Earthing & Lightning Protection Guide

8/18/2019 Earthing & Lightning Protection Guide

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EARTHING & LIGHTNING PROTECTION

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CODES OF PROTECTION OF STRUCTURES AGAINST LIGHTNING.BS 6651 : Protection of structures against lightning.

BSEN 62305 : Embrace the whole concept of lightning protection from design to installation.

IEC 61024-1 : Protection of structures against lightning.IEC 60364-5-54 : Earthing arrangements and protective conductors.

KS C 9609 : Lightning rod.

UL96 : Lightning Protection Components.

EARTH RODS.When earth rods are used, they should be driven into the ground beneath, or as close as practicable to,

the structure and down conductor. The practice of siting terminations away from the building is normally

unnecessary and uneconomical.

Where ground conditions are favourable for the use of rods in parallel, the reduction in earth resistance

is small when the separation between the rods becomes less than their driven length.

Lightning protection system for tall buildings(over 20m high) showing air terminations, down

conductors, bonds to projections above roof.

Earth terminations : arrangement of earth electrodes.

Air termination mesh should be not greater than 10m X 20m. Down conductor should be not more than 10m apart.

Air termination bondedto steel reinforcing orsteel frame of buliding.

Earth electrode


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AIR TERMINATIONS.Air termination networks may consist of vertical or horizontal conductors or combinations of both.

For large flat roofs, this is achived typically by use of an air termination network mesh of approximately 10m x 20m.

On multiple ridge roofs, additional conductors are necessary if the separation, S(in metres), of the ridgesis greater than 10 +2H, where H is the height of the ridge (in metres). See Fig.5

On a reinforced concrete structure, the air termination should be connected to the reinforcing bars in the number

of positions needed for down conductors.

Air terminations for a flat roof


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Air terminations for flat roofs at different levels

Air terminations for large areas of roof of various profiles.

Perimeter = 24 + 24+ 12+ 12 = 72mNumber of down conductoors required= 72/20 = 4.

NOTE 1 If S > 10 +2H, additional longitudinal conductors are needed so that the distance between conductorsNOTE 1does not exceed 10m.NOTE 2 If the length of the roof exceeds 20m. additional transverse conductors are necessary.NOTE 3 Down conductors are omitted for clarity.


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Air terminations for tall conducting structures.

Example of lightning protection system for brick chimneys.

The air termination network for a tall reinforced concreteor steel structure should be as follows:a) horizontal conductors on roofs from a 10m X 20m network;b) bonds to steelwork at comers, at 20m intervals around theb) periphery and on the tower 0.5m above the lower roof level;c) key bonding to the building steelwork.


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DOWN CONDUCTORS.The function of a down conductor is to provide a low impedance path from the air termination to the earth

electrode so that the lightning current can be safely conducted to earth.

Depending upon the form of the building, it is often necessary to have multiple down conductors in parallel,some or all of which may be part of the building structure itself. For example, a steel framed or reinforced concrete

structure might need no added down conductors as the framework itself provides an efficiant natual network

of many paths to earth ; conversely a structure made entirely from non-conducting materials would need

down conductors deployed according to the size and form of the structure.

Patterns of down conductors(natural or not) for various forms of tall building.

The down conductors may be natural (parts of the building framework) or added strips or rods on external faces.On structures exceeding 20m in height, down conductors should be spaced not more than 10m apart.


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Air termination and zone of protection for simple structure with explosive or

highly flammable contents.

CORROSION.Electrolytic corrosion between dissimilar metals :

The contact of dissimilar metals, unless the contact surfaces are kept completely dry and protected

against the ingress of moisture, is likely to initiate and accelerate corrosion.

Chemical corrosion of copper :

Although copper is highly resistant to many types of chemical attack, lead coating is recommended where

it is subject to serve corrosion due to the presence of sulphur compounds.

INSPECTION.All lightning protection systems should be visually inspected by a competent person during installation,

after completetion and after alteration or extension, in order to verify that they conform to the recommendations in

BS6651, Visual inspections should be repeated at fixed intervals, preferably not exceeding 12 months.

To prevent flashover between mast/conductor and protected building, the minimum clearance distance has to be 2m,whichever is the greater.

This clearance has to under maximum sag conditions, i.e. snow ice on the aerial conductor.


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COPPER CONDUCTOR & COPPER TAPE

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ANNEALED STRANDED COPPER CONDUCTOR

COPPER CONDUCTOR PVC INSULATED GROUNDING WIRE

Stranded constructionNumber/diameter

No./mm

ConductorSize(mm

2

)

ElectricResistance max.

/mm2

10

16

25

35

50

70

95

120

150

185

240

300

-

1.15

0.727

0.524

0.387

0.268

0.193

0.153

0.124

0.0991

0.0754

0.0601

-

4.7

5.9

7

8.1

9.6

11.4

13

14.4

16

18.3

20.5

-

142

225

312

427

617

854

1034

1280

1600

2064

2641

7/1.35

Compact

Stranded

C.C

Reference

Overall Diametermm(approx.)

Approximately Weightkg/km

PART NO

CT - 2003

CT - 2503CT - 3003

CT - 3806

CT - 5003

CT - 5006

20

2530

38

50

50

3

3

3

6

3

6

50M

50M

50M

25M

40M

20M

0.27kg

0.67kg

0.80kg

1.45kg

1.33kg

2.68kg

W TQ’ty per coil

Dimensions(mm)Weight per m

ConductNominal sectional area

mm2

ConstructionNo./mm

610162535507095

120150185240300

7/1.047/1.35C.C.C.C.C.C.C.C.C.C.C.C.

C.C.C.C.C.C.C.C.C.C.

2.42.42.42.62.62.82.83.1

3.13.43.64.04.5

--

0.190.290.410.530.731.00

1.161.542.012.493.05

Nominal thicknessof insulation

mm

IEC Standard Designation : IEC60228

Soft drawn stranded copper : BS6360

HIGH CONDUCTIVITY COPPER TAPE (BS EN13601)

*C.C. : Circular Compact stranded shape

Remarks : The numerical values in this table are taken at 20

**Tinned Copper Tape : 30M*Steel Tape(H.D.G) is available.

•High conductivity copper

•Insulation : Green Color (UV stability)

PART NO

IBCB - 253

IBCB - 256

IBCB - 506

25

25

50

3

6

6

5M

5M

5M

0.77kg

1.53kg

2.95kg

W TQ’ty per coil

Dimensions(mm)Weight per m

PVC COVERED COPPER TAPE

T

T

W

W

Approx. weight of cable

kg/m

Green/Yellow PVC Covered Soft drawn stranded copper : BS 6004 / PVC Green or Green/Yellow insulation : IEC60502

Earthing & Lightning Protection Guide

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