.7.1.

www.dehn.de LIGHTNING PROTECTION GUIDE 261

Fig. 9.7.3 Video surveillance system – Surge protection

camera

inclinationdand swivel head

junction box

coax ortwo-wire cable

control cable 230 V power cableelectrical distributor

1

32

3 2 1

Surge arresterDEHNguard modular

1 BLITZDUCTOR XT BXT ML4 BD...(e.g. 24 V)

32 BLITZDUCTOR XT BXT ML4 BE HF 5for two-wire cableor UGKF for coax cable

monitor

junction box

control boardcamerainclination andswivel head

system cable

control cable

Page 263: Lightning Protection Guide

www.dehn.de262 LIGHTNING PROTECTION GUIDE

9.8 Surge protection for public address systems(PA systems)

Public address systems are applied as compactdevices with standardised performance character-istics as well as in 19 “ modular design. They areused for voice, music and signal transmission. Forthis the wanted signal is modulated to a carriervoltage (50, 70, 100 V) and transmitted to theloudspeakers.This transmitter transforms the low impedance ofthe loudspeaker to a higher value, thus reducingthe signal current. This allows also telecommunica-tion cables (0.6 or 0.8 mm diameter) to be used.

Most different kinds of loudspeakers are used. Thenominal power in the range of fitting or surface-mounted loudspeakers being at approx. 6 – 30 W,

of loudspeaker columns at approx. 20 – 100 W andof horns at approx. 10 – 60 W. The lowest nominalpower of amplifiers in modular design is about 100 W going up to 600 W and more.

In a line or group, loudspeakers of different powercan be used in common. The minimum power ofthe amplifier is equal to the sum of power of theindividual loudspeakers. Not the sum of the loud-speakers‘ nominal power is decisive for the addi-tion, but rather the sum of power levels actuallychosen at the tappings of the transmitters.

Designing of the conductor system of a publicaddress system is subject to EN 50174-2.

Fig. 9.8.1 Public address system in modular design with surge protective devices

1

2 7

3

4

5

6

3

4

5

8

7

DGA FF TV, Part No. 909 7031 DGA G BNC, Part No. 929 0423

DR M 2P 150, Part No. 953 204(currents > 1 A – 25 A)orBCT MLC BE 110, Part No. 919 327BCT BAS, Part No. 919 506(currents < 1A)

2 DCO RK ME 110, Part No. 919 923AD DCO RK GE, Part No. 919 979(currents < 0.5 A)

7FS 9E HS 12, Part No. 924 0194

DR M 2 P 255, Part No. 953 2006

230 V supply

coax

75 Ω

loudspeaker 100 V

DCF 77 antenna

PC terminal RS 232

intercom withcontrol andselection keys

power amplifier

Tuner

CD Player

central unit withinput slots

relay module 100 V

EBB

EBB

EBB

EBB

EBB

BXT ML4 BD HF 5, Part No. 920 371BXT BAS, Part No. 920 300

5 S PRO, Part No. 909 8218

230 V supply

loudspeaker 100 V

EBB

Page 264: Lightning Protection Guide

In the quoted EN standard, surge protection isdescribed in the installation guidelines under6.11.3. Beside the mentioned protection of theconductors, the main focus, namely the protectionof the devices installed in the conductor system, ispointed out.

In the following presentation we do not refer toany further regulations which might be applicable(e.g. building regulation, public address emer-gency systems, danger alarm in case of fire andraid, etc.).

Major PA systems have a 19 “ modular design (Fig-ure 9.8.1) and are in the vicinity of a permanentlyoccupied working place.

Therefore the existing interconnecting line to thePC or the site of the intercom is determining forthe use of the surge arresters given under and

. A protection of the line usually isrequired if the distance is > 5 m.

Dimensioning of the surge arresters listed underand requires to determine the maximum

current in the corresponding conductor branch.This is done by the relation I = P/U, with U beingthe carrier voltage and P the power of the amplifi-er to dimension the surge arrester and thepower of the loudspeaker to dimension the surgearrester . In case of several loudspeakers in closespatial vicinity, P is the sum of the individual loud-speaker’s power.

It is recommended to connect all earthing termi-nals of the surge arresters to with an adja-cent equipotential bonding point (mini EB bar).

If loudspeakers are positioned in lightning protec-tion zone LPZ 0A (area with hazard of direct light-ning strike) of buildings without external lightningprotection system, combined lightning current andsurge arresters have to be installed (Figure 9.8.2). Ifhere only a lightning current arrester is installed,the loudspeakers in the building installed in thistrack can be damaged.

If loudspeakers are positioned in lightning protec-tion zone LPZ 0B (area without hazard of lightningstrike) of buildings with external lightning protec-tion system, surge arresters have to be installed atthe entrance of the building (Figure 9.8.3).

1

BCT MLC BE 110, Part No. 919 327BCT BAS, Part No. 919 506(currents < 1 A)

EBB

1

1

protective angle

DCO RK ME 110, Part No. 919 923AD DCO RK GE, Part No. 919 979(currents < 0,5 A)

1

EBB

www.dehn.de LIGHTNING PROTECTION GUIDE 263

Fig. 9.8.3 Building with external lightning protection and horn inLPZ 0B protected by surge arresters

Fig. 9.8.2 Building without external lightning protection and horn inLPZ 0A protected by combined lightning current and surgearresters

Page 265: Lightning Protection Guide

In a dangerous situation, hazard alert systems (firealarm systems or burglar alarm systems) shall sig-nal actively, and remain passive in safe situations.Malfunctions of these systems (no response in caseof danger, or alarm signal in case of no danger) areundesirable and expensive. False alarms sent byhazard alert systems result in expenses, which, inthe industrial countries, amount to several hun-dred million Euro per year. Another aspect of mal-functions is the possible direct or indirect dangerto human lives. In this context, we may rememberthe malfunction of the fire alarm system in thetower of the Frankfurt Rhein-Main airport in 1992,where a false activation of the fire extinguishingsystem occurred because of a lightning strike.Within a few minutes, the air traffic controllershad to leave the control room. In this critical situa-tion, approaching airplanes had to be redirectedto other airports. Considerable delays occurred inthe air traffic.

False alarms of hazard alert systems are also dis-turbing in another respect:

⇒ When false alarms accumulate, the operatorcan no longer rely on the system and questionsthe significance of the system (investment) assuch.

⇒ The guard starts ignoring alarm messages.

⇒ Neighbours will be disturbed by acousticalarms.

⇒ Action forces (e.g. fire brigade) will be boundunnecessarily.

⇒ The activation of the fire extinguishing systemcauses interruptions of operations.

⇒ Damage is caused by not signalling existinghazard.

All these factors cause unnecessary expenses. Theycan be avoided, when possible causes for falsealarms are already recognised in the design stageand are eliminated by suitable preventive meas-ures. For this purpose, the German Insurance Asso-ciation (Gesamtverband der Deutschen Ver-sicherungswirtschaft e.V. - GDV) published VdSguidelines (VdS 2095; VdS 2311; VdS 2833). One ofthe measures also requested in the VdS guidelinesis lightning and surge protection.A coordinated lightning and surge protection pre-vents a false alarm caused by atmospheric dis-

charges and improves the availability of the earlydetection of dangers and alarms.When installing comparable alarm transmissionsystems, for which, out of financial reasons, a VdSapproval is not used (e.g. residential building), theguidelines may also be used for project design andfor the construction as well as for agreeing individ-ual measures between constructors and operators.

Indeed, most of the nowadays installed fire alarmsystems have an increased surge immunity inaccordance with IEC 61000-4-5 for primary and sec-ondary wires as well as for the mains inputs. How-ever, a comprehensive protection against damageby lightning discharge and surges can only beachieved by external and internal lightning protec-tion measures (Figure 9.9.1 to Figure 9.9.4).

Monitoring principlesDifferent monitoring principles are applied forhazard alert systems:

⇒ Impulse line technology

The information from the triggering alarmdevice is transferred in digital form. Thisallows to recognise the alarm device and theexact localisation of the trouble spot (Figure9.9.1).

⇒ d.c. line technology

Each alarm line is permanently monitoredaccording to the closed-circuit principle. If analarm device is activated in the line, this line isinterrupted and an alarm is triggered in thecontrol and indication equipment. Hereby,however, only the alarm line can be identifiedbut not the individual detector (Figures 9.9.3and 9.9.4).

Regardless of the used monitoring principle, thelines of the hazard alert system must be integratedinto the lightning and surge protection of thecomplete system.

Protection recommendationsFor protection of alarm lines with d.c. line tech-nology, BLITZDUCTOR XT, Type BXT ML4 BE ... isrecommended. It is chosen according to the volt-age of the alarm lines, which is normally 12 or 24 V.

www.dehn.de264 LIGHTNING PROTECTION GUIDE

9.9 Surge protection for hazard alert systems

Page 266: Lightning Protection Guide

BLITZDUCTOR XT, Type BXTML4 BE is recommended inorder not to change the loopresistance of the alarm linestoo much.

Regardless of the line topolo-gy, the outputs of the controland indication equipment, ase.g. for acoustic and visualsignalisation, should be pro-tected by BLITZDUCTOR XT.Care should be taken that thenominal current of the pro-tective devices is not exceed-ed. In case of nominal cur-rents > 0.5 A, DEHNrail, TypeDR M 2P 30 protective devicehas to be used alternatively.

The control and indicationunit is normally connected to an exchange line of afixed-network operator (e.g.Deutsche Telekom) by meansof a telephone dial unit. Forthis application, the SPD typeBLITZDUCTOR XT, BXT ML4BD 180 is suitable (see alsoChapter 9.14 “Surge protec-tion for telecommunicationsaccesses”).

The surge protection of thepower supply is important,too. It is recommended to useDEHNguard modular surgeprotective devices here (seeTable 9.9.2).

For alarm systems, which arecertified by the GermanInsurance Association, (sys-tems recognised by VdS), themanufacturer of the alarmsystem should be contacted.The installations as well asthe lightning and surge pro-tection equipment have to beset up in accordance with VdS2095, VdS 2311 or VdS 2833.

www.dehn.de LIGHTNING PROTECTION GUIDE 265

L1 N PE

4

4

4

6

6

2

6

6

2

8 8 8 8 8

8 8 8 8 84

2

2

2

3

1

magneticcontactsglass breakagedetector

IR detector 1

IR detector 2

impact sound detector

robbery alarm button 1+2

block lock 1

block lock 2

activation acknowledging 1

activation acknowledging 2

buzzer 1

siren 1

siren 2

flashlight

Detector group 1

Detector group 2

Detector group 3

Detector group 4

Detector group 5

Detector group 6

Detector group 7

Burglar group

Block lock

Area 1

Block lock

Area 2

Signal transmitter

Exterior alarm system 1

Sabotage line

Exterior alarm system 2

Exterior alarm system 3

Cont

rol a

nd in

dica

tion

uni

t

L1 N PE 3

1

2

2

2

2

10

2

2A− A+

B− B+

Exterior alarmsystem 1

Exterior alarmsystem 2

Exterior alarmsystem 3

siren 1

siren 2

flashlight

Cont

rol a

nd in

dica

tion

uni

t analogue ring

SPD

Telecom

annunciator

Fig. 9.9.1 Lightning and surge protection for the control unit of a burglar alarm system withimpulse line technology

Fig. 9.9.2 Lightning and surge protection for the control unit of a fire alarm system – Analogue ring

Page 267: Lightning Protection Guide

As an example, the enclosed diagrams contain aproposal for surge protection of fire alarm andburglar alarm control and indication units, whichare operated on the principle of d.c. line tech-nology or pulse engineering.If the fire and burglar alarm post and the controlunit shall be integrated into a lightning protection

system, then all lines entering the building shall beconnected with lightning current arresters or com-bined lightning current and surge arresters. SeeTables 9.9.1 and 9.9.2.

A distinct increase of the operational reliability ofthese systems can be reached with specific light-

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L1 N PE

1

3

2

33

3 3

Detector line 1

Detector line 2

Exterior alarm system 1

Exterior alarm system 2

Exterioralarm system 3

siren 1

siren 2

flashlight

Cont

rol a

nd in

dica

tion

uni

t buzzer

magnetic contacts andglass breakage detector

IR detector 1block lock 1

activationacknowledging

deviceIR detector 2

activationacknowledgingdevice

block lock 2

burglaralarmbutton

SPD

Telecom

magnetic contacts andglass breakage detector

No. Protective deviceBLITZDUCTOR XT ...

Short definitionFour pole, universal device as terminal block for protection ofIT systems and devices consisting of a base part and a protectionmodule with integrated LifeCheck

Part No.

BXT ML4 BE 12 orBXT ML4 BE 24+ BXT BAS

Combined lightning current and surge arrester for use in the EMC-orientated lightning protection zones concept at the boundariesLPZ 0A to LPZ 1 or LPZ 0A to LPZ 2

920 322or 920 324+ 920 300

1

BXT ML4 BD 180+ BXT BAS

Combined lightning current and surge arrester for use in the EMC-orientated lightning protection zones concept at the boundariesLPZ 0A to LPZ 1 or LPZ 0A to LPZ 2

920 347+ 920 300

2

Fig. 9.9.3 Lightning and surge protection for the control unit of a burglar alarm system with d.c. line technology

Table 9.9.1 Short definition of the SPDs

Page 268: Lightning Protection Guide

ning and surge protection of hazard alert systems.On the one hand, this refers to the prevention offalse alarms when no danger exists, and on theother, costs eventually arising from this, can beprevented. This again, allows an effective damagelimitation by informing the auxiliary personnelreliably. This counteracts a possible formation of

catastrophic conditions (e.g.danger to human lives, pol-lution of the environment,etc.). Notice that in case ofinjuries to persons or envi-ronmental damage, theoperator of a plant is liablefirst. This comprehensiveresponsibility for securitycan normally be expectedfrom managers or execu-tives of a company. How-ever, in the legal sense, anoperator of a plant is a tech-nical layman, who is notable to estimate, if threatscan arise from a technicalsolution. Therefore, skilledpersons as suppliers of tech-nical solutions must ensurein each individual case, thatthe solutions offered alsocorrespond to the actualrequirements. Retreating tothe accepted rules of tech-nology is not sufficient, if

the state of the art already describes a higher qual-ity solution. This may entitle a technical layman(plant operator) to claim recourses.

Regardless of the fact, whether fire alarm systemsare VdS-approved systems or not, they should befurnished with a surge protection.

www.dehn.de LIGHTNING PROTECTION GUIDE 267

L1 N PE

2

2

2

2

10

4

8

8

4

2

2

2

2

1

3

Detector group 1

Detector group 2

Detector group 3

Detector group 4

Exterior alarm system 1

Exterior alarm system 2

Exterior alarm system 3

siren 1

siren 2

flashlight

Cont

rol a

nd in

dica

tion

uni

t

annunciator

sprinkler system

FB control panel

FB key depot

main detector

SPD

Telecom FB = fire brigade

3

No.

Protection for ... SPDs Part No.

DEHNventil DV M TN 255

DEHNventil DV M TT 2P 255

Multi pole, modular combined lightning current and surge arrester, Type 1 (LPZ 0A – LPZ 2)

Protection for ... SPDs Part No.

TN system

TT system

3-phase TN-C system

3-phase TN-S system

3-phase TT system

Single-phase TN-S system

Single-phase TN-C system

Single-phase TT system

DEHNguard DG M TNC 275

DEHNguard DG M TNS 275

DEHNguard DG M TT 275

DEHNguard DG M TN 275

DEHNguard DG S 275

DEHNguard DG M TT 2P 275

952 300

952 400

952 310

952 200

952 070

952 110

Multi pole, modular surge arrester, Type 2 (LPZ 0B – LPZ 1 and higher)

951 200

951 110

Fig. 9.9.4 Lightning and surge protection for the control unit of a fire alarm system with d.c. line tech-nology

Table 9.9.2 Selection of SPDs

Page 269: Lightning Protection Guide

In modern office buildings and public utilities, likeschools, KNX bus systems are used for the automa-tion of sequences of operations of the buildingcontrol system. KNX offers the possibility to realisecomplex processes with a single, upwards compat-ible system. However, this future-proof investmentcan be quickly destroyed by lightning discharges.Then, the building automation is not available andfurther costs are caused by replacement and recon-figuration of the system. Therefore, measures shallbe taken against the direct and indirect effects of a lightning discharge when designing andinstalling such complex systems (Figure 9.10.1).

Lightning protection or surge protection?

Basic conditions must be considered when choos-ing the surge arresters correctly. This does not onlyinclude the system-specific electric data, like nomi-nal voltage, nominal current, frequency, but alsothe threat parameters, which must be controlled.It makes a difference, if the risk of direct lightningstrikes into buildings, where the KNX is installed,must be considered when designing the protectivemeasures, or if safety against surges is desired only.If direct lightning strikes and the high destructionpotential involved should be handled properly, theinfrastructure of the KNX system must be designedaccording to the lightning protection zones con-cept. The lightning protection zones concept is

standardised in IEC 62305-4 (EN 62305-4) anddescribes the protective measures against light-ning electromagnetic impulses. An important partis the classification of the infrastructure to be pro-tected in lightning protection zones. The higherthe ordinal number of the lightning protectionzones, the smaller must be the electromagneticthreat parameters. Electrical and electronic sys-tems like the KNX system have to be classified inaccordance with their electromagnetic immunityinto lightning protection zones, which also offeran electromagnetic environment in case of a directlightning strike to ensure that the equipment con-tinues to function without getting disturbed oreven destroyed.

If an external lightning protection system isinstalled in accordance with IEC 62305-3 (EN62305-3), an effective lightning and surge protec-tion is necessary and is to be implemented for theKNX according to the lightning protection zonesconcept. Within the context of KNX systems, themeasures taken are often called primary and sec-ondary protective measures.

If the aim of the protective measures is only theprotection against surges (secondary protection),the hazard potential of a direct lightning strike isnot taken into account. In the case of a direct orvery near lightning strike into buildings with built-in KNX, damage must be expected there. Onlyinterferences resulting from inductive or capaci-tive coupling, as they occur during lightning dis-charges some kilometres away or during switchingoperations, can be controlled. Lightning dis-charges create electromagnetic interference fields,which can cause dangerously high voltages andcurrents in installation loops.

Cabling between buildings

In an extended building complex, which isequipped with a lightning protection system, aKNX installation shall be integrated and protectedagainst transient surges. A gatehouse is approxi-mately 50 m away from a main building. Bothbuildings are equipped with a lightning protectionsystem. Since the gatehouse is connected to theKNX installation of the main building via a busline, measures for internal lightning protectionmust be taken both for the 230/400 V line as wellas for the bus line.

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9.10 Lightning and surge protection for KNX systems

Fig. 9.10.1 Application of the BUStector (Part No. 925 001)

Page 270: Lightning Protection Guide

General conditions 1:Connecting the two buildings with a buried cable(copper cable).Solution 1: Figure 9.10.2, Table 9.10.1

General conditions 2:Connection of the two buildings with cable andlines in a supply duct, the reinforcement of whichis integrated into the equipotential bonding atboth ends. This condition is also fulfilled by anearthing strip steel 50 mm2 laid upon the buriedcables and connected to the equipotential bond-ing bar at both ends.Solution 2: Figure 9.10.3, Table 9.10.1

General conditions 3:The KNX connection between both buildings isachieved via an optical fibre connection (OFC). Ifthe fibre-optic cable has a metal braid inside thecable (protection against rodents), this braid has tobe connected to the equipotential bonding at thepoint where it enters the building.Solution 3: Figure 9.10.4, Table 9.10.1

For the design and implementation of an KNX sys-tem, it is absolutely necessary that designers andcontractors take appropriate measures for the cor-rect operation of such a system. Of particular con-

www.dehn.de LIGHTNING PROTECTION GUIDE 269

No. Protection for ... SPDs Part No.

3-phase TN-C system3-phase TN-S system3-phase TT system

3-phase TN-C system3-phase TN-S system3-phase TT system

DEHNventil DV M TNC 255DEHNventil DV M TNS 255DEHNventil DV M TT 255

BLITZDUCTOR XT, Typ BXT ML4 BD 180+ BXT BAS

DEHNguard DG M TNC 275DEHNguard DG M TNS 275DEHNguard DG M TT 275

BUStector BT 24

951 300951 400951 310

920 347920 300

952 300952 400952 310

925 001

1

2

3

4

KNX distribution board KNX distribution board

main building complex gatehouse

power cable

bus cable

3 4

1 2

3

4

2 1

EBBEBB EBB

Table 9.10.1 Short description of the SPDs

Fig. 9.10.2 Lightning and surge protection for cabling systems installed between buildings without interconnection of the foundation earthelectrodes

Page 271: Lightning Protection Guide

cern should be into which surroundings the KNXsystem is integrated and installed. Interfaces toother infrastructures, like low-voltage systems,telecommunications and data systems have to beprotected against interferences or even destruc-tion as the KNX itself.

Proper lightning protection systems and surge pro-tection systems and the corresponding surge pro-tective devices are available for protection againstthe effects of interferences. These can protect thefuture-proof KNX building installation cost-effec-tively due to technical and economic considera-tions during the design and by expert installation.

www.dehn.de270 LIGHTNING PROTECTION GUIDE

KNX distribution board KNX distribution board

main building complex gatehouse

power cable

bus cable

cable ductor 50 mm2 steel

43

EBB EBB EBB

4

3

KNX distribution board KNX distribution board

main building complex gatehouse

power cable

optical fibre cable

43

1 1

4

3

EBB EBB EBB

Optical fibre / KNX converter

Fig. 9.10.3 Lightning and surge protection for cabling systems installed between buildings with interconnection of the foundation earth electrodes

Fig. 9.10.4 Lightning and surge protection for cabling systems installed between buildings without interconnection of the foundation earthelectrodes, with KNX optical fibre cabling

Page 272: Lightning Protection Guide

Surges not only cause malfunctions but alsodestructions and thus, failures of computer sys-tems, by which the operation can be persistentlyimpaired because of longer down times. Besides aprotected power supply and data backup, the reli-able utilisation of computer systems also requiresprotection concepts against surges.

Causes of damageFailures of computer systems are typically causedby

⇒ distant lightning strikes generating conductedtransient overvoltages in power supply lines,data lines, or communication lines

⇒ close lightning strikes generating electromag-netic fields, by which transient surges areinduced in power supply lines, data lines, orcommunication lines

⇒ direct lightning strikes creating impermissiblepotential differences and partial lightning cur-rents in the building installations.

Choice of surge protective devicesFor an effective surge protection it is necessarythat the measures for the different systems arecoordinated by the involved experts like electricalengineering technicians, computer specialists andtelecommunications technicians as well as themanufacturer. In case of bigger projects, it is neces-sary to consult an expert (e.g. from an engineeringcompany).

Protection of the power equipmentFigure 9.11.1 shows an administration building asan example. For the power supply, lightning cur-rent arresters Type 1 (e.g. DEHNbloc Maxi) andSPDs Type 2 (e.g. DEHNguard modular) can be

www.dehn.de LIGHTNING PROTECTION GUIDE 271

9.11 Surge protection for Ethernet and Fast Ethernetnetworks

Fig. 9.11.1 Administration building with highly available installation parts

4

5 5

1

4

4

11

12

9

65

7

3

2

86

11

6

10

1

2

3

4

5

6

7

12

8

9

11

10

MDB

SDB

SDB

serv

er

buildingdistri-butionboard

telephoneterminal board

TC floor distri-bution board

EBB

No. SPD Type Part No.

DEHNbloc MaxiDEHNrapid LSADisconnection blockMounting frame forterm. blocks 10 x 10 TCEquipotential bonding barDEHNguard modularDEHNrail modularDEHNpatch

DEHNlink(upstream splitter)SFL-ProtectorNET-Protector for 8x2DA19" bayDEHNflex MTelephone protectionmodule DSMDATA-Protector

DBM 1 255

DRL 10 B 180 FSD

TL2 10 DA LSA

MB2 10 LSA

K12

DG M TNS 275

DR M 2P 255

DPA MCAT6 RJ45H 48

DLI TC 1 I

SFL PRO

NET PRO TC 2 LSA

EG NET PRO 19"

DFL M 255

DSM TC 1 SK

DATA PRO 4TP

900 025

907 401

907 996

907 995

563 200

952 400

953 200

929 110

929 027

912 260

929 072

929 034

924 396

924 271

909 955

EDP

TC system

Page 273: Lightning Protection Guide

installed. DEHNrail, SFL-Protector, or DEHNflex M,for example, can be used for protection of the ter-minal equipment.

Protection of the data and telephone linesWhether data or voice transmission is concerned,both require appropriate protective componentsfor safe operation. Even if fibre optic cables

between building distributors and floor distribu-tors are the standard practice, copper wires are stillused between the floor distributor and the termi-nal equipment. Therefore, it is necessary to protectactive components with DEHNpatch for example.Terminal equipment should also be protected forexample by DEHNpatch.

www.dehn.de272 LIGHTNING PROTECTION GUIDE

Page 274: Lightning Protection Guide

M-Bus is used for the transmission of readingsfrom consumption meters. All devices connectedto an M-Bus system can be read off centrally, eitherdirectly on the spot or per data transmission froman external head office. This increases the housingquality of the tenants, and the energy budget ofan entire building can be controlled anytime.

The following describes surge protective measuresthat meet the availability claim of this system.

The M-BusThe M-Bus (meter bus) is a cost-optimised field busfor the transmission of energy consumption data.As shown in Figure 9.12.1, a central master (in thesimplest case a PC with a level converter down-stream of the PC) communicates via a two-wire buswith the units sharing the bus. Using M-Bus

repeaters, the installation can be divided in M-Bussegments. Each segment can include up to 250slaves like heat counters, water meters, powermeters, gas meters, and also sensors and actuatorsof any type. More and more manufacturers imple-ment the electric M-Bus interface including proto-col layer into their consumption meters.The M-Bus corresponds to European standard andis described in standard EN 1434.

Previously, the energy data of individual buildingswere transferred via on-wire connections from thenetwork to the master station. Frequently, in caseof widespread building complexes, the data istransmitted via a modem connection.

The M-Bus system is used for the consumption costaccounting and remote monitoring of

www.dehn.de LIGHTNING PROTECTION GUIDE 273

9.12 Surge protection for M-Bus

direct connection

RS 232

RS 485level transformer

RS 485 M-Bus

M-Bus control unit

bus segment

M-Bus

telephone connection

modem modem

RS 232

M-Bus control unit

RS 485

level transformer

M-Bus M-Bus

M-Bus control unit remote monitoring of

an M-Bus system with5 supply meters

RS 232

RS 232

modem

repeater

telephone network

Fig. 9.12.1 Example of an M-Bus system

Page 275: Lightning Protection Guide

⇒ local and district heating systems

⇒ multifamily residences

The readout of the supply meters can be per-formed by central and decentralised systems. If thesupply meters are situated immediately close, thesimple and economical central system networkarchitecture is chosen. This includes a star-shapedconnection of each individual meter to the controlcentre. In case of a decentralised system, the dataof the meters installed on the spot is first collectedin substations and is then sent via a bus line to thecontrol centre.

The M-Bus is a two-wire bus system, which is pow-ered by an isolated supply source from the busmaster. For all other units sharing the M-Bus, noreference to the ground may be created duringoperation. The maximum bus voltage amounts to42 V.

The expansion of the network as well as the maxi-mum bit rate is limited by the number of M-Busdevices, the protective wiring, the cable routing,and the cable types used.The total sum of all cables as well as of the con-nected M-Bus devices and of protective wiringscreates a capacitance in the M-Bus segment. Thiscapacitance restricts the baud rate.

The maximum baud rate per M-Bus segment canbe determined by means of the following table(Table 9.12.1).

If surge protective devices are used, the capaci-tances and series impedances of the surge protec-tive devices must be considered and taken intoaccount when defining the network clients. Thefollowing tables show the capacitances and theseries impedances of the surge protective devices(Table 9.12.2).

Choice of surge protective devices for M-Bus sys-temsFor establishing an M-Bus system, the bus lines arealso installed outside the buildings. Therefore, thedevices are exposed to the danger of destructionby transient surges of lightning discharges andmust be protected accordingly. In the following,the surge protective circuit for M-Bus systems isdescribed in detail considering two applications.

Example of application: Building with externallightning protection systemIf a building has an external lightning protectionsystem, the lightning equipotential bonding mustbe implemented. This comprises connecting of thelightning protection system to pipelines, metalinstallations within the building and the earth-ter-mination system. In addition, all earthed parts ofthe power supply and data processing systemsmust be integrated into the lightning equipoten-tial bonding. All live lines of power supply anddata processing cables and lines entering and com-ing out of the building or structure are indirectlyconnected to the lightning equipotential bondingvia lightning current arresters. If no lightning cur-rent arresters are installed at the service entranceof the building (for example in the low-voltage

www.dehn.de274 LIGHTNING PROTECTION GUIDE

Total capacityM-Bus segment

up to 382 nF

up to 1528 nF

up to 12222 nF

Max.data transmision rate

9600 Baud

2400 Baud

300 Baud

SPDs Part No.BLITZDUCTOR CT BCT MLC BD 48

BLITZDUCTOR CT BCT MLC BE 24

BLITZDUCTOR CT BCT MLC BE 5

DEHNconnect DCO RK MD 48

DEHNconnect DCO RK ME 24

DEHNconnect DCO RK MD HF 5

919 345

919 323

919 320

919 942

919 921

919 970

Capacity: line/line Series impedance per line≤ 0.6 nF

≤ 0.7 nF

≤ 3 nF

≤ 0.6 nF

≤ 0.5 nF

≤ 19 pF

2.2 Ω

2.2 Ω

1.4 Ω

0.4 Ω

1.8 Ω

1 Ω

Table 9.12.1 Max. data transmission rate

Table 9.12.2 Capacitances and series impedances of surge protective devices

Page 276: Lightning Protection Guide

consumer's installation of the low-voltage maindistribution), the operator must be informed thatthese must be added.

Further measures for protection of electrical instal-lations and systems include installing of surge pro-tective measures. These measures also allow theprotection of the electrical installations and sys-tems in the event of a direct lightning strike asadditional measure to the lightning equipotentialbonding.

If lightning equipotential bonding and the instal-lation of surge protective measures are imple-mented as carefully as the external lightning pro-tection system, this contributes to a reliable per-formance of electrical systems. Failures, even in theevent of direct lightning strikes, are reduced.

Cascaded use of lightning current and surge ar-restersEnergy coordination is the principle of a cascadedapplication of lightning current and surgearresters. Energy coordination is usually achievedby the impedance of the connecting cable of atleast 15 m length between the SPDs. If this is notpossible, the surge protection concept can be indi-vidually adjusted to the requirements of the sys-tem by the installation of coordinated lightningcurrent arresters DEHNbloc Maxi and of DEHN-guard surge arresters.

Another possibility is using DEHNventil. This com-bined SPD unites lightning current and surgearrester in one device, requires no decoupling coil,and is available as complete prewired unit forevery low-voltage (TN-C, TN-S, TT) system (Table9.12.3).

www.dehn.de LIGHTNING PROTECTION GUIDE 275

3 1

4 2

3 4

1 23 4

1 2

1 3

2 4

1 3

2 4

1 2

3 4

1 2

3 4

3 4

1 2

3 4

1 2

10 11

1

2

3

4

5

8 9

6 7

12

UPS

building 1

modem

PC Server

COM 2processor

COM 1processor

repeater

0 ... 20 mA

temperature sensorPT 100

M-Bus box M-Bus box

building 2

230 V power supply

M-B

us

cable length≥ 15 m

Fig. 9.12.2 Protection concept for M-Bus systems in buildings with external lightning protection system

Page 277: Lightning Protection Guide

Up to cable lengths of ≤ 5 m between DEHNventiland terminal equipment, sufficient protectionexists without additional surge protective devices.For greater cable lengths, additional surge protec-tive devices have to be installed at terminal equip-ment, e.g. DEHNrail.Tables 9.12.3, 9.12.4 and 9.12.5 list surge protectivedevices to be applied in accordance with the con-secutive numbers in Figure 9.12.2.

Application example:

Building without external lightning protectionsystem

Figure 9.12.3 shows an example how a networkedM-Bus system must be wired in order to get an effi-cient protection against surges.

Tables 9.12.6 and 9.12.7 list the surge protectivedevices to be used.

www.dehn.de276 LIGHTNING PROTECTION GUIDE

No. in Fig. 9.12.2 Protection for ... SPDs Part No.

3-phase TN-C system

3-phase TN-S system

3-phase TT system

Single-phase TN system

Single-phase TT system

DEHNventil DV M TNC 255

DEHNventil DV M TNS 255

DEHNventil DV M TT 255

DEHNventil DV M TN 255

DEHNventil DV M TT 2P 255

951 300

951 400

951 310

951 200

951 110

10

951 300

951 400

951 310

951 200

951 110

No. in Fig. 9.12.2 Protection for ... SPDs BLITZDUCTOR CT Type Part No.

M-Bus

0 – 20 mA, 4 – 20 mA

temperature measure-ment PT 100, PT 1000

BCT MLC BD 48 + base part BCT BAS

BCT MLC BE 24 + base part BCT BAS

BCT MLC BE 5 + base part BCT BAS

919 345 + 919 506

919 323 + 919 506

919 320 + 919 560

8

9

1 7to

No. in Fig.9.12.2 Protection for ... SPDs Part No.

3-phase TN-C system

3-phase TN-S system

3-phase TT system

Single-phase TN system

Single-phase TT system

DEHNbloc DB 3 255 H – phase L1/L2/L3 to PEN

DEHNbloc DB 3 255 H – phase L1/L2/L3 to PE +DEHNbloc DB 1 255 H – N to PE

DEHNbloc DB 3 255 H – phase L1/L2/L3 to N+ DEHNgap DGP BN 255 – N to PE

2 x DEHNbloc DB 1 255 H – phase L + N to PE

DEHNbloc DB 1 255 H – phase L to N+ DEHNgap DGP BN 255 – N to PE

900 120

900 120900 222

900 120900 132

900 222

900 222900 132

10

3-phase TN-C system

3-phase TN-S system

3-phase TT system

Single-phase TN system

Single-phase TT system

DEHNguard DG M TNC 275

DEHNguard DG M TNS 275

DEHNguard DG M TT 275

DEHNguard DG M TN 275

DEHNguard DG M TT 2P 275

952 300

952 400

952 310

952 200

952 110

11 12

Table 9.12.3 Selection of combined SPD with regard to the power supply system

Table 9.12.4 Surge protection for signal interfaces

Table 9.12.5 Surge protection for the 230 V power supply

Page 278: Lightning Protection Guide

www.dehn.de LIGHTNING PROTECTION GUIDE 277

3 1

4 2

3 4

1 23 4

1 2

1 3

2 4

1 3

2 4

1 2

3 4

1 2

3 4

3 4

1 2

3 4

1 2

10

1

2

3

4

5

8 9

6 7

11

UPS

building 1

modem

PC server

COM 2processor

COM 1processor

repeater

0 ... 20 mA

temperature sensorPT 100

M - Bus box M - Bus box

building 2

230 V power supplyM

-Bus

No. in Fig. 9.12.3 Protection for ... SPDs Part No.

10 11

3-phase TN-C-System

3-phase TN-S-System

3-phase TT-System

Single-phase TN-System

Single-phase TT-System

DEHNguard DG M TNC 275

DEHNguard DG M TNS 275

DEHNguard DG M TT 275

DEHNguard DG M TN 275

DEHNguard DG M TT 2P 275

952 300

952 400

952 310

952 200

952 110

No. in Fig. 9.12.3 Protection for ... SPDs Part No.

M-Bus

0 – 20 mA, 4 – 20 mA

Temperature measurement PT 100, PT 1000

DEHNconnect DCO RK MD 48

DEHNconnect DCO RK ME 24

DEHNconnect DCO RK MD HF 5

919 942

919 921

919 970

8

9

1 7to

Fig. 9.12.3 Protection concept for M-Bus systems in buildings without external lightning protection system

Table 9.12.6 Surge protection for signal interfaces

Table 9.12.7 Surge protection for the power supply

Page 279: Lightning Protection Guide

The application of PROFIBUS as communicationssystem in process-related and production-relatedfields as well as its use as multi-data cell and multi-object control medium results in high availabilityrequirements on this bus system. These availabilityrequirements face a high degree of surge risks dueto the application sites.

PROFIBUSIs the SIEMENS name for communication products(hardware / software) of the PROFIBUS standard(Process Field Bus) standardised in the Germanstandard DIN 19245 and EN 50170. AlternativeSiemens names for PROFIBUS FMS and PROFIBUSDP are SINEC L2 and SINEC L2-DP. While PROFIBUSFMS is designed for baud rates up to 500 kBit/sonly, PROFIBUS DP is able to transfer data with arate of up to 12 MBit/s. First of all, the main appli-cation of PROFIBUS FMS (SINEC L2) is the handlingof big quantities of data at the process manage-ment and group control level. The fast PROFIBUSDP is designed for applications in the field of thedecentralised periphery of programmable controlsystems.

The most recent development in the PROFIBUSsegment is the intrinsically safe PROFIBUS PA,which, in process engineering, can also be used inareas where explosion hazards may occur.

A two-wire bus cable serves normally as transmis-sion medium. The physical characteristics of thebus system essentially correspond to the RS 485standard.

The bus sharing units can be connected in variousways:

⇒ Connection via 9-pin D subminiature plug(usual pin assignment 3/8)

⇒ Connection via screw terminals

⇒ Connection via bus terminals.

Selection of surge protective devices

Building with external lightning protection systemIf a building has an external lightning protectionsystem, lightning equipotential bonding must beimplemented. This includes connecting the light-ning protection system to pipelines, metal installa-tions within the building, and the earthing system.Additionally, all earthed parts of the power supplyand data processing systems must be integratedinto the lightning equipotential bonding. All livewires of power supply and data processing cablesand lines leading into and coming out of the struc-ture are indirectly connected to the lightningequipotential bonding via lightning currentarresters. If no lightning current arresters areinstalled in the low-voltage consumer's system, theoperator must be informed that these have to berefitted.

Further measures for protection of electrical instal-lations and systems include the installation ofsurge protection systems. As an additional meas-ure to lightning equipotential bonding, thesedevices also allow the protection of electrical

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9.13 Surge protection for PROFIBUS FMS, PROFIBUS DP,and PROFIBUS PA

No. in Fig. 9.13.1 SPD DEHN-Type Part No.

at service entrance

at bus station

BLITZDUCTOR XT BXT ML4 B 180+ Base part BXT BAS

BLITZDUCTOR XT BXT ML4 BE HF 5+ Base part BXT BAS

920 310920 300

920 370920 300

1

2

Table 9.13.1 Surge protection for bus lines of PROFIBUS DP/PROFIBUS FMS

Table 9.13.2 Surge protection for bus lines of PROFIBUS PA

No. in Fig. 9.13.2 DEHN-Type Part No.SPD

at bus station BLITZDUCTOR XT BXT ML4 BD EX 24+ Base part BXT BAS EX

or DEHNpipe DPI MD EX 24 M 25

920 381920 301

929 960

Page 280: Lightning Protection Guide

www.dehn.de LIGHTNING PROTECTION GUIDE 279

1 2 3 4

switchgear cabinet /services management room

equipotential bonding

bus line

bus station1 − 4

230/400 V

1

4 5 6

2 2 1

5 46

Fig. 9.13.1 Lightning and surge protection for SIMATIC Net PROFIBUS FMS and DP

Fig. 9.13.2 Use of surge protective devices in an intrinsically safe PROFIBUS PA

switchgear cabinet /services management room

equipotential bonding

PROFIBUS PA

230/400 V

non-hazardous area hazardous area

3

654

1 5

5 5 5

Page 281: Lightning Protection Guide

installations and systems, even in case of a directlightning strike. If lightning equipotential bonding and the instal-lation of surge protection systems are performedas carefully as the external lightning protectionsystem, failures are reduced even at direct light-ning strikes.

The 230/400 V a.c. supply lines going from outsideto the low-voltage main distribution board will be

protected by a DEHNventil modular, an SPD Type 1.This complete prewired unit is available for everylow voltage system (TN-C, ‚TN-S, TT) (Table 9.13.3).In addition to the operating state/fault indicationwhich is not supplied by operating currents, thisSPD Type 1 has a 3-pole terminal for remote sig-nalling.

Up to conductor lengths of ≤ 5 m between DEHN-ventil and terminal equipment, there is sufficientprotection without additional protective devices.

www.dehn.de280 LIGHTNING PROTECTION GUIDE

No. in Fig.9.13.1 und 9.13.2

Part No.

951 300

951 305

951 400

951 405

951 310

951 315

951 200

951 205

951 110

951 115

4

952 300

952 305

952 400

952 405

952 310

952 315

952 200

952 205

952 110

952 115

Combined arresters – Type 1

Surge arresters – Type 2

5

Protection for ...

3-phase TN-C system

3-phase TN-S system

3-phase TT system

Single-phase TN system

Single-phase TT system

3-phase TN-C system

3-phase TN-S system

3-phase TT system

Single-phase TN system

Single-phase TT system

for 230 V supply

for 24 V d.c. supply

SPDs

DEHNventil DV M TNC 255

DEHNventil DV M TNC 255 FM

DEHNventil DV M TNS 255

DEHNventil DV M TNS 255 FM

DEHNventil DV M TT 255

DEHNventil DV M TT 255 FM

DEHNventil DV M TN 255

DEHNventil DV M TN 255 FM

DEHNventil DV M TT 2P 255

DEHNventil DV M TT 2P 255 FM

DEHNguard DG M TNC 275

DEHNguard DG M TNC 275 FM

DEHNguard DG M TNS 275

DEHNguard DG M TNS 275 FM

DEHNguard DG M TT 275

DEHNguard DG M TT 275 FM

DEHNguard DG M TN 275

DEHNguard DG M TN 275 FM

DEHNguard DG M TT 2P 275

DEHNguard DG M TT 2P 275 FM

DEHNrail DR M 2P 255

DEHNrail DR M 2P 255 FM

DEHNrail DR M 2P 30

DEHNrail DR M 2P 30 FM

953 200

953 205

953 201

953 206

Surge arresters – Type 3

6

Table 9.13.3 Surge protection for power supply

Page 282: Lightning Protection Guide

Longer conductors require additional surge pro-tective devices at terminal equipment, e.g. DEHN-rail.

Tables 9.13.1 and 9.13.2 show surge protectivedevices for bus lines and Table 9.13.3 lists the surgeprotective devices to be installed for the powersupply.

Building without external lightning protectionsystemIf there is no external lightning protection system,the bus sharing units must be connected to surgeprotective devices. Here, the use of lightning cur-rent arresters on the power supply and data cablesis not required. In Figure 9.13.1 and 9.13.2 thecombined arrester Type 1 with No. (4) on the pow-er line nor the lightning current arrester with No.(1) on the bus line are not required.

www.dehn.de LIGHTNING PROTECTION GUIDE 281

Page 283: Lightning Protection Guide

Beside the power supply line, telecommunicationlines are the most important line connection to theoutside. For the high-technological process inindustrial plants and offices, an always functioninginterface to the “outside world” is essential forsurvival today. The user faces difficult problemswhen this service is unavailable. The damage toone's image due to surge-related equipment trou-ble of the network termination NT (NTBA, NTPM,or data network terminating unit) is only oneaspect of these incidents. High downtime costsarise for the user for a short time, since customer'sorders can not be handled, for example, or compa-ny records can only be updated locally, and can nolonger be provided nationwide. Regarding thequestion of protection-worthiness, the focus is noton the protection of the hardware but on the per-manent availability of an important service by thefixed-network operator.According to the statistics of the damage insurersof electronic devices, the most frequent cause ofdamage are surges. The most relevant type of the formation is thesurge caused by direct or distant lightning effects.Surges due to direct lightning strikes into a build-ing or structure is the severest load but the rarercase.Telecommunication lines often cover a surface of afew km2 as network.With a frequency of lightning strikes of approxi-mately 1 to 5 lightning strikes per km2 and yeare.g. in Germany, frequent surge inductions have tobe expected for large area networks.A complete lightning protection system includingexternal and internal lightning protection meas-ures is the safest way to protect a building or struc-ture against the effects of lightning discharges.This total measure, however, is the duty of theowner of the structure and also comprises thecomplete lightning equipotential bonding withinthe internal lightning protection system and there-fore also the protection of the telecommunicationcables. This is described in the lightning protectionstandards IEC 62305-3 (EN 62305-3) and IEC 62305-4 (EN 62305-4).

The threatThe connecting cables to the local exchange aswell as the internal house wiring is implementedby copper cables whose shielding effect is very low.By laying cables between several buildings, highpotential differences can arise between the build-

ing installation and the incoming cables. A poten-tial increase on the wires by galvanic and inductivecoupling has to be expected. When arrangingpower supply and communication lines in parallel,switching surges in the power mains can also causeinterferences to the telecommunication lines. Pro-ceeding from cases of damage in installations,surge protective devices were sought for the NT,which could also be installed subsequently.A common customer preference, but also a ques-tion of reliability of the offered service, is the useof a surge protective circuit already at the inputside in order to prevent the penetration of danger-ous surges into the NT and via the NT. Surge pro-tection for the a/b wires and the 230 V power sup-ply of the modem is recommended. The sameapplies to telephone systems, where outputs toextensions must be additionally protected.

Surge protection for ADSL with analogue port orISDN access

Requirements for an ADSL connectionAdditionally to the conventional telephone exten-sion, an ADSL connection requires, according toaccess version, a network interface card or ATMcard in the PC and a particular ADSL modem plus asplitter for the separation of telephone and datacommunication traffic. The telephone extensioncan alternatively be installed with analogue orISDN access.The splitter separates the analogous voice signal orthe digital ISDN signal of the ADSL data under con-sideration of all important system parameters likeimpedances, attenuation, levels, etc. Consequentlyit fulfils the function of a crossover network. Thesplitter is connected at its input side to the tele-phone outlet. At its output side, it provides thehigher frequency signals of the ADSL frequencyband for the ADSL modem on the one hand, andon the other hand, it controls the communicationin the low frequency range with the NTBA or theanalogous terminal equipment. Since the splittershould be compact and cost-effective, it is usuallydesigned in passive form, i.e. without own powersupply.ADSL modems are manufactured in differenttypes. External devices very often use a separatesplitter. The ADSL modem is connected to the PCvia an Ethernet (10 MBit/s), ATM25, or a USB inter-face. Additionally, the modem requires a 230 Vsupply voltage (Figures 9.14.1 and 9.14.2).

www.dehn.de282 LIGHTNING PROTECTION GUIDE

9.14 Surge protection for telecommunication accesses

Page 284: Lightning Protection Guide

Surge protection for data transmission ISDN primary rate multiplex accessISDN (Integrated Services Digital Network) is usedto provide different services in a common publicnetwork. Both voice as well as data can be trans-

ferred by digital transmission. A network termina-tion unit (NT) is the transfer interface for the sub-scriber. The supply line of the digital localexchange is a 4-wire line. Additionally, the NT ispowered with 230 V.

www.dehn.de LIGHTNING PROTECTION GUIDE 283

telecommunicationnetwork

consumer

analoguetelephone

NT 1)

splitter

PC

Ethernet 10 MBitor ATM 25

RJ 45ADSL modem

230 V~

SDB

No.

1 4

3

1) Network Termination5

3

2 4

Type Part No.

BLITZDUCTOR® XT 920 347BXT ML4 BD 180 + BXT BAS +920 300

DRL DRL 10 B 180 FSD 907 401+ DRL PD 180 +907 430+ EF 10 DRL +907 498

NT-Protector NT PRO 909 958

DATA-Protector DATA PRO 4TP 909 955

DEHNlink DLI TC 1 I 929 027

DSM DSM TC 1 SK 924 271

DEHNguard® modularDG M TNS 275 952 400

1

2

4

5

3

telecommunicationnetwork

consumer

ISDNtelephone

NT1)

splitter

PC

ADSLmodem

230 V~

S0

RJ 45NTBA

SDB1) Network Termination2) Broad Band Termination Unit

*BLITZDUCTOR® CT and NT Protector have been officiallyapproved by Deutsche Telekom for protection of NTBAs

Ethernet 10 MBitor ATM 25

RJ 45

No.

1

3

6

3

2 4 5

1

2

3

4

5

6

Type Part No.

BLITZDUCTOR® XT 920 347BXT ML4 BD 180 + BXT BAS +920 300

DRL DRL 10 B 180 FSD 907 401+ DRL PD 180 +907 430+ EF 10 DRL +907 498

NT-Protector NT PRO 909 958

DATA-Protector DATA PRO 4TP 909 955

ISDN-Protector ISDN PRO 909 954

DEHNlink DLI ISDN I 929 024DSM DSM IDSN SK 924 270

DEHNguard® modular DG M TNS 275 952 400

BBTU2)

Fig. 9.14.1 Lightning and surge protection for ADSL with analogue connections

Fig. 9.14.2 Lightning and surge protection for ISDN and ADSL connections

Page 285: Lightning Protection Guide

Figure 9.14.2 shows the protection of an ISDN con-nection with th corresponding surge protectivedevices.

The primary rate multiplex accessThe Network Termination for Primary rate Multi-plex access (NTPM) has 30 B channels with 64 kBit/sand one D channel with 64 kBit/s. Via the primary

rate access, data transmission can be handled up to2 MBit/s. The NT is powered by the U2m interface –the subscriber interface is called S2m. PABX with ahigh number of extensions or data transmissionlines with high data volumes are connected to thisinterface .Figure 9.14.3 shows the protection of such a con-nection against surges.

www.dehn.de284 LIGHTNING PROTECTION GUIDE

telecommunicationnetwork

consumer

NTPM

analoguetelephone

TC system1) Network Termination

No.

SDB

1

5

1 1 1

2 23

U2m S2m-

NT1)

1

2

3

4

Type Part No.

BLITZDUCTOR® XT 920 375BXT ML4 BD HF 24 + BXT BAS +920 300

DRL DRL 10 B 180 FSD 907 401+ DRL HD 24 +907 470+ EF 10 DRL +907 498

DEHNlink DLI TC 1 I 929 027

DSM DSM TC 1 SK 924 271

DEHNguard® modularDG M TNS 275 952 400

SFL-Protector SFL PRO 912 260

Fig. 9.14.3 Surge protection for telecommunications systems “ISDN Primary rate Multiplex access”

Page 286: Lightning Protection Guide

In chemical and petrochemical industrial plants,potentially explosive areas develop frequently dur-ing the manufacture, processing, storage, andtransportation of flammable materials (e.g. gaso-line, alcohol, liquid gas, explosive dust), where anysource of ignition must be avoided to preventexplosions. Relevant protective provisions refer tothe threat of atmospheric discharges (lightning) tosuch installations. Here it has to be considered thatthere is a fire risk and explosion hazard by direct orindirect lightning discharges due to the partiallywidespread extension of such installations.To achieve necessary plant availability and also thenecessary safety of the system, a conceptual actionis necessary for protection of process-specific elec-tric and electronic parts of the plant against light-ning currents and surges.

Lightning Protection Zones ConceptIntrinsically safe circuits are often used in areaswhere explosion hazard may occur. Figure 9.15.1shows the principal design of such a system andthe assignment in lightning protection zones. Dueto the necessary, very high availability of the sys-tems and in order to meet the high requirementson safety in the hazardous area, the following

areas were divided into lightning protection zoneLPZ 1 and lightning protection zone LPZ 2:

⇒ Electronic evaluation unit in the control room(LPZ 2)

⇒ Temperature transducer at the tank (LPZ 1)

⇒ Interior of the tank (LPZ 1)

In accordance with the lightning protection zonesconcept according to IEC 62305-4 (EN 62305-4), alllines at the LPZ boundaries must be equipped withcorresponding surge protective devices asdescribed below.

External lightning protectionThe external lightning protection system is theentire equipment installed and existing outside ator in the installation to be protected for intercep-tion and conducting the lightning current into theearth-termination system.A lightning protection system for explosive areascorresponds to lightning protection system Class IIat normal conditions. In well-founded, individualcases and under special conditions (legal provi-sions), or by the result of a risk analysis in accor-dance with IEC 62305-2 (EN 62305-2) it can differfrom the standards.

www.dehn.de LIGHTNING PROTECTION GUIDE 285

9.15 Lightning and surge protection for intrinsically safecircuits

metal container withsufficient material thickness

air ventilation

intermeshed equipotential bonding

building shield, e.g.steel reinforcement

air-termination system

conductor toremote potential

Fig. 9.15.1 Division of a hazardous location into lightning protection zones (LPZ)

Page 287: Lightning Protection Guide

In order to prevent direct lightning strikes to tankfacilities they are very often protected by air-ter-mination rods with additional air-terminationcables in case of greater distances (Figure 9.15.2).

In any case, the following requirements are basedon lightning protection system Class II. As with alllightning protection systems, the separation dis-tance must also be maintained here.

Lightning equipotential bonding outside the haz-ardous areaThe application of surge protective devices in thelow voltage installation and for telecommunica-tion lines outside the hazardous area (controlroom) shows no peculiarities with respect to otherapplications. In this context it should be noted thatthe surge protective devices for lines of LPZ 0A toLPZ 1 (Figures 9.15.3 and 9.15.4) must have a light-ning current discharge capacity, which is specifiedin test waveform 10/350 μs. The surge protectivedevices of the different requirement classes mustbe coordinated among each other.

Equipotential bondingIn all areas where explosion hazard may occur, aconsistent equipotential bonding has to be imple-mented. Also building supports and parts of theconstruction, pipelines, containers, etc., must beincluded in the equipotential bonding so that avoltage difference must not be feared, even in theevent of a failure. The connections of the equipo-tential bonding conductors must be securedagainst self-loosening. The equipotential bondingmust be carefully realised, installed, and tested incompliance with IEC 60364-4-41, IEC 60364-5-54and IEC 60364-6-61. Using surge protective devicesof the BLITZDUCTOR product range, the cross sec-tion of the earth conductor for equipotentialbonding must be at least 4 mm2 Cu.

Surge protection in intrinsically safe circuitsAlready during the design process, the lightningprotection zones and hazardous areas shall be har-monised. The consequence is that the require-ments both for use of surge protective devices inhazardous areas and at the LPZ boundaries mustbe met likewise. Thus, the installation site of thesurge protective device was determined precisely.It is located at the boundary of LPZ 0B and LPZ 1.This prevents the penetration of dangerous surgesinto Ex zone 0 or 20, since the surges are already

discharged previously. Also, the availability of thetemperature transmitter, which is important forthe process, is considerably increased in this way.Furthermore, the requirements according to EN 60079-14 must be met (Figure 9.15.5):

⇒ Use of surge protective devices with a mini-mum discharge capacity of 10 impulses with 10 kA (8/20 μs), each without malfunction orimpairment of the surge protective function(Table 9.15.1).

⇒ Mounting of the surge protective device into ametallic shielded enclosure and earthing withat least 4 mm2 Cu.

⇒ Installation of the cables between the surgeprotective device and the equipment in a met-al pipe earthed at both ends or the applicationof shielded cables with a maximum length of 1 m.

In accordance with the definition of the protectionconcept, the programmable controller in the con-trol room is defined as LPZ 2. The intrinsically safecable leaving the temperature transmitter is alsoled at the boundary from LPZ 0B to LPZ 1 via a

www.dehn.de286 LIGHTNING PROTECTION GUIDE

concrete tubof the tank

air-terminationrod

air-terminationconductors

Fig. 9.15.2 Air-termination system for a tank with air-terminationrods and conductors

Page 288: Lightning Protection Guide

www.dehn.de LIGHTNING PROTECTION GUIDE 287

Z

EBB

lightning equipotential bonding

cathodic protected tank pipe

exte

rnal

ligh

tnin

g pr

otec

tion

syst

em

gas

water

powersupply

foundation earth electrode

heating

BLITZDUCTOR

BXT ML4 BD EX 24

2’

4’

1’3’

protected

2

4

13BLITZDUCTOR

BXT ML4 BD EX 24

2’

4’

1’3’

prot

ecte

d

2

4

13

Ex zone 0

cable length max. 1 m

EB

BLITZDUCTOR XTBXT BAS EX, BXT ML4 BD EX 24 /

BXT ML4 BC EX 24

Ex zone 1, 2

min. 4 mm2min. 4 mm2

Fig. 9.15.3 Lightning equipotential bonding according to IEC 62305-3 (EN 62305-3) based on main equipotential bonding according toIEC 60364-4-41 and IEC 60364-5-54

Fig. 9.15.4 DEHNventil DV TT 255 in aswitchgear cabinet for protectionof the power supply system

Fig. 9.15.5 Surge protective devices in intrinsically safe circuits

Page 289: Lightning Protection Guide

surge protective device BLITZDUCTOR CT, BCTMOD MD EX 24. This protective device at the oth-er end of the field line between the buildings musthave the same discharge capacity as the protectivedevice installed at the tank. After the surge protec-tive device, the intrinsically safe line is led via anisolation amplifier (Figures 9.15.5 and 9.15.6).From there, the shielded cable is laid to the pro-grammable controller in LPZ 2. Because of the two-sided earth connection of the cable shield, no pro-tective device is required at boundary LPZ 1 to LPZ 2, since the residual electromagnetic interfer-ence still to be expected is strongly attenuated bythe cable shield earthed at both ends.

Criteria for the choice of surge protective devicesin intrinsically safe circuitsThe example treating a temperature transducer(Table 9.15.1) shows which aspects must beobserved for choosing surge protective devices(SPD):

Insulation resistance of the equipmentIn order to prevent measuring errors by compen-sating currents, the sensor signals from the tankare often isolated electrically. The transducer hasan insulation resistance of < 500 V a.c. betweenthe intrinsically safe 4 ... 20 mA current loop andthe earthed temperature sensor. Consequently the equipment is considered as floating. The use

of surge protective devicesmust not interfere with thisisolation from earth. If the transducer has an in-sulation resistance of < 500 Va.c., the intrinsically safe circuit is regarded as earth-ed. This requires protec-tive devices, the voltageprotection level of which is below the insulationresistance of the earthedtransducer (e.g. Up (wire/PG)≤ 35 V) at a nominal dis-charge current of 10 kA(pulse shape 8/20 μs).

Type of protection (explo-sive atmoshperes): IntrinsicSafety – Category ia or ib ?The transducer and the

surge protective device are installed in protectionzone LPZ 1 so that the category ib is sufficient forthe 4 ... 20 mA current loop. The used surge protec-tion fulfils the highest requirements in conformitywith certification according to ia and consequent-ly, is also suitable for ib applications.

www.dehn.de288 LIGHTNING PROTECTION GUIDE

Technical data Measuringtransducer TH02

Surge protective deviceBCT MOD MD EX 30

Installation site

Type of protection

Voltage

Current

Frequency

Immunity

Test standards

Isolatedfromearth500V

Inner capacitance Ci

Inner inductance Li

zone 1

ib

Ui max. = 29.4 V d.c.

Ii max. = 130 mA

fHart = 2200 Hzfrequency-modulated

acc. to NE 21, e.g.0.5 kV line/line

ATEX, CE

Yes

Ci = 15 nF

Li = 220 μH

zone 1

ia

Uc = 34.8 V d.c.

IN = 500 mA

fG = 6 MHz

discharge capacity 10 kA (8/20 μs)Y/L SPD T

ATEX, CE, IEC 61643-21

Yes

negligibly small

negligibly small

Fig. 9.15.6 BCT MOD MD EX 24 for intrinsically safe circuits

Table 9.15.1 Example of a temperature transducer

Page 290: Lightning Protection Guide

Permissible maximum values for L0 and C0Before an intrinsically safe circuit is put into opera-tion, the proof of its intrinsic safety must be pro-vided. For this purpose, the supply unit, the trans-ducer, the used cables, as well as the surge protec-tive devices must fulfil the interconnection condi-tions. If necessary, the inductances and capaci-tances of the protective devices must also be takeninto consideration. In accordance with the EC typeexamination certificate (PTB 99 ATEX 2092), theinternal capacitances and inductances are negligi-ble in the surge protective device type BCT MODMD EX 24 of DEHN + SÖHNE (Figure 9.15.6) andneed not be taken into account when consideringthe interconnection conditions.

Maximum values for voltage Ui and current IiAccording to its technical specifications for intrinsi-cally safe circuits, the transducer to be protectedhas a maximum supply voltage Ui and a maximum

short-circuit current Ii (Table 9.15.1). The ratedvoltage Uc of the protective device must be at leastas high as the open-circuit voltage of the supplyunit. Also the nominal current of the protectivedevice must be at least as high as the short-circuitcurrent Ii of the transducer to be expected in theevent of a failure. If these parameters differ fromthe basic conditions when choosing the surgearresters, the protective device can be overloadedand, consequently, can fail or the intrinsic safety ofthe circuit is eliminated by an impermissibleincrease in temperature at the protective device.

Coordination of the surge protective devices withterminal equipmentThe NAMUR recommendation NE 21 determinesthe requirements on the immunity against inter-ferences for process technology and process con-trol equipment and its general application (e.g.transducers). The signal inputs of such equipmentmust withstand transient voltages of 0.5 kVbetween the wires (differential-mode interfer-ence) and of 1.0 kV between wire and earth (com-mon-mode interference). The test arrangementand the waveform are described in the EN 61000-4-5basic standard. According to the amplitude of thetest pulse, a corresponding surge immunity isassigned to the terminal equipment. These immu-nities of the terminal equipment are documentedby the surge immunity (1 – 4). 1 means the lowestand 4 the highest surge immunity. When there is arisk of lightning and surge effects, the conductedinterference pulses (voltage, current and energy)must be limited to a value that lies within theimmunity of the terminal equipment. The coordi-nation characteristics Q on the protective

devices indicate a direct ref-erence to the test level ofthe terminal equipment. P1describing the requestedtest level of the terminalequipment and Type 2, thedischarge capacity of theprotective device of 10 kA(waveform 8/20 μs).

A threat to chemical andpetrochemical installationsby a lightning discharge andthe electromagnetic influ-ence resulting from it, iscovered in the relevant

www.dehn.de LIGHTNING PROTECTION GUIDE 289

Intrinsicallysafe interface

SPD typeappoved by FISCO1)

Part No.

0 – 20 mA,4 – 20 mA(also with HART)

Digital I/O

NAMUR signal

PROFIBUS-PA

Foundation Fieldbus

BCT MOD MD EX 24 + BCT BAS EX

BCT MOD MD EX 30 + BCT BAS EX

DCO RK MD EX 24

DPI MD EX 24 M 2

919 580 + 919 507

919 581 + 919 507

919 960

929 960

PROFIBUS-DP BCT MOD MD HFD EX 6 + BCT BAS EX 919 583 + 919 5071) FISCO = Fieldbus Intrinsically Safe Concept

Table 9.15.2 Surge protective devices for use in intrinsically safe circuits and bus systems

Fig. 9.15.7 Surge arrester for field devices – DEHNpipe,DPI MD EX 24 M 2

Page 291: Lightning Protection Guide

guidelines. During the realisation of the lightningprotection zones concept in design and implemen-tation of such installations, the risks of a sparkingby a direct strike or discharging of conductedinterference energies can be minimised within asafety-related and also economically justifiable

scope. The used surge arresters must fulfil therequirements of explosion protection, the coordi-nation to the terminal equipment, as well as therequirements from the operational parameters ofthe measuring and control circuits (Table 9.15.2).

www.dehn.de290 LIGHTNING PROTECTION GUIDE

Page 292: Lightning Protection Guide

There is an unabated trend for the utilisation ofregenerative energy gained from wind turbines,solar, photovoltaic and biogas plants or geother-mal heat. This is an enormous market potential notonly for the energy industry but also for the suppli-ers and the electrical trade and that worldwide.

In Germany meanwhile about 19,000 wind tur-bines supply a total power of almost 21,000megawatt which is more than three percent of thepower needed.

The prognoses for the future turn out to be posi-tive. According to the German wind power insti-tute (Deutsches Windenergie-Institut, DEWI),approximately 4,000 wind turbines are supposedto be installed on the open seas until 2030.

Thus, a nominal power of approx. 20,000megawatt could be produced by offshore wind-farms. The importance of wind turbines is obvious.Looking at the growth rates of this power market,the reliable availability of energy is also an impor-tant aspect.

Danger resulting from lightning effects

An operator of these installations cannot afforddowntimes. On the contrary, the high capitalinvestments for a wind turbine shall amortizewithin a few years. Wind turbines are comprehen-sive electrical and electronic installations, concen-trated on a very small area. Everything, what elec-trical engineering and electronics offer, can befound: switchgear cabinets, motors and drives, fre-quency converters, bus systems with actuators andsensors. It goes without saying that surges cancause considerable damage there. Due to theexposed position and the overall height, wind tur-bines are exposed to direct lightning effects. Therisk of being hit by lightning increases quadratical-ly versus the height of the structure. Multi-megawatt wind turbines with blades reach a totalheight up to 150 m and are therefore particularlyexposed to danger. A comprehensive lightning andsurge protection is required.

Frequency of lightning strikes

The annual number of cloud-to-earth lightningflashes for a certain region results from the well-known isokeraunic level. In Europe, a mean num-ber of one to three cloud-to-earth flashes per km2

and year applies to coast areas and low mountainranges.

For dimensioning lightning protection installa-tions, it has to be considered that in case of objectswith a height of > 60 m, and which are exposed tolightning, also earth-to-cloud flashes can come up,so-called upward flashes, beside cloud-to-earthflashes. This results in greater values as specified inthe above formula.Furthermore, earth-to-cloud flashes starting fromhigh exposed objects carry high charges of a light-ning current, which are of special importance forthe protection measures at rotor blades and forthe design of lightning current arresters.

StandardisationThe guidelines of Germanischer Lloyd are the basisfor the design of the protection concept.The German Insurance Association (GDV) recom-mends in its publication VdS 2010 “Risikoorien-tierter Blitz- und Überspannungsschutz” (Risk ori-ented lightning and surge protection) to imple-ment at least lightning protection systems Class IIfor wind turbines in order to meet the minimumrequirements for protection of these installations.

Protection measuresThe main concern in this technical contribution isthe realisation of lightning protection measuresand measures of protection against surges for theelectric and electronic devices / systems of a windturbine.The complex problems of the protection of rotorblades and swivelling parts and bearings require adetailed examination. They are also producer-spe-cific and type-specific.

www.dehn.de LIGHTNING PROTECTION GUIDE 291

9.16 Lightning and surge protection of multi-megawattwind turbines

Fig. 9.16.1 Impulse current laboratory DEHN + SÖHNE – Max. light-ning impulse current 200 kA, wave form 10/350 μs

Page 293: Lightning Protection Guide

DEHN + SÖHNE offers the following engineeringand testing service in the company’s impulse cur-rent laboratory to provide best solutions for theindividual customer (Figure 9.16.1):

⇒ Testing of customer-specific, pre-wired con-nection units for protection of the electricalinstallation

⇒ Testing of the lightning current carryingcapacity of bearings

⇒ Lightning current test at down conductors andreceptors of rotor blades

These tests in the laboratory prove the effective-ness of the chosen protection measures and con-tribute to the optimisation of the “protectionpackage”.

Lightning Protection Zones ConceptThe lightning protection zones concept is a struc-turing measure for creating a defined EMC envi-ronment within a structure (Figure 9.16.2). Thedefined EMC environment is specified by the elec-tromagnetic immunity of the used electric equip-ment.

Being a protection measure, the lightning protec-tion zones concept includes therefore a reductionof the conducted and radiated interferences atboundaries down to agreed values. For this reason,the object to be protected is subdivided into pro-tection zones. The protection zones result fromthe structure of the wind turbine and shall consid-er the architecture of the structure. It is decisivethat direct lightning parameters affecting light-ning protection zone LPZ 0A from outside arereduced by shielding measures and installation ofsurge protective devices to ensure that the electricand electronic systems and devices situated insidethe wind turbine can be operated without inter-ferences.

Shielding measuresThe nacelle should be designed as a metal shieldthat is closed in itself. Thus a volume can beobtained inside the nacelle with a considerablyattenuated, electromagnetic field compared tothe outside. The switchgear and control cabinets inthe nacelle and, if existing, in the operation build-ing should also be made out of metal. The con-necting cables should be provided with an outer,conductive shield. With respect to interferencesuppression, shielded cables are effective againstEMC coupling only if the shields are connectedwith the equipotential bonding on both sides. Theshields must be contacted with encircling contactterminals to avoid long and for EMC improper“pigtails”.

Earth-termination systemFor earthing a wind turbine, the reinforcement ofthe tower should always be integrated. Installa-tion of a foundation earth electrode in the towerbase, and, if existing, in the foundation of an oper-ation building, should also be preferred in view ofthe corrosion risk of earth conductors.

The earthing of the tower base and the operationbuilding (Figure 9.16.3) should be connected by anintermeshed earthing in order to get an earthingsystem with the largest surface possible.

The extent to which additional potential control-ling ring earth electrodes must be arrangedaround the tower base depends on the factwhether too high step and touch voltages mustpossibly be reduced to protect the operator in caseof a lightning strike.

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LPZ 2

LPZ 1

LPZ 1LPZ 2

outgoinglines

operation building

nacelle

electromagnetic shield

shielded cable route

shielded pipe or the like

Fig. 9.16.2 Lightning protection zones concept for a wind turbine

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Protective circuit for conductors at the boundaryof lightning protection zone LPZ 0A to LPZ 1 andhigherBesides shielding against radiated sources of inter-ference, protection against conducted sources ofinterference at the boundaries of the lightningprotection zones must also be provided for reliableoperation of the electric and electronic devices.

At the boundary of lightning protection zone LPZ 0A to LPZ 1 (conventionally also called light-ning equipotential bonding) SPDs must be used,which are capable of discharging considerable par-tial lightning currents without damage to theequipment. These SPDs are called lightning currentarresters (SPDs Type 1) and tested with impulsecurrents, wave form 10/350 μs.

At the boundary of LPZ 0B to LPZ 1 and LPZ 1 andhigher, only low energy impulse currents have tobe controlled which result from voltages inducedfrom the outside or from surges generated in thesystem itself. These protection devices are calledsurge protective devices (SPDs Type 2) and testedwith impulse currents, wave form 8/20 μs.

Surge protective devices should be chosen accord-ing to the operating characteristics of the electricand electronic systems.After the discharge, surge protective devices to beused in the power supply system must be capableof extinguishing safely the follow currents comingfrom mains afterwards. Beside the impulse currentcarrying capability, this is the second importantaspect of design.

Figure 9.16.4 shows lightning current arresterDEHNbloc with encapsulated spark gap.

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reinforcementof the building

mast / tower

concrete foundation

reinforcement

ring earth electrode

earthconductor

cable duct foundation earth electrode

Fig. 9.16.3 Intermeshed network of earth electrodes of a wind turbine

Fig. 9.16.4 Application of DEHNbloc Maxi coordinated lightningcurrent arrester for 400/690 V TN-C systems

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This lightning current arrester can be mountedamong bare live system parts in the installation tobe protected without having to take minimum dis-tances into account. The protective device DEHN-bloc is used, for example, for low voltage linescoming from the wind turbine.

Surge arresters (Figure 9.16.5) are dimensioned forloads as they occur in case of inductive couplingsand switching operations. Within the scope ofenergy coordination, they have to be connecteddownstream of the lightning current arresters.They include a thermally monitored metal oxidevaristor.Contrary to surge protective devices for powersupply systems, special attention has to be paid onsystem compatibility and the operating character-istics of the measuring and control or data linewhen installing SPDs in data processing systems.These protective devices are connected in serieswith the data processing lines and must be able to

reduce the interference level below the immunityof the equipment to be protected.

Considering a single telephone line within thelightning protection zones concept, the partiallightning current on this conductor can be as-sumed to be blanket 5 %. For a lightning protec-tion system Class III/IV, this would amount to a par-tial lightning current of 5 kA, wave form 10/350 μs.

Figure 9.16.6 shows the approved multipurposedevice BLITZDUCTOR XT, BCT MOD BE as a light-ning current and surge arrester. This protectivedevice can be used for protection of equipment inEMC lightning protection zone I and higher. BLITZ-DUCTOR XT is designed as a four-terminal networkand limits both common-mode interferences aswell as differential-mode interferences. It can befixed directly in the course of terminal blocks or,instead of these terminals, on supporting rails. Itsspecial design allows a space-saving arrangement.

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Fig. 9.16.5 DEHNguard surge arrester,DG MOD 750 + DG M WE 600

Fig. 9.16.6 Application of BLITZDUCTOR XT lightning current andsurge arrester

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According to the require-ments of DIN VDE 0855-300radio transmitting / receiv-ing systems in Germany are designed in such a waythat incoupled lightningcurrents will be safely dis-charged to the earth elec-trode via the earthing con-ductor. Hence also the trans-mitter/receiver station (radiobase station RBS) has to beprotected against surgesdue to lightning currents.The radio base station (RBS)comprises the power supply(power supply unit PSU),the radio transmitting tech-nology and the transmittingtechnology for the fixednetwork (optional).

9.17.1 Power supply230/400 V a.c.

The power supply of theRBS has to be independentfrom the power supply ofthe building. Supplying viathe subdistribution / floordistribution shall be avoid-ed. The energy meter shallbe near the service entrancebox. The distribution of cir-cuits is effected upstreamthe RBS or directly inside (inGermany almost exclusive-ly subdistributions are in-stalled directly in and nearthe RBS). The DEHNventil DV M TT 255,a combined lightning cur-rent and surge arrester onspark gap basis, protects thepower supply unit (PSU) of aRBS. This surge protectivedevice is an arrester Type 1designed for the protectionof power supply units intransmitting / receiving sys-tems.

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9.17 Surge protection for radio transmitter/receiver stations (mobile radio)

roof area

basement area

service entrance

kWh

powerdistribution

cabinet

lighting

air-conditioning

socket outlet

existing earth electrode

MEBB

EBB

RBS (radiobase station)

Fig. 9.17.2 Electrical circuit diagram

Fig. 9.17.1 Dual cell site

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The DEHNventil DV M TT 255 either can be in-stalled in the subdistribution directly upstream theRBS or in the area of the service entrance. The pro-tective device being installed in the subdistribu-tion, there is a selected input of lightning currentand a selected output in the service entrance area.Figure 9.17.2 shows the circuit diagram with thelocation of the surge protective equipment. In ad-dition Figure 9.17.3 shows the structural diagramof an RBS on a roof and the application of DEHN-ventil DV M TT 255. Producers of transmitting /receiving systems sometimes perform a standard-ised application of surge arresters Type 2 accordingto Table 9.17.2. Figure 9.17.3 also shows where toinstall the DEHNguard modular DG M TT 275.

The application of lightning current and surge pro-tective equipment depends on the type of low-voltage system (TT system, TN-C system or TN-S sys-tem). The international standard IEC 60364-5-53describes the use of lightning current and surgearresters in accordance with the “Protection atindirect contact” in low-voltage consumer’s sys-tems. In addition to this requirement of protectionagainst life hazards, care has to be taken when

using surge protective equipment, that there is anenergy coordination with the terminal devices tobe protected. The coordination of the DEHNventilDV M TT 255 and hence the protection capabilityof this surge protective equipment even withoutusing a surge arrester Type 2 in the RBS has beencomprehensively tested at different PSUs.In order to realise a coordinated surge protectionat all sites of an operator and to be independent indesigning with regard to the different networksystems, the DEHNventil DV M TT 255 a protectivedevice with “3 + 1” circuit provides a universalsolution for TN-C, TN-S and TT systems.A quality characteristic of special importance forusing combined lightning current and surgearresters is a sufficient follow current extinguish-ing capability and follow current limiting/selectivi-ty. Thus false tripping of the system fuses and thedisconnection from power supply is avoided. Thisquality characteristic of the combined lightningcurrent and surge protective equipment or com-bined SPDs called “selectivity” is necessary. Ifapplied in the range of transmitting/receiving sys-tems, a selectivity according to Table 9.17.1 isrequired.

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elevator building

roof surface

antenna

SD

low-voltage supply

mast

antenna lines

RBS (radiobase station)

DV M TT 255

antenna line

meshed operational equipotential bonding (MOEB)

DG M TT 275

Fig. 9.17.3 Basic structure of a RBS with DV M TT 255 and DG M TT 275

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9.17.2 Fixed networkconnection (ifexisting)

Depending on the net-work operator, eitherfixed network links (cop-per cable) or radio linksare chosen to connectthe RBS with the primaryswitching technology(base station controller(BSC), mobile switchingcentre (MSC). In case of afixed network connec-tion partial lightningcurrents also will flowthrough the telecommu-nication cable if a directlightning strikes theantenna system. Herecombined SPDs providesufficient protection aswell. Surge protectiveequipment according toTable 9.17.3 is applied.

9.17.3 Radio trans-mission tech-nology

The radio transmissionband (frequency) andthe connection mechan-ics (connector) are thedecisive factors concern-ing the selection of suitable surge protectiveequipment for the protection of the radio trans-mission technology. Sufficient discharge capability,remote supply voltages of point-to-point (PTP)radio systems, and depending on the application,also low passive intermodulation (PIM) have to betaken into account. Table 9.17.4 shows a choice ofDEHN + SÖHNE protection products.

9.17.4 Lightning protection, earthing,equipotential bonding

With regard to earthing, equipotential bonding,lightning and surge protection mainly DIN VDE

0855-300 (national) as well as IEC 62305-3 (EN62305-3) are applicable for design and installationof transmitting/receiving systems. A difference hasto be made whether a transmitting/receiving sys-tem shall be installed on an building or structurewith an already existing or planned lightning pro-tection system or whether the object under consid-eration is without lightning protection system. Themeasures of earthing and equipotential bondingthen have to be met the requirements of DIN VDE0855-300 or IEC 62305-3 (EN 62305-3). Chapter5.2.4.2 of the Lightning Protection Guide describespossible measures of protection against lightningapplicable for cell sites.

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No tripping of afuse...

...at an earthfault/short-circuitcurrent up to

TypePart No.

20 A gL/gG 50 kAeffDEHNventil DV M TT 255951 310

No. in Fig.9.17.2

Purpose of use Type Part No.

“Basic surge protection” DEHNguard modularDG M TT 275

952 310

No. in Fig.9.17.2

Connection system Type Part No.

LSA-PLus, series 2

screw terminal (D+Srecommendation)

DEHNrapid DRL 10 B 180 FSD

BLITZDUCTOR XT BXT BD 180BLITZDUCTOR XT Base part BXT BAS

907 401

920 347920 300

No. in Fig.9.17.2

Band/Frequency Type Part No.

GSM/876 ... 960 +GSM/1710 ... 1880UMTS

Microwave link/2400

WLAN/2400

TETRA/380 ... 512

DEHNgate DGA L4 7 16 B orDEHNgate DGA L4 N B

DEHNgate DGA G N

DEHNgate DGA G BNC

DEHNgate DGA L4 7 16 S

929 048929 049

929 044

929 042

929 047

No. in Fig.9.17.2

Table 9.17.1 Selectivity surge arrester Type 1

Table 9.17.2 Standardised surge arrester Type 2

Table 9.17.3 Surge protection for the fixed network connection

Table 9.17.4 Surge protection for the transmission technology

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9.18.1 Lightning and surge protection for photovoltaic (PV) systems

The guaranteed service life of 20 years for photo-voltaic generators and their exposed installationsites as well as the sensitive electronics of theinverter really require effective lightning andsurge protection. Not only house owners install a PV system on theirrooftop but also private operating companiesmake more and more investments in shared sys-tems, which are erected on large-surface roofs, ontraffic structures, or unused open areas.Because of the big space requirements of the pho-tovoltaic generator, PV systems are especiallythreatened by lightning discharges during thun-derstorms. Causes for surges in PV systems areinductive or capacitive voltages deriving fromlightning discharges as well as lightning surgesand switching operations in the upstream powersupply system. Lightning surges in the PV systemcan damage PV modules and inverters. This canhave serious consequences for the operation ofthe system. Firstly, high repair costs, for example,those of the inverter, have a negative effect, and,secondly, the system failure can result in consider-able profit cuts for the operator of the plant.

Necessity of lightning protectionFor the installation of PV systems it must be gener-ally distinguished between an installation on abuilding with or without lightning protection. Forpublic buildings, e.g., assembly places, schools,hospitals, in Germany building regulations requestlightning protection systems for safety reasons. Forthis purpose, buildings or structures are differenti-ated, for which, according to their location, con-struction type, or utilisation, a lightning strikecould easily have severe consequences. Such build-ings or structures in need of protection have to beprovided with a permanently effective lightningprotection system.In case of privately used buildings lightning pro-tection is often refrained from. This happens part-ly out of financial reasons, but also because oflacking sensibility with respect to this topic.If a building without external lightning protectionwas selected as location for a PV system, the ques-tion arises, if, with the additional installation ofthe PV generator on the roof, lightning protectionshould be provided for the entire structure.According to the current scientific state of the art,

the installation of PV modules on buildings doesnot increase the risk of a lightning strike, so thatthe request for lightning protection can not bederived directly from the mere existence of a PVsystem. However, there may be an increased dan-ger for the electric facilities of the building in theevent of a lightning strike. This is based on the factthat, due to the wiring of the PV lines inside thebuilding in existing risers and cable runs, strongconducted and radiated interferences may resultfrom lightning currents. Therefore, it is necessary,to estimate the risk by lightning strikes, and totake the results from this into account for thedesign. IEC 62305-2 (EN 62305-2) states proceduresand data for the calculation of the risk resultingfrom lightning strikes into structures and for thechoice of lightning protection systems. For thispurpose DEHN + SÖHNE offers the software DEHNsupport. The risk analysis presented hereensures that it is possible to draw up a lightningprotection concept which is understood by all par-ties involved, and which meets optimum technicaland economic requirements, i.e. the necessary pro-tection can be guaranteed with as little expendi-ture as possible.

The German Insurance Association has picked upthe risk estimate in their guideline VdS 2010“Risikoorientierter Blitz- und Überspannungs-schutz für Objekte” (Risk oriented lightning and surge protection for objects) (taken from IEC62305-2 (EN 62305-2)) and present lightning pro-tection measures for buildings or structures as theyare seen by the insurance industry. In Table 3, thisguideline assigns classes of lightning protectionsystems and measures against surges to objects in asimplified manner. Furthermore, the guideline alsorefers to buildings with alternative power supplyinstallations, as for example, buildings with a PVsystem (> 10 kW). According to this, for suchobjects lightning protection level (LPL) III has to betaken into account. Hence a LPS Class III is requiredas well as additional surge protective measures.A system of protection against lightning (LPS)designed for class III meets the usual requirementsfor PV and solar thermal systems: “Photovoltaicand solar thermal systems on buildings must notinterfere the existing lightning protection meas-ures. Photovoltaic and solar thermal systems shallbe protected by isolated air-termination systemsaccording to 5.2 and 6.3 of IEC 62305-3 (EN 62305-3)against direct lightning strikes. If a direct connec-

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9.18 Lightning and surge protection for PV systems andsolar power plants

Page 300: Lightning Protection Guide

tion can not be avoided, the effects of partiallightning currents entering the building have to betaken into consideration.”

Protection of photovoltaic inverters againstsurges also in case of direct lightning strikesIf a PV system shall be installed on a building withexternal lightning protection system, one of thebasic requirements is that the PV modules arewithin the protective area of an isolated air-termi-nation system. Additionally, the separation dis-tance between the PV supporting frame and theexternal lightning protection system has to bekept in order to prevent uncontrolled sparkover.Otherwise considerable partial lightning currentscan be carried into the building or structure.

Often the operator wants the whole roof to becovered with PV modules in order to gain a possi-bly high economic profit. In these cases the separa-tion distance often can not be realised and the PVsupporting frame has to be integrated into theexternal lightning protection. Here, the effects ofthe currents coupled into the building or structurehave to be taken into consideration and a light-ning equipotential bonding has to be provided.Meaning that lightning equipotential bondingnow also is necessary for the d.c. conductors carry-ing lightning current. According to IEC 62305-3 thed.c. conductors have to be protected by surge pro-tective devices (SPDs) Type 1. Surge protectivedevices Type 1 on spark gap basis, for use on thed.c. voltage side, were not available up to now.The problem was that the spark gap once be-ing tripped, could not bequenched again and hencethe arc persisted.

With the combined lightningcurrent and surge arresterDEHNlimit PV 1000 (Figure9.18.1.1) DEHN + SÖHNE suc-ceeded in developing a directcurrent extinguishing sparkgap arrester. Thus DEHNlimitPV 1000 is the ideal arresterfor use in photovoltaic pow-er plants. The encapsulatedcreeping spark gap technolo-gy provides a safe protectionof the PV generator and theinverter also in case of direct

lightning currents. This combined arrester is appli-cable for PV systems up to 1000 V UOC STC . DEHN-limit PV 1000 has a high lightning current dis-charge capability of 50 kA 10/350 μs.

Single pole photovoltaic arrester Type 2 with inte-grated short-circuiting deviceThe inner structure of DEHNguard PV 500 SCP asurge arrester Type 2 (Figure 9.18.1.2) sets new pat-terns for safety. In this arrester the proved doubleeffect of the monitoring and disconnecting deviceThermo Dynamic Control has been combined withan additional short-circuiting device. This com-pletely new kind of arrester monitoring ensuresoperation safety without risk of fire hazard, evenif the devices are overloaded for example at insula-tion faults in the PV generator circuit. The follow-ing example explains the effectiveness of theshort-circuiting device in DEHNguard PV 500 SCP:

1. Figure 9.18.1.3: An insulation fault arises dur-ing the operation of the PV system.

2. Figure 9.18.1.4: With the consequence of thesurge arrester being overloaded by the ex-ceeding maximum continuous voltage Uc .

3. Figure 9.18.1.5: The combined disconnectionand short-circuiting device of DEHNguard PV500 SCP will be activated. It is able to carry ashort-circuit current up to 50 A automaticallyuntil the PV system is repaired. This ensures asafe operation without risk of fire hazard forthe system even at an insulation fault in the PVgenerator circuit.

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Fig. 9.18.1.1 Combined arrester Type 1, DEHNlimit PV,to protect photovoltaic inverters from surgesalso in case of direct lightning strikes

Fig. 9.18.1.2 Single pole photovoltaicarrester Type 2,DEHNguard PV 500 SCP,with integrated short-circuiting device

Page 301: Lightning Protection Guide

Examples of application

Buildings without external lightning protectionsystemFigure 9.18.1.6 shows the surge protection conceptfor a PV system on a building without externallightning protection system. Possible installationsites of the surge protective devices can be:

⇒ d.c. input of the inverter

⇒ a.c. output of the inverter

⇒ low-voltage (l.v.) supply

DEHNguard, an SPD Type 2 is installed in the l.v.incoming feeder. This DEHNguard M Type of surgearrester, a complete prewired unit is available foreach low-voltage system (TN-C, TN-S, TT) (Table9.18.1.1). If the distance between the PV inverterand the installation site of the DEHNguard is notgreater than 5 m (l.v. supply), the a.c. output of theinverter is sufficiently protected. At greater con-ductor lengths additional surge protective devicesSPDs Type 2 are necessary upstream the a.c. inputof the inverter (Table 9.18.1.1).At the d.c. input of the inverter each of the incom-ing string conductors has to be protected to earthby a DEHNguard surge protective device Type PV500 SCP installed between plus and minus. Thisinstallation provides safe surge protection for PVsystems with a generator voltage up to 1000 V d.c..

The operating voltage of the chosen surge protec-tive devices shall be approx. 10 % higher than theexpected open-circuit voltage of the solar genera-tor during maximum solarisation on a cold winterday.

Buildings with external lightning protection sys-tem and separation distance keptThe correct operating condition of the lightningprotection system has to be proven by existing testreports or by maintenance tests. If faults are foundduring the examination of the external lightningprotection system (i.e. intense corrosion, loose andfree clamping elements), the constructor of the PVsystem has the duty to inform the owner of thebuilding about these faults in writing. The PV system on the roof surface should bedesigned under consideration of the existingexternal lightning protection system. For this pur-pose, the PV system has to be installed within theprotection zone of the external lightning protec-

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=

~+

SCP SCP

=

~+

+

SCP SCP

=

~+

+

SCP SCP

Fig. 9.18.1.3 Isolation fault at the PV generator

Fig. 9.18.1.4 Overloading of SPD due to an isolation fault

Fig. 9.18.1.5 Activation of the DEHNguard PV 500 SCP disconnect-ing and short-circuiting device ensures safe operatingstate also in case of an isolation fault in the PV gener-ator circuit

Page 302: Lightning Protection Guide

tion system to ensure its protec-tion against a direct lightningstrike. By using suitable air-termi-nation systems, like air-termina-tion rods, for example, direct light-ning strikes into the PV modulescan be prevented. The necessaryair-termination rods possibly to beinstalled additionally, must bearranged to prevent a direct strikeinto the PV module within theirprotection zone and, secondly, anycasting of a shadow on the mod-ules.It has to be considered that a sepa-ration distance s must be keptbetween the PV components andmetal parts like lightning protec-tion systems, rain gutters, sky-lights, solar cells or antenna sys-tems in compliance with IEC62305-3 (EN 62305-3). The separa-tion distance has to be calculatedaccording to IEC 62305-3 (EN62305-3)3. The PV system shown inFigure 9.18.1.7 is located in theprotective area of the externallightning protection system. Figure9.18.1.7 illustrates the concept of

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kWh kWh

=~

1

2 3

SEB

a.c.output

d.c.input

meter/maindistribution

DNO

earthingconductor

Fig. 9.18.1.6 Surge protection concept for a PV system on a building without external light-ning protection

1

2

3

Figure9.18.1.6

Protectionfor...

SPDs Part No.

TN-C system DEHNguard M, DG M TNC 275DEHNguard M, DG M TNC 275 FM

952 300952 305

TN-S system DEHNguard M, DG M TNS 275DEHNguard M, DG M TNS 275 FM

952 400952 405

L.v. supply

TT system DEHNguard M, DG M TT 275DEHNguard M, DG M TT 275 FM

952 310952 315

2 x(each between plusand minus to earth)

DEHNguard, DG PV 500 SCPDEHNguard, DG PV 500 SCP FM

950 500950 505

Dc input of the inverter

TN system DEHNguard M, DG M TN 275DEHNguard M, DG M TN 275 FM

952 200952 205

Ac output of the inverter/ac, inverter installed in the attic

TT system DEHNguard M, DG M TT 2P 275DEHNguard M, DG M TT 2P 275 FM

952 110952 115

Table 9.18.1.1 Selection of the surge protective devices for PV systems on buildings without external lightning protection system

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surge protection for a PV systemon a building with external light-ning protection system and a suffi-cient separation distance of the PVmodules to the external lightningprotection system.An essential part of a lightningprotection system is the lightningequipotential bonding for all con-ductive systems entering the build-ing from the outside. The require-ments of lightning equipotentialbonding are met by direct connec-tion of all metal systems and byindirect connection of all live sys-tems via lightning current arrest-ers. The lightning equipotentialbonding should be performedpreferably near the entrance ofthe structure in order to prevent apenetration of partial lightningcurrents into the building. Thelow-voltage power supply of thebuilding is protected by a DEHN-ventil ZP, a multi-pole combinedlightning current and surge arrest-er with spark gap technology. It isdesigned for installation on 40 mmDIN rails on the meter mountingboard. The surge protective devicehas to be chosen according to thetype of power supply system (Table9.18.1.2).This combined lightning currentand surge arrester unites lightningcurrent and surge arrester in onedevice has no interaction limitingreactor and is available as com-plete prewired unit for every low-voltage system (TN-C, TN-S, TT).There is sufficient protection with-out additional protective devicesbetween DEHNventil and terminalequipment up to a cable length of< 5 m. For greater cable lengthsSPDs Type 2 or 3 have to be used inaddition. If the distance betweenthe a.c. output of the inverter andthe application site of DEHNventilis not greater than 5 m, no furtherprotective devices are required forthe a.c. side.

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kWh kWh

<s<s

=~

1

2 3

SEB

a.c.output

d.c.input

meter/maindistribution

DNO

Fig. 9.18.1.7 Surge protection concept for a PV system on a building with external lightningprotection system and the separation distance is being kept

Fig. 9.18.1.8 Surge protection concept for a PV system on a building with external lightningprotection system and the separation distance is not being kept

kWh kWh

ss

=~

1

2 3

SEB

a.c.output

d.c.input

meter/maindistribution

DNO

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At the d.c. input of the inverter each of the incom-ing string conductors has to be protected to earthby a DEHNguard surge protective device Type PV500 SCP installed between plus and minus.

Buildings with external lightning protection sys-tem and separation distance not keptOften the whole roof is covered with PV modulesin order to gain a possibly high economic profit.For the mounting technicians, however, then it isoften not possible to keep the required separationdistance. At these points a direct conductive con-nection must be provided between the externallightning protection system and the metal PV com-ponents. In this case, however, the effects of the

currents carried into the structure or building viathe d.c. conductors have to be taken into accountand hence lightning equipotential bonding has tobe ensured. Meaning that now also the lightningcurrent carrying d.c. conductors have to be includ-ed into the lightning equipotential bonding (Fig-ure 9.18.1.8). According to IEC 62305-3 (EN 62305-3), surge protective devices Type 1 have to beinstalled at the d.c. conductors. Here DEHNlimit PV1000, the combined lightning current and surgearrester is used, which in this case will be connect-ed in parallel with the string conductor. The com-bined arrester DEHNlimit PV 1000 has been espe-cially developed for application in photovoltaicpower plants. The encapsulated creeping spark

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1

2

3

Figure9.18.1.7

Protection for... SPDs Part No.

TN system DEHNguard M, DG M TN 275DEHNguard M, DG M TN 275 FM

952 200952 205

A.c. output of the inverter/a.c., inverter installed in the attic

TT system DEHNguard M, DG M TT 2P 275DEHNguard M, DG M TT 2P 275 FM

952 110952 115

2 x(each between plusand minus to earth)

DEHNguard, DG PV 500 SCPDEHNguard, DG PV 500 SCP FM

950 500950 505

D.c. input of the inverter

L.v. supplyTN-C system DEHNventil ZP, DV ZP TNC 255 900 390TN-S system andTT system

DEHNventil ZP, DV ZP TT 255 900 391

1

2

3

Figure9.18.1.8

Protection for... SPDs Part No.

TN-C system DEHNventil M, DV M TN 255DEHNventil M, DV M TN 255 FM

951 200951 205

TT-S system andTT system

DEHNventil M, DV M TT 255DEHNventil M, DV M TT 255 FM

951 110951 115

A.c. output of the inverter/a.c., inverter installed in the attic

Each string conductor DEHNlimit, DLM PV 1000 900 330D.c. input of the inverter

L.v. supplyTN-C system DEHNventil ZP, DV ZP TNC 255 900 390TN-S system andTT system

DEHNventil ZP, DV ZP TT 255 900 391

Table 9.18.1.2 Selection of the surge protective devices for PV systems on buildings with external lightning protection system and the separation distance is being kept

Table 9.18.1.3 Selection of the surge protective devices for PV systems on buildings with external lightning protection and the separationdistance is not being kept

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gap technology provides safe protection of the PVgenerator, even at direct lightning currents.Lightning equipotential bonding has to be per-formed also for the l.v. input. The DEHNventil ZP, asurge protective device with spark gap technologyis used there (Table 9.18.1.3). If the distancebetween the PV inverter and the l.v. input is notgreater than 5 m, the a.c. output of the inverter isalso protected. Surge protection measures alwaysare effective only locally, which applies also for theprotection of the PV inverter. The PV inverterbeing installed in the attic, additional surge pro-tective devices are necessary to protect the a.c.output of the inverter, to be performed in this casealso by the DEHNventil surge protective devicesType 1. This protective device is used because thepartial lightning currents flowing via the protec-tive conductor and the a.c. supply conductor haveto be controlled by the surge protective device.

NoteThe surge protection of so-called thin-film moduleapplications possibly requires separate considera-tion.

9.18.2 Lightning and surge protection forsolar power plants

For such a complex type of installation as a solarpower plant, it is necessary to make an assessmentof the damage risk due to lightning strikes accord-ing to IEC 62305-2 (EN 62305-2), the result to betaken into account on designing. In case of a solarpower plant the aim is to protect both the opera-tion building and the PV array against damage byfire (direct lightning strike), and the electrical andelectronic systems (inverters, remote diagnosticssystem, generator main line) against the effects oflightning electromagnetic impulses (LEMP).

Air-termination system and down-conductor sys-temFor protecting the PV array against direct lightningstrikes, it is necessary to arrange the solar modulesin the protection zone of an isolated air-termina-tion system. Its design is based on lightning protec-tion system Class III for PV systems greater 10 kW incompliance with VdS guideline 2010. According tothe class of lightning protection system, the heightand the quality of the air-termination rods re-quired is determined by means of the rollingsphere. Furthermore, it has to be ensured that theseparation distance s is kept between the PV sup-porting frames and the air-termination rods incompliance with IEC 62305-3 (EN 62305-3). Also,the operation building is equipped with an exter-nal lightning protection system Class III. The downconductors are connected with the earth-termina-tion system by using terminal lugs. Due to the cor-rosion risk at the point where the terminal lugscome out of the soil or concrete, they have to bemade out of corrosion-resistant material (stainlesssteel V4A, Material No. 1.4571) or, in case of usinggalvanised steel they have to be protected by cor-responding measures (applying sealing tape orheat-shrinkable tubes, for example).

Earthing systemThe earthing system of the PV system is designedas a ring earth electrode (surface earth electrode)with a mesh size of 20 m x 20 m (Figure 9.18.2.1).The metal supporting frames which the PV mod-ules are fixed onto, are connected to the earth-termination system approx. every 10 m. The earth-ing system of the operation building is designed as a foundation earth electrode according to DIN18014 (German standard). The earth-termination

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operation

building

Air-termination rod

Generator junction box

PV array

Earth-termination systemMesh size 20 x 20 m

d.c. line

Fig. 9.18.2.1 Layout of a large PV installation in an open area

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system of the PV system and the one of the opera-tion building have to be connected with each othervia at least one conductor (30 mm x 3.5 mm steelstrip V4A, Material No. 1.4571 or galvanised steel).The interconnection of the individual earthing sys-tems reduces considerably the total earthing resist-ance. The intermeshing of the earthing systemscreates an equipotential surface which reduces

considerably the voltage load of lightning effectson the electric connecting cables between PV arrayand operation building. The surface earth elec-trodes are laid at least 0.5 m deep in the soil. Themeshes are interconnected with four-wire connec-tors. The joints in the soil have to be wrapped withan anticorrosive band. This also applies to V4Asteel strips laid in the soil.

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=∼

foundation earth electrode

generatorjunctionboxbuilding with inverter

PV modules

steel telescopiclightning protection mast

1 2

33

No. in Fig.9.18.2.2

Protection for... SPDs Part No.

TN-C systemTN-S systemTT system

DEHNventil, DV M TNC 255DEHNventil, DV M TNS 255DEHNventil, DV M TT 255

951 300951 400951 310

1

D.c. input of the inverter DEHNlimit, DLM PV 1000 900 330

Generator junction box DEHNguard DG PV 500 SCPDEHNguard DG PV 500 SCP FM

950 500950 505

2

3

Fig. 9.18.2.2 Basic circuit diagram – Surge protection for a solar power plant

Table 9.18.2.1 Selection of surge protective devices for solar power plants

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Lightning equipotential bondingIn principle, all conductive systems, entering theoperation building from outside, have to be gen-erally included into the lightning equipotentialbonding. The requirements of lightning equipo-tential bonding are fulfilled by the direct connec-tion of all metal systems and by the indirect con-nection of all live systems via lightning current

arresters. Lightning equipotential bonding shouldbe performed preferably near the entrance of thestructure in order to prevent partial lightning cur-rents from penetrating the building. In this case(Figure 9.18.2.2), the low voltage power supply inthe operation building is protected by a multi poleDEHNventil combined lightning current and surgearrester (see Table 9.18.2.1).

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=∼

1

32

4

4

acquisitionunit for

measured values

NTBA modem

No. in Fig.9.18.2.3

Protection for... SPDs Part No.

Network and data input of an NTBA NT PRO 909 9581

Measuring and control systems and devices withfour-wire data transmission e.g. RS 485 bus systems

BLITZDUCTOR VT, BVT RS 485 5 918 4012

Wind direction indicators, e.g. analoguetransmission of measured values 4 to 20 mA

BLITZDUCTOR XT, BXT ML4 BE 24+ Base part BXT BAS

920 324920 3003

Sensor for environment and moduletemperature

BLITZDUCTOR XT, BXT ML4 BE 5+ Base part BXT BAS

920 320920 300

4

Fig. 9.18.2.3 Protection concept for data acquisition and evaluation

Table 9.18.2.2 Surge protective devices for data acquisition and evaluation

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Furthermore, the d.c. lines entering the PV invert-er in the operation building have to be protectedby a suitable spark-gap-based lightning currentarrester, such as DEHNlimit PV 1000, a combinedlightning current and surge arrester.

Surge protective measures in the PV arrayIn order to reduce the load on the isolation insidethe solar modules at a lightning strike into the iso-lated air-termination system, thermally controlledsurge protective devices are installed in a genera-tor junction box as close as possible to the PV gen-erator. For generator voltages up to 1000 V d.c., aDEHNguard PV 500 SCP type of surge protectivedevice is installed here between plus and minus toearth. In this case surge protective devices Type 2are sufficient because the PV modules are withinthe protective area of the external lightning pro-tection.In practice, it is a proven method to use surge pro-tective devices with floating contacts to indicatethe operating state of the thermal disconnectiondevice. Thus, the intervals between the regular on-site inspections of the protection devices areextended.The surge protective devices in the generator junc-tion boxes assume the protection for the PV mod-ules locally and ensure that no sparkovers causedby conducted or field-related interferences comeup at the PV modules.

NoteThe surge protection of so-called thin-film moduleapplications possibly requires separate considera-tion.

Surge protective measures for data processingsystemsThe operation building provides a remote diagnos-tics system, which is used for a simple and quickfunction check of the PV systems. This allows theoperator to recognise and remedy malfunctions in

good time. The remote supervisory control systemprovides the performance data of the PV genera-tor constantly in order to optimise the output ofthe PV system.As shown in Figure 9.18.2.3, measurements ofwind velocity, module temperature and ambienttemperature are performed via external sensors atthe PV system. These measurements can be readdirectly from the acquisition unit. The data acquisi-tion unit provides interfaces like RS 232 or RS 485,which a PC and/or modems are connected to forremote enquiry and maintenance. Thus, the ser-vice engineers can determine the cause of a mal-function by telediagnosis and then directly elimi-nate it. The modem in Figure 9.18.2.3 is connectedto the network termination unit (NTBA) of an ISDNbasic access.The measuring sensors for wind velocity and mod-ule temperature are also installed in the zone pro-tected against lightning strikes like the PV mod-ules. Thus, no lightning currents come up in themeasuring leads, but probably conducted tran-sient surges resulting from induction effects in theevent of lightning strikes into the isolated air-ter-mination system.

In order to provide a reliable trouble-free and con-tinuous transmission of the measured data to themeasuring unit, it is necessary, to lead the sensorcables entering the building via surge protectivedevices (Table 9.18.2.2). When choosing the pro-tective devices, it has to be ensured that the meas-urements cannot be impaired. The forwarding ofthe measured data via the telecommunication net-work per ISDN modem must be provided as well, inorder to provide a continuous control and optimi-sation of the performance of the installation. Forthis purpose, the Uk0 interface upstream of theNTBA which the ISDN modem is connected to, isprotected by a surge protective adapter. Thisadapter ensures additional protection for the 230 V power supply of the NTBA.

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Standards, guidelines, regulationsBGBl. Nr. 70 vom 27. Spetember 2002 (S. 3777)[engl.: “German Civil Code No. 70 dated 27 Sep-tember 2002 (p. 3777) Regulation for the simplifi-cation of law in the range of safety and healthprotection concerning the provision of workequipment and its use, the safe operation ofmonitoring requiring systems and the organisa-tion of the occupational health and safety equip-ment regulations (Classification as per GermanHealth and Safety at Work Regulations (BetrSichV)”]

BGR 104 – Explosionsschutz-Regeln – Ex-RL –12/2002[engl.: “Employer’s Liability Insurance AssociationRegulations 104 – Explosion protection regula-tions – Ex-RL – 12/2002 Regulations to avoid thehazards of explosive atmosphere”]

DIN 4131: 2007-04German standardTitle (German): Antennentragwerke aus StahlTitle (English): Steel radio towers and masts

DIN 18014: 2007-09German standardTitle (German): FundamenterderTitle (English): Foundation earth electrode – General planning criteria

DIN 18384: 2000-12German standardTitle (German): BlitzschutzanlagenTitle (English): Lightning protection systems

DIN 48805: 1989-08German standardTitle (German): Blitzschutzanlage; StangenhalterTitle (English): Lightning protection system; rodholders

DIN 48820: 1967-01German standardTitle (German): Sinnbilder für Blitzschutzbauteilein ZeichnungenTitle (English): Symbols for building parts forlightning protection drawings

DIN 48828: 1989-08German standardTitle (German): Blitzschutzanlage; Leitungshalter

Title (English): Lightning protection system; con-ductor holders

DIN EN 62305-2 Beiblatt 1: 2007-01German standardTitle (German): Blitzschutz – Teil 2: Risiko-Mana-gement: Abschätzung des Schadensrisikos fürbauliche Anlagen – Beiblatt 1: Blitzgefährdung inDeutschlandTitle (English): Protection against lightning – Part 2: Risk management: Assessment of risk forstructures – Supplement 1: Lightning threat inGermany

DIN EN 62305-2 Beiblatt 2: 2007-02German standardTitle (German): Blitzschutz – Teil 2: Risiko-Mana-gement – Beiblatt 2: Berechnungshilfe zurAbschätzung des Schadensrisikos für baulicheAnlagenTitle (English): Protection against lightning – Part 2: Risk management – Supplement 2: Calcula-tion assistance for assessment of risk for structures

DIN EN 62305-3 Beiblatt 1: 2007-01German standardTitle (German): Blitzschutz – Teil 3: Schutz vonbaulichen Anlagen und Personen – Beiblatt 1:Zusätzliche Informationen zur Anwendung derDIN EN 62305-3 (VDE 0185-305-3)Title (English): Protection against lightning – Part 3: Physical damage to structures and life hazard - Supplement 1: Additional informationfor the application of DIN EN 62305-3 (VDE 0185-305-3)

DIN EN 62305-3 Beiblatt 2: 2007-01German standardTitle (German): Blitzschutz – Teil 3: Schutz vonbaulichen Anlagen und Personen – Beiblatt 2:Zusätzliche Informationen für besondere baulicheAnlagenTitle (English): Protection against lightning – Part 3: Physical damage to structurees and lifehazard – Supplement 2: Additional informationfor special structures

DIN EN 62305-3 Beiblatt 3: 2007-01German standardTitle (German): Blitzschutz – Teil 3: Schutz vonbaulichen Anlagen und Personen – Beiblatt 3:Zusätzliche Informationen für die Prüfung undWartung von Blitzschutzsystemen

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Literature

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Title (English): Protection against lightning – Part 3: Physical damage to structurees and lifehazard – Supplement 3: Additional informationfor the testing and maintenance of lightning pro-tection systems

DIN VDE 0100-702 (VDE 0100-702): 2003-11German standardTitle (German): Errichten von Niederspannungs-anlagen - Anforderungen für Betriebsstätten,Räume und Anlagen besonderer Art – Teil 702:Becken von Schwimmbädern und andere BeckenTitle (English): Erection of low voltage installa-tions – Requirements for special installations orlocations – Part 702: Swimming pools and otherbasins

DIN VDE 0101 (VDE 0101): 2000-01HD 637 S1: 1999German standardStarkstromanlagen mit Nennwechselspannungenüber 1 kV

DIN VDE 0115-1 (VDE 0115-1): 2002-06German standardBahnanwendungen – Allgemeine Bau- undSchutzbestimmungen – Teil 1: ZusätzlicheAnforderungenTitle (English): Railways applications – Generalconstruction and safety requirements – Part 1:Additional requirements

DIN VDE 0151 (VDE 0151): 1986-06German standardWerkstoffe und Mindestmaße von Erdernbezüglich der KorrosionTitle (English): Material and minimum dimensionsof earth electrodes with respect to corrosion

DIN VDE 0618-1 (VDE 0618-1): 1989-08German standardBetriebsmittel für den Potentialausgleich; Poten-tialausgleichsschiene (PAS) für den Hauptpoten-tialausgleichTitle (English): Equipment for equipotential bond-ing; equipotential busbar for main equipotentialbonding

DIN VDE 0800-1 (VDE 0800-1): 1989-05German standardFernmeldetechnikAllgemeine Begriffe, Anforderungen und Prüfun-gen für die Sicherheit der Anlagen und Geräte

DIN VDE 0800-2 (VDE 0800-2): 1985-07German standardFernmeldetechnik – Teil 2: Erdung und Poten-tialausgleich

DIN VDE 0800-10 (VDE 0800-10): 1991-03German standardFernmeldetechnik – Teil 10: Übergangsfestlegun-gen für Errichtung und Betrieb der AnlagenTitle (English): Telecommunications – Part 10:Transitional requirements on erection and opera-tion of installations

DIN VDE 0845 Beiblatt 1 (VDE 0845 Beiblatt 1):2007-01German standardÜberspannungsschutz von Einrichtungen derInformationstechnik (IT-Anlagen)Title (English): Overvoltage protection of informa-tion technology equipment (IT installations)

DIN VDE 0855-300 (VDE 0855-300): 2002-07German standardFunksende-/-empfangssysteme für Senderaus-gangsleistungen bis 1 kW Sicherheitsanforderun-genTitle (English): Transmitting/receiving systems fortransmitter RF output power up to 1 kW – Part300: Safety requirements

EN 1127-1: 2005-03Title (German): Expolsionsfähige Atmosphären –Explosionsschutz – Teil 1: Grundlagen undMethodik; Deutsche Fassung prEN 1127-1: 2004Title (English): Explosive atmospheres – Explosionprevention and protection – Part 1: Basic conceptsand methodology; German version prEN 1127-1:2004

EN 1434-3: 1997-04Title (German): Wärmezähler – Teil 3: Datenaus-tausch und Schnittstellen; Deutsche Fassung EN 1434-3: 1997Title (English): Heat meters – Part 3: Dataexchange and interfaces; German version EN 1434-3: 1997

EN 50162 (VDE 0150): 2005-05Title (German): Schutz gegen Korrosion durchStreuströme aus Gleichstromanlagen; DeutscheFassung: EN 50162: 2004

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Title (English): Protection against corrosion bystray current from direct current systems; Germanversion: EN 50162: 2004

EN 50164-1: 1999Lightning Protection Components (LPC) – Part 1:Requirements for connection components

EN 50164-2: 2002Lightning protection components (LPC) – Part 2:Requirements for conductors and earth electro-des

EN 50164-3: 2006Lightning Protection Components (LPC) – Part 3:Requirements for isolating spark gaps

EN 50174-2 (VDE 0800-174-2): 2001-09Information technology – Cabling installation –Part 2: Installation planning and practices insidebuildings

EN 50308 (VDE 0127-100): 2005-03Wind turbines – Protective measures – Require-ments for design, operation and maintenance

EN 50310 (VDE 0800-2-310): 2006-03Application of equipotential bonding and earth-ing in buildings with information technologyequipment

EN 61643-11: 2007-08Low-voltage surge protective devices – Part 11:Surge protective devices connected to low-volt-age power systems – Requirements and tests

Geräte- und Produktsicherheitsgesetz – GPSG,Stand 060104[engl.: German Code on Equipment and ProductSafety (Equipment Reliability and Consumer Prod-uct Safety Act), State 2004-01-06]

Germanischer LloydRules and regulations, Chapter IV: Non-maritimetechnology; Section 1: Regulations on the certifi-cation of wind turbines

IEC 64/1168/CDV: 200-01Erection of low voltage installations – Part 5:Selection and erection of electrical equipment;Chapter 53: Switchgear and controlgear; Section534: Devices for protection against overvoltages;Amendment A2

IEC 60050-826: 2004-08, modifiedInternational electrotechnical vocabulary – Part 826: Electrical installations

IEC 60060-1: 1989-11 + Corrigendum 1: 1992-03High voltage test techniques – Part 1: Generaldefinitions and test requirements

IEC 60079-0: 2004-01EN 60079-0: 2004-03Electrical apparatus for explosive gas atmospheres– Part 0: General requirements

IEC 60079-11: 2004-12Electrical apparatus for potentially explosiveatmospheres – Intrinsic safety ‘i’

IEC 60079-14: 2002-10Electrical apparatus for explosive gas atmospheres– Part 14: Electrical installations in hazardousareas (other than mines)

IEC 60099-4: 2006-07EN 60099-4: 2007-04Surge arresters – Part 4: Metal-oxide surgearresters without spark gaps for a.c. systems

IEC 60364-4-41: 2005-12 HD 60364-4-41: 2007Low-voltage electrical installations – Part 4-41:Protection for safety – Protection against electricshock

IEC 60364-5-54: 2002-06Electrical installations of buildings – Part 5-54:Selection and erection of electrical equipment –Earthing arrangements, protective conductorsand protective bonding conductors

IEC 60364-5-548: 1996-02Electrical installatin of buildings – Part 5: Selectionand erection of electrical equipment – Section 548:Earthing arrangements and equipotential bond-ing for information technology installations

IEC 60364-6: 2006-02Low-voltage electrical installations – Part 6: Verifi-cation

IEC 60364-7-71: 2006-02Low-voltage electrical installations – Part 7-701:Requirements for special installations or locations– Locations containing a bath or shower

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IEC 60364-7-705: 2006-07Low-voltage electrical installations – Part 7-705:Requirements for special installations or locations– Agricultural and horticultural premises

IEC 60364-7-712: 2002-05Electrical installations of buildings – Part 7-712:Requirements for special installations or locations– Solar photovoltaic (PV) power supply systems

IEC 60664-1: 2007-04Insulation coordination for equipment withinlow-voltage systems – Part 1: Principles, require-ments and tests

IEC 60728-11: 2005-01Cable networks for television signals, sound sig-nals and interactive services – Part 11: Safety

IEC 60950-1: 2005-12Information technolgy equipment – Safety – Part 1: General requirements

IEC 60950-1: 2006-08 – Corrigendum 1Information technology equipment – Safety – Part 1: General requirements

IEC 61000-4-3: 2006-02Electromagnetic compatibility (EMC) – Part 4-3:Testing and measurement techniques – Radiated,radio-frequency, electromagnetic field immunitytest

IEC 61000-4-5: 2005-11Electromagnetic compatibility (EMC) – Part 4-5:Testing and measurement techniques; Surgeimmunity test

IEC 61158-2: 2003-05Digital data communications for measurementand control – Fieldbus for use in industrial controlsystems – Part 2: Physical layer specification andservice definition

IEC 61158-2: 2004-07 – Corrigendum 1Corrigendum 1 – Digital data communications formeasurement and control – Fieldbus for use inindustrial control systems – Part 2: Physical layerspecification and service definition

IEC 61241-17: 2005-01Electrical apparatus for use in the presence ofcombustible dust – Part 17: Inspection and main-

tenance of electrical installations in hazardousareas (other than mines)

IEC 61400-1: 2007-03Wind turbines – Part 1: Design requirements

IEC 61400-2: 2006-03Wind turbines – Part 2: Design requirements forsmall wind turbines

IEC 61400-24: 2002-07Wind turbine generator systems – Part 24: Light-ning protection

IEC 61643-1: 2005-03Low-voltage surge protective devices – Part 1:Surge protective devices connected to low-volt-age power distribution systems – Requirementsand tests

IEC 61643-21: 2000-09Low-voltage surge protective devices – Part 21:Surge protective devices connected to telecom-munications and signalling networks – Perfor-mance requirements and testing methods

IEC 61643-21: 2001-03 – Corrrigendum 1Low-voltage surge protective devices – Part 21:Surge protective devices connected to telecom-munications and signalling networks – Perfor-mance requirements and testing methods

IEC 61643-22: 2004-11Low-voltage surge protective devices – Part 22:Surge protective devices connected to telecom-munications and signalling networks – Selectionand application principles

IEC 61663-1: 1999 + Corrigendum 1999EN 61663-1 (VDE 0845-4-1): 2000-07Lightning protection – Telecommunication lines –Part 1: Fibre optic installation

IEC 61663-2: 2001EN 61663-2 (VDE 0845-4-2): 2002-07Lightning protection – Telecommunication lines –Part 2: Lines using metallic conductors

IEC 62305-1: 2006-01 EN 62305-1: 2006-10Protection against lightning – Part 1: Generalprinciples

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IEC 62305-2: 2006-01 EN 62305-2: 2006-10Protection against lightning – Part 2: Risk man-agement

IEC 62305-3: 2006-01 EN 62305-3: 2006-10Protection against lightning – Part 3: Physicaldamage to structures and life hazard

IEC 62305-4: 2006-01 EN 62305-4: 2006-10Protection against lightning – Part 4: Electricaland electronic systems within structures

IEC 64364-5-53: 2002-06Electrical installations of buildings – Part 5-53:Selection and erection of electrical equipment –Isolation, switching and control

VDN-Richtlinie 2004-08[engl.:] Association of German Network Operators– Directive 2004-08: Surge protective installationsType 1. Directive on the use of surge protectiveinstallations Type 1 (hitherto requirement class B)in main current supply systems; 2nd edition;VWEW Energieverlag GmbH, Frankfurt

VdS Richtlinie 2031: 2005-10[engl.:] VdS Directive 2031: 2005-10: Lightningand surge protection in electrical systems. Guide-lines for damage prevention;VdS Cologne

BooksHasse, P.; Wiesinger, J.Handbuch für Blitzschutz und Erdung; 4. Auflage,1993; Pflaum Verlag München / VDE Verlag GmbHBerlin – Offenbach

Hasse, P.Overvoltage protection of low-voltage systems –Rev. Ed. (IEE power engineering series; no. 33);2nd Edition, 2000; The Institution of ElectricalEngineers

Müller, K.P.Wirksamkeit von Gitterschirmen, zum BeispielBaustahlgewebematten, zur Dämpfung des elek-tromagnetischen Feldes; 2. VDE/ABB-Blitzschutz-tagung, 6./7.11.1997; Neu-Ulm: Neue Blitzschutz-normen in der Praxis; VDE Verlag GmbH Berlin –Offenbach

Raab, V.Überspannungsschutz von Verbraucheranlagen –Auswahl, Errichtung, Prüfung; 2. Auflage, 2003;Verlag Technik, Berlin

Wetzel, G.R.; Müller, K.P.EMV-Blitzschutz; 1. VDE/ABB-Blitzschutztagung,29.02/01.03.1996; Kassel: Blitzschutz für Gebäudeund elektrische Anlagen; VDE Verlag GmbH,Berlin – Offenbach

Overmöhle, K.Nutzung regenerativer Energien – Kurzanalysedes Marktes für Windkraftprojektierer in Deutsch-land; Update 2002

Brosch, P. F.Band 36: Frequenzumrichter; 4. Auflage, 2000;Verlag Moderne Industrie

VDE-SchriftenreiheSchutz von IT-Anlagen gegen Überspannungen;Band 119, 2006; VDE Verlag GmbH, Berlin –Offenbach

Rudolph, W.; Winter, O.EMV nach VDE 0100; EMV für elektrische Anlagenvon Gebäuden: Erdung und und Potentialaus-gleich nach EN 50130,TN-, TT- und IT-Systeme, Ver-meidung von Induktionsschleifen, Schirmung,Lokale Netze; 3. Auflage, 2000; VDE-Schriften-reihe, Band 66; VDE Verlag GmbH Berlin – Offen-bach

Wettingfeld, K.Explosionsschutz nach DIN VDE 0165 undBetriebssicherheitsverordnung; 3. Auflage, 2005;VDE-Schriftenreihe Band 65; VDE Verlag GmbHBerlin – Offenbach

Scripts

BLIDS Blitz-InformationsdienstleistungSiemens AG, ATD IT PS KHE, Siemensallee 84, Karlsruhe

VDE-Info 12Blitzkugelverfahren – Untersuchung von blitzein-schlaggefährdeten Bereichen am Beispiel desAachener Doms; 1. Auflage, 1998

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V. Kopecky

Erfahrungen in der Prüfung von inneren Blitz-schutzanlagen; Elektropraktiker-Online;www.elektropraktiker.de

LonWorksInstallationshandbuch; LON Nutzer Organisatione. V. (LNO); 11/2000

MIL-STD-285: 1956-25 June: Military StandardAttenuation Measurements for enclosures, elec-tromagnetic Shielding, for electronic Test purpos-es, method of United States Government; 1956;Printing Office, Washington

Dipl.-Chem. Dr. Jürgen KulkaDie Betriebssicherheitsverordnung – eine Umset-zungshilfe; 2. Aktualisierte Auflage, März 2005;

Staatliches Amt für Arbeitsschutz Essen, Zentrumfür Umwelt und Energie der HandwerkskammerDüsseldorf, Niederrheinische Industrie- und Han-delskammer Duisburg /Wesel /Kleve

Thern, StephanJährliche und regionale Blitzdichteverteilung inDeutschland; 4. VDE /ABB-Blitzschutztagung am 8. und 9. November 2001 in Neu-Ulm; VDE-Fach-bericht 58, S. 9 – 17; VDE Verlag GmbH, Berlin –Offenbach

DEHN-SoftwareDEHNsupportPlanning software for lightning protection systems

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DEHN + SÖHNE Brochures

Lightning Protection EB

Main catalogue EB

DEHNcondutor System – CUI Conductor

DEHNiso-Distance Holder: The Modular Lightning Protection System

Surge Protection UE

Main catalogue UE

DEHN protects Wind Turbines

DEHN protects Cell Sites

Safety for Sewage Plants

DEHN protects Photovoltaic Systems

DEHN protects the Oil and Gas Industry

DEHN protects Medium Voltage Systems

Is your surge arrester capable of thinking?

DEHN protects Antenna Feeders

Innovative Products for Industrial Applications

BLITZDUCTOR CT with LifeCheck

DEHNprotects Biogas Plants

LSA with Lightning Current Carrying Capacity

Yellow/Line – Easy choice surge protection

DEHN stops Surges

Coordinated Surge Protection

Surge Protection – Easy choice

Practical Surge Protection in Line with Standardisation

Lightning and Surge Protection for Telecommunications and Signalling Networks

Safety Equipment EK

Main catalogue EK

DEHN Safety Equipment – Success needs Safety

Further Brochures

DEHN tests and analyses

DEHN protects

Digital Video (DVD)

DEHNtour

DS 427 E

DS 139 E

DS 111 E

DS 570 E

DS 103

DS 104

DS 107 E

DS 109

DS 122

DS 125 E

DS 136 E

DS 137

DS 142 E

DS 143 E

DS 144

DS 145 E

DS 150

DS 614 E

DS 641 E

DS 649 E

SD 61 E

SD 63 E

DS 396 E

DS 695 E

DS 113

DS 509

DS 707

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Acceptance inspection . . . . . . . . . . . . . . . . . . . . .42Additional inspection . . . . . . . . . . . . . . . . . . . . . .42ADSL connection . . . . . . . . . . . . . . . . . . . . . . . . .282Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . .255Air-termination masts isolated from the building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Air-termination masts spanned with cables . . . .87Air-termination rod . . . . . . . . . . . . . . . . . . . . . . .71Air-termination rod with distance holder . . . . . .71Air-termination system for green and flat roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69Air-termination system for steeples and churches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74Air-termination system for structures withthatched roof . . . . . . . . . . . . . . . . . . . . . . . . . . . .65Air-termination systems . . . . . . . . . . . . . . . . . . . .48Air-termination systems for buildings with gable roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59Air-termination systems for wind turbines . . . . .75Air-termination systems on metal roofs . . . . . . .62Amplitudes of test currents . . . . . . . . . . . . . . . .171Angled support for air-termination rods . . . . . .72Anode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127Antenna installations . . . . . . . . . . . . . . .60, 93, 152Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .250Anticorrosion measures . . . . . . . . . . . . . . . . . . .133Anticorrosive band . . . . . . . . . . . . . . . .98, 125, 133Assembly dimensions for air-termination anddown-conductor systems . . . . . . . . . . . . . . . . . . .97

Backup protection . . . . . . . . . . . . . . . . . . . . . . .201Bare copper . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132Base insulation . . . . . . . . . . . . . . . . . . . . . . . . . .119Biogas plant . . . . . . . . . . . . . . . . . . . . . . . . . . . .234Black tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122BLITZDUCTOR CT . . . . . . . . . . . . . . . . . . . .175, 206BLITZDUCTOR XT . . . . . . . . . . . . . . . . . . . . . . . .221Building regulations . . . . . . . . . . . . . . . . . . . . . . .24Burglar alarm systems . . . . . . . . . . . . . . . . . . . .264

Cable duct systems . . . . . . . . . . . . . . . . . . . . . . .226Cable networks . . . . . . . . . . . . . . . . . . . . . . . . . .250Cable shields . . . . . . . . . . . . . . . . . . . . . . . . . . . .162Cabling between buildings . . . . . . . . . . . . . . . .268Calculating of L0 and C0 . . . . . . . . . . . . . . . . . . .220Calculation Δh . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

Cathode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127

Cell site installations . . . . . . . . . . . . . . . . . . . .87, 90

Characteristics of lightning current . . . . . . . . . . .14

Charge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16, 20

Chimneys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

Choice of lightning protection measures . . . . . .39

Classification in explosion groups . . . . . . . . . . .220

Classification into temperature classes . . . . . . .220

Classification of electrical equipment . . . . . . . .220

Cloud-to-cloud flash . . . . . . . . . . . . . . . . . . . . . . .14

Cloud-to-earth flash . . . . . . . . . . . . . . . . . . . .15, 16

Combination of earth electrodes . . . . . . . . . . .111

Combination of flat strip earth electrodes and earth rods . . . . . . . . . . . . . . . . . . . . . . . . . .114

Combined lightning current and surge arrester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173

Common-mode interference . . . . . . . . . . . . . . .211

Compact installations . . . . . . . . . . . . . . . . . . . . .171

Competent person . . . . . . . . . . . . . . . . . . . . . . . .41

Components for external lightning protection of a residential building . . . . . . . . . . . . . . . . . . .100

Components for thatched roofs . . . . . . . . . . . . .66

Concentration cell . . . . . . . . . . . . . . . . . . . . . . .130

Condition of the earth-termination system . . . .43

Conductivity of the connections . . . . . . . . . . . . .43

Conductor holder for ridge tiles . . . . . . . . . . . .102

Conductor holders for flat roofs . . . . . . . . . . . . .62

Cone-shaped protection zone . . . . . . . . . . . . . . .54

Connecting cable on the earth side . . . . . . . . .201

Control earth electrode . . . . . . . . . . . . . . .106, 143

Control systems . . . . . . . . . . . . . . . . . . . . . . . . . .214

Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . .182

Copper sulphate electrode . . . . . . . . . . . . . . . . .128

Corrosion . . . . . . . .70, 115, 118, 125, 127, 128, 130

Corrosion cell . . . . . . . . . . . . . . . . . . . . . . . . . . .128

Corrosion of earth electrodes . . . . . . . . . . . . . .127

Corrosion protection . . . . . . . . . . . . . . . . . .98, 127

Corrosive waste . . . . . . . . . . . . . . . . . . . . . . . . . .133

Courtyards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

CUI conductor . . . . . . . . . . . . . . . . . . . . . . . . . . .144

Current splitting coefficient Kc . . . . . . . . . . . . .135

Cut-off frequency fG . . . . . . . . . . . . . . . . . . . . . .209

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Damage factor . . . . . . . . . . . . . . . . . . . . . . . . . . .34Damage probabilities . . . . . . . . . . . . . . . . . . . . . .33Data transmission . . . . . . . . . . . . . . . . . . . . . . . .283Data transmission rate . . . . . . . . . . . . . . . . . . . .211Deflection of the air-termination rod . . . . . . . . .80DEHNbloc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .176DEHNflex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174DEHNgrip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102DEHNguard . . . . . . . . . . . . . . . . . . . . . . . . .175, 176DEHNsnap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102DEHNventil . . . . . . . . . . . . . . . . . . . . .172, 176, 205Differential-mode interference . . . . . . . . . . . . .211Dimensions for an external lightning pro-tection system . . . . . . . . . . . . . . . . . . . . . . . . . . . .97Dimensions for ring earth electrodes . . . . . . . . .98Discharge capacity . . . . . . . . . . . . . . . . . . . . . . .209Disconnection selectivity . . . . . . . . . . . . . . . . . .205Distance between down conductors . . . . . . . . . .82Down conductor installed along a downpipe . .86Down-conductor system . . . . . . . . . . . . . . . . .81, 92Down-conductor systems for courtyards . . . . . . .86Downward flash . . . . . . . . . . . . . . . . . . . . . . . . . .15

Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105Earth connection . . . . . . . . . . . . . . . . . . . . . . . .167Earth connection of a metal facade . . . . . . . . . .85Earth electrode . . . . . . . . . . . . . . . . . . . . . . . . . .105Earth electrode materials . . . . . . . . . . . . . . . . . .132Earth electrode resistance . . . . .106, 107, 109, 115Earth electrode Type A . . . . . . . . . . . . . . . .116, 125Earth electrode Type B . . . . . . . . . . . .117, 118, 124Earth electrodes for structures with black tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123Earth electrodes in rocky ground . . . . . . . . . . .125Earth entries . . . . . . . . . . . . . . . . . . . . . . . . . . . .133Earth potential . . . . . . . . . . . . . . . . . .106, 110, 112Earth rod . . . . . . . . . . . . . . . . . . .106, 111, 114, 125Earth rods connected in parallel . . . . . . . . . . . .113Earth-termination system . . . . . . . . . . . . . .105, 116Earth-termination system for equipotential bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .148Earth-to-cloud flash . . . . . . . . . . . . . . . . . . . .15, 16Earthing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .223Earthing concept . . . . . . . . . . . . . . . . . . . . . . . .239Earthing conductor . . . . . . . . . . . . . . . . . . . . . . .106

Economic efficiency of protective measures . . . .39Economic losses of protective measures . . . . . . .39Effect of the corrosion current . . . . . . . . . . . . .130Electrical isolation . . . . . . . . . . . . . . . . . . . . . . . .135Electrical isolation using optocouplers . . . . . . .215Electrical temperature control system . . . . . . . .212Electrochemical corrosion . . . . . . . . . . . . . . . . .127Electrode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127Electrolyte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127Electromagnetic field . . . . . . . . . . . . . . . . . . . . .158Electromagnetic shield . . . . . . . . . . . . . . . . . . . .159Electropotential . . . . . . . . . . . . . . . . . . . . . . . . .128Energy coordination . . . . . . . . . . . . . .171, 175, 182Entrance to the building . . . . . . . . . . . . . . . . . .151Equalising currents . . . . . . . . . . . . . . . . . . . . . . .168Equipotential bonding . . . . . . . .107, 116, 147, 223Equipotential bonding bar . . . . . . . . . . . . . . . .149Equipotential bonding conductors . . . . . . . . . .148Equipotential bonding for information tech-nology installations . . . . . . . . . . . . . . . . . . . . . .151Equipotential bonding for low voltage con-sumer’s installation . . . . . . . . . . . . . . . . . . . . . . .151Equipotential bonding for metal installations .147Equipotential bonding network . . . .160, 164, 166Equipotential surface of the foundation earthelectrode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .136Equivalent interception areas . . . . . . . . . . . . . . .32Equivalents for SPD classifications . . . . . . . . . . . .12Ethernet networks . . . . . . . . . . . . . . . . . . . . . . .271Expert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41Explosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .204Explosion groups . . . . . . . . . . . . . . . . . . . . . . . .220Explosive areas . . . . . . . . . . . . . . . . . . . . . . . . . .285Extension of LPZ . . . . . . . . . . . . . . . . . . . . . . . . .164External lightning protection . . . . . . . . . . . . . . .46External lightning protection of a residentialbuilding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100External lightning protection system for wind turbines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75External zones . . . . . . . . . . . . . . . . . . . . . . . . . . .155

Fast Ethernet networks . . . . . . . . . . . . . . . . . . .271FEM-calculation model . . . . . . . . . . . . . . . . . . . . .79Fermenter . . . . . . . . . . . . . . . . . . . . . . . . . .235, 238Fibre concrete foundation slabs . . . . . . . . . . . .123

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Fibre optic installations . . . . . . . . . . . . . . . . . . .153

Field devices . . . . . . . . . . . . . . . . . . . . . . . . . . . .242

Final striking distance . . . . . . . . . . . . . . . . . . . . . .50

Fire alarm systems . . . . . . . . . . . . . . . . . . . . . . . .264

Fixed earthing points . . . . . . . . . . . . . . . . . . . . .160

Flat tiles or slabs . . . . . . . . . . . . . . . . . . . . . . . . .103

Flat-roofed structures . . . . . . . . . . . . . . . . . . . . . .60

Follow current extinguishing capability Uc (Ifi) .181

Follow current limiting (for spark-gap based SPDs Type 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . .182

Foundation earth electrode . . . . . . . .106, 113, 118

Foundation earth electrode with terminal lug .118

Foundation earth electrodes for structures with white tank . . . . . . . . . . . . . . . . . . . . . . . . .122

Fracture resistance . . . . . . . . . . . . . . . . . . . . . . . .79

Fracture resistance of self-supporting air-ter-mination rod . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79

Frequency converter . . . . . . . . . . . . . . . . . . . . . .227

Frequency of lightning strikes . . . . . . . . . . . . . . .31

Galvanised steel connecting cables . . . . . . . . .133

Galvanised steel mats . . . . . . . . . . . . . . . . . . . . .160

General Provisions . . . . . . . . . . . . . . . . . . . . . . . .26

Generic cabling systems . . . . . . . . . . . . . . . . . . .216

Geometric-electrical mode . . . . . . . . . . . . . . . . . .49

Grooved pantiles . . . . . . . . . . . . . . . . . . . . . . . .103

Grooved tiles . . . . . . . . . . . . . . . . . . . . . . . . . . . .103

Hazard alert systems . . . . . . . . . . . . . . . . . . . . .264

Hazardous areas . . . . . . . . . . . . . . . . . . . . .218, 286

Hedgehog roof . . . . . . . . . . . . . . . . . . . . . . . . . . .64

Height of an air-termination rod . . . . . . . . . . . .52

Hot-dip galvanised steel . . . . . . . . . . . . . . . . . . .132

HVI conductor . . . . . . . . . . . . . . . . . . . . . . . . .87, 92

Impulse earth resistance . . . . . . . . . . . . . .106, 113

Induced surges . . . . . . . . . . . . . . . . . . . . . . . . . .174

Induction factor Ki . . . . . . . . . . . . . . . . . . . . . . .135

Inductive coupling . . . . . . . . . . . . . . . . . . . . . . .145

Influence of lightning on IT cabling sub-systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .218

Information technology installations 170, 172, 175

Information technology system . . . . . . . . . . . . .206

Input circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . .211

Inspection and maintenance of the LEMP protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .179Inspection of a lightning protection system . . . .41Inspection of the design . . . . . . . . . . . . . . . . . . . .42Inspection report . . . . . . . . . . . . . . . . . . . . . . . . .44Inspections during the construction phase . . . . .42Installation of down-conductor systems . . . . . . .83Installation standards . . . . . . . . . . . . . . . . . . . . . .11Installations above the roof . . . . . . . . . . . . . . . . .65Insulation resistance . . . . . . . . . . . . . . . . . . . . . .222Integrated decoupling elements . . . . . . . . . . . .212Interactive services . . . . . . . . . . . . . . . . . . . . . . .250Interferences . . . . . . . . . . . . . . . . . . . . . . . . . . . .211Intermeshed earth-termination system . . . . . . .239Intermeshing of earth-termination systems . . .125Internal down-conductor systems . . . . . . . . . . . .87Internal lightning protection . . . . . . . . . . . . . . . .46Internal zones . . . . . . . . . . . . . . . . . . . . . . . . . . .156Intrinsically safe circuits . . . . . . . . . . . . . . .218, 285Intrinsically safe SPD . . . . . . . . . . . . . . . . . . . . . .221Inverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .299ISDN access . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282Isolated air-termination systems . . . . . . . . . . . . .73Isolated and non-isolated air-termination systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56Isolated down-conductor . . . . . . . . . . . . . . . . . . .89Isolated external lightning protection system . .87Isolating spark gaps . . . . . . . . . . . . . . . . . .133, 148IT cabling subsystems . . . . . . . . . . . . . . . . . . . . .218IT installations . . . . . . . . . . . . . . . . . . . . . . . . . . .176IT system . . . . . . . . . . . . . . . . . . . . . . . . . . .184, 192

Kinds of interferences . . . . . . . . . . . . . . . . . . . .211KNX systems . . . . . . . . . . . . . . . . . . . . . . . . . . . .268

Lattice shield . . . . . . . . . . . . . . . . . . . . . . . . . . .158Leader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15Legal regulations . . . . . . . . . . . . . . . . . . . . . . . . .24LEMP protection management . . . . . . . . . . . . .156LEMP risk levels . . . . . . . . . . . . . . . . . . . . . . . . . .155Lengths of the connecting leads for SPDs . . . . .197Lightning current arrester . . . . . . . . . . . . . . . . .172Lightning current parameters . . . . . . . . . . . . . . .22Lightning discharge . . . . . . . . . . . . . . . . . . . . . . .14Lightning equipotential bonding . . . . . . . . . . .170

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Lightning impulse current carrying capability .169Lightning impulse current Iimp . . . . . . . . . . . . . .181Lightning protection earthing . . . . . . . . . . . . . .106Lightning protection for metal roofs . . . . . . . . .63Lightning protection level . . . . . . . . . . . . . . .22, 47Lightning protection mast . . . . . . . . . . . . . . . . . .72Lightning protection system . . . . .24, 46, 155, 246Lightning protection zone . . . . . . . . . . . . .155, 230Lightning protection zones concept . . . . . . . . . . . . . . . . . . . .155, 244, 285, 292Limit values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22Limiting voltage . . . . . . . . . . . . . . . . . . . . . . . . .208Location of the lightning discharge . . . . . . . . . .14Long strike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83Loss factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36LPZ 0A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155LPZ 0B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155LPZ 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156LPZ 2 ... n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156

M-Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .273Magnetic field . . . . . . . . . . . . . . . . . . . . . . . . . . .158Magnetic shield attenuation . . . . . . . . . . . . . . .158Main equipotential bonding . . . . . . . . . . . . . . .147Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Maintenance of the lightning protection system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41Material combinations . . . . . . . . . . . . . . . . . . . . .98Material combinations of earth-termination systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133Material factor Km . . . . . . . . . . . . . . . . . . . . . . .135Material, configuration and min. cross sections of air-termination conductors, air-terminationrods and down conductors . . . . . . . . . . . . . . . . .96Material, configuration and min. dimensions of earth electrodes . . . . . . . . . . . . . . . . . . . . . . .134Max. temperature rise ΔT in K of different conductor materials . . . . . . . . . . . . . . . . . . . . . . .82Maximum continuous operating voltage . . . . .211Maximum continuous voltage Uc . . . . . . . . . . .181Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . .43Measuring points . . . . . . . . . . . . . . . . . . . . . . . . .86Measuring systems . . . . . . . . . . . . . . . . . . . . . . .214Melting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .204Melting through . . . . . . . . . . . . . . . . . . . . . . . . . .62

Mesh method . . . . . . . . . . . . . . . . . . . . . . . . .53, 60Mesh-shape arrangement . . . . . . . . . . . . . . . . .166Meshed arrangement . . . . . . . . . . . . . . . . . . . . .166Meshed equipotential bonding network . . . . .160Metal installations . . . . . . . . . . . . . . .166, 171, 173Metal roof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58Metal roof with round standing seam . . . . . . . .64Metal structures mounted on the roof withoutconductive connection . . . . . . . . . . . . . . . . . . . . .59Metal subconstruction . . . . . . . . . . . . . . . . . . . . .85Min. thickness of metal plates . . . . . . . . . . . . . . .58Mobile radio . . . . . . . . . . . . . . . . . . . . . . . . . . . .295

Natural components of a down-conductor system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84Natural components of air-termination systems 58Natural earth electrode . . . . . . . . . . . . . . . . . . .106No melting . . . . . . . . . . . . . . . . . . . . . . . . . . . . .204Nominal current IL . . . . . . . . . . . . . . . . . . . . . . .209Nominal discharge current In . . . . . . . . . . .181, 209Non-isolated lightning protection system . . . . .82Non-reinforced concrete . . . . . . . . . . . . . . . . . .119Non-reinforced foundations . . . . . . . . . . . . . . .119NTBA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282NTPM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282Number of down conductors . . . . . . . . . . . . . . . .82

On-site inspection . . . . . . . . . . . . . . . . . . . . . . . .43Operating current . . . . . . . . . . . . . . . . . . . . . . . .211Optoelectronic components . . . . . . . . . . . . . . .215Outdoor lighting systems . . . . . . . . . . . . . . . . . .230Overlapped constructions . . . . . . . . . . . . . . . . .103

Parabolic antennas . . . . . . . . . . . . . . . . . . . . . . .60Parallel connection . . . . . . . . . . . . . . . . . . . . . . .197Peak value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Perimeter insulation . . . . . . . . . . . . . . . . . . . . . .119Phase-side connecting cable . . . . . . . . . . . . . . .200Photovoltaic systems . . . . . . . . . . . . . . . . . . . . .298Points threatened by corrosion . . . . . . . . . . . . . .98Position fixing element . . . . . . . . . . . . . . . . . . . .62Position fixing for the air-termination con-ductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128Potential control . . . . . . . . . . . . . . . . . . . . .106, 142

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Potential gradient area . . . . . . . . . . . . . . . . . . . .18Potential of the earth´s surface . . . . . . . . . . . . .106Potential rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Potential values and corrosion rates of common metal materials . . . . . . . . . . . . . . . . . .129Power feed-in . . . . . . . . . . . . . . . . . . . . . . . . . . .239Power supply installations . . . . . . . . .167, 171, 174Power supply system . . . . . . . . . . . . . . . . . . . . .180Primary rate multiplex access . . . . . . . . . . . . . . .283Probabilities of damage . . . . . . . . . . . . . . . . . . . .33Product standards . . . . . . . . . . . . . . . . . . . . . . . . .13PROFIBUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .278Protected zone . . . . . . . . . . . . . . . . . . . . . . . . . . .50Protection against electric shock under fault conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183Protection against electric shock under normal conditions . . . . . . . . . . . . . . . . . . . . . . . .182Protection against life hazards . . . . . . . . . . . . .182Protection circuit . . . . . . . . . . . . . . . . . . . . . . . .211Protection from rain . . . . . . . . . . . . . . . . . . . . . . .63Protection level . . . . . . . . . . . . . . . . . . . . . . . . . .212Protection of terminal devices . . . . . . . . . . . . . .180Protection of the data and telephone lines . . .272Protective angle method . . . . . . . . . . . . . . . .53, 56Protective area . . . . . . . . . . . . . . . . . . . . . . . . . . .52Protective equipotential bonding . . . . . . . . . . .147Protective equipotential bonding conductors .148Public address systems . . . . . . . . . . . . . . . . . . . .262

Qualification of the inspectors . . . . . . . . . . . . . .41

Radio transmitter /receiver stations . . . . . . . . .295Radio transmitting technology . . . . . . . . . . . . .295Radius of the rolling sphere . . . . . . . . . . . . . . . . .49Rating of the terminal cross-sections . . . . . . . .201Reference earth . . . . . . . . . . . . . . . . . . . . . . . . .105Reference electrode . . . . . . . . . . . . . . . . . . . . . .128Reference potential . . . . . . . . . . . . . . . . . . . . . .128Reinforced concrete . . . . . . . . . . . . . . . . . . . . . .119Remote monitoring system . . . . . . . . . . . . . . . .241Repeat inspection . . . . . . . . . . . . . . . . . . . . . . . . .42Ridge and hip tiles . . . . . . . . . . . . . . . . . . . . . . .102Ring distances and depths of the potential control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143Ring earth electrode . . . . . . . . . . . . . .106, 114, 143

Ring equipotential bonding . . . . . . . . . . . . . . .173Ring equipotential bonding bar . . . . . . . . . . . .165Risk assessment . . . . . . . . . . . . . . . . . . . . . . . . . . .29Risk components . . . . . . . . . . . . . . . . . . . . . . . . . .36Risk management . . . . . . . . . . . . . . . . . . . . . . . . .29Rolling sphere method . . . . . . . . . . . . . . . . . . . . .48Roof conductor holder . . . . . . . . . . . . . . . . . . . .104Roof conductor holders on flat roofs . . . . . . . . .60Roof with standing seam . . . . . . . . . . . . . . . . . . .64Roof-mounted structures . . . . . . . . . . . . . . . . . . .92Roof-mounted structures made of electricallynon-conductive material . . . . . . . . . . . . . . . . . . .59

Sag of the rolling sphere . . . . . . . . . . . . . . . . . . .52Seasonal fluctuations . . . . . . . . . . . . . . . . . . . . .108Selection criteria for SPD . . . . . . . . . . . . . . . . . .221Selection features . . . . . . . . . . . . . . . . . . . . . . . .209Self-supporting air-termination rods . . . . . . . . .76Separation distance 56, 60, 65, 89, 95, 98, 135, 138Sequence of lightning current . . . . . . . . . . . . . . .14Series connection (V-shape) . . . . . . . . . . . . . . . 197Sewage plants . . . . . . . . . . . . . . . . . . . . . . . . . . .244Shield connection system capable of carryinglightning currents . . . . . . . . . . . . . . . . . . . . . . . .153Shield earthing . . . . . . . . . . . . . . . . . . . . . . . . . .162Shielded cables . . . . . . . . . . . . . . . . . . . . . . . . . .164Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . .225, 292Shielding effect . . . . . . . . . . . . . . . . . . . . . . . . . .158Shielding factor . . . . . . . . . . . . . . . . . . . . . . . . .159Shielding measures . . . . . . . . . . . . . . . . . . . . . . .168Short strike . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Short-circuit withstand capability . . . . . . . . . . .181Signal frequency . . . . . . . . . . . . . . . . . . . . . . . . .211Signal transmission . . . . . . . . . . . . . . . . . . .212, 262Slate roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103Solar power plants . . . . . . . . . . . . . . . . . . .298, 304Sound signals . . . . . . . . . . . . . . . . . . . . . . . . . . .250Sources of damage . . . . . . . . . . . . . . . . . . . . . . . .34SPD classification . . . . . . . . . . . . . . . . . . . . . . . .206SPD Type 1 . . . . . . . . . . . . . . . . . . . . . . . . . . .12, 181SPD Type 2 . . . . . . . . . . . . . . . . . . . . . . . . . . .12, 181SPD Type 3 . . . . . . . . . . . . . . . . . . . . . . . . . . .12, 181Specific earth resistance . . . . . . . . . . . . . . .106, 108Specific energy . . . . . . . . . . . . . . . . . . . . . . . .16, 21SPS Protector . . . . . . . . . . . . . . . . . . . . . . . . . . . .175

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Stabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .257Stages of protection . . . . . . . . . . . . . . . . . . . . . .212Stainless steels . . . . . . . . . . . . . . . . . . . . . . . . . . .132Star-shape arrangement . . . . . . . . . . . . . . . . . .166Star-type earth electrodes . . . . . . . . . . . . . . . . .111Steel mats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160Steel reinforcement of concrete foundations .133Steel tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .238Steel with copper sheath . . . . . . . . . . . . . . . . . .132Steepness . . . . . . . . . . . . . . . . . . . . . . . . .16, 19, 208Step voltage . . . . . . . . . . . . . . . . . . . .106, 140, 230Straight surface earth electrode . . . . . . . . . . . .110Stress caused by wind loads . . . . . . . . . . . . . . . . .77Strip foundation . . . . . . . . . . . . . . . . . . . . . . . . .120Supplementary equipotential bonding . . .147, 150Supplementary protective equipotential bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147Surface earth electrode . . . . . . . . . . .106, 114, 115Surge protection for electrical temperature control systems . . . . . . . . . . . . . . . . . . . . . . . . . .212Surge protective devices . . . . . . . . . . . . . . . . . .180

Technical characteristics of SPDs . . . . . . . . . . . .181Technical documentation . . . . . . . . . . . . . . . . . . .44Technical property management . . . . . . . . . . . .215Telecommunication accesses . . . . . . . . . . . . . . .282Telecommunication lines . . . . . . . . . . . . . . . . . .153Temperature classes . . . . . . . . . . . . . . . . . . . . . .220Temperature-dependent changes in length of air-termination and down conductors . . . . . .98Terminal cross-section . . . . . . . . . . . . . . . . . . . .201Terminal lug . . . . . . . . . . . . . . . . . . . . . . . . . . . .118Terminals for equipotential bonding . . . . . . . .149Test voltage waveform . . . . . . . . . . . . . . . . . . . .208Thatched roof . . . . . . . . . . . . . . . . . . . . . . . . . . . .65Tilt resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

TN system . . . . . . . . . . . . . . . . . . . . . . . . . .183, 184TN-C system . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183TN-C-S system . . . . . . . . . . . . . . . . . . . . . . . . . . .183TN-S system . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183Tolerable risk of lightning damage . . . . . . . . . . .39Touch voltage . . . . . . . . . . . . . . .106, 140, 144, 230TOV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .182Trafficable roofs . . . . . . . . . . . . . . . . . . . . . . . . . .68Transient surges in hazardous areas . . . . . . . . .219Tripod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73TT system . . . . . . . . . . . . . . . . . . . . . . . . . . .183, 185TV signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .250Two-conductor terminals . . . . . . . . . . . . . . . . . .197Type designation of the protective modules . .207Types of inspection . . . . . . . . . . . . . . . . . . . . . . . .41Types of loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

Underground terminals and connections . . . .133Upward flash . . . . . . . . . . . . . . . . . . . . . . . . . .15, 16Use of SPDs in various systems . . . . . . . . . . . . . .182

V-shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197Vaporisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62Video surveillance systems . . . . . . . . . . . . . . . . .259Visual inspection . . . . . . . . . . . . . . . . . . . . . . . . . .42Voltage protection level Up . . . . . . . . . . . .181, 208Voltaic cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128

Walkable roofs . . . . . . . . . . . . . . . . . . . . . . . . . .68White tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122Wind contact surface of the air-termination rod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78Wind contact surface of the bracing . . . . . . . . . .78Wind load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76Wind turbines . . . . . . . . . . . . . . . . . . . . . . . . . . .291Work contracts . . . . . . . . . . . . . . . . . . . . . . . . . . .12

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Aerial photo of DEHN + SÖHNE . . . . . . . . . . . . . . . . . . . . . . .3

Fig. 2.1.1 Downward flash (cloud-to-earth flash) . . . . . . . . . . . . . . . . .14

Fig. 2.1.2 Discharge mechanism of a negative downward flash (cloud-to-earth flash) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Fig. 2.1.3 Discharge mechanism of a positive downward flash (cloud-to-earth flash) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Fig. 2.1.4 Upward flash (earth-to-cloud flash) . . . . . . . . . . . . . . . . . . .15

Fig. 2.1.5 Discharge mechanism of a negative upward flash (earth-to-cloud flash) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Fig. 2.1.6 Discharge mechanism of a positive upward flash (earth-to-cloud flash) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Fig. 2.1.7 Possible components of downward flashes . . . . . . . . . . . . .17

Fig. 2.1.8 Possible components of upward flashes . . . . . . . . . . . . . . . .17

Fig. 2.2.1 Potential distribution of a lightning strike into homo-genous soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Fig. 2.2.2 Animals killed by shock current due to hazardous step voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Fig. 2.2.3 Potential rise of the earth-termination system of a build-ing compared to the remote earth due to the peak value of the lightning current . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Fig. 2.2.4 Threat to electrical installations by potential rise at the earth-termination system . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Fig. 2.3.1 Induced square-wave voltage in loops via the current steepness Δi/Δt of the lightning current . . . . . . . . . . . . . . . .19

Fig. 2.3.2 Example for calculation of induced square-wave voltages in squared loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Fig. 2.4.1 Energy deposited at the point of strike by the load of the lightning current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Fig. 2.4.2 Effect of an impulse current arc on a metal surface . . . . . . .21

Fig. 2.4.3 Plates perforated by the effects of long-time arcs . . . . . . . .21

Fig. 2.5.1 Heating and force effects by the specific energy of light-ning current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Fig. 2.5.2 Electrodynamic effect between parallel conductors . . . . . . .22

Fig. 3.2.3.1 Lightning density in Germany (average of 1999 – 2005) . . .30

Fig. 3.2.3.2 Equivalent interception area Ad for direct lightning strikes into a stand-alone structure . . . . . . . . . . . . . . . . . . .32

Fig. 3.2.3.3 Equivalent interception areas Ad , Al , Aa for direct lightningstrikes into structures/supply lines and Am , Ai for indirectlightning strikes near the structures/supply lines . . . . . . . . .32

Fig. 3.2.9.1 Flow chart for selection of protective measures for the types of loss L1 ... L3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Fig. 3.2.10.1 Basic procedure in case of a purely economic consider-ation and calculation of the yearly costs . . . . . . . . . . . . . . .40

Fig. 3.2.10.2 Flow chart for the choice of protective measures in case of economic losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Fig. 4.1 Components of a lightning protection system . . . . . . . . . . .46

Fig. 4.2 Lightning protection system (LPS) . . . . . . . . . . . . . . . . . . . .47

Fig. 5.1.1 Method for designing of air-termination systems for highbuildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

Fig. 5.1.1.1 Starting upward leader defining the point of strike . . . . . . .49

Fig. 5.1.1.2 Model of a rolling sphere; Ref: Prof. Dr. A. Kern, Aachen . . . .49

Fig. 5.1.1.3 Schematic application of the “rolling sphere” method at a building with considerably structured surface . . . . . . . . . .50

Fig. 5.1.1.4 Construction of a new administration building: Model with “rolling sphere” acc. to lightning protection system Type I, Ref.: WBG Wiesinger . . . . . . . . . . . . . . . . . . . . . . . . .51

Fig. 5.1.1.5 Construction of a DAS administration building: Top view(excerpt) on the zones threatened by lightning strikes for lightning protection system Class I, Ref.: WBG Wiesinger . . .51

Fig. 5.1.1.6 Aachen Cathedral: Model with environment and “rollingspheres” for lightning protection systems Class II and III,Ref.: Prof. Dr. A. Kern, Aachen . . . . . . . . . . . . . . . . . . . . . . . .51

Fig. 5.1.1.7 Penetration depth p of the rolling sphere . . . . . . . . . . . . . . .52

Fig. 5.1.1.8 Air-termination system for installations mounted on the roof with their protective area . . . . . . . . . . . . . . . . . . . . . . .52

Fig. 5.1.1.9 Calculation Δh for several air-termination rods according to rolling sphere method . . . . . . . . . . . . . . . . . . . . . . . . . . .52

Fig. 5.1.1.10 Meshed air-termination system . . . . . . . . . . . . . . . . . . . . . .53

Fig. 5.1.1.11 Protective angle and comparable radius of the rolling sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54

Fig. 5.1.1.12 Protective angle α as a function of height h depending on the class of lightning protection system . . . . . . . . . . . . . . . .54

Fig. 5.1.1.13 Cone-shaped protection zone . . . . . . . . . . . . . . . . . . . . . . . .54

Fig. 5.1.1.14 Example of air-termination systems with protective angle α . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54

Fig. 5.1.1.15 Area protected by an air-termination conductor . . . . . . . . . .54

Fig. 5.1.1.16 External lightning protection system, volume protected by a vertical air-termination rod . . . . . . . . . . . . . . . . . . . . . .54

Fig. 5.1.1.17 Protection of small-sized installations on roofs against direct lightning strikes by means of air-termination rods . . .56

Fig. 5.1.1.18 Gable roof with conductor holder . . . . . . . . . . . . . . . . . . . . .56

Fig. 5.1.1.19 Flat roof with conductor holders: Protection of the dome-lights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

Fig. 5.1.1.20 Isolated external lightning protection system with two separate air-termination masts according to the protectiveangle method: Projection on a vertical area . . . . . . . . . . . . .57

Fig. 5.1.1.21 Isolated external lightning protection system, consisting of two separate air-termination masts, connected by a horizontal air-termination conductor: Projection on a vertical surface via the two masts (vertical section) . . . . . . .57

Fig. 5.1.2.1 Air-termination system on a gable roof . . . . . . . . . . . . . . . .59

Fig. 5.1.2.2 Height of a roof superstructure made of electrically non-conductive material (e.g. PVC), h ≤ 0.5 m . . . . . . . . . . . . . .59

Fig. 5.1.2.3 Additional air-termination system for ventilation pipes . . . .59

Fig. 5.1.2.4 Building with photovoltaic system, Ref.: Wettingfeld Lightning Protection, Krefeld, Germany . . . . . . . . . . . . . . . .60

Fig. 5.1.2.5 Antenna with air-termination rod . . . . . . . . . . . . . . . . . . . . .60

Fig. 5.1.3.1 Air-termination system . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Fig. 5.1.3.2 Air-termination system on a flat roof . . . . . . . . . . . . . . . . . .61

Fig. 5.1.3.3 Use of air-termination rods . . . . . . . . . . . . . . . . . . . . . . . . . .61

Fig. 5.1.3.4 Bridged attic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Fig. 5.1.3.5 Example how to protect a metal roof attic, if melting through is unacceptable (front view) . . . . . . . . . . . . . . . . . .61

Fig. 5.1.3.6 Synthetic flat roof sheetings – Roof conductor holder Type KF/KF2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

Fig. 5.1.4.1 Types of metal roofs, e. g. roofs with round standing seam .63

Fig. 5.1.4.2 Example of damage: Metal plate cover . . . . . . . . . . . . . . . .63

Fig. 5.1.4.3 Air-termination system on a metal roof – Protection against holing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63

Fig. 5.1.4.4a Conductor holders for metal roofs – Round standing seam .64

Fig. 5.1.4.4b Conductor holder for metal roofs – Round standing seam . .64

Fig. 5.1.4.5 Model construction of a trapezoidal sheet roof, conductorholder with clamping frame . . . . . . . . . . . . . . . . . . . . . . . . .64

Fig. 5.1.4.6 Model construction of a roof with standing seam . . . . . . . .64

Fig. 5.1.4.7 Air-termination rod for a domelight on a roof with roundstanding seam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

Fig. 5.1.5.1 Air-termination system for buildings with thatched roofs . . .65

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Fig. 5.1.5.2 Components for thatched roofs . . . . . . . . . . . . . . . . . . . . . .66

Fig. 5.1.5.3 Thatched roof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66

Fig. 5.1.5.4 Historical farmhouse with external lightning protection (Ref. Photo: Hans Thormählen GmbH & Co.KG) . . . . . . . . . .66

Fig. 5.1.5.5 Sectioning at the central building . . . . . . . . . . . . . . . . . . . . .67

Fig. 5.1.5.6 Schematic diagram and diagram of the down conductorinstallation at the rafter . . . . . . . . . . . . . . . . . . . . . . . . . . . .67

Fig. 5.1.5.7 HVI conductor led through the cornice plank . . . . . . . . . . . .68

Fig. 5.1.6.1 Lightning protection for car park roofs – Building pro-tection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

Fig. 5.1.6.2 Lightning protection for car park roofs – Building and life protection IEC 62305-3 (EN 62305-3); Annex E . . . . . . . . . .69

Fig. 5.1.7.1 Green roof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70

Fig. 5.1.7.2 Air-termination system on a green roof . . . . . . . . . . . . . . . .70

Fig. 5.1.7.3 Conductor leading on the covering layer . . . . . . . . . . . . . . .70

Fig. 5.1.8.1 Connection of roof-mounted structures . . . . . . . . . . . . . . . .70

Fig. 5.1.8.2 Isolated air-termination system, protection provided by an air-termination rod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71

Fig. 5.1.8.3 Air-termination rod with distance holder . . . . . . . . . . . . . . .71

Fig. 5.1.8.4 Angled support for air-termination rods . . . . . . . . . . . . . . . .72

Fig. 5.1.8.5 Supporting element for the air-termination rod . . . . . . . . . .72

Fig. 5.1.8.6 Isolated air-termination system for photovoltaic system . . .72

Fig. 5.1.8.7 Isolated air-termination system for roof-mounted struc-tures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72

Fig. 5.1.8.8 Additional protection in the transition area by anticorro-sive band for underground application . . . . . . . . . . . . . . . . .72

Fig. 5.1.8.9 Installation of a steel telescopic lightning protection mast .72

Fig. 5.1.8.10 Installed air-termination system; Ref.: Blitzschutz Wettingfeld , Krefeld. Germany . . . . . . . . . . . . . . . . . . . . . .73

Fig. 5.1.8.11 Tripod support for self-supporting insulating pipes . . . . . . .73

Fig. 5.1.8.12 Isolated air-termination systems with DEHNiso-Combi . . . .73

Fig. 5.1.8.13 Detail picture of DEHNiso-Combi . . . . . . . . . . . . . . . . . . . . .74

Fig. 5.1.8.14 Isolated air-termination system with DEHNiso-Combi . . . . .74

Fig. 5.1.9.1 Installing the down-conductor system at a steeple . . . . . . .74

Fig. 5.1.10.1 WT with integrated receptors in the rotor blades . . . . . . . . .75

Fig. 5.1.10.2 Lightning protection for wind speed indicators at WT . . . . .76

Fig. 5.1.11.1 Protection against direct lightning strikes by self-support-ing air-termination rods . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

Fig. 5.1.11.2 Procedure for installation of air-termination systems according to IEC 62305-3 (EN 62305-3) . . . . . . . . . . . . . . . .77

Fig. 5.1.11.3 Self-supporting air-termination rod with variable tripod . . .77

Fig. 5.1.11.4 Division of Germany into wind load zones and corres-ponding values of dynamic pressure and max. wind speedRef.: DIN 4131:1991-11: Steel antenna frames, Berlin:Beuth-Verlag, GmbH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

Fig. 5.1.11.5 Comparison of bending moment courses at self-support-ing air-termination rods with and without braces (length = 8.5 m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80

Fig. 5.1.11.6 FEM model of a self-supporting air-termination rod with-out bracing (length = 8.5 m) . . . . . . . . . . . . . . . . . . . . . . . .81

Fig. 5.1.11.7 FEM model of a self-supporting air-termination rod with bracing (length = 8.5 m) . . . . . . . . . . . . . . . . . . . . . . . . . . .81

Fig. 5.2.2.1.1 Loop in the down conductor . . . . . . . . . . . . . . . . . . . . . . . . .83

Fig. 5.2.2.1.2 Down-conductor system . . . . . . . . . . . . . . . . . . . . . . . . . . . .84

Fig. 5.2.2.1.3 Air-termination system with connection to the gutter . . . . .84

Fig. 5.2.2.1.4 Earthed downpipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84

Fig. 5.2.2.2.1 Use of natural components – new buildings made of ready-mix concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85

Fig. 5.2.2.2.2 Metal subconstruction, conductively bridged . . . . . . . . . . . .85

Fig. 5.2.2.2.3 Earth connection of a metal facade . . . . . . . . . . . . . . . . . . .85

Fig. 5.2.2.2.4 Down conductor installed along a downpipe . . . . . . . . . . . .86

Fig. 5.2.2.3.1 Measuring point with number plate . . . . . . . . . . . . . . . . . . .86

Fig. 5.2.2.4.1 Air-termination system installed on large roofs – Internaldown-conductor system . . . . . . . . . . . . . . . . . . . . . . . . . . . .86

Fig. 5.2.2.5.1 Down-conductor systems for courtyards . . . . . . . . . . . . . . .86

Fig. 5.2.3.1 Air-termination masts isolated from the building . . . . . . . . .87

Fig. 5.2.3.2 Air-termination masts spanned with cables . . . . . . . . . . . . .87

Fig. 5.2.3.3 Air-termination masts spanned with cables with cross connection (meshing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87

Fig. 5.2.4.1 Isolated air-termination system with distance holder . . . . . .89

Fig. 5.2.4.2 Isolated air-termination system for cell sites – Application of DEHNconductor system . . . . . . . . . . . . . . . . . . . . . . . . . .89

Fig. 5.2.4.1.1 Basic development of a creeping discharge at an isolateddown conductor without special coating . . . . . . . . . . . . . . .90

Fig. 5.2.4.1.2 Components of HVI Conductor . . . . . . . . . . . . . . . . . . . . . . .90

Fig. 5.2.4.1.3 HVI conductor I and components of the DEHNconductor system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90

Fig. 5.2.4.2.1 Integration of a new 2G/3G antenna into the existing lightning protection system by using the HVI conductor . . .91

Fig. 5.2.4.2.2a Insulating pipe within the antenna area . . . . . . . . . . . . . . . .91

Fig. 5.2.4.2.2b Connection to the antenna frame structure for directingpotential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91

Fig. 5.2.4.2.3a Fan with air-termination rod and spanned cable . . . . . . . . .92

Fig. 5.2.4.2.3b Air-termination rod, elevated ring conductor connected to the isolated down-conductor system . . . . . . . . . . . . . . . .92

Fig. 5.2.4.2.4 Keeping the required separation distance with voltage-controlled isolated down conductor (HVI) . . . . . . . . . . . . . .92

Fig. 5.2.4.2.5 Air termination system with spanned cable and isolateddown-conductor system . . . . . . . . . . . . . . . . . . . . . . . . . . . .92

Fig. 5.2.4.3.1 Total view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93

Fig. 5.2.4.3.2 Isolated air-termination system and isolated ring con-ductor, Ref.: H. Bartels GmbH, Oldenburg, Germany . . . . . . .94

Fig. 5.2.4.3.3 Down conductor of isolated ring conductor . . . . . . . . . . . . .94

Fig. 5.2.4.3.4 Total view on a newly installed external lightning protec-tion system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

Fig. 5.2.4.4.1 Calculation of the required separation distance . . . . . . . . . .95

Fig. 5.4.1 Detail examples of an external lightning protection sys-tem at a building with a sloped tiled roof . . . . . . . . . . . . . .97

Fig. 5.4.2 Air-termination rod for chimneys . . . . . . . . . . . . . . . . . . . . .97

Fig. 5.4.3 Application on a flat roof . . . . . . . . . . . . . . . . . . . . . . . . . . .97

Fig. 5.4.4 Dimensions for ring earth electrodes . . . . . . . . . . . . . . . . . .98

Fig. 5.4.5 Points threatened by corrosion . . . . . . . . . . . . . . . . . . . . . . .98

Fig. 5.4.1.1 Air-termination system – Compensation of expansion with bridging braid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

Fig. 5.4.2.1a External lightning protection of a residential building . . . .100

Fig. 5.4.2.1b External lightning protection of an industrial structure . . .101

Fig. 5.4.2.2 DEHNsnap and DEHNgrip conductor holders . . . . . . . . . . .102

Fig. 5.4.3.1 Conductor holder with DEHNsnap for ridge tiles . . . . . . . .102

Fig. 5.4.3.2 SPANNsnap with plastic DEHNsnap conductor holder . . . .102

Fig. 5.4.3.3 FIRSTsnap for mounting on existing ridge clamp . . . . . . . .102

Fig. 5.4.3.4 UNIsnap roof conductor holder with preformed strut – Used on grooved pantiles . . . . . . . . . . . . . . . . . . . . . . . . . .103

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Fig. 5.4.3.5 UNIsnap roof conductor holder with preformed strut – Used on smooth tiles, e.g. plain tiles . . . . . . . . . . . . . . . . .103

Fig. 5.4.3.6 UNIsnap roof conductor holder with preformed strut – Used on slate roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103

Fig. 5.4.3.7 Conductor holder for direct fitting on the seams . . . . . . . .104

Fig. 5.4.3.8 Roof conductor holder for hanging into the bottom seam of pantile roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104

Fig. 5.4.3.9 ZIEGELsnap, for fixing between flat tiles or plates . . . . . . .104

Fig. 5.4.3.10 PLATTENsnap roof conductor holder for overlapped con-struction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104

Fig. 5.5.1 Earth surface potential and voltages at a foundation earth electrode FE and control earth electrode CE flownthrough by currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105

Fig. 5.5.2 Current distribution from the spherical earth electrode . . .107

Fig. 5.5.3 Earth electrode resistance RA of a spherical earth elec-trode with Ø 20 cm, 3 m deep, at ρE = 200 Ωm as a function of the distance x from the centre of the sphere . .107

Fig. 5.5.4 Specific earth resistance ρE of different ground types . . . .108

Fig. 5.5.5 Specific earth resistance ρE as a function of the seasons without influencing of rainfall (burial depth of the earth electrode < 1.5 m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108

Fig. 5.5.6 Determination of the specific earth resistance ρE with a four-terminal measuring bridge acc. to the WENNER method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108

Fig. 5.5.7 Earth electrode resistance RA as a function of length I of the surface earth electrode at different specific earth resistance ρE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110

Fig. 5.5.8 Earth potential UE between supply conductor and earth surface as a function of the distance from the earth elec-trode, at an earth strip (8 m long) in different depths . . . .110

Fig. 5.5.9 Max. step voltage US as a function of the burial depth for a stretched earth strip . . . . . . . . . . . . . . . . . . . . . . . . . .110

Fig. 5.5.10 Earth electrode resistance RA of earth rods as a function of their length I at different specific earth resistances ρE . .111

Fig. 5.5.11 Earth electrode resistance RA of crossed surface earth electrode (90 °) as a function of the burial depth . . . . . . . .112

Fig. 5.5.12 Earth potential UE between the supply conductor of the earth electrode and earth surface of crossed surface earthelectrode (90 °) as a function of the distance from the cross centre point (burial depth 0.5 m) . . . . . . . . . . . . . . . .112

Fig. 5.5.13 Impulse earth resistance Rst of single or multiple star-type earth electrodes with equal length . . . . . . . . . . . . . . .113

Fig. 5.5.14 Reduction factor p for calculating the total earth elec-trode resistance RA of earth rods connected in parallel . . .113

Fig. 5.5.15 Earth electrode resistance RA of surface and earth rods as a function of the length of the earth electrode I . . . . . .115

Fig. 5.5.1.1 Minimum lengths of earth electrodes . . . . . . . . . . . . . . . . .116

Fig. 5.5.1.2 Earth electrode Type B – Determination of the mean radius – example calculation . . . . . . . . . . . . . . . . . . . . . . .117

Fig. 5.5.1.3 Earth electrode Type B – Determination of the mean radius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

Fig. 5.5.2.1 Foundation earth electrode with terminal lug . . . . . . . . . .118

Fig. 5.5.2.2 Mesh of a foundation earth electrode . . . . . . . . . . . . . . . .118

Fig. 5.5.2.3 Foundation earth electrode . . . . . . . . . . . . . . . . . . . . . . . .119

Fig. 5.5.2.4 Foundation earth electrode in use . . . . . . . . . . . . . . . . . . .119

Fig. 5.5.2.5 Arrangement of a foundation earth electrode in a strip foundation (insulated basement wall) . . . . . . . . . . . . . . . .120

Fig. 5.5.2.6 Arrangement of a foundation earth electrode in a strip foundation (insulated basement wall and foundation slab) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120

Fig. 5.5.2.7 Arrangement of a foundation earth electrode in case of a closed floor slab (fully insulated) . . . . . . . . . . . . . . . . . . .121

Fig. 5.5.2.8 Fixed earthing terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . .121

Fig. 5.5.2.9 Arrangement of the foundation earth electrode in case of a closed tank “white tank” . . . . . . . . . . . . . . . . . . . . . .122

Fig. 5.5.2.10 Arrangement of the earth electrode in case of a closed tank “black tank” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123

Fig. 5.5.3.1 Ring earth electrode around a residential building . . . . . . .124

Fig. 5.5.4.1 Couplings of DEHN earth rods . . . . . . . . . . . . . . . . . . . . . .124

Fig. 5.5.4.2 Driving the earth rod in with a work scaffolding and a vibrating hammer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125

Fig. 5.5.6.1 Intermeshed earth-termination system of an industrial facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126

Fig. 5.5.7.1.1 Application example of a non-polarisable measuring electrode (copper /copper sulphate electrode) for tapping a potential within the electrolyte (cross-sectional view) . . .128

Fig. 5.5.7.2.1 Galvanic cell: iron/copper . . . . . . . . . . . . . . . . . . . . . . . . . .128

Fig. 5.5.7.2.2 Concentration cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128

Fig. 5.5.7.2.3 Concentration cell: Iron in soil / Iron in concrete . . . . . . . . .130

Fig. 5.5.7.2.4 Concentration cell: Galvanised steel in soil / steel (black) in concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130

Fig. 5.6.1 Illustration – Separation distance . . . . . . . . . . . . . . . . . . . .135

Fig. 5.6.2 Potential difference with increasing height . . . . . . . . . . . .136

Fig. 5.6.3 Air-termination mast with kc = 1 . . . . . . . . . . . . . . . . . . . .136

Fig. 5.6.4 Flat roof with air-termination rod and ventilation outlet . .137

Fig. 5.6.5 Determination of kc with two masts with overspanned cable and an earth electrode Type B . . . . . . . . . . . . . . . . . .137

Fig. 5.6.6 Determination of kc for a gable roof with 2 down con-ductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137

Fig. 5.6.7 Gable roof with 4 down conductors . . . . . . . . . . . . . . . . . .138

Fig. 5.6.8 Value of coefficient kc in case of a meshed network of air-termination conductors and an earthing Type B . . . . . .139

Fig. 5.6.9 Material factors of an air-termination rod on a flat roof . . .139

Fig. 5.6.10 Value of coefficient kc in case of an intermeshed net-work of air-termination, ring conductors interconnecting the down conductors and an earthing Type B . . . . . . . . . . .140

Fig. 5.7.1 Illustration of touch voltage and step voltage . . . . . . . . . .141

Fig. 5.7.2 Potential control – Illustration and symbolic course of the gradient area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142

Fig. 5.7.3 Possible potential control in entrance area of the building .143

Fig. 5.7.4 Potential control performance for a flood light or cell site mast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143

Fig. 5.7.5 Connection control at the ring/ foundation earth elec-trode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143

Fig. 5.7.1.1 Area to be protected for a person . . . . . . . . . . . . . . . . . . . .144

Fig. 5.7.1.2 Structure of the CUI conductor . . . . . . . . . . . . . . . . . . . . . .144

Fig. 5.7.1.3 Withstand voltage test under sprinkling . . . . . . . . . . . . . . .145

Fig. 5.7.1.4 CUI conductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .145

Fig. 5.7.1.5 (a) Loop formed by conductor and person (b) Mutual inductance M and induced voltage Ui . . . . . . . .146

Fig. 6.1.1 Principle of lightning equipotential bonding consisting of lightning and main equipotential bonding (in future:protective equipotential bonding) . . . . . . . . . . . . . . . . . . .147

Fig. 6.1.2 K12 Equipotential bonding bar, Part No. 563 200 . . . . . . . .149

Fig. 6.1.3 Pipe earthing clamp, Part No. 408 014 . . . . . . . . . . . . . . . .150

Fig. 6.1.4 Pipe earthing clamp, Part No. 407 114 . . . . . . . . . . . . . . . .150

Fig. 6.1.5 Pipe earthing clamp, Part No. 540 910 . . . . . . . . . . . . . . . .150

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Fig. 6.1.6 Equipotential bonding with straight-through connection . .150

Fig. 6.2.1 DEHNbloc NH lightning current arrester installed in a busbar terminal field of a meter installation (refer to Fig.6.2.2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151

Fig. 6.2.2 DEHNventil ZP combined arrester directly snapped on the busbars in the terminal field of the meter cabinet . . . .151

Fig. 6.3.1 Lightning equipotential bonding with isolated air-termi-nation system, type DEHNconductor, for professional an-tenna systems according to IEC 62305-3 (EN 62305-3) . . .152

Fig. 6.3.2 Isolated construction of a lighning protection system at a cell site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152

Fig. 6.3.3 SAK shield connection system capable of carrying light-ning currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .153

Fig. 6.3.4 Lightning equipotential bonding for connection of a tele-communication device BLITZDUCTOR CT (application permitted by Deutsche Telekom) . . . . . . . . . . . . . . . . . . . . .154

Fig. 6.3.5 DEHN equipotential bonding enclosures (DPG LSA) for LSA-2/10 technology, capable to carry lightning current . .154

Fig. 7.1.1 Lightning protection zones concept according to IEC 62305-4 (EN 62305-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . .155

Fig. 7.1.2 Example for realisation of the lightning protection zones concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156

Fig. 7.3.1 Reduction of the magnetic field by means of lattice shields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158

Fig. 7.3.2 Magnetic field at a lightning strike (LEMP) IEC 62305-4 (EN 62305-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158

Fig. 7.3.3 Volume for electronic devices within LPZ 1 . . . . . . . . . . . .158

Fig. 7.3.4 Magnetic field at a lightning strike (LEMP) IEC 62305-4 (EN 62305-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159

Fig. 7.3.5 Magnetic field at a distant lightning strike (LEMP) IEC 62305-4 (EN 62305-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . .159

Fig. 7.3.6 Use of reinforcing rods of a building or structure for shielding and equipotential bonding . . . . . . . . . . . . . . . . .160

Fig. 7.3.7a Galvanised construction steel mats for shielding the building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160

Fig. 7.3.7b Use of galvanised construction steel mats for shielding,e.g. in case of planted roofs . . . . . . . . . . . . . . . . . . . . . . . .160

Fig. 7.3.8 Shielding of a structure or building . . . . . . . . . . . . . . . . . .161

Fig. 7.3.9 Earthing bus according to DIN VDE 0800-2 (German standard)) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161

Fig. 7.3.1.1 No shield connection – No shielding from capacitive/inductive couplings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163

Fig. 7.3.1.2 Shield connection at both ends – Shielding from capaci-tive/inductive couplings . . . . . . . . . . . . . . . . . . . . . . . . . . .163

Fig. 7.3.1.3 Shield connection at both ends – Solution: Direct and in-direct shield earthing . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163

Fig. 7.3.1.4 Shield connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164

Fig. 7.3.1.5 Shield connection at both ends – Shielding fromcapacitive/ inductive coupling . . . . . . . . . . . . . . . . . . . . . . .164

Fig. 7.4.1 Equipotential bonding network in a structure or building .165

Fig. 7.4.2 Ring equipotential bonding bar in a computer facility . . . .165

Fig. 7.4.3 Connection of the ring equipotential bonding bar with the equipotential bonding network via fixed earthing point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165

Fig. 7.4.4 Integration of electronic systems into the equipotential bonding network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166

Fig. 7.4.5 Combination of the integration methods according to Figure 7.4.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166

Fig. 7.5.1.1 Connection of EBB with fixed earthing point . . . . . . . . . . .167

Fig. 7.5.2.1 Transformer outside the structure or building . . . . . . . . . . .167

Fig. 7.5.2.2 Transformer inside the structure or building (LPZ 0 inte-grated in LPZ 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168

Fig. 7.5.2.3 Example for equipotential bonding in a structure or build-ing with several entries or the external conductive parts and with an internal ring conductor as a connection be-tween the equipotential bonding bars . . . . . . . . . . . . . . . .168

Fig. 7.5.2.4 Internal lightning protection with a common entry of all supply lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .169

Fig. 7.5.2.5 DEHNventil combined lightning current and surge arrester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170

Fig. 7.5.2.6 Lightning equipotential bonding for power supply and information technology systems situated centrally at one point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170

Fig. 7.5.2.7 Lightning current arrester at LPZ boundary LPZ 0A – LPZ 1 170

Fig. 7.5.3.1 Comparison of the amplitudes of test currents wave form 10/350 μs and 8/20 μs, each at equal loads . . . . . . . .171

Fig. 7.6.2.1 Only one SPD (0/1/2) required (LPZ 2 integrated in LPZ 1) .171

Fig. 7.6.2.2 DEHNventil M TT 255 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172

Fig. 7.6.3.1 Combination aid for Yellow/Line SPD classes (see also Figure 7.8.2.2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172

Fig. 7.7.1.1 Ring equipotential bonding and fixed earthing point for connection of metal installations . . . . . . . . . . . . . . . . . . . .173

Fig. 7.7.2.1 Electromagnetic compatibility in case of a lightning strike .174

Fig. 7.7.2.2 Surge protective device for terminal circuits DEHNflex M . .174

Fig. 7.7.2.3 Multi-pole surge arrester DEHNguard M TT . . . . . . . . . . . .175

Fig. 7.7.3.1 Protection of industrial electronic equipment (e.g. an SPC) by BLITZDUCTOR CT and SPS Protector . . . . . . . . . . .175

Fig. 7.8.1.1 DEHNbloc 3-pole – Lightning current arrester and DEHNventil ZP – Combined arrester . . . . . . . . . . . . . . . . . .176

Fig. 7.8.1.2 DEHNguard TT H LI – Multi-pole surge arrester with service life indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . .176

Fig. 7.8.1.3 DEHNventil M TNS – Modular combined arrester . . . . . . . .176

Fig. 7.8.2.1 Coordination according to let-through method of 2 SPDs and one terminal device (according to IEC 61643-21) . . . .177

Fig. 7.8.2.2 Examples for the energy coordinated use of arresters ac-cording to the Yellow/Line TYPE of arresters and structure of the Yellow/Line TYPE of arresters symbol . . . . . . . . . . . .177

Fig. 8.1.1 Use of SPDs in power supply systems (schematic dia-gram) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .180

Fig. 8.1.3.1 RCD destroyed by lightning impulse current . . . . . . . . . . . .185

Fig. 8.1.3.2 “3-0” circuit in TN-C systems . . . . . . . . . . . . . . . . . . . . . . .185

Fig. 8.1.3.3a “4-0” circuit in TN-S systems . . . . . . . . . . . . . . . . . . . . . . .185

Fig. 8.1.3.3b “3+1” circuit in TN-S systems . . . . . . . . . . . . . . . . . . . . . .185

Fig. 8.1.3.4 Use of SPDs in TN-C-S systems . . . . . . . . . . . . . . . . . . . . . .186

Fig. 8.1.3.5 Use of SPDs in TN-S systems . . . . . . . . . . . . . . . . . . . . . . . .186

Fig. 8.1.3.6 SPDs used in TN systems – Example: Office Building – Separation of the PEN in the main distribution board . . . .187

Fig. 8.1.3.7 SPDs used in TN systems – Example: Office Building – Separation of the PEN in the subdistribution board . . . . . .188

Fig. 8.1.3.8 SPDs used in TN systems – Example: Industry – Sepa-ration of the PEN in the subdistribution board . . . . . . . . . .189

Fig. 8.1.3.9 SPDs used in TN systems – Example: Residential building .190

Fig. 8.1.4.1 TT system (230/400 V); “3+1” circuit . . . . . . . . . . . . . . . . .190

Fig. 8.1.4.2 Use of SPDs in TT systems . . . . . . . . . . . . . . . . . . . . . . . . .191

Fig. 8.1.4.3 SPDs used in TT systems – Example: Residential Building .192

Fig. 8.1.4.4 SPDs used in TT systems – Example: Office building . . . . . .193

Fig. 8.1.4.5 SPDs used in TT systems – Example: Industry . . . . . . . . . . .194

Fig. 8.1.5.1a IT system without neutral conductor; “3-0” circuit . . . . . . .195

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Fig. 8.1.5.1b IT system with neutral conductor; “4-0” conductor . . . . . .195

Fig. 8.1.5.1c IT system with neutral conductor; “3+1” circuit . . . . . . . . .195

Fig. 8.1.5.2 Use of SPDs in IT systems without neutral conductor . . . . .196

Fig. 8.1.5.3 Use of SPDs in 400 V IT systems – Example without neutral conductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .196

Fig. 8.1.5.4 Use of SPDs in 230/400 V IT systems – Example with neutral conductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197

Fig. 8.1.6.1 Surge protective devices in V-shape series connection . . . .198

Fig. 8.1.6.2 Principle of „two-conductor terminals (TCT)“ – Illustra-tion of a single-pole unit . . . . . . . . . . . . . . . . . . . . . . . . . .198

Fig. 8.1.6.3 Pin connection terminal (PCT) 2 x 16 . . . . . . . . . . . . . . . . .198

Fig. 8.1.6.4 Connection of surge protective devices in cable branches .198

Fig. 8.1.6.5 DEHNbloc Maxi S: coordinated lightning current arrester for the busbar with integrated backup fuse . . . . . . . . . . . .198

Fig. 8.1.6.6 Surge protective device Type 2 V NH for use in NH fuse bases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .198

Fig. 8.1.6.7 Recommended max. cable lengths of surge protective devices in branch circuits . . . . . . . . . . . . . . . . . . . . . . . . . .199

Fig. 8.1.6.8a Unfavourable conductor routing from the “consumer’s point of view” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199

Fig. 8.1.6.8b Fabourable conductor routing from the “consumer’s point of view” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199

Fig. 8.1.6.9 Arrangement of surge protective devices in a system and the resulting effective cable length . . . . . . . . . . . . . . . . . .200

Fig. 8.1.6.10 Series connection V-shape . . . . . . . . . . . . . . . . . . . . . . . . .200

Fig. 8.1.6.11 V-shape series connection of the DEHNventil M TNC com-bined lightning current and surge protective device by means of a busbar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .200

Fig. 8.1.6.12 Parallel wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .201

Fig. 8.1.6.13 Cable routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .201

Fig. 8.1.7.1 One-port protective circuit . . . . . . . . . . . . . . . . . . . . . . . . .201

Fig. 8.1.7.2 Two-port protective circuit . . . . . . . . . . . . . . . . . . . . . . . . .201

Fig. 8.1.7.3 SPD with through-wiring . . . . . . . . . . . . . . . . . . . . . . . . . .202

Fig. 8.1.7.4 Example: DEHNventil, DV TNC 255 . . . . . . . . . . . . . . . . . . .202

Fig. 8.1.7.5 Example: DEHNguard (M) TNC/TNS/TT . . . . . . . . . . . . . . .202

Fig. 8.1.7.6 Example: DEHNrail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .203

Fig. 8.1.7.7 Performance of NH fuses bearing impulse current loads . .203

Fig. 8.1.7.8 Current and voltage of a blowing 25 A NH fuse being charged with lightning impulse currents (10/350 μs) . . . . .204

Fig. 8.1.7.9 Use of a separate backup fuse for surge protective devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .204

Fig. 8.1.7.10 Reduction of the follow current with the patented RADAX Flow principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205

Fig. 8.1.7.11 Disconnection selectivity of DEHNventil to NH fuse holders with different rated currents . . . . . . . . . . . . . . . . .205

Fig. 8.2.1 SPD classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .206

Fig. 8.2.2 Limiting performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207

Fig. 8.2.3 Note on special applications . . . . . . . . . . . . . . . . . . . . . . . .207

Fig. 8.2.4 Nominal voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207

Fig. 8.2.5 Test arrangement for determining the limiting voltage at a rate of voltage rise of du/dt = 1kV/μs . . . . . . . . . . . . . . .208

Fig. 8.2.6 Sparkover performance of an SPD at du/dt = 1kV/μs . . . . .208

Fig. 8.2.7 Test arrangement for determining the limiting voltage at nominal discharge current . . . . . . . . . . . . . . . . . . . . . . . . .209

Fig. 8.2.8 Limiting voltage at nominal discharge current . . . . . . . . . .209

Fig. 8.2.9 Nominal current of BLITZDUCTOR CT . . . . . . . . . . . . . . . . .209

Fig. 8.2.10 Typical frequency response of a BLITZDUCTOR CT . . . . . . .209

Fig. 8.2.11 Building with external lightning protection system and cables installed between buildings . . . . . . . . . . . . . . . . . . .210

Fig. 8.2.12 Building without external lightning protection system and cables installed between buildings . . . . . . . . . . . . . . .210

Fig. 8.2.13 Building with external lightning protection system and cables installed inside of the building . . . . . . . . . . . . . . . . .210

Fig. 8.2.14 Building without external lightning protection system and cables installed inside of the building . . . . . . . . . . . . .210

Fig. 8.2.15 Block diagram of temperature measuring . . . . . . . . . . . . .214

Fig. 8.2.1.1 Optocoupler – Schematic diagram . . . . . . . . . . . . . . . . . . .215

Fig. 8.2.2.1 Levels of building automation . . . . . . . . . . . . . . . . . . . . . .216

Fig. 8.2.3.1 Universal cabling structure . . . . . . . . . . . . . . . . . . . . . . . . .217

Fig. 8.2.3.2 Influence of lightning on IT cabling subsystems . . . . . . . . .218

Fig. 8.2.4.1 Calculating of L0 and C0 . . . . . . . . . . . . . . . . . . . . . . . . . . .220

Fig. 8.2.4.2a Intrinsically safe SPD . . . . . . . . . . . . . . . . . . . . . . . . . . . . .221

Fig. 8.2.4.2b Schematic diagram of BXT ML4 BD EX 24 . . . . . . . . . . . . .221

Fig. 8.2.4.3 SPD in hazardous location – Insulation resistance > 500 V a.c. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222

Fig. 8.2.4.4 Application – Insulation resistance < 500 V a.c. . . . . . . . .222

Fig. 8.2.5.1 Correct installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224

Fig. 8.2.5.2 Most frequent installation . . . . . . . . . . . . . . . . . . . . . . . . .224

Fig. 8.2.5.3 Wrong method of equipotential bonding . . . . . . . . . . . . . .225

Fig. 8.2.5.4 Wrong conductor leading . . . . . . . . . . . . . . . . . . . . . . . . . .225

Fig. 8.2.5.5 Separation of cables in cable duct systems . . . . . . . . . . . . .226

Fig. 9.1.1 Schematic diagram of a frequency converter . . . . . . . . . . .227

Fig. 9.1.2 EMC conforming shield connection of the motor supply line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .227

Fig. 9.1.3 Structure of a frequency converter with SPD . . . . . . . . . . .228

Fig. 9.2.1 Insulation of the place around the lamp pole to reduce the risk of touch voltage in case of lightning strike . . . . . .230

Fig. 9.2.2 Potential control to reduce the arising step voltage at lightning strikes into a lamp pole . . . . . . . . . . . . . . . . . . . .231

Fig. 9.2.3 230 V wall lamp as outdoor lighting in lightning protec-tion zone LPZ 0A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .231

Fig. 9.2.4 Lamp pole with 3 x 230/400 V outdoor lighting in light-ning protection zone LPZ 0A . . . . . . . . . . . . . . . . . . . . . . . .232

Fig. 9.2.5 230 V wall lamp as outdoor lighting in lightning protec-tion zone LPZ 0B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .232

Fig. 9.2.6 Lamp pole with 3 x 230/400 V outdoor lighting in light-ning protection zone LPZ 0B . . . . . . . . . . . . . . . . . . . . . . . .232

Fig. 9.3.1 System layout of a biogas plant . . . . . . . . . . . . . . . . . . . . .234

Fig. 9.3.2 Use of the DEHNiso-Combi system to protect a fermenter with film dome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .236

Fig. 9.3.3 Protection of a fermenter with film dome by steel tele-scopic lightning protection masts . . . . . . . . . . . . . . . . . . . .236

Fig. 9.3.4 Fermenter protected with air-termination masts isolated by 1 HVI conductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .237

Fig. 9.3.5 Fermenter protected with air-termination masts isolated by 2 HVI conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .237

Fig. 9.3.6 Fermenter out of screwed sheet metal . . . . . . . . . . . . . . . .238

Fig. 9.3.7 Isolated air-termination system to protect a fermenter out of sheet metal (Ref.: Büro für Technik, Hösbach) . . . . .238

Fig. 9.3.8 Welded steel tank (Ref.: Eisenbau Heilbronn GmbH) . . . . .238

Fig. 9.3.9 Intermeshed earth-termination system for a biogas plant .239

Fig. 9.3.10 Sectional view of an overall circuit diagram of a biogas plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .240

Fig. 9.3.11 Surge protection for information technology systems . . . .242

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Fig. 9.3.12 Combined lightning current and surge arrester modules with LifeCheck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .243

Fig. 9.3.13 Surge arrester DEHNpipe for outdoor areas for screwing into 2-wire process field devices . . . . . . . . . . . . . . . . . . . . .243

Fig. 9.4.1 Schematic structure of a sewage plant . . . . . . . . . . . . . . . .244

Fig. 9.4.2 Division of a sewage plant control into lightning protect-ion zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .245

Fig. 9.4.3 Electrical lines going into the sewage plant control . . . . . .246

Fig. 9.4.4 Protective angle method according to IEC 62305-3 (EN 62305-3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .247

Fig. 9.4.5 Lightning equipotential bonding according to IEC 62305-3 (EN 62305-3) . . . . . . . . . . . . . . . . . . . . . . . . .247

Fig. 9.4.6 DEHNventil installed into a switchgear cabinet for pro-tection of the power supply system . . . . . . . . . . . . . . . . . .248

Fig. 9.4.7 DCO ME 24 surge protective device installed into a switchgear cabinet for protection of the complete mea-suring and control system . . . . . . . . . . . . . . . . . . . . . . . . .249

Fig. 9.4.8 DCO ME 24 surge protection device installed into aswitchgear cabinet, incoming lines from double bottom . .249

Fig. 9.5.1 Horizontal and vertical distances of antenna arrange-ments requiring no earthing connection . . . . . . . . . . . . . . .250

Fig. 9.5.2 Examples of permitted earth electrodes . . . . . . . . . . . . . . .251

Fig. 9.5.3 Earthing and equipotential bonding of antennas on buildings without external lightning protection system . . .252

Fig. 9.5.4 Antenna with air-termination rod on a flat roof of build-ings with external lightning protection system . . . . . . . . . .252

Fig. 9.5.5 Antenna with air-termination rod and highly insulating distance holder on pitched roofs with external lightning protection system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .252

Fig. 9.5.6 Surge protective devices downstream the equipotential bonding bar for the coaxial cable shields in case of an-tenna systems with external lightning protection system and isolated air-termination system . . . . . . . . . . . . . . . . . .252

Fig. 9.5.7 Surge protective devices downstream the equipotential bonding bar for the coaxial cable shields in case of an-tenna systems without external lightning protection system and with isolated air-termination system . . . . . . . .253

Fig. 9.5.8 Combined lightning current and surge arresters down-stream the equipotential bonding bar for the coaxial cable shields in case of antenna systems without exter-nal lightning protection system . . . . . . . . . . . . . . . . . . . . .253

Fig. 9.5.9 Combined lightning current and surge arresters down-stream the equipotential bonding bar for the coaxial cable shields in case of underground cable networks . . . . .254

Fig. 9.6.1 Modern automatic milking system . . . . . . . . . . . . . . . . . . .255

Fig. 9.6.2 Automatic feeding system . . . . . . . . . . . . . . . . . . . . . . . . .255

Fig. 9.6.3 Ventilation and flushing system . . . . . . . . . . . . . . . . . . . . .255

Fig. 9.6.4 Heating system with heat recovery and service water supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .255

Fig. 9.6.5 Electrical milking system with control box . . . . . . . . . . . . .256

Fig. 9.6.6 Cow with collar and registration chip . . . . . . . . . . . . . . . . .256

Fig. 9.6.7 Lightning and surge protection for agricultural install-ations, residential building and office . . . . . . . . . . . . . . . . .257

Fig. 9.6.8 Lightning and surge protection for agricultural install-ations, stabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .257

Fig. 9.7.1 Video surveillance system – Lightning and surge pro-tection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .259

Fig. 9.7.2 Camera for video surveillance in the protective area of the air-termination rod . . . . . . . . . . . . . . . . . . . . . . . . . . . .260

Fig. 9.7.3 Video surveillance system – Surge protection . . . . . . . . . .261

Fig. 9.8.1 Public address system in modular design with surge pro-tective devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262

Fig. 9.8.2 Building without external lightning protection and horn in LPZ 0A protected by combined lightning current and surge arresters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .263

Fig. 9.8.3 Building with external lightning protection and horn in LPZ 0B protected by surge arresters . . . . . . . . . . . . . . . . . .263

Fig. 9.9.1 Lightning and surge protection for the control unit of a burglar alarm system with impulse line technology . . . . . .265

Fig. 9.9.2 Lightning and surge protection for the control unit of a fire alarm system – Analogue ring . . . . . . . . . . . . . . . . . . .265

Fig. 9.9.3 Lightning and surge protection for the control unit of a burglar alarm system with d.c. line technology . . . . . . . . .266

Fig. 9.9.4 Lightning and surge protection for the control unit of a fire alarm system with d.c. line technology . . . . . . . . . . . .267

Fig. 9.10.1 Application of the BUStector (Part No. 925 001) . . . . . . . .268

Fig. 9.10.2 Lightning and surge protection for cabling systems in-stalled between buildings without interconnection of the foundation earth electrodes . . . . . . . . . . . . . . . . . . . . .269

Fig. 9.10.3 Lightning and surge protection for cabling systems in-stalled between buildings with interconnection of the foundation earth electrodes . . . . . . . . . . . . . . . . . . . . . . . .270

Fig. 9.10.4 Lightning and surge protection for cabling systems in-stalled between buildings without interconnection of the foundation earth electrodes, with KNX optical fibre cabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .270

Fig. 9.11.1 Administration building with highly available installation parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .271

Fig. 9.12.1 Example of an M-Bus system . . . . . . . . . . . . . . . . . . . . . . .273

Fig. 9.12.2 Protection concept for M-Bus systems in buildings with external lightning protection system . . . . . . . . . . . . . . . . .275

Fig. 9.12.3 Protection concept for M-Bus systems in buildings with-out external lightning protection system . . . . . . . . . . . . . .277

Fig. 9.13.1 Lightning and surge protection for SIMATIC Net PROFIBUS FMS and DP . . . . . . . . . . . . . . . . . . . . . . . . . . . .279

Fig. 9.13.2 Use of surge protective devices in an intrinsically safePROFIBUS PA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .279

Fig. 9.14.1 Lightning and surge protection for ADSL with analogue connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .283

Fig. 9.14.2 Lightning and surge protection for ISDN and ADSL connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .283

Fig. 9.14.3 Surge protection for telecommunications systems “ISDN Primary rate Multiplex access” . . . . . . . . . . . . . . . . . . . . . .284

Fig. 9.15.1 Division of a hazardous location into lightning protectionzones (LPZ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .285

Fig. 9.15.2 Air-termination system for a tank with air-termination rods and conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .286

Fig. 9.15.3 Lightning equipotential bonding according to IEC 62305-3 (EN 62305-3) based on main equipotential bonding ac-cording to IEC 60364-4-41 and IEC 60364-5-54 . . . . . . . . .287

Fig. 9.15.4 DEHNventil DV TT 255 in a switchgear cabinet for pro-tection of the power supply system . . . . . . . . . . . . . . . . . .287

Fig. 9.15.5 Surge protective devices in intrinsically safe circuits . . . . .287

Fig. 9.15.6 BCT MOD MD EX 24 for intrinsically safe circuits . . . . . . . .288

Fig. 9.15.7 Surge arrester for field devices – DEHNpipe,DPI MD EX 24 M2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .289

Fig. 9.16.1 Impulse current laboratory DEHN + SÖHNE – Max. light-ning impulse current 200 kA, wave form 10/350 μs . . . . . .291

Fig. 9.16.2 Lightning protection zones concept for a wind turbine . . .292

Fig. 9.16.3 Intermeshed network of earth electrodes of a wind turbine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .293

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Fig. 9.16.4 Application of DEHNbloc Maxi coordinated lightning current arrester for 400/690 V TN-C systems . . . . . . . . . . .293

Fig. 9.16.5 DEHNguard surge arrester, DG MOD 750 + DG M WE 600 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .294

Fig. 9.16.6 Application of BLITZDUCTOR XT lightning current and surge arrester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .294

Fig. 9.17.1 Dual cell site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .295

Fig. 9.17.2 Electrical circuit diagram . . . . . . . . . . . . . . . . . . . . . . . . . .295

Fig. 9.17.3 Basic structure of a RBS with DV M TT 255 and DG M TT 275 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .296

Fig. 9.18.1.1 Combined arrester Type 1, DEHNlimit PV, to protect photovoltaic inverters from surges also in case of direct lightning strikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .299

Fig. 9.18.1.2 Single pole photovoltaic arrester Type 2, DEHNguard PV 500 SCP, with integrated short-circuiting device . . . . . .299

Fig. 9.18.1.3 Isolation fault at the PV generator . . . . . . . . . . . . . . . . . . .300

Fig. 9.18.1.4 Overloading of SPD due to an isolation fault . . . . . . . . . . .300

Fig. 9.18.1.5 Activation of the DEHNguard PV 500 SCP disconnecting and short-circuiting device ensures safe operating state also in case of an isolation fault in the PV generator circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .300

Fig. 9.18.1.6 Surge protection concept for a PV system on a building without external lightning protection . . . . . . . . . . . . . . . . .301

Fig. 9.18.1.7 Surge protection concept for a PV system on a building with external lightning protection system and the sepa-ration distance is being kept . . . . . . . . . . . . . . . . . . . . . . . .302

Fig. 9.18.1.8 Surge protection concept for a PV system on a building with external lightning protection system and the sepa-ration distance is not being kept . . . . . . . . . . . . . . . . . . . .302

Fig. 9.18.2.1 Layout of a large PV installation in an open area . . . . . . . .304

Fig. 9.18.2.2 Basic circuit diagram – Surge protection for a solar power plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .305

Fig. 9.18.2.3 Protection concept for data acquisition and evaluation . . .306

Table 1.1.1 Lightning protection standard valid since January 2006 . . . .11

Table 1.1.2 Equivalents for SPD classifications (In the following the Lightning Protection Guide uses the designation SPD Type 1, SPD Type 2, SPD Type 3) . . . . . . . . . . . . . . . . . . . . . .12

Table 2.5.1 Temperature rise ΔT in K of different conductor materials . .22

Table 2.6.1 Maximum values of lightning current parameters and their probabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Table 2.6.2 Minimum values of lightning current parameters and their probabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Table 3.2.3.1 Site factor Cd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

Table 3.2.3.2 Equivalent interception areas Al and Ai in m2 . . . . . . . . . . . .33

Table 3.2.3.3 Environment factor Ce . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Table 3.2.4.1 Damage factor PB to describe the protective measures against physical damage . . . . . . . . . . . . . . . . . . . . . . . . . . .34

Table 3.2.4.2 Damage factor PSPD to describe the protective measures surge protective devices as a function of the lightning protection level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

Table 3.2.5.1 Sources of damage, types of damage and types of loss according to the point of strike . . . . . . . . . . . . . . . . . . . . . . .35

Table 3.2.7.1 In addition to the risk components RU , RV and RW , there is the frequency of direct lightning strikes into the supply line NL and the frequency of direct lightning strikes into the connected building or structure NDA (compare Figure 3.2.3.). In case of the risk component RZ , however, the fre-quency of lightning strikes next to the supply line Nl hasto be reduced by the frequency of direct lightning strikes into the supply line NL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Table 3.2.8.1 Typical values for the tolerable risk RT . . . . . . . . . . . . . . . . .38

Table 3.3.1.1 Longest interval between inspections of the LPS acc. to IEC 62305-3, Table E.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42

Table 5.1.1.1 Relations between lightning protection level, interception criterion Ei , final striking distance hB and min. peak value of current I Ref.: Table 5, 6 and 7 of IEC 62305-1 (EN 62305-1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50

Table 5.1.1.2 Sag of the rolling sphere over two air-termination rods or two parallel air-termination conductors . . . . . . . . . . . . . . . .53

Table 5.1.1.3 Mesh size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53

Table 5.1.1.4 Protective angle α depending on the class of lighting protection system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55

Table 5.1.1.5 Min. thickness of metal plates . . . . . . . . . . . . . . . . . . . . . . .58

Table 5.1.4.1 Lightning protection for metal roofs – Height of the air-termination tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63

Table 5.2.1.1 Distance between down conductors according to IEC 62305-3 (EN 62305-3) . . . . . . . . . . . . . . . . . . . . . . . . . .82

Table 5.2.2.1 Max. temperature rise ΔT in K of different conductor materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

Table 5.3.1 Material, configuration and min. cross sections of air-ter-mination conductors, air-termination rods and down con-ductors according to IEC 62305-3 (EN 62305-3) Table 6 . . .96

Table 5.4.1 Material combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

Table 5.4.1.1 Calculation of the temperature-related change in length ΔL of metal wires in lightning protection . . . . . . . . . . . . . . .99

Table 5.4.1.2 Expansion pieces in lightning protection – Recommendedapplication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

Table 5.4.2.1a Components for external lightning protection of a resi-dential building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100

Table 5.4.2.1b Components for external lightning protection of a resi-dential structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101

Table 5.5.1 Formulae for calculating the earth electrode resistance RAfor different earth electrodes . . . . . . . . . . . . . . . . . . . . . . .109

Table 5.5.7.2.1 Potential values and corrosion rates of common metal materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129

Table 5.5.7.4.1 Material combinations of earth-termination systems for different area ratios (AC > 100 x AA) . . . . . . . . . . . . . . . . .133

Table 5.5.8.1 Material, configuration and min. dimensions of earth electrodes according to IEC 62305-3 (EN 62305-3) Table 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .134

Table 5.7.1 Ring distances and depths of the potential control . . . . . .143

Table 6.1.1 Cross sections for equipotential bonding conductors . . . . .149

Table 7.2.1 LEMP protection management for new buildings and for comprehensive modifications of the construction or the utilisation of building according to IEC 62305-4 (EN 62305-4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157

Table 7.3.1 Magnetic attenuation of lattices at a nearby lightning strike acc. to IEC 62305-4 (EN 62305-4) . . . . . . . . . . . . . . .159

Table 7.3.1.1 Specific shield resistance ρc for different materials . . . . . .162

Table 7.3.1.2 Electric strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162

Table 7.5.2.1 Required lightning impulse current carrying capability of surge protective devices SPDs Type 1 according to the lightning protection level LPL and the type of low voltage consumer’s installation . . . . . . . . . . . . . . . . . . . . . . . . . . . .169

Table 7.8.2.1 Symbol of the SPD class . . . . . . . . . . . . . . . . . . . . . . . . . . .178

Table 7.8.2.2 Assignment of the Yellow/Line class of the SPDs at the LPZ boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178

Table 8.1.1 Classification of SPDs according to VDE, IEC and EN . . . . .181

Table 8.1.7.1 Material coefficient k for copper and aluminium con-ductors with different insulating material . . . . . . . . . . . . .202

Table 8.2.1 Type designation of the protection modules . . . . . . . . . . . .208

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Table 8.2.2 Nominal currents of the protection modules BCT . . . . . . . .208

Table 8.2.3 Selection features for an electrical temperature measur-ing equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .213

Table 8.2.5.1 Separation of telecommunications and low voltage supply lines (based on EN 50174-2) . . . . . . . . . . . . . . . . . .225

Table 9.2.1 Min. dimensions of earthing conductors for interconnect-ing lamp poles in LPZ 0A and for connecting to the earth-termination system of the building or structure . . . . . . . . .230

Table 9.3.1 DEHNiso-Combi Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .236

Table 9.3.2 Material recommendation for earthing and equipotentialbonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .239

Table 9.3.3 Surge protection for the power supply . . . . . . . . . . . . . . .241

Table 9.3.4 Surge protection for information technology systems . . . .242

Table 9.3.5 Surge arresters for the measuring and control tech-nology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .242

Table 9.3.6 Surge arresters for field devices . . . . . . . . . . . . . . . . . . . . .242

Table 9.7.1 Lightning and surge protection for signal lines . . . . . . . . . .260

Table 9.7.2 Lightning and surge protection for power supply lines . . . .260

Table 9.9.1 Short definition of the SPDs . . . . . . . . . . . . . . . . . . . . . . . .266

Table 9.9.2 Selection of SPDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .267

Table 9.10.1 Short description of the SPDs . . . . . . . . . . . . . . . . . . . . . . .269

Table 9.12.1 Max. data transmission rate . . . . . . . . . . . . . . . . . . . . . . . .274

Table 9.12.2 Capacitances and series impedances of surge protective devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .274

Table 9.12.3 Selection of combined SPD with regard to the power supply system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .276

Table 9.12.4 Surge protection for signal interfaces . . . . . . . . . . . . . . . . .276

Table 9.12.5 Surge protection for the 230 V power supply . . . . . . . . . . .276

Table 9.12.6 Surge protection for signal interfaces . . . . . . . . . . . . . . . . .277

Table 9.12.7 Surge protection for the power supply . . . . . . . . . . . . . . . .277

Table 9.13.1 Surge protection for bus lines of PROFIBUS DP/ PROFIBUS FMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .278

Table 9.13.2 Surge protection for bus lines of PROFIBUS PA . . . . . . . . .278

Table 9.13.3 Surge protection for power supply . . . . . . . . . . . . . . . . . . .280

Table 9.15.1 Example of a temperature transducer . . . . . . . . . . . . . . . .288

Table 9.15.2 Surge protective devices for use in intrinsically safe circuits and bus systems . . . . . . . . . . . . . . . . . . . . . . . . . . .289

Table 9.17.1 Selectivity surge arrester Type 1 . . . . . . . . . . . . . . . . . . . . .297

Table 9.17.2 Standardised surge arrester Type 2 . . . . . . . . . . . . . . . . . . .297

Table 9.17.3 Surge protection for the fixed network connection . . . . . .297

Table 9.17.4 Surge protection for the transmission technology . . . . . . .297

Table 9.18.1.1 Selection of the surge protective devices for PV systems on buildings without external lightning protection system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .301

Table 9.18.1.2 Selection of the surge protective devices for PV systems on buildings with external lightning protection system and the separation distance is being kept . . . . . . . . . . . . .303

Table 9.18.1.3 Selection of the surge protective devices for PV systems on buildings with external lightning protection and the separation distance is not being kept . . . . . . . . . . . . . . . . .303

Table 9.18.2.1 Selection of surge protective devices for solar power plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .305

Table 9.18.2.2 Surge protective devices for data acquisition and eva-luation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .306

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