ANSI C 37.42 Cortacircuitos

IEEE Std C37.41™-2008(Revision of

IEEE Std C37.41-2000)

IEEE Standard Design Tests for High-Voltage(>1000 V) Fuses, Fuse and DisconnectingCutouts, Distribution Enclosed Single-Pole AirSwitches, Fuse Disconnecting Switches, and FuseLinks and Accessories Used with These Devices

IEEE3 Park Avenue New York, NY 10016-5997, USA

13 March 2009

IEEE Power & Energy SocietySponsored by theSwitchgear Committee

C37.

41TM

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IEEE Std C37.41TM-2008 (Revision of

IEEE Std C37.41-2000)

IEEE Standard Design Tests for High-Voltage (>1000 V) Fuses, Fuse and Disconnecting Cutouts, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Fuse Links and Accessories Used with These Devices

Sponsor Switchgear Committee of the IEEE Power & Energy Society Approved 10 November 2008

IEEE-SA Standards Board


Abstract: Required procedures for performing design tests for high-voltage distribution class and power class fuses, as well as for fuse disconnecting switches and enclosed single-pole air switches, are specified. These design tests, as appropriate to a particular device, include the following test types: dielectric, interrupting, load-break, radio-influence, short-time current, temperature-rise, time-current, manual-operation, thermal-cycle, bolt-torque, and liquid-tightness. Keywords: distribution enclosed single-pole air switches, fuse accessories, fuse design tests, fuse disconnecting switches, fuse enclosure package, high-voltage fuses

____________________________ The Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue, New York, NY 10016-5997, USA Copyright © 2009 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published 13 March 2009. Printed in the United States of America. IEEE is a registered trademark in the U.S. Patent & Trademark Office, owned by the Institute of Electrical and Electronics Engineers, Incorporated. PDF: ISBN 978-0-7381-5844-0 STD95852 Print: ISBN 978-0-7381-5845-7 STDPD95852 Second printing 22 May 2009. Changes made to Table 7 and Table 8. To obtain errata information, please go to http://standards.ieee.org/reading/ieee/updates/errata/index.html. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher.


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iv Copyright © 2009 IEEE. All rights reserved.

Introduction

This introduction is not part of IEEE Std C37.41-2008, IEEE Standard Design Tests for High-Voltage (>1000 V) Fuses, Fuse and Disconnecting Cutouts, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Fuse Links and Accessories Used with These Devices.

IEEE Std C37.41-2008 is a revision of IEEE Std C37.41-2000, done in order to bring it up to date and into agreement with current requirements for high-voltage fuses and switches. Distribution class oil cutouts were devices formerly covered by IEEE/ANSI standards. However, ANSI C37.44-1981, which covered specifications for such devices, has been withdrawn. Since these devices are now considered obsolete, testing for oil cutouts has been removed from this standard. The rules covering homogeneous series testing of expulsion fuses have been greatly expanded, and homogeneous series testing for parallel current-limiting fuses has been introduced. Certain information, previously in ANSI C37.53.1, concerning the testing of motor-starter fuses has been incorporated. Several changes to current-limiting fuse testing have been made to align more closely with the latest IEC test requirements. At the request of testing authorities, several clarifications concerning test methods and interpretation of results have been added. The Revision of Fuse Standards Working Group of the IEEE Subcommittee on High-Voltage Fuses prepared the standard. Liaison was maintained with the International Electrotechnical Commission (IEC) during the development of the revisions in order to incorporate the latest activities at the time of publication.

The Switchgear Committee of the IEEE Power and Energy Society has recently approved and published IEEE Std C37.100.1™-2007 [B4].a Although IEEE Std C37.100.1-2007 is not specifically referenced in this document, any information that may apply to fuse devices has been incorporated.

This standard is one of a series of complementary standards covering various types of high-voltage fuses and switches, arranged so that certain standards apply to all devices while other standards provide additional specifications for a particular device. For any device, IEEE Std C37.40™, this IEEE Std C37.41™, plus any additional standards covering that device, constitute a complete standard for the device. In addition, IEEE Std C37.48™ provides application, operation, and maintenance guidance for all the devices, and it is supplemented by IEEE Std C37.48.1™-2002 [B3], which is an operation, classification, application, and coordination guide for current-limiting fuses.

At the time this standard was approved, this series was comprised of the following standards:

ANSI C37.42, American National Standard Specifications for High Voltage Expulsion Type Distribution Class Fuses, Cutouts, Fuse Disconnecting Switches and Fuse Links.

ANSI C37.46, American National Standard for High Voltage Expulsion and Current-Limiting Type Power Class Fuses and Fuse Disconnecting Switches.

ANSI C37.47, American National Standard for High-Voltage Current-Limiting Type Distribution Class Fuses and Fuse Disconnecting Switches.

IEEE Std C37.40™, IEEE Standard Service Conditions and Definitions for High-Voltage Fuses, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Accessories.

IEEE Std C37.41™, IEEE Standard Design Tests for High-Voltage (>1000 V) Fuses, Fuse and Disconnecting Cutouts, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Fuse Links and Accessories Used with These Devices.

aThe numbers in brackets correspond to those of the bibliography in Annex F .


v Copyright © 2009 IEEE. All rights reserved.

IEEE Std C37.43™, IEEE Standard for Specifications for High-Voltage Expulsion, Current-Limiting and Combination Type Distribution and Power Class External Fuses, With Rated Voltages from 1kV through 38kV, Used for the Protection of Shunt Capacitors.

IEEE Std C37.45™, IEEE Standard Specifications for High-Voltage Distribution Class Enclosed Single-Pole Air Switches with Rated Voltages from 1 kV through 8.3 kV.

IEEE Std C37.48™, IEEE Guide for Application, Operation, and Maintenance of High-Voltage Fuses, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Accessories.

IEEE Std C37.48.1™, IEEE Guide for the Operation, Classification, Application, and Coordination of Current-Limiting Fuses with Rated Voltages 1−38 kV.

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vi Copyright © 2009 IEEE. All rights reserved.

Patents

Attention is called to the possibility that implementation of this draft standard may require use of subject matter covered by patent rights. By publication of this draft standard, no position is taken with respect to the existence or validity of any patent rights in connection therewith. The IEEE is not responsible for identifying Essential Patent Claims for which a license may be required, for conducting inquiries into the legal validity or scope of Patents Claims or determining whether any licensing terms or conditions provided in connection with submission of a Letter of Assurance, if any, or in any licensing agreements are reasonable or non-discriminatory. Users of this draft standard are expressly advised that determination of the validity of any patent rights, and the risk of infringement of such rights, is entirely their own responsibility. Further information may be obtained from the IEEE Standards Association.

Participants

At the time this standard was submitted to the IEEE-SA Standards Board, the Revision of fuse Standards Working Group had the following membership:

John G. Leach, Chair Glenn R. Borchardt, Secretary

Chris Ambrose John G. Angelis L. Ronald Beard Sheila Brown Fernando Calderon H. Edward Foelker Dan Gardner

Stephen P. Hassler Gary Haynes Frank G. Ladonne James R. Marek Frank J. Muench Donald M. Parker R. Neville Parry

Philip Rosen Tim E. Royster John S. Schaffer Mark W. Stavnes Frank M. Stepniak John G. St.Clair Janusz Zawadzki

This document was sponsored by the Switchgear Committee of the IEEE Power and Energy Society. When this document was approved, the members of the Switchgear Committee had the following membership:

Ted A. Burse, Chair Bill Long, Vice Chair

Ken Edwards, Secretary Michael Wactor, Standards Coordinator

Roy Alexander Chris Ambrose John G. Angelis Charles J. Ball Paul D. Barnhart Robert Behl W. J. (Bill) Bergman Anne Bosma John Brunke Ray Capra Patrick DiLillo Alexander Dixon Randall Dotson Denis Dufournet Peter W. Dwyer Douglas Edwards Marcel Fortin

Mietek Glinkowski S. S. (Dave) Gohil Keith I. Gray Carlos Isaac Richard Jackson Frank G. Ladonne Stephen Lambert John G. Leach Dave Lemmerman James R. Marek Neil McCord Nigel P. McQuin Steven Meiners Alec Monroe Georges Montillet Anne F. Morgan Frank J. Muench

Yasin Musa Jeffrey Nelson T. W. Olsen Michael Orosz Robert J. Puckett Carl Reigart Timothy Royster Roderick Sauls Devki Sharma Michael D. Sigmon R. Kirkland Smith H. M. Smith David Stone Alan D. Storms Thomas Tobin Rich York Janusz Zawadzki


vii Copyright © 2009 IEEE. All rights reserved.

The following members of the balloting committee voted on this standard. Balloters may have voted for approval, disapproval, or abstention. William J. Ackerman Steven Alexanderson Michael Baldwin Steven Bezner William Bloethe Glenn Borchardt James Bouford Harvey Bowles Chris Brooks Robert Brown Eldridge Byron Thomas Callsen Yunxiang Chen Tommy Cooper F. A. Denbrock Carlo Donati Gary Engmann Marcel Fortin Daniel Gardner Manuel Gonzalez Edwin Goodwin Randall Groves

Ajit Gwal John Harder Ronald Hartzel Gary Heuston William Hurst Richard Jackson Joseph L. Koepfinger David W. Krause Jim Kulchisky Saumen Kundu Frank G. Ladonne Chung-Yiu Lam Stephen Lambert John G. Leach R. Long Federico Lopez G. Luri Frank Mayle Gary Michel Georges Montillet Frank J. Muench

Jerry Murphy Jeffrey Nelson Michael S. Newman Joe Nims T. W. Olsen Miklos Orosz Donald Parker R. Neville Parry Iulian Profir Michael Roberts Timothy Robirds Charles Rogers Timothy Royster Thomas Rozek Bartien Sayogo James E. Smith James Smith Francois Soulard James Swank Michael Swearingen John Vergis Janusz Zawadzki

When the IEEE-SA Standards Board approved this standard on 10 November 2008, it had the following membership:

Robert M. Grow, Chair Tom A. Prevost, Vice Chair Steve M. Mills, Past Chair Judith Gorman, Secretary

Victor Berman Richard DeBlasio Andrew Drozd Mark Epstein Alexander Gelman William R. Goldbach Arnold M. Greenspan Kenneth S. Hanus

James Hughes Richard H. Hulett Young Kyun Kim Joseph L. Koepfinger* John Kulick David J. Law Glenn Parsons

Ronald C. Petersen Chuck Powers Narayanan Ramachandran Jon Walter Rosdahl Anne-Marie Sahazizian Malcolm V. Thaden Howard L. Wolfman Don Wright

*Member Emeritus

Also included are the following nonvoting IEEE-SA Standards Board liaisons:

Satish K. Aggarwal, NRC Representative

Michael Janezic, NIST Representative

Jennie M. Steinhagen

IEEE Standards Program Manager, Document Development

Matthew J. Ceglia IEEE Standards Program Manager, Technical Program Development


viii Copyright © 2009 IEEE. All rights reserved.

Contents

1. Overview .................................................................................................................................................... 1

1.1 Scope ................................................................................................................................................... 1 1.2 Purpose ................................................................................................................................................ 2 1.3 Background .......................................................................................................................................... 2 1.4 Description of fuse-enclosure packages (FEPs) using expulsion type indoor power class fuses ......... 2 1.5 Description of FEPs using current-limiting type indoor distribution and power class fuses ............... 3

2. Normative references .................................................................................................................................. 3

3. Required tests ............................................................................................................................................. 4

3.1 General ................................................................................................................................................ 4 3.2 Device tests .......................................................................................................................................... 5 3.3 FEP tests .............................................................................................................................................. 6 3.4 Test values ........................................................................................................................................... 6 3.5 Testing responsibility .......................................................................................................................... 6 3.6 Test report ............................................................................................................................................ 6

4. Common test requirements ......................................................................................................................... 6

4.1 General ................................................................................................................................................ 6 4.2 Test site conditions .............................................................................................................................. 7 4.3 Frequency and wave shape of test voltage ........................................................................................... 7 4.4 Devices to be tested ............................................................................................................................. 7 4.5 Acceptance criteria .............................................................................................................................. 7 4.6 Test-conductor dimensions .................................................................................................................. 8 4.7 Mounting and grounding of the device for tests .................................................................................. 9

5. Dielectric tests ...........................................................................................................................................11

5.1 General ...............................................................................................................................................11 5.2 Measurement of test voltages .............................................................................................................11 5.3 Description of power-frequency dry-withstand voltage tests .............................................................11 5.4 Description of power-frequency wet-withstand voltage tests on outdoor devices ..............................12 5.5 Description of power-frequency dew-withstand voltage tests on indoor devices ...............................12 5.6 Description of impulse withstand voltage tests ..................................................................................12 5.7 Distribution class expulsion type fuses, cutouts, and fuse disconnecting switch test connections and test values .................................................................................................................................................13 5.8 Distribution class enclosed single-pole air switch test connections and test values ...........................14 5.9 Power class expulsion fuses, power class current-limiting fuses, and power class fuse disconnecting switch test connections and test values .....................................................................................................14 5.10 Distribution class current-limiting fuse and fuse disconnecting switch test connections and test values ........................................................................................................................................................15 5.11 Distribution class, power class expulsion and current-limiting type fuses, and fuse disconnecting switches used in FEPs ...............................................................................................................................16 5.12 Distribution and power class external fuses for shunt capacitors .....................................................18

6. Interrupting tests ........................................................................................................................................18

6.1 Procedures common to all interrupting tests .......................................................................................18 6.2 Interrupting tests on a homogeneous series of expulsion type fuses...................................................20 6.3 Description of interrupting tests on distribution class open-link cutouts ............................................26 6.4 Description of interrupting tests on distribution class fuse cutouts (open and enclosed) (except current-limiting fuses) ..............................................................................................................................26


ix Copyright © 2009 IEEE. All rights reserved.

6.5 Description of interrupting tests on power class fuses and fuse disconnecting switches (except current-limiting fuses and liquid-submerged expulsion fuses) .................................................................32 6.6 Description of interrupting tests on current-limiting power and distribution fuses ............................35 6.7 Description of interrupting tests for FEPs using current-limiting-type indoor distribution and power class fuses .................................................................................................................................................48 6.8 Description of interrupting tests for FEPs using liquid-submerged, expulsion type indoor power class fuses ..........................................................................................................................................................50 6.9 Description of interrupting tests for air-insulated FEPs using expulsion type indoor power class fuses ..................................................................................................................................................................52 6.10 Description of interrupting tests for external fuses for shunt capacitors ...........................................54

7. Load-break tests.........................................................................................................................................62

7.1 Procedures common to all load-break tests ........................................................................................62 7.2 Description of load-break tests for all fused devices ..........................................................................64

8. Radio-influence tests .................................................................................................................................64

8.1 Procedures common to all radio-influence tests .................................................................................64 8.2 Description of radio-influence tests on a single device ......................................................................66 8.3 Description of radio-influence tests on multiple devices ....................................................................67 8.4 Description of radio-influence tests for assembled apparatus .............................................................67

9. Short-time current tests ..............................................................................................................................67

9.1 General ...............................................................................................................................................67 9.2 Mounting and grounding of device for the momentary test ................................................................67 9.3 Test connections .................................................................................................................................67 9.4 Test circuit ..........................................................................................................................................67 9.5 Description of 15-cycle current tests ..................................................................................................69 9.6 Description of 3-second current tests ..................................................................................................69 9.7 Description of momentary current tests ..............................................................................................69 9.8 Acceptance criteria .............................................................................................................................70

10. Temperature-rise tests .............................................................................................................................70

10.1 Procedures common to all temperature-rise tests .............................................................................70 10.2 Description of temperature-rise tests ................................................................................................71 10.3 Description of temperature-rise tests for air-insulated FEPs using expulsion type indoor power class fuses ..........................................................................................................................................................71

11. Time-current tests ....................................................................................................................................72

11.1 Procedures common to all time-current tests ....................................................................................72 11.2 Description of melting time-current tests .........................................................................................73 11.3 Description of total-clearing time-current tests ................................................................................74

12. Manual-operation, thermal-cycle, and bolt-torque tests (distribution cutouts) ........................................74

12.1 Description of manual-operation tests ..............................................................................................74 12.2 Description of thermal cycle tests .....................................................................................................75 12.3 Description of torque tests ................................................................................................................76

13. Liquid-tightness tests ...............................................................................................................................76

13.1 Description of liquid-tightness tests .................................................................................................76 13.2 Test series .........................................................................................................................................77 13.3 Acceptance criteria ...........................................................................................................................77

14. Description of expendable-cap static-relief pressure tests .......................................................................77

Annex A (informative) Recommended methods for determining the value of a sinusoidal current wave and a power-frequency recovery voltage .............................................................................................................78


x Copyright © 2009 IEEE. All rights reserved.

A.1 Current waves ....................................................................................................................................78 A.2 Power-frequency recovery voltage ....................................................................................................79

Annex B (informative) Recommended method of determining the equivalent steady-state rms current for plotting time-current curves...........................................................................................................................81

Annex C (informative) Simplified fault-current calculation .........................................................................82

C.1 Interrupting duty and rated short-time withstand current ...................................................................82

Annex D (informative) TRV parameters .......................................................................................................83

D.1 Measurement of peak factor...............................................................................................................84

Annex E (informative) Criteria for determining It testing validity ................................................................86

E.1 Introduction ........................................................................................................................................86 E.2 Interrupting processes ........................................................................................................................86

Annex F (informative) Bibliography .............................................................................................................88


1 Copyright © 2009 IEEE. All rights reserved.

IEEE Standard Design Tests for High-Voltage (>1000 V) Fuses, Fuse and Disconnecting Cutouts, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Fuse Links and Accessories Used with These Devices

IMPORTANT NOTICE: This standard is not intended to ensure safety, security, health, or environmental protection in all circumstances. Implementers of the standard are responsible for determining appropriate safety, security, environmental, and health practices or regulatory requirements. This IEEE document is made available for use subject to important notices and legal disclaimers. These notices and disclaimers appear in all publications containing this document and may be found under the heading “Important Notice” or “Important Notices and Disclaimers Concerning IEEE Documents.” They can also be obtained on request from IEEE or viewed at http://standards.ieee.org/IPR/disclaimers.html.

1. Overview

1.1 Scope

This standard specifies design test requirements for high-voltage (above 1000 V) fuses, distribution enclosed single-pole air switches, disconnecting cutouts, fuse disconnecting switches, and accessories for use on ac power and distribution systems. Devices with rated maximum voltages to 170 kV are covered. The devices to which this standard applies are as follows:

a) Distribution and power class expulsion type fuses

b) Distribution and power class current-limiting type fuses

c) Distribution and power class fuse disconnecting switches

d) Item a) through item c) used in fuse enclosure packages

e) Fuse supports of the type intended for use with distribution and power class fuses, and fuse disconnecting switches

f) Fuse and disconnecting cutouts

g) Disconnecting devices created by the use of a removable switch blade in a distribution or power class fuse support

h) Distribution class enclosed single-pole air switches


http://standards.ieee.org/IPR/disclaimers.html�

IEEE Std C37.41-2008 IEEE Standard Design Tests for High-Voltage (>1000 V) Fuses, Fuse and Disconnecting Cutouts, Distribution Enclosed Single-Pole

Air Switches, Fuse Disconnecting Switches, and Fuse Links and Accessories Used with These Devices


i) Distribution class and power class expulsion, current-limiting, and combination types of external capacitor fuses used with a capacitor unit, groups of units, or capacitor banks

j) Backup current-limiting fuses (“motor-starter fuses”) used in conjunction with high-voltage Class E2 motor starters (see ANSI/UL 347-2000 [B1])1

k) Fuse links when used exclusively with distribution class and power class fuses, and distribution class and power class fuse disconnecting switches

l) Item a) through item d) and item f) through item i) having integral load-break means

1.2 Purpose

This standard specifies the minimum testing requirements for fuses and related devices. Such standardization is needed to ensure uniform minimum product testing for devices within the document scope. Test areas covered are based on historical experience.

1.3 Background

The distribution and power class expulsion type fuses listed in 1.1 are similar to those now covered in IEC 60282-2.2 The distribution class expulsion type fuses are similar to the class “A” fuses covered in the document, and the power class fuses are similar to their class “B” fuses. Some of the current-limiting type fuses listed in 1.1 are similar to those now covered in IEC 60282-1. However, significant differences exist in the testing requirements of IEC and IEEE/ANSI. IEEE fuse standards primarily reflect applications common in North America and in countries that use electrical systems designed using similar principles. IEC standards tend to rely heavily on practices common in Europe. Since IEC testing differences include testing at different voltages for the same fuse rated voltage, and different or no testing for fuses intended for use in a surrounding temperature above 40 °C, the user is advised to exercise extreme caution if devices specified and tested per IEC standards are compared with those specified and tested per IEEE/ANSI standards. The differences in test requirements may result in devices tested to IEC not being suitable for applications where devices tested to IEEE/ANSI standards are required, or vice versa. In the headings and the text of this document, there are some areas where information is included in brackets [ ]. The information in the brackets is a term used in IEC standards that may be similar to the term used in this document, a term that is common in some parts of the world, or a term that has been used previously in IEEE or ANSI standards. Caution is again advised when making comparisons.

1.4 Description of fuse-enclosure packages (FEPs) using expulsion type indoor power class fuses

Type 1E: A fuse mounted in an enclosure with relatively free air circulation within the enclosure (e.g., an expulsion fuse mounted in an enclosure or vault).

Type 2E: A fuse mounted in a container with restricted air flow surrounding the fuse, but with relatively free air circulation within the enclosure on the outside of the container (e.g., an expulsion fuse in an enclosure with insulating barriers that form a container that restricts the air flow).

Type 3E: A fuse directly immersed in liquid and mounted in an enclosure with relatively free liquid circulating around the fuse (e.g., an expulsion fuse in a liquid-filled switchgear enclosure).

1 The numbers in brackets correspond to those of the bibliography in Annex F. 2 Information on references can be found in Clause 2.





1.5 Description of FEPs using current-limiting type indoor distribution and power class fuses

Type 1CL: A fuse mounted in a large enclosure with relatively free air circulation within the enclosure (e.g., a fuse mounted in a live-front pad-mounted transformer or in a vault). The relevant fuse rated maximum application temperature (RMAT) is based on that of the air that is cooling the fuse. It may be noted that if a fuse were mounted outdoors but in an ambient temperature above 40 ºC, conditions on the fuse would be the same.

Type 2CL: A fuse mounted in a fuse container. This is a relatively small enclosure, defined as one supporting the fuse and restricting the air, gas, or liquid flow surrounding the fuse (e.g., a fuse inside a canister in a transformer or a vault). However, the fluid flow (gas, liquid, or a combination of the two) that cools the outside surface of the container has relatively free circulation. The relevant fuse RMAT is based on that of the fluid that is cooling the container. Fuses tested in accordance with 6.6 (i.e., tested for use in air no hotter than 40 ºC), which are encapsulated with solid insulation (e.g., rubber or epoxy), can be considered to be this type of FEP when so encapsulated. In this case, the relevant fuse RMAT is based on that of the fluid that is cooling the encapsulated fuse.

Type 3CL: A fuse directly immersed in liquid and mounted in an enclosure with relatively free liquid circulation around the fuse (e.g., an oil-immersed fuse in a transformer or switchgear enclosure). The relevant RMAT is based on that of the liquid that is cooling the fuse.

NOTE—In IEEE Std C37.41TM-2000 and the versions of ANSI C37.46, ANSI C37.47, and IEEE Std C37.48TM approved before this standard, FEPs using current-limiting fuses are designated as being of types 1C through 5C. In order to simplify FEP types, include additional types, and align with IEC practice, these types have been rationalized into three categories. Type 2CL includes the former types 2C, 3C, and 4C, whereas type 3CL is the same as type 5C. The new classifications will be introduced into the other standards when they are revised.3

2. Normative references

The following referenced documents are indispensable for the application of this document (i.e., they must be understood and used, so that each referenced document is cited in text and its relationship to this document is explained). For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments or corrigenda) applies.

ANSI C37.42, American National Standard Specifications for High Voltage Expulsion Type Distribution Class Fuses, Cutouts, Fuse Disconnecting Switches and Fuse Links.4

ANSI C37.46, American National Standard for High Voltage Expulsion and Current-Limiting Type Distribution Class Fuses and Fuse Disconnecting Switches.

ANSI C37.47, American National Standard for High Voltage Current-Limiting Type Distribution Class Fuses and Fuse Disconnecting Switches.

ANSI C63.2-1987, American National Standard for Electromagnetic Noise and Field Strength Instrumentation, 10 kHz to 1 GHz—Specifications.

IEC 60282-1, High Voltage Fuses—Part 1, Current-Limiting Fuses.5

3 Notes in text, tables, and figures are given for information only and do not contain requirements needed to implement the standard. 4 ANSI publications are available from the Sales Department, American National Standards Institute, 25 West 43rd Street, 4th Floor, New York, NY 10036, USA (http://www.ansi.org/). 5 IEC publications are available from IEC Sales Department, Case Postale 131, 3, rue de Varembé, CH-1211, Genève 20, Switzerland/ Suisse. IEC publications are also available in the United States from the Sales Department, American National Standards Institute, 25 West 43rd Street, 4th Floor, New York, NY 10036, USA (http://www.ansi.org/).





IEC 60282-2, High Voltage Fuses—Part 2, Expulsion Fuses.

IEEE Std 4™-1995, IEEE Standard Techniques for High-Voltage Testing.6, 7

IEEE Std C37.20.3™, IEEE Standard for Metal-Enclosed Interrupter Switchgear.

IEEE Std C37.40™, IEEE Standard Service Conditions and Definitions for High-Voltage Fuses, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Accessories.

IEEE Std C37.43™, IEEE Standard for Specifications for High-Voltage Expulsion, Current-Limiting and Combination Type Distribution and Power Class External Fuses, With Rated Voltages from 1kV through 38kV, Used for the Protection of Shunt Capacitors.

IEEE Std C37.45™, IEEE Standard Specifications for High-Voltage Distribution Class Enclosed Single-Pole Air Switches with Rated Voltages from 1 kV through 8.3 kV.

IEEE Std C37.48™, IEEE Guide for Application, Operation, and Maintenance of High-Voltage Fuses, Distribution Enclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Accessories.

NOTE—Fuse standards listed as “ANSI C37.xx,” were formerly developed by NEMA. The responsibility for maintaining them has passed to the IEEE and will, at their next revision, carry the designation “IEEE Std C37.xx.”

3. Required tests

3.1 General

The tests to be conducted upon completion of a design or following a design change that affects performance are summarized in Table 1 and are completely specified in the appropriate standards listed below:

ANSI C37.42

IEEE Std C37.43

IEEE Std C37.45

ANSI C37.46

ANSI C37.47

6 IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA (http://standards.ieee.org/). 7 The IEEE standards or products referred to in this clause are trademarks of the Institute of Electrical and Electronics Engineers, Inc.





Table 1 —Design tests required

Design test given in

following sections of

this standard

ANSI C37.42 IEEE Std C37.43 IEEE Std C37.45

ANSI C37.46

ANSI C37.47

Specifications for high-voltage expulsion type distribution

class fuses, cutouts, fuse disconnecting switches, and

fuse links

Specifications for high-voltage

distribution and power class expulsion, current-limiting, and combination types of

external capacitor fuses for shunt

capacitors


distribution class enclosed single-pole air

switches


expulsion and current-

limiting type power class

fuses and fuse disconnecting

switches


current-limiting type distribution class fuses,

and fuse disconnecting

switches Fuse cutouts

Disconnecting cutouts

Fuse links

Capacitor line fuses

Capacitor unit fuses

5. Dielectrica X X — X — X Xb Xb 6. Interrupting X — Xc X X — Xb Xb 7. Load-break Xd Xd — Xd — — — — 8. Radio-influencea X X — X X X Xb Xb

9. Short-time current — X — — — X — —

10. Temperature-rise

X X X X X X Xb Xb

11. Time-current — — X X X — X X

12. Manual-operation, thermal-cycle, and bolt-torque

X X — — — — — —

13. Liquid-tightness — — — — — — Xe Xe

14. Expendable-cap static-relief pressure

Xf — — Xf — — — —

a Required only on fuses and fuse units when they are mounted in a particular fuse support (see 5.1 and 8.1.1). b When these types of fuses are used in enclosures, additional tests may be required. See the appropriate IEEE/ANSI standard listed above for complete requirements. c Required only on open-link fuses. dRequired only on load-break cutouts having means provided for breaking load current. eRequired only on liquid-submersible fuses used in FEP. fRequired only on expendable caps for expendable-cap cutouts.

3.2 Device tests

For devices covered by this standard, all applicable tests need not be performed on each design modification of a previously qualified design. To assure that overall performance has not been adversely affected as a result of the design modification, sufficient tests shall be performed to ensure that the modified design will have a performance that meets or exceeds the ratings and performance requirements of the standards specified in Clause 3. For devices that have been assigned ratings or performance requirements that are different from the standards specified in Clause 3, the modified design shall have ratings and performance requirements that meet or exceed the values assigned to the original device. Fuses connected in parallel shall be considered a separate design and be tested accordingly. Note that this includes fuses mounted in parallel by the fuse manufacturer and those intended by the manufacturer to be paralleled by another party. When single current-limiting fuses have been tested in accordance with IEEE Std C37.41, the testing of these fuses in parallel is subject to the homogeneous testing rules in 6.6.4.





3.3 FEP tests

The design tests for FEPs are performed to determine the adequacy of a particular type of design, style, or model of equipment to meet its assigned ratings and for satisfactory operation. In general, a fuse need not be tested if it has already been tested in an equivalent enclosure.

3.4 Test values

3.4.1 Allowable tolerances

Testing parameters in this document and the specification documents for each device are listed as a value with an allowable plus tolerance (e.g., +5% –0%), a value with an allowable minus tolerance (e.g., +0% −10%), a minimum value, a maximum value, or a range. When a range is specified, the test may be performed anywhere within that range. When a minimum value or a value with a plus tolerance is specified, the manufacturer may perform the test at any value that equals or exceeds the minimum value (e.g., voltage). When a maximum value or a value with a minus tolerance is specified, the manufacturer may perform the test at any value that is equal to or less than the maximum value allowed. When a minimum value, maximum value, or a tolerance is specified, testing by persons other than the manufacturer shall be at the specified value, or permission to test at a different level shall be obtained from the manufacturer. The general principle to be followed is that a manufacturer, for testing convenience, may choose to test with values more severe than prescribed for the tests, whereas other persons performing tests shall obtain approval from the manufacturer before more severe testing is performed.

3.4.2 Preferred values

In this standard and the specification standards referred to herein, the ratings and performance requirements represent preferred values and requirements. Special circuit or environmental conditions may require devices with ratings and performance that are different from the preferred values and requirements specified in these documents. For these devices, the user and the manufacturer shall agree upon the ratings and performance requirements.

3.5 Testing responsibility

A fuse or switch manufacturer shall test their device and supply the appropriate application data. An FEP manufacturer is responsible for ensuring that appropriate testing has been performed and for supplying the appropriate application data.

3.6 Test report

The results of all tests shall be recorded in a test report containing the data necessary to prove compliance with the applicable standards. The test report shall include the manufacturers name and completely describe the device tested. Photographs of devices as tested, type numbers, production drawings, product bulletins, or other descriptive literature for the device may be included.

4. Common test requirements

4.1 General

The requirements of Clause 4 are common to all tests. Where the conditions for a specific test deviate from these common test requirements, they are identified in the specific subclause for the test.





4.2 Test site conditions

4.2.1 Ambient temperature during test

The ambient temperature prevailing at the test site shall conform to the usual service conditions in accordance with IEEE Std C37.40.

4.2.2 Atmospheric conditions during test

Tests shall be conducted under atmospheric conditions prevailing at the time and place of the test. It is recommended that the barometric pressure and dry and wet bulb thermometer readings be recorded so that applicable correction factors can be applied to the measurements.

4.3 Frequency and wave shape of test voltage

4.3.1 Frequency of test voltage

The frequency for all power-frequency tests shall be (50 ± 2) Hz or (60 ± 2) Hz, except as otherwise specified.

4.3.2 Wave shape of test voltage

A sine wave of acceptable commercial standards shall be applied to the device. For the definition of the wave shape, see IEEE Std 4-1995.

4.4 Devices to be tested

4.4.1 Condition of device to be tested

The device shall be new and in good condition, and tests shall be applied before the device is put into commercial service, unless otherwise specified.

4.4.2 Compatibility of components

Unless otherwise specified, tests performed according to this standard shall utilize components made by the same manufacturer or as recommended for use by the manufacturer.

4.5 Acceptance criteria

The successful completion of tests listed in this standard requires that various criteria be met, including the following:

a) A device shall perform all of its intended functions. While it is not feasible to list all possible device functions, typical examples are that devices intended to drop down, drop open, or initiate operation of other devices after current interruption shall perform these functions in their intended manner on all interrupting test series (see NOTE 2).

b) A filled current-limiting fuse shall not emit filler material or flame during interrupting tests, although a minor emission of flame from a striker or indicating device is permissible, provided this does not cause breakdown or significant leakage to ground.





c) Fuses that operate an indicating device need not comply with any specific requirements but shall visually and fully operate. If a current-limiting fuse includes a device, the only function of which is to provide indication of a fuse operation, and that indicator does not operate, then although the fuse has failed to pass the test as a fuse with an indicator, the test may be used as part of a series to demonstrate that an otherwise identical nonindicating fuse has met the requirements of the standard.

d) After an interruption test, all parts of the device shall be in proper position, and the fuse shall be removable from its support in one piece as intended.

In addition, after replacing parts that are normally field replaceable (see NOTE 1), excluding a fuse holder, the condition of the device shall be as follows:

e) Mechanical requirements: In substantially the same condition as at the beginning of the test. Depending on the current interrupted during interrupting tests, it is acceptable for the bore of expulsion devices to have some amount of erosion.

f) Electrical requirements: Capable of carrying rated current continuously at the rated maximum voltage. If there is evidence to suggest the device may not be able to carry rated current continuously because of contact deterioration, a temperature-rise test shall be performed using the maximum size fuse link, fuse unit, or refill unit. This temperature-rise test shall be performed on the device at rated current for the time it takes for the temperature to stabilize. Temperatures reached by the device may be higher than those achieved by a new device. The criterion for acceptability is long-term temperature stabilization.

g) Dielectric requirements: If there is evidence of insulator contamination from the test, a power-frequency dry-withstand test shall be performed at 75% of the normal test value for the device.

After certain groups of tests, as specified in Table 7, Table 8, Table 11, and Table 19, the fuse holder may be changed. The acceptance criteria e) through g) are to be met with the fuseholder that has just been tested, even though it may not be suitable for any additional testing.

NOTE 1— Examples of parts that are normally field replaceable include replaceable fuse links, fuse units, refill units, expendable caps, and exhaust-control devices. Requirements of individual tests may limit the replacement of some parts until certain tests, or groups of tests, have been completed.

NOTE 2— The location of the lower test conductor relative to the fuseholder of a fuse or fuse cutout may, on some tests, influence its dropout characteristics by interfering with the movement of the fuse link leader (the flexible conductor used to complete the electrical circuit between the fusible element and the lower fuseholder contact). The manufacturer’s recommendations for conductor placement relative to the tested device should therefore be followed.

4.6 Test-conductor dimensions

4.6.1 Interrupting, load-break, and short-time test conductors

Electrical connections shall be made by a bare conductor connected to each terminal of the device being tested. These conductors shall be of sufficient size to carry the test current adequately for the anticipated time. The source side lead shall be connected to the upper terminal of the device and the return or load side lead to the lower terminal, unless normal service conditions, manufacturer’s recommendations, or other IEEE Std C37.41 clauses require that the connections be reversed or that the device be mounted horizontally. For general-purpose and full-range current-limiting fuses, test series 3 tests (long-time melting tests) shall use conductor sizes as specified in Table 2, unless the manufacturer specifies a different conductor size due to the typical application.





4.6.2 Dielectric and radio-influence test conductors

Electrical connections shall be made by a bare conductor connected to each terminal of the device being tested. These conductors shall be the smallest size the device terminal is designed to accept. Use of other wire sizes is acceptable if it can be demonstrated that this size does not affect the test results.

4.6.3 Temperature-rise and time-current test conductors

Electrical connections shall be made by a bare conductor connected to each terminal of the device being tested. These conductors shall be of the size and length specified in Table 2. For fuses connected in parallel, the current rating to be considered is the total current assigned by the manufacturer.

4.7 Mounting and grounding of the device for tests

4.7.1 General

Devices shall be mounted in the normal service position(s) recommended by the manufacturer. Where more than one service position exists, the orientation that results in the most onerous duty shall be used. When grounding of a particular part of the device is required during the test, the ground lead(s) shall be of a sufficient size so that it can adequately carry any anticipated current for the expected duration of current flow. If detection of the ground current is desired, then current-metering devices may be used. Specific mounting and grounding information for the various devices to be tested is described in 4.7.2 through 4.7.7.2.

Table 2 —Size and length of bare conductor for specified tests

Rated continuous current of fuse cutout, switch, or fuse suppor t (A) Size and length of bare copper leads

Distr ibution enclosed, open, and open-link cutouts when tested as a: Distr ibution

enclosed air switch

Power fuse and

distr ibution cur rent-

limiting fuse

Size of leads Minimum length

Fuse cutout Disconnecting cutout m (in)

50 — — Up to 50 No. 6 AWG Solid 1.2 (48)

— 100 — — No. 2 AWG Stranded 1.2 (48)

100 — — 100 No. 1 AWG Stranded 1.2 (48)

— 200 — — No. 2/0 AWG Stranded 1.2 (48)

200 — 200 200 No. 4/0 AWG Stranded 1.2 (48)

— 300 300 300 250 kcmil 1.2 (48) — — 400 400 400 kcmil 1.2 (48) — — 600 — 600 kcmil 1.2 (48)

4.7.2 Distribution class expulsion type fuses, cutouts, and distribution class expulsion type fuse disconnecting switches

Crossarm-mounted, distribution class, expulsion type fuses, cutouts, and fuse disconnecting switches shall be mounted on a wood crossarm that measures 9 cm × 11 cm (3½ in × 4½ in) in cross section. The device mounting bracket shall be grounded by a lead attached to the mounting bracket on the side of the crossarm opposite the device. Devices designed for other types of mounting arrangements shall be mounted in their normal service positions, and the mounting structures shall be grounded.





4.7.3 Distribution class enclosed single-pole air switches

Distribution class enclosed single-pole air switches shall be mounted on a wood crossarm that measures 9 cm × 11 cm (3½ in × 4½ in) in cross section. The mounting bracket shall be grounded by a lead attached to it on the side of the crossarm opposite the switch.

4.7.4 Power class expulsion fuses, power class current-limiting fuses, and power class fuse disconnecting switches

Power class expulsion fuses, power class current-limiting fuses, and power class fuse disconnecting switches, shall be mounted on a rigid structure. The base shall be grounded.

4.7.5 Distribution class current-limiting fuses and fuse disconnecting switches

Distribution class current-limiting fuses and fuse disconnecting switches shall be mounted on a rigid structure. The base shall be grounded.

4.7.6 Distribution and power class fuses and fuse disconnecting switches used in FEPs

Distribution fuses, power class fuses, and fuse disconnecting switches used in FEPs shall be mounted in accordance with the fuse manufacturer’s specifications. The enclosure and base of the device, as applicable, shall be grounded.

4.7.7 Distribution and power class external fuses for shunt capacitors

4.7.7.1 Capacitor line fuses

Depending on the class and type of line capacitor fuse, it shall be mounted as specified in 4.7.2, 4.7.4, 4.7.5, or 4.7.6.

4.7.7.2 Capacitor unit fuses

For interrupting tests on expulsion and current-limiting capacitor unit fuses that automatically provide an isolating gap after operation, the fuses shall be mounted in the same manner as they would be used in a capacitor bank. An energized fuse shall be placed on each side of the fuse under test, in the normal service position, to determine that any expulsion gas or part movement does not reduce clearances or dielectric properties that might cause flashovers and, as such, cause operation of these adjacent fuses. Current-limiting fuses not having a disconnect or isolating feature may be mounted in any convenient manner. For temperature-rise tests, the mounting configuration shall simulate the capacitor bank configuration where the fuse is to be used and shall be such that it does not restrict or promote heat transfer in a manner different from service conditions.





5. Dielectric tests

5.1 General

Dielectric test procedures shall be as specified in Clause 4 and as described in Clause 5. Dielectric tests are performed to determine the power-frequency dry and wet dielectric withstand voltages, and withstand voltages, from an energized part to adjacent energized or grounded parts. They are performed to test a device’s dielectric properties from terminal to terminal (open gap) or from terminals to parts that may be grounded in service. This standard does not cover dielectric testing across a blown (or unblown) fuse of any type, or across a fuseholder without a fuse link installed, since no meaningful or useful data can be obtained with such tests. Any test of this type must be performed on the fuse in its mounting. The test should be configured so that the electrical stress on the fuse and mounting, which is created by mechanical structures of the mount, the spatial relationship between other phases, and sources of voltage and grounds, match the electrical stress that the device under test will experience in use. The manufacturer of the device under test should detail any restrictions on the location of any adjacent structures or ground. Any test summary or report should detail the locations of these associated parts. Dielectric tests for unit type capacitor fuses are dependent on the capacitor bank configuration and design and cannot be assigned to the fuse itself.

5.2 Measurement of test voltages

The voltage for dielectric tests shall be measured and corrected for standard conditions in accordance with IEEE Std 4-1995.

5.3 Description of power-frequency dry-withstand voltage tests

5.3.1 Application of test voltage

The test voltage specified, with appropriate atmospheric corrections, shall be applied to the device for 1 min. Seventy-five percent of the rated dry-withstand voltage may be applied in one step and then gradually raised to the required value in not less than 5 s and not more than 30 s.

5.3.2 Acceptance criteria

There shall be no flashover or damage to the insulating material.

NOTE—The terminal-to-terminal (open gap) required dielectric withstand values for some devices are 10% higher than those from terminal to ground. However, successful completion of these gap tests does not ensure that a device, when open, will flashover to ground instead of across the open gap.





5.4 Description of power-frequency wet-withstand voltage tests on outdoor devices


The test voltage specified, with appropriate atmospheric corrections, shall be applied to the device per IEEE Std 4-1995. Corrections for relative humidity shall not be made on wet-withstand tests. Seventy-five percent of the rated wet-withstand voltage may be applied in one step and then gradually raised to the required value in not less than 5 s and not more than 30 s.

5.4.2 Application of test precipitation

Precipitation shall be applied per IEEE Std 4-1995. Due to long field experience, the conventional procedure, practice in the United States for precipitation conditions, is acceptable for devices tested according to this standard. If testing per this procedure, the water shall be projected downward toward the front of the device and at an angle of 45º from the vertical, so that the spray strikes equally on the front and on one sidewall of the device. The standard test procedure defined by IEEE Std 4-1995 is also fully acceptable for the purposes of meeting this standard, at the manufacturer’s option.



5.5 Description of power-frequency dew-withstand voltage tests on indoor devices

5.5.1 Dew test procedure

The insulation of the device shall be thoroughly cleaned. The cleaned device shall be placed in a cold chamber (refrigerator) having a temperature of –10 ºC to –15 ºC until it is thoroughly cooled (may take 10 h to 12 h). The device shall then be mounted in a test chamber having a normal temperature of 22 ºC to 25 ºC and a humidity of approximately 100%. When the device is completely covered with dew, the test voltage as specified in 5.5.2 shall be immediately applied.


The test voltage specified, with appropriate atmospheric corrections, shall be applied to the device for 10 s. Corrections for relative humidity shall not be made on dew-withstand tests. Seventy-five percent of the rated dew-withstand voltage may be applied in one step and then gradually raised to the required value in not less than 5 s and not more than 30 s.



5.6 Description of impulse withstand voltage tests

5.6.1 Impulse test voltage wave shape

The wave shape and application of the 1.2/50 μs full-wave test voltage is described in IEEE Std 4-1995 and shall have the following limits for design tests.





The impulse test wave shall have a virtual front time less than or equal to 1.2 μs, a crest voltage greater than or equal to the rated full-wave impulse withstand voltage, and a time, from initiation, of at least 50 μs for the voltage to fall to 50% of the crest value.

It may be noted that in the event that laboratory limitations are encountered due to the capacitance of the test device, the maximum rise achievable may be used if it is mutually acceptable to the user and the manufacturer.

5.6.2 Polarity of voltage for impulse withstand tests

The device being tested shall be capable of passing this test with voltages of both positive and negative polarity. Where there is evidence that one polarity (usually the positive) will consistently produce lower withstand voltages on this or similar equipment, it is acceptable to test using only that polarity.


Three consecutive impulses of the test voltage specified, with appropriate atmospheric corrections, shall be applied to the device.


If no disruptive discharge occurs during any of the three consecutive impulses, then the device has passed the test. If more than one disruptive discharge occurs, then the device has failed the test. If one disruptive discharge occurs, then nine additional impulses of the test voltage specified are applied, and if no disruptive discharge occurs, then the device has passed the test. If failure occurs in a non-self-restoring part of the insulation, then the device has failed the test.

NOTE—The terminal-to-terminal (open gap) required dielectric withstand values for some devices are 10% higher than those from terminal to ground. However, successful completion of these gap tests does not ensure that a device, when open, will flashover to ground instead of across the open gap.

5.7 Distribution class expulsion type fuses, cutouts, and fuse disconnecting switch test connections and test values

5.7.1 Test conductor arrangement

The bare wires shall project horizontally, at least 30 cm (12 in) from the terminals in a straight line approximately parallel to the face of the crossarm or steel structure, and in such a manner as to not decrease the withstand value. Any necessary bends may be made at the terminals. For enclosed cutouts, the bare wires shall be located approximately in the center of the entrance holes.

5.7.2 Terminal-to-ground tests

For terminal-to-ground tests, the fuse holder, including the conducting element (fuse link or equivalent), shall be in the closed position. The test lead connection shall be made to one of the wires projecting from the terminals. The fuse mounting bracket shall be grounded.

5.7.3 Terminal-to-terminal tests

For terminal-to-terminal tests, the fuse holder, including the conducting element (fuse link or equivalent), shall be in the open position. The test lead connection shall be made to the wire projecting from the upper terminal. The ground test lead connection shall be made to the wire projecting from the lower terminal. The mounting bracket shall not be grounded.

5.7.4 Dielectric test values





The preferred dielectric test values for distribution open, enclosed, and open-link cutouts and fuses are listed in ANSI C37.42.

5.8 Distribution class enclosed single-pole air switch test connections and test values


The bare wires shall project horizontally at least 30 cm (12 in) from the terminals in a straight line approximately parallel to the face of the crossarm or steel structure, and in such a manner as to not decrease the withstand value. Any necessary bends may be made at the terminals.


For terminal-to-ground tests, the switch blade shall be in the closed position. The test lead connection shall be made to one of the wires projecting from the terminals. The frame of the switch shall be grounded.


For terminal-to-terminal tests, the switch blade shall be in the open position. The test lead connection shall be made to the wire projecting from the upper terminal. The ground test lead connection shall be made to the wire projecting from the lower terminal. The frame of the switch shall not be grounded.


The preferred dielectric test values for distribution enclosed single-pole air switches are listed in IEEE Std C37.45.

5.9 Power class expulsion fuses, power class current-limiting fuses, and power class fuse disconnecting switch test connections and test values


The conductors shall project from the terminals of the fuse in (substantially) a straight line parallel to the fuse unit or fuse holder for an unsupported distance of at least the break distance of the fuse.


For terminal-to-ground tests, the fuse unit or fuse holder, including the conducting element (fuse link or equivalent), or the disconnecting switch blade, shall be in the closed position. The test lead connection shall be made to one of the wires projecting from the terminals. The base shall be grounded.


For terminal-to-terminal tests, the fuse unit, fuse holder, or switch blade shall be in one of the following positions:

a) For fuse disconnecting switches, the fuse unit, fuse holder, or switch blade in the fully open position

b) For dropout power fuses, with the fuse holder or fuse unit in the dropout position

c) For non-dropout power fuses, with the fuse holder or fuse unit removed from the support





The high-voltage test lead shall be connected to the wire protruding from the upper terminal, and the ground lead shall be attached to the wire projecting from the lower terminal. The base shall not be grounded. A power fuse or fuse disconnecting switch rated 72.5 kV and above shall be equipped with standard strength insulator units; one or more insulator units identical to those supporting the current-carrying parts shall be added to each of the insulator supports or columns (only for the test). A power fuse or fuse disconnecting switch rated 48.3 kV or below shall be mounted with its base insulated from a grounded metal structure by means of insulator units identical to those assembled on the fuse. In the case of a rear-connected indoor power fuse bus, support insulators of equivalent electrical characteristics shall be used to support the base (only for the test).


The preferred dielectric test values for all types of indoor and outdoor power fuses are listed in ANSI C37.46.

5.10 Distribution class current-limiting fuse and fuse disconnecting switch test connections and test values


The conductors shall project from the terminals of the fuse in substantially a straight line parallel to the fuse unit or fuse holder for an unsupported distance of at least the break distance of the fuse.


For terminal-to-ground tests, the fuse unit or fuse holder, including the conducting element (fuse link or equivalent), or the disconnecting switch blade, shall be in the closed position. The test lead connection shall be made to one of the wires projecting from the terminals. The base shall be grounded.


For terminal-to-terminal tests, the fuse unit, fuse holder, or switch blade shall be in one of the following positions:

a) For fuse disconnecting switches, the fuse unit, fuse holder, or switch blade in the fully open position

b) For dropout current-limiting fuses, with the fuse holder or fuse unit in the dropout position

c) For non-dropout current-limiting fuses, with the fuse holder or the fuse unit removed from the support

The high-voltage test lead shall be connected to the wire protruding from the upper terminal, and the ground lead shall be attached to the wire projecting from the lower terminal. The base shall not be grounded.


The preferred dielectric test values for distribution current-limiting fuses are listed in ANSI C37.47.





5.11 Distribution class, power class expulsion and current-limiting type fuses, and fuse disconnecting switches used in FEPs

5.11.1 General

When distribution class and power class expulsion or current-limiting type fuses are used in FEPs, dielectric testing of the complete FEP is required.

5.11.2 Arrangement

All fuses and other apparatus in the enclosure shall be mounted in their normal locations; the conductors shall be in their normal positions and of the size normally used in that enclosure. If the enclosure uses liquid or a gas other than air for the insulating medium, then it should be filled in accordance with the manufacturer’s specifications.


a) For terminal-to-ground tests, the fuse unit(s), fuse holder(s), or the disconnecting blade(s) shall be in the closed position.

b) Where a fuse link, fuse unit, or refill unit is required to complete the electrical circuit, it may be of any convenient size.

c) The base and the enclosure, if applicable, shall be grounded.

d) For multipole devices, all poles shall be tested. They may be energized simultaneously or separately (one at a time).

e) For devices that can be opened with a part left inserted and hanging in the opened position, an additional test shall be performed. For this test, energize the appropriate terminal(s) that will energize the part(s) that is (are) hanging in the open position. Condition b) through condition d) are applicable for this test.


a) For terminal-to-terminal tests, the fuse unit, fuse holder, or disconnecting blade shall be in one of the following positions:

1) For fuse disconnecting switches, the fuse unit, fuse holder, or disconnecting blade in the fully open position

2) For dropout-type fuses, with the fuse unit or fuse holder in the dropout position

3) For non-dropout-type fuses, with the fuse unit or fuse holder removed from the support


c) The base or the enclosure, if applicable, shall not be grounded. It may be necessary to insulate the enclosure from ground when the open gap dielectric value exceeds the terminal-to-ground value.

d) For multipole devices, all poles may be energized simultaneously.





e) The terminal(s) to be energized are as follows:

1) Incoming terminal(s) with outgoing terminal(s) grounded

2) Outgoing terminal(s) with incoming terminal(s) grounded

If the device is completely symmetrical, only test 1) is required.

5.11.5 Closed-position, pole-to-pole (phase-to-phase) tests for multipole devices

a) For pole-to-pole closed-position tests, the fuse unit(s), fuse holder(s), or disconnecting blade(s) shall be in the closed position.


c) The base and the enclosure, if applicable, shall not be grounded. It may be necessary to insulate the enclosure from ground when the pole-to-pole dielectric value exceeds the terminal-to-ground value.

d) One pole at a time shall be energized with all other poles grounded. For three-pole devices, if the outer poles are symmetrical with respect to the center pole, then testing of only one outer pole and the center pole is required.

5.11.6 Open-position, pole-to-pole (phase-to-phase) tests for multipole devices

a) For pole-to-pole open-position tests, the fuse unit, fuse holder, or disconnecting blade shall be in one of the following positions:

1) For fuse disconnecting switches, in the fully open position

2) For dropout-type fuses, with the fuse unit or fuse holder in the dropout position

3) For non-dropout-type fuses, with the fuse unit or fuse holder removed from the support


c) The base and the enclosure, if applicable, shall not be grounded. It may be necessary to insulate the enclosure from ground when the pole-to-pole dielectric value exceeds the terminal-to-ground value.

d) Taking one pole at a time, each end shall be energized separately, with all other poles on that end grounded. For three-pole devices, if the outer poles are symmetrical with respect to the center pole, then testing each end of only one outer pole and each end of the center pole is required.


The preferred terminal-to-ground, terminal-to-terminal, and pole-to-pole test values for all types of power class fuses are specified in ANSI C37.46. The preferred terminal-to-ground, terminal-to-terminal, and pole-to-pole test values for all types of distribution class current-limiting fuses are specified in ANSI C37.47. For all distribution class expulsion type fuses, the values are specified in ANSI C37.42.





5.12 Distribution and power class external fuses for shunt capacitors

5.12.1 Capacitor line fuses

Capacitor line fuses shall be tested per the requirements for the appropriate equipment, as specified in 5.7, 5.9, 5.10, or 5.11.

5.12.2 Capacitor unit fuses

Capacitor unit fuses are normally mounted on the bus of the capacitor bank, or sometimes on one of the bushings of the capacitor. The dielectric strength of the system is determined by the insulation level of the bus of the capacitor bank, the capacitor bushing, and/or the way the fuse is positioned in the system. The dielectric strength of a capacitor unit fuse cannot be evaluated without consideration of the mounting arrangement.

6. Interrupting tests

6.1 Procedures common to all interrupting tests

6.1.1 General

Interrupting test procedures shall be as specified in Clause 4 and as described in Clause 6.

6.1.2 Test circuit

6.1.2.1 Test circuit configuration

The interrupting tests shall be made using a single-phase, alternating-current circuit. The circuit elements used to control the current and X/R ratio shall be in series with each other and the fuse. The testing circuit frequency shall be the rated frequency ±2 Hz. If 60 Hz test facilities are not available, then tests at 50 Hz ± 2 Hz are acceptable for verifying 60 Hz ratings. Note that 50 Hz tests may produce lower peak let-through currents but may let through more I2t than 60 Hz tests. The parameters of the test circuits and other testing information are specified in Table 6 through Table 20 and the associated clauses. The current applied to a tested device is specified as a prospective or test current. These current parameters given in Table 6, Table 7, Table 8, Table 11, Table 14, Table 17, Table 19, and Table 20 are expressed in symmetrical amperes. However, the test circuit will provide a symmetrical or associated asymmetrical short-circuit current, depending on the making angle, as required by the appropriate table. Where an asymmetrical current is produced, it shall be equal to or greater than the asymmetrical current associated with the symmetrical current and X/R ratio specified in the appropriate table (see Figure C.1). If tests are made at an X/R ratio higher than is specified in the appropriate table, then the test duty may be more severe, because the prospective asymmetrical current will be equal to or greater than the asymmetrical current associated with the symmetrical current and specified X/R ratio. However, it is not permissible to decrease the prospective symmetrical current to achieve the proper asymmetrical current value. Typical test circuits are shown in Figure D.1. Methods of determining transient recovery voltage (TRV) parameters are also shown in Annex D. Overvoltage protective equipment used for protecting test circuit apparatus shall not significantly affect the current through the fuse or the recovery voltage across the fuse.





6.1.2.2 Determination of the X/R ratio and the prospective or test current of the test circuit

6.1.2.2.1 X/R and prospective current for short-duration tests

To determine the X/R ratio and prospective short-circuit current of the test circuit, the device to be tested shall be replaced or bypassed in the test circuit with a connection having negligible impedance, thereby creating a “bolted fault” condition. Where the interrupting tests involve short melting times (i.e., less than or equal to 1.5 cycles), both the X/R ratio and the prospective symmetrical short-circuit current may be determined as follows. To determine the symmetrical short-circuit current, power shall be applied at the point on the voltage wave that minimizes the offset in the first loop (i.e., power should be applied at an angle approximately equal to the value of the arctan [X/R] with respect to voltage zero, where X/R is the estimated X/R ratio of the test circuit). The symmetrical current may be calculated in accordance with Figure A.1. The root-mean-square (rms) current should be measured during the first cycle of current. To determine the X/R of the circuit, an asymmetrical prospective current is required. X/R can then be obtained from the ratio of the peak asymmetrical current (of a fully asymmetrical current) to the rms symmetrical current, using Figure C.1, or by appropriate equivalent digital analysis.

6.1.2.2.2 X/R and test current for long-duration tests

Where the interrupting tests involve long melting times (i.e., greater than 1.5 cycles), it may be appropriate to use alternate methods to determine the circuit X/R ratio and test current. For these tests, the test current may be taken as the prospective current (measured per 6.1.2.2.1) if the melting time is still quite short or the rms value of the current measured immediately prior to the initiation of arcing. The reason for measuring the actual circuit current during the test rather than the prospective current (i.e., with the test device replaced by a link of negligible impedance) is that heating of circuit components or other factors may result in a lower actual current at device melting than the current measured during a practical-duration bolted fault current test. It should be noted that when the alternate test method for test series 3 tests on current-limiting fuses is used (6.6.2), the “melting time” for determining the X/R and test current is from the time when the high-voltage current starts to flow to the time when the fuse melts. If the fuse begins to arc immediately (i.e., the elements have melted before changeover occurs), then the current shall be taken as the prospective current (see 6.1.2.2.1).

6.1.2.3 Application of test power

The device shall be tested in the circuit described in 6.1.2.1 and 6.1.2.2, with the negligible impedance connection removed. Power shall be applied at a point on the voltage wave that produces the conditions specified in the appropriate table covering the particular device being tested.

6.1.2.4 Recovery voltage

After current interruption, the power-frequency recovery voltage shall be maintained across an open device for the duration specified in Table 6, Table 7, Table 8, Table 11, Table 14, Table 17, and Table 19. Where test station limitations make it difficult for the full value of recovery voltage to be maintained for specified durations longer than 10 s, the test circuit may be switched to an auxiliary source. Such changeover shall not be made until a time of at least 10 s has elapsed from current interruption. Any necessary circuit interruption to





effect this changeover shall not exceed 0.2 s duration. The auxiliary source shall be capable of supplying a current of at least 1 A, while maintaining the specified recovery voltage, for the remainder of the specified duration. Any breakdown of the fuse during this voltage-holding period (i.e., an increase in leakage current through the fuse to 1 A or more) shall be considered an unsuccessful fuse interruption. Current monitoring may be by any convenient method. One acceptable method is to set the tripping level of a circuit breaker, used to protect the auxiliary source, to approximately 1 A. If additional resistance and/or reactance is switched into the test circuit after device interruption to monitor leakage current and/or reduce the severity of effects resulting from a device failure during the voltage maintenance period, such switching may occur at any convenient time after current interruption, providing there is no interruption in the recovery voltage. If there is an interruption, switching shall not occur before 10 s has elapsed from current interruption, and any necessary circuit interruption to effect this changeover shall not exceed 0.2 s duration. If impedance is added to the circuit after current interruption, the voltage across the tested device must be monitored and must remain above the device’s rated maximum voltage for the recovery voltage period.


The condition of the device after interrupting tests shall be as specified in 4.5.

6.2 Interrupting tests on a homogeneous series of expulsion type fuses

6.2.1 Information common to all devices

6.2.1.1 General information

The types of devices that are covered by 6.2 are devices that use replaceable components such as fuse links, fuse units, or fuse refill units. The devices that use replaceable fuse links are distribution class fuses, fuse cutouts, liquid immersed fuses, some types of power class fuses, and some types of expulsion type capacitor fuses. The devices that use replaceable refill units or replaceable fuse units are some types of power class fuses and some types of capacitor fuses. All of these devices are fuses, so for brevity, if the text covers all of these devices in a particular category(s), the term “fuse” will be used except when the information relates to a specific device. The performance of the whole device is a function of the interaction of reusable and replaceable components, and the performance tests specified in this standard cover the specific combinations of components tested. Successful performance of other combinations cannot necessarily be implied from these tests, so it is important that the specific components tested be noted (for example in test reports). When a group of fuse current ratings meet the requirements of a homogeneous series, as defined in this standard, homogeneous series testing requires that only certain ratings be tested to qualify all other ratings in the series. This is particularly significant in the case of expulsion fuses that use replaceable links, since the variety of links that can be used in a particular fuse can be very large. Although protective performance of certain specific combinations of a fuse and fuse link can only be assured by the testing performed on this combination, use of the homogeneous rules as specified in the text, tables, and table notes of this standard can significantly reduce the necessity for performing, what could be, a prohibitively large number of tests. It should be noted that, while some fuse links may have mechanical interchangeability as defined in ANSI C37.42, only by a knowledge of the homogeneous requirements and the testing that has been performed can a manufacturer determine whether a particular fuse link is suitable for use in a particular device. Distribution class fuses or power fuses that differ in design from those previously tested only in their insulators (to increase or decrease their dielectric properties) may require testing but only at the high current levels (above the 400 A to 500 A test) specified in the table.





It should be noted that interrupting tests alone do not qualify that a device is suitable for field service. Other tests specified in this standard, plus other tests deemed necessary by a manufacturer to ensure proper field performance, may be required.

6.2.1.2 Devices that use replaceable fuse links

For devices that use replaceable fuse links, testing as specified in this standard is normally performed by the manufacturer of the fuse, using their own replaceable fuse link or other fuse links that they accept as being satisfactory for use in their device. Additionally, when a fuse consists of a fuse support and a fuseholder that uses replaceable fuse links, the same manufacturer usually makes both. However there are some cases where the manufacturer of replaceable fuse links will wish to demonstrate the suitability of such links for use in another manufacturer’s fuse. Such testing is done solely by the link manufacturer, who has total responsibility for the performance of that fuse link and fuse combination. Changes to the fuse or the replaceable fuse link may require retesting, as specified in 3.1. If changes to a fuse are made that could affect the performance of a link, the user, when informed of these changes, shall inform the link manufacturer of such changes. It is then the responsibility of the fuse link manufacturer to assess the impact of the changes on the overall performance of the combination, and to perform such additional testing as is necessary to demonstrate that the new combination is satisfactory. Again, these performance tests cover the specific combinations used, and successful performance of other combinations cannot be implied from the tests. However, after the specified testing and with certain other limited testing and/or examination of the relevant fuse links, the manufacturer of a fuse may be able to determine:

Whether other types of fuse links made by them, or a different manufacturer, are acceptable for use in their device (i.e., fuse links not type “K” and “T”)

Whether another manufacturer’s fuse links are acceptable for use in their device (of the same type e.g., ”K” or “T”)

Whether the tested fuse links are acceptable for use in other devices they manufacture

The manufacturer of a fuse listed in 6.2.1 may use the following characteristics for qualifying fuse links for these situations:

a) They use the same materials and construction techniques as the tested K and T fuse links.

b) The element mass is equal to or greater than the minimum fuse link of the homogeneous series tested and equal to or less than the maximum fuse link of the homogeneous series tested.

c) The number of conductors used to complete the electrical circuit between the fusible element and the remaining parts of the device shall be the same as used in the tested fuse links. In addition, the cross section shall be the same as the tested links.

d) The distance between the element’s attachment points is equal to or more than 0.75 times the shortest element attachment spacing of the K and T link series tested and is equal to or less than 1.33 times the longest element attachment points spacing tested.

e) The speed ratio of the other type of link(s) falls somewhere within the K and T boundaries specified in ANSI C37.42.

If these conditions are not met, the fuse links need to be tested in the particular fuse. Fuses that use replaceable fuse links work as a system in which the main bore of the fuseholder interrupts the higher currents and the fuse link’s tube interrupts the lower currents. The specified test series may need to be augmented by additional tests to prove correct operation in the region(s) of current where the interrupting duty is transferred from one interrupting mechanism to another. Because fuse designs differ widely, specifying test requirements applicable to all designs is not possible. However, the general criterion to be observed is to test in the region where the low current interrupter sees a maximum interrupting current, and the high current





interrupter sees a minimum interrupting current. The interrupting mechanisms shall be shown to operate correctly to effect proper interruption within this transitional current region. For many fuse links 50 A and less, the maximum current for the fuse link may be the 400 A to 500 A test specified. For other link sizes and fuse links designed for special applications, the maximum current may be considerably higher. Devices that use replaceable fuse links shall be capable of operating with the lowest current rated fuse link that is recommended for use in the fuseholder. Frequently, laboratory limitations do not allow very small fuse links to be tested to the requirements of this standard, and a 6 K fuse link will normally prove to be adequate to demonstrate the satisfactory performance of fuses with fuse links having lower current ratings. Other testing and checks of the fuse links construction may be used to verify the ability of these small fuse links to operate properly and interrupt the circuit.

6.2.1.3 Devices that use replaceable fuse units or refill units

For devices that use replaceable components such as fuse units or refill units, testing as specified in this standard is normally performed by the manufacturer of the fuse, using their own replaceable components or other replaceable components that they accept as being satisfactory for use in their device. Additionally, when a fuse consists of a fuse support and a fuseholder that uses replaceable components, the same manufacturer usually makes both. However, there are some cases where the manufacturer of replaceable components will wish to demonstrate the suitability of such components for use in another manufacturer’s fuse. Such testing is done solely by the component manufacturer, who has total responsibility for the performance of that component and fuse combination. Changes to the fuse or the replaceable component may require retesting. If changes to a fuse are made that could affect the performance of a component, then the user, when informed of these changes, shall inform the component manufacturer of such changes. It is the responsibility of the component manufacturer to assess the impact of the changes on the overall performance of the combination and to perform such additional testing as is necessary to demonstrate that the new combination is satisfactory. Again, these performance tests cover the specific combinations used, and the successful performance of other combinations cannot be implied from the tests. However, after the specified testing and with certain other limited testing and/or examination of the relevant fuse components, the manufacturer of a fuse may be able to determine:

Whether other types of components made by them or a different manufacturer are acceptable for use in their device (i.e., other types of fuse units or refill units)

Whether another manufacturer’s components are acceptable for use in their device

Whether the tested components are acceptable for use in other devices they manufacture

The manufacturer of the fuse devices listed in 6.2.1 may use the following characteristics for qualifying fuse units and refill units for these situations:

a) They use the same materials and construction techniques as the tested fuse units or refill units.

b) The element mass is equal to or greater than the smallest fuse of the homogeneous series tested and equal to or less than the maximum fuse of the homogeneous series tested.

c) The number of conductors used to complete the electrical circuit between the fusible element and the remaining parts of the device shall be the same as used in the tested components. In addition, the cross section shall be the same as the tested components.

d) The distance between the element’s attachment points is equal to or more than 0.75 times the shortest element attachment spacing of the smallest component tested and is equal to or less than 1.33 times the longest element attachment points spacing tested.

If these conditions are not met, then the fuse units or refill units need to be tested in the particular fuse.





6.2.2 Testing requirements

Testing performed in accordance with 6.4, 6.5, and 6.8, if appropriate, shall be made in accordance with the rules for a homogeneous series as specified in 6.2.3 and 6.2.4 and the appropriate table notes. Table 3 covers devices that use replaceable fuse links originally intended for use in fuse cutouts but that are now also used in other types of fuses. In a homogeneous series of expulsion type fuses, interrupting tests on a fuse that uses these fuse links need only to be made in accordance with Table 3. Tests for liquid-submerged expulsion fuses need only to be made in accordance with Table 4, and tests for power fuses that use replaceable refill units or replaceable fuse units need only to be made in accordance with Table 5.

6.2.3 Rules for determining a homogeneous series for devices that use replaceable fuse links

6.2.3.1 Homogeneous series compliance

These devices are considered as forming a homogeneous series when their characteristics comply with the following:

a) Fuse links shall be made by the same manufacturer.

b) Rated voltage, rated interrupting current, and frequency shall be the same.

c) All materials used in the devices shall be the same, except that different sized fuses or fuse links may use different element diameters and lengths for the fusible element, and the leader or leaders may be different (a leader is a flexible conductor used to complete the electrical circuit between the fusible element section and the conductor’s termination on the fuse, or fuseholder). However, the winding techniques for this(these) leader(s) shall be the same.

d) The bore diameter and length of the areas that facilitate the high current-interrupting process for the fuse or fuseholder shall be the same. All other dimensions of the fuse, or fuseholder, shall be the same.

e) All materials used in the fusible element designs shall be of the same type. Fuse links with different element designs or construction techniques require additional testing.

f) Any mechanical means that aids in the arc interruption process must be the same.

When determining compliance with the properties of a device for homogeneous series, any strain wire that is connected in parallel with the fuse element in order to relieve it of tensile strain can be ignored if the strain wire is sized, and of a material, such that it carries a negligible amount of current at the fuse’s rated current.

6.2.3.2 Fuse link sizes to be used for testing these devices

Experience has shown that for distribution fuses, fuse cutouts, and power class fuses, which use replaceable links as specified in Table 3, testing using a homogeneous series defined as follows will demonstrate the suitability of all K and T ratings smaller than the maximums listed:

a) The minimum current rating of fuse links for 50 A and 100 A rated fuses, fuse cutouts, and power fuses is a 6 K fuse link, and for 200 A rated devices, it is a 140 K fuse link.

b) The maximum current rating of fuse links for 50 A rated devices is a 50 T fuse link, for 100 A rated devices it is a 100 T fuse link, and for 200 A rated it is a 200 T fuse link.

The manufacturers of distribution class fuses or power fuses that do not produce K and T links may qualify their device with another manufacturer’s K and T links or by using other types of fuse links they do manufacture and testing the smallest fastest link they make and the largest slowest link they make that use the same construction techniques as typical of most K and T fuse links. If the link sizes used do not correspond to the current ratings specified (e.g., 6 A and 100 A links for a 100 A fuse), then the fuse sizes used shall be noted in the test report and the manufacturer’s literature.





Other types of links, having significantly different designs and ratings than the specified K and T links, may require additional testing, as agreed upon between the user and the manufacturer.

6.2.3.3 Fuse sizes to be used for testing liquid-submerged expulsion fuses

Experience has shown that for the liquid-submerged expulsion fuses specified in Table 4, testing using a homogeneous series defined as follows will demonstrate the suitability of all ratings smaller than the maximum tested. Furthermore, for liquid-submerged expulsion fuses that use replaceable fuse links, the testing will show that other types of links than those tested are suitable for use, providing they are produced by the same manufacturer, and the only difference between the tested links and the other types is the diameter and length of the element. Only the fuse manufacturer can determine whether another manufacturer’s fuse link is suitable for their device (see 6.2.1):

a) The minimum current rating of fuse, or fuse and fuse link, for testing at test series 1 and 2 is the smallest fuse link produced by the manufacturer.

b) The maximum current rating of fuse, or fuse and fuse link, for testing at test series 1 is the largest fuse link produced by the manufacturer.

Table 3 —Homogeneous series test requirements for expulsion fuses that use replaceable fuse links

Type of fuse C37.41

Test table number

Test series Fuse units to be tested

Minimum current rating

Maximum current rating

Single-voltage rated distribution class fuses and fuse cutouts

Table 7 1,2,3 X X

4,5 X Slant-voltage rated distribution class fuses and fuse cutouts

Table 8 1,2,3,6 X X

4,5 X

Power class fuses Table 11 1,2,3,4 X X

5,6 X

Capacitor line fuses—inductive currentsa

Table 7 Table 8

Table 11

1 ,2 ,3 1,2,3,6 1,2,3,4

X X

Capacitor line fuses—capacitive currents Table 19 3,

4 X X

Capacitor unit fuses—inductive currentsa

Table 7 Table 11

1,2,3

1,2,3,4 X X

Capacitor unit fuses—capacitive currents Table 19 1,

2 X X aSee 6.10.2 for devices requiring this test.





Table 4 —Homogeneous series test requirements for liquid-submerged expulsion fuses

Type of fuse C37.41 Test table number

Test series

Fuse units to be tested



Liquid-submerged expulsion fuses Table 17

1 X X

2 X

6.2.4 Rules for determining a homogeneous series for devices that use a replaceable refill unit or a replaceable fuse unit

6.2.4.1 Homogeneous series compliance

These types of devices normally have the higher current-interrupting areas and the lower current-interrupting areas contained within the fuse, fuseholder, or the refill unit. For these tests, power fuses are considered as forming a homogeneous series when their characteristics comply with the following:

a) All components shall be made by the same manufacturer.

b) Rated voltage, rated interrupting current, and frequency shall be the same. All materials used in the devices shall be the same, except that different current rated devices may use different diameters and lengths for the fusible element.

c) The conductors used to complete the electrical circuit between the fusible element and the remaining parts of the device shall be the same number as the device tested. In addition, the cross section shall be the same as the device tested.

d) All materials and dimensions of components involved in the interrupting process shall be the same.

e) Any mechanical means that aids in the arc interruption process must be the same.

6.2.4.2 Fuse sizes to be used for devices that have a replaceable refill unit or a replaceable fuse unit

These devices have either an integral element within the fuse unit or have a replaceable fuse refill unit within the fuseholder. Experience has shown that for the types of power fuses that use replaceable fuse units or replaceable refill units as specified in Table 5, testing using a homogeneous series defined as follows will demonstrate the suitability of all ratings smaller than the maximum:

a) The minimum current rating of fuse, or fuse with a refill unit, for testing at test series 1 through 6 is the smallest fuse or fuse refill unit produced by the manufacturer.

b) The maximum current rating of fuse, or fuse with refill unit, for testing at test series 1 through 4 is the largest fuse or refill unit produced by the manufacturer.

When a group of fuses have been tested using the homogeneous series rules, additional units that vary in only certain aspects from the tested design (for example, in a fuse employing separate high current and low current mechanisms, where one is different but the other is not) may not require a full series of tests. In this case, for example, a fuse may be part of one homogeneous series for test series 1 through 4, and a different homogeneous series for tests 5 and 6.





Table 5 —Homogeneous series test requirements for power class expulsion fuses that use replaceable fuse units or replaceable refill units

Type of fuse C37.41

test table number

Test series Fuse units to be tested



Power class fuses Table 11 1, 2, 3, 4 X X

5, 6 X Capacitor line fuses—inductive currentsa Table 11 1, 2, 3, 4 X X

Capacitor line fuses—capacitive currents Table 19 3, 4 X X

aSee 6.10.3 for devices requiring this test.

6.3 Description of interrupting tests on distribution class open-link cutouts

Tests shall be made at the rated maximum voltage in accordance with Table 6. A description of the required test series is as follows:

Test series 1: Verification of fuse operation with prospective currents equal to its rated interrupting current.

Test series 2: Verification of fuse operation with small overload currents.

6.4 Description of interrupting tests on distribution class fuse cutouts (open and enclosed) (except current-limiting fuses)

6.4.1 Test series for single-voltage-rated fuse cutouts

Tests shall be made at the rated maximum voltage in accordance with Table 7. Fuses that form a part of a homogeneous series require only the interrupting tests as specified in 6.2 and associated Table 3. A description of the required test series is as follows:

Test series 1: Verification of fuse operation with prospective currents equal to its rated interrupting current.

Test series 2: Verification of fuse operation with the prospective currents ranging from 70% to 80% of its rated interrupting current.

Test series 3: Verification of fuse operation with prospective currents ranging from 20% to 30% of its rated interrupting current.

Test series 4: Verification of fuse operation with prospective currents in the range of 400 A to 500 A.

Test series 5: Verification of fuse operation with small overload currents.





Table 6 —Interrupting performance tests and test circuit parameters for distribution class open-link cutouts

Parameters Test series 1a 2a

Power-frequency recovery voltage Rated maximum voltage: +5%, −0% TRV — See Footnote b

Prospective (available) current— rms symmetrical Rated interrupting current +5%, −0% From 2.7 to 3.3 times fuse link ratingc

X/R ratio (power factor) Not less than 1.33 (not more than 0.60) From 0.75 to 1.33 (from 0.80 to 0.60) Making angle related to voltage zero—degrees Random timing

Allowable shunt capacitance A lumped capacitance not exceeding 0.65 µF may be shunted across the fuse. —

Current rating of fuse link Mind Maxd Mind Number of tests 3 3 2 Number of tests on each cutoute 3 3 2 Duration of power-frequency recovery voltage after interruption Not less than 0.5 s a Prior to 1999, a sufficient number of tests were to be made at maximum rated voltage to satisfy the interrupting requirements, using

the X/R ratio and allowable shunt capacitance values that are given in the table for test series 1. Based on current understanding, the additional tests represent the minimum requirements for adequate testing of a new device that does not have the benefit of extensive field experience.

bThe TRV for this test circuit shall be critically damped. Shunting the load reactance with a resistance having a value equal to approximately 40 times the value of the reactance is usually adequate to critically damp the circuit. However, if this value does not result in critical damping, the resistance may be reduced to achieve critical damping. For testing convenience, an oscillatory TRV may be acceptable with the agreement of the manufacturer. Critical damping is obtained when

XffR

no

2=

where fo is the natural frequency of the test circuit without damping fn is the power frequency X is the reactance of the circuit at power frequency cIf the test involves a melting time appreciably higher than 2 s, then the current may be increased to obtain a melting time of approximately 2 s. dThe minimum fuse link rating is 6 K, and the maximum fuse link rating is 50 T; if not available, any available 6 A and 50 A fuse link

is acceptable. eAfter each test, only the parts that are normally field replaceable shall be replaced.





Table 7 —Interrupting performance tests and test circuit parameters for single-voltage-rated distribution class fuse cutouts (except current-limiting fuses and open-link cutouts)

Parameters Test series

1 2 3 4 5 Power-frequency recovery voltage

Rated maximum voltage: +5%, −0%

TRV See Table 9, column 1 See Table 9, column 3

See Footnote a

Prospective or test current—rms symmetrical

Rated interrupting current +5%, −0%:

From 70% to 80% rated interrupting

current

From 20% to 30% rated interrupting

currentb

From 400 A to 500 Ac

From 2.7 to 3.3 times fuse link

ratingd X/R ratio (power factor) See Table 10 From 1.3 to 0.75

(from 0.6 to 0.8) Making angle related to voltage zero—degrees

1st test: from −5 to +15 2nd test: from 85 to 105 3rd test: from 130 to 150

From 85 to 105 Random timing

Fuse link ratinge Min Max Min Max Min Max Min Min Number of tests required with above fuse link ratingf 3 3 3 3 1 1 2 2

Number of tests required on each fuseholder and fuse supportf

3 3 3 3 2 4

Number of fuseholders to be testedf 1 1 1 1 1 1

Number of fuse supports to be testedf 1 1 1 1 1 1

Duration of power frequency recovery voltage after interruption

Dropout fuses Not less than 0.5 s

Nondropout fuses Not less than 0.5 s

a The TRV for this test circuit shall be critically damped. Shunting the load reactance with a resistance having a value equal to approximately 40 times the value of the reactance is usually adequate to damp the circuit critically. However, if this value does not result in critical damping, then the resistance may be reduced to achieve critical damping. For testing convenience, an oscillatory TRV may be acceptable with the agreement of the manufacturer. Critical damping is obtained when

XffR

no

2=

where fo is the natural frequency of the test circuit without damping fn is the power frequency X is the reactance of the circuit at power frequency b For cutouts with an interrupting rating of 2.8 kA or less, test series 3 need not be made. c For cutouts rated at 200 A, test series 4 need not be made. d If the test involves a melting time appreciably higher than 2 s, the current may be increased to obtain a melting time of approximately 2 s. e “Min” and “max” represent the minimum and maximum rated currents of a homogeneous series; see 6.2. f A fuse cutout support [fuse base] shall be capable, at a minimum, of the number of tests listed as “Number of tests required on each fuseholder and its fuse support.” For test series 1, this represents three tests with the minimum fuse link rating using one fuseholder and support, and three tests with the maximum fuse link rating using another fuseholder and support. The same quantities would be used for test series 2, whereas for test series 3, one fuse holder and its support would be used for the two required tests. For test series 4 and 5, the same fuseholder and support is used for the four required tests. Only the manufacturer has the discretion to permit a fuseholder, or cutout support to be used for more than the specified number of individual tests. After each test on a fuseholder that uses replaceable links, only the fuse link and the expendable cap, if used, may be replaced. Only the manufacturer has the discretion to use an expendable cap for more than one test if it is determined that the cap was not damaged during a previous test. If the fuse element is an integral part of the fuseholder, then the number of fuseholders to be tested is the number listed for “Number of tests required on each fuseholder and fuse support.” The mounting brackets used for the cutout testing should be as specified in ANSI C37.42. Any deviation from this specification shall be noted in the test report for the device.





6.4.2 Test series for slant-voltage-rated (multiple-voltage-rated) fuse cutouts (example: 15/27 kV)

Tests shall be made at the rated maximum voltages specified and in accordance with Table 8. Fuses that form a part of a homogeneous series require only the interrupting tests as specified in 6.2 and associated Table 3. A description of the required test series is as follows:

Test series 1: Verification of fuse operation with prospective currents equal to its rated interrupting current and conducted at its maximum voltage to the left of the slant.

Test series 2: Verification of fuse operation with prospective currents ranging from 70% to 80% of its rated interrupting current and conducted at its maximum voltage to the left of the slant.

Test series 3: Verification of fuse operation with prospective currents ranging from 20% to 30% of its rated interrupting current and conducted at its maximum voltage to the right of the slant.

Test series 4: Verification of fuse operation with prospective currents in the range of 400 A to 500 A and conducted at its maximum voltage to the right of the slant.

Test series 5: Verification of fuse operation with small overload currents and conducted at its maximum voltage to the right of the slant.

Test series 6: Verification of fuse operation of two fuse cutouts in electrical series connection with prospective currents equal to the rated interrupting current of both series devices and conducted at its maximum rated voltage to the right of the slant.





Table 8 —Interrupting performance tests and test circuit parameters for slant-voltage-rated (multiple-voltage-rated) distribution class fuse cutouts


1 2 3 4 5 6a Power-frequency recovery voltage

Rated maximum voltage to the left of the slant +5%, −0% Rated maximum voltage to the right of the slant +5%, −0%

Transient recovery voltage (TRV) See Table 9, column 1 See Table 9,

column 2 See Table 9,

column 4 See Noteb See Table 9, column 2

Prospective or test current— rms symmetrical

Rated interrupting

current +5%, −0%

From 70% to 80% rated

interrupting current


interrupting currentc

From 400 A to 500 Ad

From 2.7 to 3.3 times fuse

link ratinge

Rated interrupting current +5%, −0%

X/R ratio (power factor) See Table 10

From 1.3 to 0.75 (from 0.6 to 0.8)

See Table 10

Making angle related to voltage zero—degrees

1st test: from −5 to +15 2nd test: from 85 to 105 3rd test: from 130 to 150

From 85 to 105 Random timing 1st test: from −5 to +15 2nd test: from 85 to 105 3rd test: from 130 to 150

Fuse link ratingf Min Max Min Max Min Max Min Min Min,g Max,g Number of tests required with above fuselink ratingh 3 3 3 3 1 1 2 2 3 3

Number of tests required on each fuseholder and fuse supporth

3 3 3 3 2 4 3 3

Number of fuseholders to be testedh 1 1 1 1 1 1 1 1

Number of fuse supports to be testedh

1 1 1 1 1 1 1 1

Duration of power-frequency recovery voltage after interruption

Dropout fuses Not less than 0.5 s

Non-dropout fuses Not less than 0.5 s

a Test series 6 uses two identically rated cutouts in electrical series connection. Test-circuit ground must not be between the cutouts. b The TRV for this test circuit shall be critically damped. Shunting the load reactance with a resistance having a value equal to approximately 40-

times the value of the reactance is usually adequate to critically damp the circuit. However, if this value does not result in critical damping, the resistance may be reduced to achieve critical damping. For testing convenience, an oscillatory TRV may be acceptable with the agreement of the manufacturer. Critical damping is obtained when:

XffR

no

2=

where fo is the natural frequency of the test circuit without damping fn is the power frequency X is the reactance of the circuit at power frequency c For cutouts with an interrupting rating of 2.8 kA or less, Test Series 3 need not be made. d For cutouts rated 200 A, Test Series 4 need not be made. e If the test involves a melting time appreciably higher than 2 s, the current may be increased to obtain a melting time of approximately 2 s. f “Min” and “max” represent the minimum and maximum rated currents of a homogeneous series, see 6.2. g Use same fuse link rating in both cutouts.





h A fuse cutout support [fuse base] shall be capable, at a minimum, of the number of tests listed as “Number of tests required on each fuseholder and its fuse support”. For test series 1, this represents three tests with the minimum fuse link rating using one fuseholder and support, and three tests with the maximum fuse link rating using another fuseholder and support. The same quantities would be used for test series 2, while for test series 3, one fuse holder and its support would be used for the two required tests. For test series 4 and 5, the same fuseholder and support is used for the four required tests. Only the manufacturer has the discretion to permit a fuseholder, or cutout support, to be used for more than the specified number of individual tests. After each test on a fuseholder that uses replaceable links, only the fuse link and the expendable cap, if used, may be replaced. Only the manufacturer has the discretion to use an expendable cap for more than one test, if it is determined that the cap was not damaged during a previous test. If the fuse element is an integral part of the fuseholder, the number of fuseholders to be tested is the number listed for “Number of tests required on each fuseholder and fuse support.” The mounting brackets used for the cutout testing should be as specified in Std. C37.42. Any deviation from this specification shall be noted in the test report for the device.

Table 9 —Inherent TRV test circuit parameters for distribution class fuse cutouts, liquid-submerged expulsion fuses, and distribution class capacitor line fuses

Rated maximum voltage (kV) Column 1 Column 2 Column 3 Column 4

Single-voltage-

rated devices

Slant-voltage-

rated devices

Applicable test tables and test series Table 7, test series 1,

2, and 3 Table 8, test series 1

and 2 Table 17, test series 1 Table 19, test series 3

and 4

Table 8, test series 3 and test series 6

Table 7, test series 4 Table 8, test series 4

Frequency (f) (kHz) +10%, –0%

Peak factora +10%, –0%







2.6–2.8 — 6.1 1.3 — — 37.0 1.45 — — 5.2–5.5 — 4.3 1.3 — — 37.0 1.45 — — 7.8–8.3 7.8/15.0–

8.3/15.5 3.3 1.3 2.3 1.3 31.0 1.55 24.0 1.60

15.0–15.5 15.0/ 27.0– 15.5/27.0

2.3 1.3 1.7 1.3 24.0 1.60 15.0 1.60

22.0–27.0 27.0/38.0 1.7 1.3 1.5 1.3 15.0 1.60 10.0 1.60 38.0 — 1.5 1.3 — — 10.0 1.60 — —

aPeak factor = ( ) ( )X/Rarctan sinkVin oltagerecovery vfrequency power 2

kVin peak TRVfirst

××

X/R is the value from Table 7, Table 8, Table 17, or Table 19. Peak factor should be determined based on symmetrical current.

TRV envelope is a (1– cos) shape, with time-to-peak (in microseconds) kHzin 2

1000f

=

RRRV = Average rate of rise of the (transient) recovery voltage (in volts/microseconds)

peak totime

peak TRVfirst =

= 2 2 (power-frequency recovery voltage in kV) × [sin (arctan X/R)] × (peak factor) × (f in kHz)





Table 10 —Minimum X/R ratios for distribution class fuse cutout interrupting tests (except current-limiting fuses and open-link cutouts)

Rated maximum voltage (kV) Table 7, test series 1, 2, and 3 Table 8, test series 1, 2, 3, and 6

Table 7 and Table 8, test series 4

Single-voltage-rated cutouts

Slant-voltage-rated cutouts

Rated interrupting current—

symmetrical rms amperes

Minimum X/R Minimum X/R

2.6–2.8 — ≤ 16000 5 1.5 5.2–5.5 — ≤ 12500 5 1.5

7.8–8.3 — ≤ 10000 8 1.8 > 10000 12

15.0–15.5 7.8/15.0–8.3/15.5 ≤ 7100 8 2.4 > 7100 12

22.0–27.0 15.0/27.0–15.5/27 ≤ 2500 8 3.7 > 2500 12

38.0 27.0/38.0 ≤ 10000 15 5.1

6.5 Description of interrupting tests on power class fuses and fuse disconnecting switches (except current-limiting fuses and liquid-submerged expulsion fuses)

6.5.1 General

Tests shall be made at the voltages specified and in accordance with Table 11. Power fuses that form a part of a homogeneous series are tested as specified in 6.2 and associated Table 3 or Table 5. A description of the required test series is as follows:

Test series 1: Verification of fuse operation with prospective currents equal to its rated interrupting current and conducted at 87% of its rated maximum voltage.

Test series 2: Verification of fuse operation with prospective currents ranging from 87% to 91% of its rated interrupting current and conducted at its rated maximum voltage.



Test series 5: Verification of fuse operation with prospective currents in the 400 A to 500 A range and conducted at its rated maximum voltage.

Test series 6: Verification of fuse operation with small overload currents and conducted at its rated maximum voltage.

6.5.2 Test requirements for expulsion fuses with exhaust-control devices

Expulsion fuses can be used in an enclosure if fitted with an exhaust-control device. The exhaust-control device must contain the gaseous by-products of the fault-interrupting event to an extent that is sufficient to maintain dielectric integrity of the enclosure during and immediately after the fuse clears. Since fuses can be applied in various enclosure designs, fuses with exhaust-control devices can be tested in a manner to verify the exhaust-control device provides this required function independent of the enclosure. Expulsion fuses shall be tested with a ground plane below the fuse when the bottom terminal of the fuse is connected to the source side





of the circuit. In other words, a conductive plane perpendicular to the orientation of the fuse shall be in place below the fuse such that the potential across the fuse during the test is also applied from the bottom of the exhaust-control device to this plane. As shown in Figure 1, this plane shall be located no further than the minimum electrical clearance distance “R” as recommended by the fuse manufacturer.

Figure 1 —Location of ground plane for fuse fitted with exhaust-control device





Table 11 —Interrupting performance tests and test circuit parameters for power class fuses (except current-limiting fuses)


1 2a 3 4 5 6

Power-frequency recovery voltage

87% of rated maximum

voltage +5%, 0%

Rated maximum voltage +5%, 0%

TRV See Table 12, column 1 See Table 12, column 3

See Footnote b


Rated interrupting

current +5%, 0%







From 400 A to 500 Ac,d

From 2.7 to 3.3 times link or

fuse unit ratingd

X/R ratio (power factor) Not less than 15 (not greater than 0.067) See Table 13 From 1.3 to

0.75 (from 0.6 to 0.8)

Making angle related to voltage zero—degrees

1st test: from –5 to +15 2nd test: from 85 to 105 3rd test: from 130 to 150

From 85 to 105

Random timing

Current rating of fuse link or fuse unit

Min Max Min Max Min Max Min Max Min Min

Number of tests 3 3 3 3 3 3 1 1 2 2 Number of tests on each fuse employing refill units or fuse linkse

3 3 3 3 3 3 2 4

Number of tests on each nonrenewable fuse

1 1 1 1 1 1 1 1 1 1

Number of tests on each exhaust-control device, if applicable

3 3 3 3 3 3 2 4

Duration of power- frequency recovery voltage after interruption

Dropout fuses Not less than dropout time or 0.5 s, whichever is greater

Non-dropout fuses Not less than 10 minf Not less than 1 min

aIf test series 1 tests are made at 100% of rated maximum voltage, then test series 2 tests need not be made. bThe TRV for this test circuit shall be critically damped. Shunting the load reactance with a resistance having a value equal to

approximately 40 times the value of the reactance is usually adequate to critically damp the circuit critically. However, if this value does not result in critical damping, then the resistance may be reduced to achieve critical damping. For testing convenience, an oscillatory TRV may be acceptable with the agreement of the manufacturer. Critical damping is obtained when

XffR

n

o2

=

where fo is the natural frequency of test circuit without damping fn is the power frequency X is the reactance of the circuit at power frequency

cIf the values are lower than those of series 6, then series 5 tests need not be made. dIf the test involves a melting time appreciably higher than 2 s, then the current may be increased to obtain a melting time of approximately 2 s. eAfter each test, the refill unit or fuse link and expendable cap (if used) shall be replaced. fIf leakage current through the fuse is monitored following interruption, then the recovery voltage may be removed after leakage current

has been less than 1 mA for a 2 min duration.





Table 12 —TRV test circuit parameters for power class expulsion fuses, power and distribution class current-limiting fuses, and power class capacitor line fuses

Rated maximum voltage (kV)a

Column 1 Column 2 Column 3 Applicable test table and test series Table 11, test series 1, 2, 3, and 4

Table 14, test series 1 Table 19, test series 3 and 4

Table 14, test series 2 Table 11, test series 5

Frequency (f) (kHz) +10%, 0%

Peak factorb + 10%, 0%


Peak factorb +10%, 0%


Peak factorb +10%, 0%

2.8 8.5 1.4 3.3 1.5 38.0 1.45 5.1–5.5 6.0 1.4 2.7 1.5 29.0 1.55

8.3 4.7 1.4 2.3 1.5 19.0 1.65 15.0–17.2 3.2 1.4 1.8 1.5 18.0 1.65 22.0–27.0 2.1 1.4 1.3 1.5 12.0 1.65

38.0 1.6 1.4 1.1 1.5 8.0 1.65 aFor rated maximum voltages above 38 kV, the TRV parameters of the test circuit are not specified. Appropriate values may be selected by agreement between the users and the manufacturer.

bPeak factor = ( ) ( )X/Rarctan sinkVin oltagerecovery vfrequency power 2

kVin peak TRVfirst

××

X/R is the value from Table 11 for test series 1, 2, 3, and 4 and from Table 13 for test series 5 for expulsion type power fuses; Table 14 for current-limiting fuses; and Table 19 for power class capacitor fuses. Peak factor should be determined based on symmetrical current.

TRV envelope is a (1– cos) shape, with time-to-peak (in microseconds) kHzin 2

1000f

=

RRRV = Average rate of rise of the (transient) recovery voltage (in volts/microseconds)

peak totime

peak TRVfirst =

= 2 2 (power-frequency recovery voltage in kV) × [sin (arctan X/R)] × (peak factor) × (f in kHz)

Table 13 —Minimum X/R ratios for test series 5 for power class fuses (except current-limiting fuses)

Rated maximum voltage (kV)

Minimum X/R ratio

2.8–5.5 1.5 8.3 1.8

15.0–27 8.0 38.0–48.3 12.0 72.5–170 15.0

6.6 Description of interrupting tests on current-limiting power and distribution fuses

6.6.1 Test series

Tests shall be made at the voltages specified and in accordance with Table 14. Descriptions of the required test series are as follows.

It is not necessary to make interrupting tests on fuse units of all current ratings of a homogeneous series; see 6.6.4 for requirements to be met and tests to be performed.





Test series 1:

a) Current-limiting power fuses: Verification of fuse operation with prospective currents equal to its rated interrupting current I1 and conducted at 87% of its rated maximum voltage, and with prospective currents equal to 87% of its rated interrupting current I1 and conducted at its rated maximum voltage. At the manufacturer’s option, these two tests can be combined in a single test, a prospective current of I1 at rated maximum voltage, as is done for distribution and motor-starter fuses.

b) Current-limiting distribution and motor-starter fuses: Verification of fuse operation with prospective currents equal to its rated interrupting current I1 and conducted at its rated maximum voltage.

Test series 2:

Verification of fuse operation with prospective current I2 at which current initiation occurs when a high level of energy is stored in the inductance of the circuit.

Test series 3:

Verification of fuse operation at low current I3.

a) For backup fuses, I3 is the rated minimum interrupting current assigned by the manufacturer.

b) For general-purpose fuses, I3 is the current value that causes melting of the fuse in no less than 1 h.

c) For full-range fuses, I3 is the minimum test current. The minimum test current is a current that is less than the minimum continuous current that causes melting of the fusible element(s) with the fuse applied at the maximum ambient temperature specified by the manufacturer. See 6.6.2.3 for the method of determining this current.





Table 14 —Interrupting performance tests and test circuit parameters for current-limiting power, distribution class, and motor-starter fuses

Parameters Type of fuse Test series 1 2 3a

Power-frequency recovery voltage

Power 87% of rated maximum voltage +5%, −0%

Rated maximum voltage +5%, −0%

Rated maximum voltage +5%, −0%

Distribution and motor starterb

Rated maximum voltage +5%, –0%

Not required

TRV Power and distribution See Table 12, column 1 See Table 12,

column 2 See Footnote c

Motor starterd See Footnote d

Prospective or test current rms symmetrical

Power I1 +5%, −0% 87% of I1 +5%, −0%e I2 I3 +0%, −10% Distribution and

motor starter I1 +5%, −0% Not required

X/R ratio (power factor) Power and motor

starter Not less than 15 (not greater than 0.067) From 2.3 to 1.3

(From 0.4 to 0.6) Distribution Not less than 10 (not greater than 0.100)

Making angle after voltage zero—degrees

Power, distribution, and motor starter

Not applicable 0 to 20 Random timing

Instantaneous current at initiation of arcing

Power, distribution and motor starter

Not applicable 0.85 I2 to 1.06 I2 Not applicable

Initiation of arcing after voltage zero—degrees


For one test: from 40 to 65 For two tests: from 65 to 90f

Not applicable Not applicable

Duration of power-frequency recovery voltage after interruption

Dropout fuse


Not less than dropout time or 1s, whichever is greater

Non-dropout fuse

Not less than 60 s g Not less than 60 s, or 10 min h

Current rating of fuse or fuse unit


See 6.6.4

Number of tests (see 6.6.4) Power 3 3 3 2 Distribution and

motor starter 3 Not required 3 2

aTest series 3 tests verify the operation of the fuse at low currents. For the value of these currents, see 6.6.1. When test station limitations prevent the maintenance of constant current, the tolerance on the current may be exceeded during not more than 20% of the melting time, provided that the current at the initiation of arcing is within the tolerance specified, and the minimum time for melting of general-purpose and full-range fuses is maintained. To avoid testing at the specified voltage for the full test period, an alternative method for test series 3 tests is specified in 6.6.2. The test method for test series 3 tests for full-range fuses is specified in 6.6.3.

bSee item j) of 1.1. cThe TRV for this test circuit shall be critically damped. Shunting the load reactance with a resistance having a value equal to approximately 40 times the

value of the reactance is usually adequate to critically damp the circuit. However, if this value does not result in critical damping, then the resistance may be reduced to achieve critical damping. For testing convenience, an oscillatory TRV may be acceptable with the agreement of the manufacturer. Critical damping is obtained when:

XffR

n

o2

=

where fo is the natural frequency of test circuit without damping fn is the power frequency X is the reactance of the circuit at power frequency

dBecause of the special application conditions for motor-starter fuses, they are tested in critically damped circuits and with a minimum of 1 min duration of recovery voltage. Motor-starter fuses may be tested with power class TRV and power-frequency recovery voltage durations with the consent of the manufacturer.

eTest need not be performed if tests at the I1 level are made at 100% of rated maximum voltage. fSince the operating conditions can produce a wide variety of stresses on the fuse, and as the interrupting tests are intended (in principal) to produce the most severe conditions (mainly as regards the arc energy and the thermal and mechanical stresses for this value of current), it is recognized that these conditions will be practically obtained at least once when making the three tests indicated. gIf series 2 tests are not made, then the duration shall be not less than that specified for a test series 2 test (see Footnote h). hThe duration of recovery voltage shall be 10 min for the following specific cases: Test series 2: for backup (except motor starter), general-purpose, and full-range types. Test series 3: for general-purpose and full-range types, and backup (except motor-starter) fuses having a melting time >100 s. These longer periods of recovery voltage duration only apply to the largest current rating of a homogeneous series.





Series It:

Verification of operation for fuses that exhibit crossover current(s) (see 6.6.11).

In the case of fuses that incorporate different arc-quenching mechanisms within the same physical envelope (for example, current-limiting elements and expulsion elements in series), test series 1, 2, and 3 shall be augmented by additional tests to prove correct operation in the region(s) of current It where the interrupting duty is transferred from one interrupting mechanism to another. Since fuse designs differ widely, specifying precise test requirements that are applicable to all designs is not possible. However, the general criterion to be observed is to test in the region where the low current interrupter sees a maximum interrupting current and the high current interrupter sees a minimum interrupting current. It is the responsibility of the fuse manufacturer to demonstrate by the It interrupting test that the interrupting mechanisms are operating correctly to effect proper current interruption within the transitional current region. Typical criteria used in assessing compliance with this requirement are discussed in Annex E.

The following additional requirements may apply:

If, when making tests in accordance with series 2, the requirements of series 1 are completely met for one or more tests (TRV parameters excepted), then these tests need not be repeated as a part of series 1.

Traditionally, the I2 test condition has approximated a condition of maximum arc energy in the tested fuse. If a particular design exhibits maximum arc energy at a significantly different current than that meeting the I2 criteria, then additional tests should be performed at a current that approximates the maximum arc energy.

In very exceptional cases, the current I2 may be higher than the rated maximum interrupting current I1. Series 1 and 2 shall then be replaced by six tests at rated maximum interrupting current with making angles as nearly as possible equally distributed with approximately 30° between each. [Parameters used will be those of series 2 (see Table 14) except making angle and value of instantaneous current at initiation of arcing.]

If during series 1 tests, it is impossible to initiate arcing as early as 65° after voltage zero, then the requirement of one test with the initiation of arcing from 40° to 65° after voltage zero is replaced by an additional test (making a total of three) with initiation of arcing from 65° to 90° after voltage zero.

NOTE 1— Values of I1, I2, I3, and It are the rms values of the ac component of the current.

NOTE 2— As a guide, the value of the current I2 to comply with this requirement may be determined by one of the following methods:

a) From the following equation, if one test at a current 150 times the current rating or higher has been made under symmetrical fault initiation in series 1:

1

112 I

iiI =

where

I2 is prospective current for series 2

i1 is instantaneous current at instant of melting in series 1

I1 is prospective current in series 1

b) By taking between three and four times the current that corresponds to a melting time of 0.01 s on the time/current characteristic.





HIGH- VOLTAGE SOURCE

TRANSFER SWITCH

FUSE LOW- VOLTAGE SOURCE

R 1 R X L1

6.6.2 Alternative test methods for series 3 tests on current-limiting fuses

6.6.2.1 General

Test series 3 may be performed using a single high-voltage source throughout the test (as in series 1 or series 2). Where melting times are long, and/or where there are limitations in test-station capability, series 3 may be conducted as a two-part test. For the first part of the test, the current is supplied from a low-voltage source. For the second part, which includes the interruption of the current by the fuse, the current shall be supplied from a high-voltage source. The test circuit for the two-part test is shown in Figure 2.

Figure 2 —Alternative test circuit for series 3 test of current-limiting fuses

It is also permissible to perform a two-part test using a single high-voltage source where the power factor for part of the melting period is of a lower value. In this case, the changeover to the correct power factor must occur before arcing commences.

6.6.2.2 Circuit requirements and testing procedures for a two-part test

a) The circuit requires a low-voltage power source that is able to cause the desired current to flow through the fuse under test and that provides a means for holding the current constant during the test. The value of the low-voltage current may be higher than I3 for some or all of the melting test period, as explained in item b) and item c) of 6.6.2.3.

b) The circuit also requires a high-voltage source, as described in 6.1.2. The value of the high-voltage current is the current I3, as defined in 6.6.1.

c) Provision shall be made for switching either manually or automatically from the low-voltage source to the high-voltage source at the desired instant during each test. The time interval during which the current is interrupted shall not exceed 0.2 s. It should be noted that, at the X/R values specified for this test, the current should have very little asymmetry when the circuit is randomly switched to the high-voltage source. A synchronous closing switch is, therefore, not necessary for closing in the high-voltage circuit. If the fuse manufacturer allows a higher X/R ratio than specified for the test, then a synchronous closing switch may be necessary for controlling the symmetry of the current.

d) In general, the changeover shall take place while at least one fuse element is still carrying current. For a multi-element fuse, this would be in the period when elements are melting successively, as shown by step increases in the voltage developed across the fuse.

e) With the consent of the manufacturer, it is permissible for the changeover to be delayed until all the fuse elements (but not an indicator element, where included in the fuse design) have melted. This procedure is of value in cases where it is difficult to detect the onset of element melting, or where the value of melting current has to be significantly higher than the chosen value of series 3 current, as explained in item b) and item c) of 6.6.2.3. The voltage of the LV circuit should be chosen to minimize any arcing that could occur before the switchover to the HV circuit. In general, this will require a circuit voltage of less than 100 V, unless the design of the fuse is such that LV arcing will not significantly affect the HV arcing process





Test method e) is held to be more onerous for the fuse than test method d). Testing to method d) is closer to actual service conditions; therefore, if a failure occurs when method e) is used, the series 3 tests may be repeated using method d).

6.6.2.3 Value of melting current for series 3 tests

a) For tests on backup fuses where the melting time is less than 1 h, the low-voltage source shall be set to the value I3 and maintained at this value throughout the test.

b) For general-purpose fuses where a minimum time to melt of 1 h is required, the current of the low-voltage source shall be set to I3, but it may be increased after 1 h by up to 1.15 times I3 to induce melting.

c) For full-range fuses, I3 shall be determined using 6.6.3.1. The low-voltage source may be set to a value higher than I3 throughout the test in order to avoid an unnecessarily long testing time, provided the resulting melting time is not less than 1 h.

After 1 h, the low-voltage current may be increased by up to 1.15 times its original value to induce melting.

6.6.3 Test method for series 3 tests on full-range current-limiting fuses

6.6.3.1 Method of determining the minimum test current (I3) of the fuse

This procedure may be performed by the manufacturer. Three samples shall be used for the determination of the I3 value. Each sample is placed in a stable thermal environment, such as a temperature-controlled oven, that is set to the maximum temperature for which the fuse is rated by the manufacturer to have an interrupting capability (rated maximum application temperature). Once the fuse body has reached a stable temperature, any circulating air fans must be switched OFF for the remainder of the test. Current is then applied to the fuse. When the fuse body temperature has again stabilized, the value of the current is increased. This process is repeated until the fuse melts open. For the purpose of this test, temperature is defined as being stable when the temperature rise above ambient increases by less than 2% per hour. The increments by which the current is increased are not specified but could typically be in the range of 5% to 10%. It should be recognized that larger increases will reduce the number of steps but may result in a more onerous test current, whereas smaller increases will yield a more accurate test current but require more testing steps. The highest current that each of the three fuses carried without melting is then considered. I3 is defined as 0.9 times the lowest current of these three values. The 0.9 is used to allow for manufacturing tolerances; hence, the I3 test is then performed with a current slightly less than the lowest current that could melt a fuse when it operates, surrounded by the maximum temperature for which it is rated by the manufacturer.

6.6.3.2 Method of performing the series 3 tests

Full-range-type fuses shall be capable of interrupting the lowest current that can produce melting when the fuse is subjected to its rated maximum application temperature. This temperature shall be at least 40 °C. It is necessary to ensure that the series 3 test simulates this condition to check the ability of the fuse to withstand any high temperatures generated during operation. Test series 3 shall, therefore, be performed using the following method.





Each sample shall be placed in a stable thermal environment, such as a temperature-controlled oven, which is set at the rated maximum application temperature of the fuse. Once the fuse body has reached a stable temperature, any circulating air fans used shall be switched OFF for the remainder of the test. Stability is defined as having the fuse within 2% of the oven temperature in degrees Celsius. A two-part interrupting test is then carried out as described in 6.6.2. The high-voltage current I3 is determined from the thermal testing described in 6.6.3.1. Temperatures higher than the rated maximum application temperature may be used to expedite melting, if agreed to by the manufacturer. In all cases, the melting time shall be at least 1 h. Physical changes in fuse components that result from long-term application and that may affect interruption should be considered when conducting testing.

6.6.4 Interrupting tests on a homogeneous series of fuses

When a group of fuse current ratings meets the requirements of a homogeneous series, as defined in this standard, homogeneous series testing requires that only certain ratings be tested to qualify all other ratings in the series. Current-limiting fuses are available as fuses that have only one barrel, as two or more parallel barrels permanently connected by the fuse manufacturer, and as fuse units (having one or more connected barrels) that can be connected in parallel by the user in accordance with the manufacturer’s instructions. Table 15 covers single-barrel fuses and may also be used for multiple-barrel fuses permanently connected by the manufacturer, at the manufacturer’s discretion. Table 16 covers fuses made by connecting fuse units in parallel, usually when the user makes such a connection. However, this table can also be used for the homogeneous testing of parallel barrels permanently connected together by the manufacturer, if this results in less tests being necessary.





Table 15 —Homogeneous series test requirement for single fuse units

Homogeneous series achieved by Test series Fuse units to be tested

A B C Progressive monotonic change in n or s, or both, with respect to rated current n(A) ≤ n(B) ≤ n(C) s(A) ≤ s(B) ≤ s(C)

1 X — X

2a X — X

3 X Xb X Constant n, increasing s s(A) < s(B) < s(C)

1 X — X

2a X — X

3 — — X Constant s, increasing n n(A) < n(B) < n(C)

1 X — X

2 — — X

3c X — X Symbols in Table 15 are defined as follows:

A fuse unit of lowest current rating B any fuse unit of a current rating between A and C C fuse unit of highest current rating X shows the tests that are to be performed n the number of parallel fuse elements s cross-sectional area of each fuse element

The parameters to be considered are as follows: s(A), s(B), and s(C), the cross sections of the individual main fuse element in A, B, and C. n(A), n(B), and n(C), the number of main fuse elements in A, B, and C.

aThe test current I2 for fuse units A and C will have been chosen according to the current ratings of fuse units A and C, respectively. bEvery rating need not be tested; however, with diminishing current ratings, a test is to be made only for the current rating at which the number of elements is reduced. cThe fuse unit(s) with the lowest current rating shall contain at least two main fuse elements in addition to the element, if present, used for operating an indicator or striker.





Table 16 —Homogeneous series test requirements for fuses using parallel fuse units

Homogeneous series

achieved by paralleling

multiple fuse units

Test series

Fuse unit assembly to be tested

A'a C'a B C 1 X X — X

2b Xc X — X

3d Xe X Xf X The symbols used in Table 16 are defined as follows:

y the number of parallel fuse units for a given fuse A' fuse assembly of lowest current rating that uses the smallest number of parallel units, y(A') C' fuse assembly of the highest current rating using the same number of parallel units as A' [i.e.,

y(C') = y(A')] B any fuse assembly of a current rating between A' and C that has individual fuse units no larger

than those used in C' C fuse assembly of the highest current rating, using the maximum number of parallel units, each

the same as the unit used in C' X shows the tests that are to be performed n the number of parallel main fuse elements in a single fuse unit s cross-sectional area of each main fuse element in a single fuse unit

The parameters to be considered are as follows:

s(A'), s(C'), s(B), and s(C), the cross sections of the individual main fuse elements in A', C', B and C. n(A') n(C'), n(B), and n(C), the number of main fuse elements in A', C', B, and C'.

aThis is typically a single fuse unit, y = 1. If the smallest number of parallel fuse units have been previously tested or qualified, as part of a homogeneous series, additional testing is unnecessary.

bThe test current I2 for fuse unit assemblies A', C', and C will have been chosen according to the current ratings of fuse units A', C', and C, respectively.

cIf s(A') equals s(C') but n(A') < n(C'), then this test is unnecessary (see Table 15, “constant s, increasing n”). dFor a constant s and changing n, only A' and C need be tested, provided A' has at least two main fuse elements in addition to

the element, if present, used for operating an indicator or striker. eIf n(A') equals n(C') but s(A') < s(C'), then this test is unnecessary (see Table 15, “constant n, increasing s”). fEvery intermediate rating need not be tested. In the case of full-range and general-purpose fuses, ratings between C' and A'

shall be tested only when the number of elements is reduced. Ratings between C and C' need not be tested, provided the individual fuse units that make up the rating have been tested, or are covered, as part of the homogeneous series testing C' through A'. For backup fuses, ratings between C' and A' shall be tested only when the number of elements is reduced (except see Footnote d). When one or more fuse units have been tested or are covered as part of the homogeneous testing rules, using more of the same fuse unit in parallel does not require additional test series 3 testing. However, in this case, the minimum interrupting rating for the larger number of parallel fuse units cannot be claimed to be lower than the appropriately proportioned value relative to the actual tested value [see item c) of 6.6.6].

Fuse units are considered as forming a homogeneous series when their characteristics comply with the following:

a) Rated voltage, interrupting current, and frequency shall be the same.

b) All materials shall be the same.

c) All dimensions of the fuse unit shall be the same, except the cross section of the fuse elements and the number of fuse element(s), as detailed below in item d) through item h).

d) In any fuse unit, the main fuse elements shall be identical.

e) The laws governing the variations in the cross sections of individual fuse elements along their length shall be the same.

f) All variations in thickness, width, and number shall be monotonic (continually varying in the same direction for a given direction of the same variable) with respect to rated current; thus, balancing an increase in cross section by reducing the number of fuse elements, and vice versa, is not allowed.





g) The variation in distance, if any, between individual fuse elements and in distance, if any, between the fuse element(s) and fuse barrel shall be monotonic with respect to the rated current.

h) A special fuse element used for an indicator or striker is exempt from item e) and item f) above; however, this element shall be the same for all the fuse units.

i) A fuse unit that uses more than one barrel permanently connected in parallel contains identical elements in each barrel, except for an indicator or striker that may be in only one barrel. Individual barrels meet the requirements a) through h).

j) Fuses that use parallel assemblies composed of separate fuse units, where the individual fuse units meet the requirements a) through i).

k) Fuses connected in parallel are from the same manufacturer and have the same design and rating.

l) All parallel fuse units are mounted in their designated fuse supports or in accordance with the manufacturer’s specifications.

It should be noted that, when the user connects fuses in parallel, it is particularly important that they be mounted as specified by their manufacturer. Unless a fuse manufacturer has determined that the mounting arrangement of a specific design of parallel fuses is not critical, the manufacturer shall make available to the user instructions as to how such fuses should be connected in parallel (i.e., how they have been tested). In the absence of specific instructions, the installation should allow for an even sharing of the current between the fuse units; this requires equal length leads, equal resistance and inductance in the current paths, and the fuse units should experience equivalent external magnetic fields. If a user connects fuses in parallel without the manufacturer’s knowledge or consent, after appropriate testing as specified in this and other standards, the manufacturer should be informed. Changes to a fuse’s design may subsequently render them unsuitable for paralleling, without additional testing (see 3.2).

6.6.5 Interpretation of homogeneous series interrupting test results (single fuse units)

If the results of tests made according to Table 15 are successful, then any current rating of fuse units within the homogeneous series shall be deemed to comply with the interrupting requirements of this standard. If a fuse unit does not perform satisfactorily on one or more test series, that fuse unit shall be rejected from the homogeneous series; however, such failure does not necessarily cause rejection of the other current ratings. It should be noted that a particular range of current ratings in one barrel size or configuration may constitute one homogeneous series for one test duty but two or more homogeneous series for the purpose of another test duty. General-purpose fuse units not tested because they are within the homogeneous series are considered to have met the requirements for being able to interrupt currents causing melting in 1 h. If the tested fuse units have been shown to interrupt lower currents (having a longer melting time than 1 h), the rules of item a) through item c) in the subsequent list can be used to determine the low current interrupting ability of untested units. Full-range fuse units not tested because they are within the homogeneous series are considered to have met the requirements for being able to interrupt any continuous current that causes them to melt at their rated maximum application temperature. The values of minimum interrupting current of backup fuse units not tested are determined from test series 3 tests that have been performed as follows:

a) Constant n, increase of s: It is assumed that the melting time at I3 for fuse unit A and B is not less than that for fuse unit C. The test in accordance with Table 15, therefore, proves that fuse units A and B have a minimum interrupting current ascertained by reading from their time/current characteristics the currents corresponding to the melting time given by the minimum interrupting current of fuse unit C and its time/current characteristics.





b) Constant s, increase of n: The minimum interrupting current I3 of fuse units A and C may or may not be the same. If they are the same, I3 is deemed to apply to fuse unit(s) B. If they are different, a straight line is drawn through the points corresponding to the respective minimum interrupting currents on the time/current characteristics and, plotted to a log-log scale, of fuse units A and C. The intersection of this line and the time/current characteristics of fuse unit(s) B is(are) deemed to define the minimum interrupting current of fuse unit(s) B.

c) Values of the minimum interrupting current less than those derived from either item a) or item b) shall be proved by a separate test.

6.6.6 Interpretation of homogeneous series interrupting test results of parallel fuse units

If the results of tests made according to Table 14 are successful, then any current rating of parallel fuse units within the homogeneous series shall be deemed to comply with the interrupting requirements of this standard. If parallel fuse units do not perform satisfactorily on one or more test series, that combination of fuse units shall be rejected from the homogeneous series; however, such failure does not necessarily cause rejection of the other current ratings. It should be noted that a particular range of current ratings may constitute one homogeneous series for one test duty but two or more homogeneous series for the purpose of another test duty. General-purpose fuse units not tested because they are within the homogeneous series are considered to have met the requirements for being able to interrupt currents causing melting in 1 h. If the tested fuse units have been shown to interrupt lower currents (having a longer melting time than 1 h), the rules in item a) through item c) in the subsequent list can be used to determine the low current-interrupting ability of untested units. Full-range fuse units not tested because they are within the homogeneous series are considered to have met the requirements for being able to interrupt any continuous current that causes them to melt at their rated maximum application temperature.





The values of minimum interrupting current of backup-type parallel fuse units not tested are determined from test series 3 tests that have been performed as follows:

a) Constant n, increase of s: It is assumed that the melting time at I3 for any fuse units having a smaller s and the same n as fuse B that has been tested is not less than for B. The test in accordance with Table 16, therefore, proves that such fuses have a minimum interrupting current ascertained by reading from their time/current characteristics the currents corresponding to the melting time given by the minimum interrupting current of fuse unit or units B tested, and its time/current characteristics.

b) Constant s of fuse elements, but with a different number of parallel elements and fuse units: The minimum interrupting current I3 of fuse units A' and C may or may not be the same. If they are the same, then I3 is deemed to apply to fuse units B. If they are different, a straight line is drawn through the points corresponding to the respective minimum interrupting currents on the time/current characteristics, plotted to a log-log scale, of fuse units A' and C. The intersection of this line and the time-current characteristic(s) of fuse units B is(are) deemed to define the minimum interrupting current of fuse units B.

c) When a minimum interrupting current (M') has been established for a particular rating of single or multiple fuse units (number of parallel fuse units Y'), the minimum interrupting rating (M) of a larger number Y of parallel units can be derived from

M = M' × Y/Y'

When the minimum interrupting current has been established in this manner, test series 3 testing of the larger number of fuse units is unnecessary.

d) Values of the minimum interrupting current less than those derived from item a) through item c) shall be proved by a separate test.

6.6.7 Overvoltages produced by current-limiting fuses

Overvoltages produced during the series 1 and 2 interrupting tests specified in 6.6.1 shall be recorded by a cathode ray oscillograph, or other instrument, having a frequency response greater than that of the waveforms being measured.

6.6.8 Peak let-through [cutoff] current for current-limiting fuses

The values of the peak let-through [cutoff] current obtained from the oscillograms taken during series 1 interrupting tests specified in 6.6.1 shall not exceed those specified by the fuse manufacturer. The characteristic curve showing the relationship of peak let-through current to prospective current in the current-limiting range shall be plotted on log-log coordinate paper with peak let-through current on the y-axis and prospective current (rms symmetrical available) on the x-axis, so that the peak let-through current for each rating of current-limiting fuse can be obtained.

6.6.9 I2t characteristics for current-limiting fuses

The manufacturer shall make available values of clearing [operating] I2t and melting [pre-arcing] I2t for those prospective currents for which the fuse exhibits a current-limiting action. Values stated for the clearing I2t shall represent the highest values likely to be experienced in service. These values shall refer to the test conditions of this standard, for example, the values of voltage, frequency, and power factor. Values stated for the melting I2t shall represent the lowest values likely to be experienced in service.





The presentation of I2t values may be in simple tabular or diagrammatic form (for example, histograms) or may employ graphical presentation with prospective current as abscissa and I2t as ordinate, both scales being logarithmic with preferred dimensions as in 11.1.5. The I2t values determined as a part of the interrupting tests specified in 6.6 shall not be greater (for clearing I2t) or less (for melting I2t) than the values stated by the manufacturer.

6.6.10 Fuses intended for use in liquid-filled enclosures

Test series 1 through 3 and It may be performed in air or in a liquid-filled enclosure. Since testing in air is held to be more onerous, this may only be done with the agreement of the manufacturer. In the case of failure, the relevant test series may be repeated with the fuse in a liquid-filled enclosure, using an arrangement of test conductors suitable for that enclosure.

6.6.11 Test It for fuses that exhibit crossover current(s)

In general, tests shall be performed at a minimum of two values, It1 and It2. At least two tests shall be performed at each test value.

It1 = 1.2 It (±0.05 It) and

It2 = 0.8 It (±0.05 It) where It is the value of crossover current provided by the fuse manufacturer. If it is known that these values do not represent the most onerous conditions for the given design of fuse, then the manufacturer may nominate other values of It1 and It2. The parameters to be used when performing the tests, depending on the values of the crossover current It, are as follows:

It in the short-circuit (current-limiting) range: all test conditions as given in Table 14 as appropriate for the test current

It in the low overcurrent range, that is, below 12 times rated current: X/R and power-frequency recovery voltage as specified for test series 3

It in the intermediate current range:

Power-frequency recovery voltage = rated maximum voltage +5%, –0%

X/R (power factor):

a) 2.3 to 3.2 (0.4 to 0.3 lagging) if the crossover current It is between 12 and 25 times rated current Ir

b) 3.2 to 4.9 (0.3 to 0.2 lagging) if the crossover current It is between 25 times rated current Ir and I2

TRV: Specified by the fuse manufacturer, so as to represent typical values found in circuits for which the fuse is intended as being suitable for use, based on the necessary test currents. Guidance as to appropriate values of TRV may be obtained from test standards for other switching devices intended for use under similar circumstances. The tests should be performed in the current region where there is an abrupt or gradual crossover of interrupting duty from one interrupting mechanism to another. The test current values are to be provided by the manufacturer. The typical criteria used in assessing compliance with this requirement are discussed in Annex E.





6.7 Description of interrupting tests for FEPs using current-limiting-type indoor distribution and power class fuses

6.7.1 Use of current-limiting fuses in enclosures

Many applications require the use of current-limiting fuses in enclosures where the fuse and associated contacts may be subjected to air temperatures above 40 ºC. Other applications may require the fuse to be immersed in a liquid such as transformer oil hotter than 40 ºC. Current-limiting fuses intended for such application shall comply with the applicable design tests specified in this subclause in addition to those specified in 6.6, unless otherwise specified in 6.7. When current-limiting fuses are applied in enclosures of any type, the performance characteristics of the total system shall be evaluated. This evaluation of the total system shall be the responsibility of the supplier of the FEP. The following tests and test descriptions reflect this basic requirement. (See 1.5 for descriptions of the FEP types covered by this subclause.)

6.7.2 Fuse ambient temperatures

When a fuse intended for such an application is tested according to this subclause, it is assigned a RMAT. It is the temperature at which these tests are performed. If the maximum temperature for a particular application is known, then an appropriately tested fuse may be chosen (that is one having an RMAT equal to or greater than the maximum temperature anticipated in service). It should be noted that for some applications, the RMAT might only occur under abnormal conditions, for example, transformer overload or during equipment failure. In such cases, although a fuse can be assigned an appropriate RMAT, it may not be suitable for continuous operation at such a temperature without exceeding the maximum temperatures specified in Table 1 in IEEE Std C37.40. Indeed, some typical RMAT values may be higher than the maximum temperatures specified in Table 1. (See 1.5 for descriptions of the cooling fluid to which the RMAT refers.)

6.7.3 Description of tests to be made

The following tests shall replace the tests specified in 6.6 for certain fuse ratings (generally the maximum current rating of a homogeneous series), unless otherwise specified in this subclause.

NOTE—Generally, tests performed at a fuse’s RMAT replace the tests specified in 6.6, unless tests at a lower temperature produce more onerous conditions for the fuse.

a) Test series 1:

No additional tests are required

NOTE—Series 1 tests are considered unnecessary since elevated temperature test failures are generally related to elevated component temperatures, and series 2 tests (intended to approximate maximum arc energy) are apt to produce higher temperatures.

b) Test series 2:

For backup, general-purpose and full-range fuses, three test series 2 tests, in addition to those specified in Table 14, shall be performed with the fuses at its RMAT. The additional tests apply only to the largest current rating of a homogeneous series.





Where the RMAT is less than 15% of the melting temperature (in degrees Celsius) of the material that forms the current-limiting fuse element, experience has shown that more severe series 2 test conditions will result from tests done at the RMAT for a given fuse, rather than at the ambient temperature prevailing at the test site (used for the testing specified in 6.6.1 and Table 14). In this case, the I2 test at the RMAT replaces the test specified in 6.6.1 for the maximum current rating of a homogeneous series.

NOTE—When a fuse is tested at surrounding temperatures within the normal service conditions (–30 °C to 40 °C), the series 2 tests normally produce the highest fuse component temperatures seen in typical applications (approximately maximum arc energy). If the test is performed with the fuse starting at its RMAT, I2t and arc energy will typically be reduced slightly, because the element starts closer to its melting temperature, resulting in a slightly lower temperature-rise for all of the fuse’s components. However, due to the higher starting temperature, maximum final temperatures will be higher than with a test performed at normal service conditions. Elevated temperatures can cause a fuse to fail to interrupt fault current, since the heat can reduce the strength of cap/tube joints, carbonization of an organic based fuse body (typically an epoxy/fiberglass fuse tube), or a dielectric breakdown of the fuse element support or the fulgurite created during the interruption process. Therefore, a test that results in the maximum energy release at a particular starting temperature, combined with the highest temperature for which the manufacturer rates the fuse as being suitable (RMAT), is the most severe thermal test of fuse performance. If the melting temperature of the fuse’s element is relatively low compared with the fuse’s RMAT, a significant reduction in melt I2t, and hence, arc energy, may result in lower component temperatures or a much easier duty on the fuse. For this reason, testing at normal service conditions is still required if the RMAT is more than 15% of the element melting temperature.

c) Test series 3

Backup fuses: For a backup fuse, if the melting time observed during test series 3 tests specified in 6.6.1, and performed with a surrounding temperature below 40 ºC, resulted in a melting time greater than 100 s, then two additional test series 3 tests shall be performed with the fuse at its RMAT. These additional tests apply only to the largest current rating of a homogeneous series that has a melting time in excess of 100 s, and the duration of recovery voltage shall be 10 min.

General-purpose fuses: The test current for an FEP using a general-purpose fuse shall cause fuse melting in not less than 1 h. For tests at its RMAT, this current may require derating. Refer to IEEE Std C37.48 for further information.

Full-range fuses: The tests specified in 6.6, and Table 14, are performed with the fuse at its RMAT. No additional testing is required.

6.7.4 Test procedure

Test procedures shall be as specified in 6.1, 6.6.2, 6.6.3, and as follows. For FEP types 1CL and 3CL, the elevated temperature testing covered in 6.7 can usually be performed with the test sample placed in a stable thermal environment, such as a temperature-controlled oven, set to the temperature for which the fuse is rated by the manufacturer (RMAT). Once the fuse body has reached a stable temperature, any circulating air fans used shall be switched OFF for the remainder of the test. If a fuse only intended for use in liquid-filled enclosures is being tested, for convenience, in air (see 6.6.10), then a circulating fan need not be switched OFF during the test. Generally, when testing is performed according to 6.7, a fuse will not be mounted in actual equipment with which it will be used in service (for example, when an oven is used to create the RMAT). In this case, although the fuse should be mounted in a manner that simulates service conditions as closely as possible, it is recognized that all aspects of its mounting (for example, grounding of components) may not fully comply with all the requirements of Clause 4.





If a fuse required to be tested according to this subclause is intended for use in a fuse container (FEP type 2CL), it shall be tested in an appropriate small enclosure (forming an FEP) to simulate service conditions. If the RMAT assigned to the fuse/FEP is above 40 °C, then the fuse and enclosure combination shall be mounted in an oven or larger enclosure to permit the surrounding medium that cools the FEP (e.g., air or oil) to have a temperature equal to or greater than the assigned RMAT. Auxiliary heating, as detailed above, may be used. In general, an individual FEP need not be tested if the fuse it uses has been tested under equivalent, or more severe, conditions. When a fuse produces condensable gases (e.g., water vapor to assist in the arc interruption process), and it is intended for use with a type 2CL FEP, two series 3 tests shall be performed on the maximum rating of a homogeneous series, with the fuse in an appropriate fuse container, and with the temperature of the FEP cooling fluid between 10 ºC and 40 ºC. These tests shall be in addition to any other tests specified in 6.7 and are intended to show that any gases that could condense inside the fuse canister do not cause an electrical breakdown during the recovery voltage period. For these tests, any part of the fuse container normally grounded in service shall be connected to ground. Any fuse intended for use in an FEP that is not assigned an RMAT higher than 40 ºC may have any tests specified in 6.7 performed in a surrounding temperature of between 10 ºC and 40 ºC (that is, a fuse effectively having an RMAT of 40 ºC can generally be tested at the prevailing ambient temperature without the need for a heated enclosure). In the case of a full-range fuse, however, the series 3 minimum test current (see 6.6.3.1) shall be established in an ambient temperature of 40 ºC.

6.7.5 Temperature of device after test

The FEP shall be allowed to cool naturally during the voltage withstand period.

6.7.6 Mounting and grounding of device

The tests specified shall be performed with the current-limiting fuse or FEP mounted in a manner that will simulate the service conditions specified by the supplier of the FEP. Liquid-immersible fuses may be tested in either air or liquid at the discretion of the manufacturer.

6.7.7 Overvoltages for current-limiting fuses in enclosures

Overvoltages produced during the series 2 interrupting tests specified in 6.6.1 shall be recorded by a cathode-ray oscillograph or other instrument having a frequency response greater than that of the waveforms being measured.

6.8 Description of interrupting tests for FEPs using liquid-submerged, expulsion type indoor power class fuses

6.8.1 Applicable devices

Subclause 6.8 applies to expulsion fuses that are immersed in liquid and used in switchgear (not directly associated with transformers). It is intended to provide testing requirements for such fuses in an enclosure. It is not intended to apply to distribution oil cutouts, which are devices formally covered by this standard that are now obsolete. (See 1.4, Type 3E, for a description of the FEP covered by this subclause.)

6.8.2 Grounding

The enclosure shall be grounded as specified by the manufacturer.





6.8.3 Liquid

The enclosure shall be filled with insulating liquid(s) as specified by the manufacturer. When testing liquid-submerged fuses to verify their ratings, the liquid shall not be changed or reconditioned during the tests.

6.8.4 Condition of the device

Where parts of a tested assembly are reusable, the manufacturer’s guidelines should be followed regarding the number and type of tests. All specified cleaning, inspection, and maintenance steps recommended by the manufacturer shall be followed.

6.8.5 Mounting of device

The tests specified shall be performed with the device mounted in a manner that will simulate the normal service conditions specified by the manufacturer. Liquid-submerged expulsion fuses are sometimes used in series with current-limiting fuses. Since the objective of these tests is to determine the performance of only the expulsion fuses, these tests should be performed without the current-limiting fuse in series. The mounting of these type devices should simulate their normal mounting position and structure.

6.8.6 Test circuit and test series

Tests for liquid-submerged expulsion fuses used in enclosures shall be made in accordance with Table 17. Fuses that form a part of a homogeneous series are tested as specified in 6.2 and associated Table 4. A description of the two series of tests required is as follows:

Test series 1: Verification of operation with available currents equal to the rated interrupting current of the expulsion fuse.

Test series 2: Verification of operation with small overload currents.





Table 17 —Interrupting performance test and test circuit parameters for liquid-submerged expulsion fusesa used in enclosures

Parameters Test series 1 2

Power-frequency voltage Rated maximum voltage: +5%, 0% TRV See Table 9, column 1 See Footnote b Prospective (available) current—rms symmetrical Rated interrupting current: +5%, 0% 2.7 to 3.3 times link or fuse-unit ratingc

X/R ratio (power factor) Not less than 8 (not greater than 0.124) From 1.3 to 0.75 (from 0.6 to 0.8)

Making angle after voltage zero—degrees

1st test: from +5 to +15d

2nd test: from 85 to 105 3rd test: from 130 to 150

Random timing

Current rating of fuse link or fuse unit Min Max Min Max

Number of testse 3 3 2 2 Duration of power-frequency recovery voltage after interruption Not less than 1 min aIn some cases, these devices are designed to be used in series with a current-limiting fuse. For those devices where the current-limiting fuse is an integral part of the device, the test should be performed without the current-limiting fuse but with a device that simulates the size and shape of the current-limiting fuse except for its fusible element. bThe TRV for this test circuit shall be critically damped. Shunting the load reactance with a resistance having a value equal to approximately 40 times the value of reactance is usually adequate to critically damp the circuit. However, if this value does not result in critical damping, then the resistance may be reduced to achieve critical damping. For testing convenience, an oscillatory TRV may be acceptable with the agreement of the switchgear manufacturer. Critical damping is obtained when

XffR

n

o2

=

where

fo is the natural frequency of test circuit without damping fn is the power frequency X is the reactance of the circuit at power frequency

cIf the test involves a melting time appreciably higher than 2 s, then the current may be increased to obtain a melting time of approximately 2 s. dA phenomenon has been observed in which a wire element expulsion fuse, melting close to zero on the voltage waveform (usually a low current rating fuse with a relatively high prospective current), produces sufficient arc voltage to cause a significant current-limiting effect. Since this does not represent typical fuse behavior, such a test shall be repeated. Setting the minimum angle for this test at 5 degrees is normally sufficient to prevent this phenomenon, but if necessary, a further increase in closing angle, within the specified limits, should produce a more normal “non–current-limiting” behavior. eThe number of tests on any one holder for devices with replaceable links should be limited to the number recommended by the switchgear manufacturer.

6.9 Description of interrupting tests for air-insulated FEPs using expulsion type indoor power class fuses

6.9.1 Use of expulsion fuses in enclosures

The installation of a fuse or fuse and container combination (F/C) in an enclosure results in a total system that shall have performance capabilities suitable for the application intended. Expulsion fuses intended for this application shall comply with the interrupting tests specified in 6.9 and the applicable tests specified in 6.5. When expulsion fuses are applied in enclosures of any type, the performance characteristics of the total system shall be evaluated. The following tests reflect this basic requirement. See 1.4, Types 1E and 2E, for descriptions of the devices covered. The following tests, beyond those specified in 6.5, are conducted to





a) Verify that the enclosure containing the fuse or F/C does not adversely affect proper performance and servicing of the fuse or F/C

b) Verify that the operation of the fuse or F/C in an enclosure does not adversely affect the mechanical and dielectric integrity of the enclosure

6.9.2 Test site conditions

Normal ambient temperature conditions may prevail when testing a fuse or F/C having a rated maximum application temperature no higher than 55 °C. However, if the rated maximum application temperature is higher than 55 °C, testing shall be performed with the fuse or F/C in its rated maximum application temperature. In all cases, the device shall be stabilized at the referenced ambient temperature before the test current is applied to the fuse.

a) For Type 1E fuses, the rated maximum application temperature is the air temperature inside the enclosure.

b) For Type 2E fuses, the rated maximum application temperature is that of the air outside the container.

6.9.3 Mounting and grounding of device for test

The fuse or F/C shall be mounted in the enclosure in its normal service position. The fuse or F/C manufacturer’s guidelines for installation in an enclosure should be followed. These guidelines should present information on the minimum required electrical clearances and the minimum construction requirements for the enclosure. All conducting parts of the enclosure shall be grounded.

6.9.4 Test series

6.9.4.1 Single-phase devices

For fuses or F/Cs that are applied to protect only single-phase circuits, single-phase interrupting tests shall be performed. A three-phase test is an acceptable alternative. Using a fuse link or fuse unit having a current rating between 20 A and 50 A, the three tests of Table 11, power fuses, test series 1, shall be performed on a single fuse or F/C. However, the single-phase circuit voltage shall be equal to the single-phase voltage rating of the switchgear, and the TRV frequency and peak factor shall be appropriate for rated maximum line-to-line voltage. Use of a fuse current rating between 20 A and 50 A will result in a duty-severity representative of, or exceeding, the result when using current ratings of a larger size.

6.9.4.2 Three-phase devices

For fuses or F/Cs that are applied to protect three-phase circuits, a three-phase interrupting test is required. In a three-phase circuit with voltage equal to the maximum rated voltage of the fuse or F/C, and with either the neutral of the source grounded or the three-phase fault point grounded, but not both, a current equal to the maximum symmetrical interrupting rating of the fuse or F/C shall be applied. Fuse links or fuse units having a current rating between 20 A and 50 A shall be used. The current-making angle shall be such as to produce a current of maximum asymmetry in at least one of the phases. The circuit X/R and inherent transient recovery voltage conditions specified in Table 11, power fuses, test series 1, with peak factor based on 0.87 three-phase test voltage, shall prevail across the first phase to clear. TRV control elements may be selected by





a) Using an ideal interrupting device to interrupt the three-phase circuit

b) Current injecting one open phase while the other two phases are closed


The condition of the device after interrupting tests shall conform to 4.5, and the enclosure shall be as follows. The enclosure shall be capable of withstanding the forces resulting from the operation of the fuse or F/C. There shall be no operation-impairing deformation or effect on the enclosure and its doors, latches, and interlocks (if present), and no internal components shall be affected, except the fuse and exhaust-control device.

6.10 Description of interrupting tests for external fuses for shunt capacitors

6.10.1 General

Depending on the applications intended for the device, the interrupting tests specified in Table 18 shall be made on the device. These tests shall be performed as specified in 6.10.3, 6.10.4, and 6.10.5, as well as the referenced tables. For all interrupting tests, records of source voltage, fuse voltage, and current through the fuse shall be obtained. Instrumentation should be adequate such that the high frequencies involved during the interrupting process are accurately recorded. The metering instrumentation used should not significantly affect the recovery voltage. Appropriate metering methods will allow convenient determination, when required, of performance parameters such as peak overvoltage, arc energy, recovery voltage, peak let-through current, and I2t.

Table 18 —Types of interrupting performance tests required for capacitor fuses

Tests

Fuse type

Capacitor line fuse Capacitor unit fuses used where inductive

faults can occur

Capacitor unit fuses used where inductive faults are unlikely to

occur (see Footnote a) Power-frequency inductive currents (see 6.10.3)

X X —

Power-frequency capacitive currents (see 6.10.4)

X X X

Capacitive-discharge currents (see 6.10.5)

See Footnote b X X

aExamples of these applications are as follows: 1) Individual fuses in wye-connected banks with ungrounded neutral and ungrounded frames 2) Banks with series capacitors

bUnusual applications, such as back-to-back banks on the same pole with each bank having its own line fuse could require the fuse to be capable of interrupting capacitive discharge currents. Since the size of these banks would generally be small, most line fuses could satisfactorily handle the discharge currents. Consult the fuse manufacturer for these types of applications.





6.10.2 Determination of available short-circuit current

Determination of available short-circuit current of the test circuits shall be as specified in 6.1.2.2 and 6.10.4.

6.10.3 Interrupting tests—inductive currents

All capacitor fuses that are rated for interrupting inductive currents shall be tested for inductive fault current interrupting performance as follows:

Capacitor line fuse Table number and test series

Power fuses (except current limiting) Table 11: test series 1, 2, 3, and 4 Single-voltage-rated distribution cutouts Table 7: test series: 1, 2, and 3 Slant-voltage-rated distribution cutouts Table 8: test series 1, 2, 3, and 6 Current-limiting power and distribution fuses Table 14: test series 1 and 2

Capacitor unit fuse All capacitor unit fuses (except current limiting) Table 11: test series 1, 2, 3, and 4, or Table 7: test series

1, 2, and 3 Current-limiting capacitor unit fuse Table 14: test series 1 and 2

For the inductive current interrupting tests for capacitor unit fuses, a capacitor shall be placed in parallel with the fuse under test. This parallel capacitor shall be sized to draw a current at the test voltage of between 25% and 75% of the allowable continuous current of the fuse under test. The transient recovery voltage requirements of Table 7, Table 11, and Table 14 do not apply to the tests on capacitor unit fuses when parallel capacitors are used in the test circuit.

Capacitor unit fuses that have met the interrupting requirements when tested without parallel capacitors need not be retested with parallel capacitors in the test circuit.

Examples of applications where inductive currents can flow are as follows:

a) Capacitor line fuses

b) Capacitor unit fuses in delta-connected banks without capacitor units in series

c) Capacitor unit fuses in wye-connected banks, without capacitor units in series, and with the neutral or the frame grounded

d) Capacitor line and capacitor unit fuses, without capacitor units in series, used on single-phase circuits





6.10.4 Interrupting tests—power-frequency capacitive currents

All fuses applied to protect capacitors can be called upon to interrupt power-frequency capacitive currents. Tests shall be made in accordance with Table 19 and shall consist of the following test series:

Test type For capacitor unit fuses

For capacitor line fuses

Verification of the operation with available current equal to rated maximum capacitive interrupting current at rated maximum voltage.

Test series 1 Test series 3

Verification of the operation with available currents equal to rated minimum capacitive interrupting current at rated maximum voltage. This duty simulates progressive elements (pack) failure in a capacitor unit.

Test series 2 Test series 4

Examples of conditions where capacitive overcurrents can occur are as follows:

a) Partial capacitor failure for those applications listed in 6.10.3

b) Capacitor unit or capacitor line fuses in wye-connected banks with an ungrounded neutral

c) Banks with capacitor units in series

The test circuits and equipment arrangement for capacitive current-interrupting tests should be as follows:

The circuit elements used to control the test circuit’s short-circuit current and X/R ratio, to the requirements specified in Table 19 and Table 20, shall be in series with each other and the test specimen.

The test circuit’s source short-circuit current shall be measured per 6.1.2.2, except all circuit capacitive loading shall also be short-circuited for this measurement.

The test circuit’s capacitive current shall be controlled by capacitor units connected in series with the test specimen and with the test circuit’s short-circuit control loading.

The waveform of the current to be interrupted should, as nearly as possible, be sinusoidal. This condition is considered to be complied with if the ratio of the rms value of the current to the rms value of the fundamental component does not exceed 1.2.





Table 19 —Capacitive current-interrupting performance tests and test circuit parameters for all types of capacitor fuses

Parameters Capacitor unit fuses Capacitor line fuses

Test series Test series 1 2 3 4

Power-frequency recovery voltage (excluding dc voltage component)

Rated maximum voltage: +5%, −0% (see 6.10.6 for crest recovery voltage requirements) (See Footnote a)


Rated capacitive interrupting current +5%, −0%

Capacitive current value resulting in a

melting time of 10 s minimum

Rated capacitive interrupting current +5%, −0%

Capacitive current value resulting in a

melting time of 10 s minimum

Source

X/R ratio ≥8

TRV parameters

No TRV control required Distribution class fuses, except current limiting—see Table 9, column 1, Power class fuses and

distribution class current limiting—see Table 12, column 1

Short-circuit current

12.5 to 25 times rated capacitive interrupting current

See Table 20

Test circuit See 6.10.4 and figures listed below

(Where two figures are listed for a test series, the circuit used is optional.) Figure 3a) Figure 3b) Figure 3c) Figure 3d) Figure 3e) Figure 3e)

Switching angle related to voltage zero of source—degrees

From −10 to +10

From +85 to +105

Random timing From −10 to +10 From +85 to +105

Random timing

Current rating of fuse unit or fuse link to be tested (see Footnote b and Footnote c)

Min Max Min Max Min Max Min Max Min Max Min Max

Number of tests (see Footnote d)

3 3 3 3 2 2 3 3 3 3 2 2

Number of tests on each fuse holder for expulsion type fuses (see Footnote d)

3 3 3 3 4 3 3 3 3 4

Duration of power- frequency recovery voltage after interruption

Dropout and isolating-gap fuses

Not less than dropout time or 0.5 s, whichever is greater

Non-dropout and non-isolating-gap fuses

Not less than 1 min

aFor slant-voltage-rated cutouts, test series 3 and 4 shall be made with a test voltage at the value to the right of the slant. For example, the test voltage for 15/27 kV rated cutouts shall be 27 kV.

bFor all types of expulsion fuses that use replaceable links, the minimum and maximum fuse links to be used for the tests are related to the ampere rating of the fuse and the basic construction of the fuse link. For all fuses rated 50 A maximum, the minimum size link for testing is a 6 A type K and the maximum is a 50 A type T; for fuses rated 100 A maximum, the minimum size link for testing is a 6 A type K, and the maximum size link for tests is a 100 A type T; for fuses rated above 50 A to 100 A maximum, the minimum size link is a 65 A type K, and the maximum is a 100 A type T; for fuses rated above l00 A to 200 A maximum, the minimum link is a l40 A type K and the maximum link is a 200 A type T. If the construction of intermediate fuse links differs from the construction of the minimum or maximum rated fuse links, and this difference in construction is likely to affect interruption performance adversely, then additional testing of such ratings is required.

c“Min” and “Max” represent the minimum and maximum rated currents of a homogeneous series, see 6.2 and 6.6.4. dAfter each test, only the parts normally field replaceable shall be replaced.





G Vs

Vf

Cp

Ct

FIf

SCB CS

G Vs

Vf

Cp

FIfS

CB CSCt

c)

R1XL1

G Vs

Vf

Ct

FIf

S (Optional)

CB CS

d)

R2C1

R1 XL1

G Vs

Ct

FIfS

CB CS

e)

Vf

R2C1

R1 XL1

R1XL1

a)

G Vs

VfCpFIf

S

CB CSCt

b)

R1 XL1

Figure 3 —Typical circuit diagrams for capacitive current interrupting tests





NOTE 1—Definitions for Figure 3 are as follows:

C1 is the transient recovery voltage frequency control for the source CB is the circuit breaker Cp are the capacitors corresponding to the capacitors in parallel with the failed unit CS is the laboratory closing or isolating switch Ct are the capacitors for producing the required capacitive test current F is the fuse under test G is the power source If is the fuse current If = Vs × 2π × (power frequency in Hz) × Ct R1 is the resistance to control the X/R of the source R2 is the damping resistance to control the peak factor of the source S is the switch for initiating the fuse operation Vf is the rated maximum fuse voltage (i.e., the power-frequency component of this voltage, after

the fuse interrupts the current, shall be equal to or greater than the rated maximum voltage of the fuse)

For a) and b) in Figure 3:

+×=

tp

tsf CC

C)V(V

For c), d), and e) in Figure 3: Vf = Vs

Vs is the source voltage XL1 is the inductive reactance of the source

NOTE 2—For d) and e) in Figure 3, damping circuits, other than those shown for controlling the inherent TRV parameters of the test circuit, may be used by mutual agreement between manufacturer and test laboratory. Such use shall be noted and explained in the test report. NOTE 3—In circuits a), b), and c) in Figure 3, the effect of capacitance on the recovery voltage appearing across the fuse is taken into account by Cp. This value represents between 300 kVAR and 400 kVAR. Experience has shown that the value of Cp is not critical on the capacitive interrupting performance of fuses. Cp shall be

( ) ( ) ( )kV1000μF 2f

pV

C ≥

NOTE 4—For a) and d) in Figure 3, closing the switch S initiates the fuse operation, and for b), c), and e) in Figure 3, opening the shunting switch S initiates the fuse operation. Note that closing of the switch CS may also be used to initiate the fuse operation for the test circuit shown in d) in Figure 3. The impedance of the shunting switch S, including the connected cable, used for the test circuits as shown in b), c), and e) in Figure 3, should be minimized to ensure that with the switch closed, the current through the fuse does not exceed 1.5 times the current rating of the fuse, as shown on the nameplate. As an alternative, a small impedance may be connected in series with the fuse, thereby reducing the current through the fuse and increasing the current through the parallel connected shunting switch.





Table 20 —Source short-circuit current for capacitor line fuses

Continuous current rating of fuse unit or fuse link as shown on the nameplate (A)

Short-circuit level of source in rms symmetrical amperesa,b,c

>1 and 50 1250–2500 >50 and 100 2500–5000 >100 and 200 5000–10 000 >200 and 300 7500–15 000

>300 10 000–20 000 aThe values for the short-circuit level have been selected based on 2% to 4% e. The e chosen is representative of the percent voltage regulation attributed to capacitor bank installations in the field and is estimated as follows:

100100%Δ ×≈×≈SC

C

C

LII

XXe

where

XL is the inductive reactance of the source XC is the capacitive reactance of the load IC is the continuous current rating of the fuse unit or fuse link as shown on the nameplate (A) ISC is the symmetrical rms short-circuit current of the fault

bCurrent-limiting fuses conforming to a homogeneous series should use the short-circuit current values listed above, based on the maximum continuous current rating in the homogeneous series.

cIf the inductive interrupting current rating of the fuse is less than the values shown, use this lower value.

6.10.5 Interrupting tests—capacitor discharge

This test verifies the maximum parallel stored energy where the capacitor unit fuse will operate successfully. After the circuit-interrupting operation, the components of the fuse (except for those intended for field replacement) shall be substantially in the same condition as they were prior to the test. Erosion of the bore of the fuse tubes of expulsion fuses is acceptable. Flashover to ground or adjacent fuses, emission of flame or filler material from current-limiting fuses, or bursting of any parts is not acceptable. A minor spark or flame from an indicating device is acceptable.

The test circuit for capacitor discharge current interrupting tests shall be as follows:

a) The capacitance of the test circuit shall be such that the stored energy (joules) in the capacitor(s) has the specified value at the test voltages specified below.

The capacitor(s) shall be charged by means of dc to one of the following voltages:

1.00(+10% – 0%) 2fV for expulsion fuses

2.00(+10% – 0%) 2fV for current-limiting fuses

where

Vf is the rated maximum voltage of the fuse in rms volts.

At the manufacturer’s option, if the required energy cannot be achieved with the capacitors available, then the charge voltage may be increased as necessary above the 10% allowed.





b) If an unlimited “joule rating” is claimed for the fuse, then the charge voltage may be increased such that at the instant of interruption, the voltage remaining on the bank shall not be less than

20.2 fV

where

Vf is the rated maximum voltage of the fuse in rms volts.

c) The oscillatory frequency of the test circuit shall not be less than

fV.F 80= where

F is the frequency (hertz), Vf is the rated maximum voltage of the fuse (rms volts)

No additional inductance shall be added to the test circuit. If the test circuit conditions do not permit the required discharge frequency to be obtained, then the actual discharge frequency recorded during the tests shall be specified along with the maximum stored energy (joules) rating when it is published or when the rating information is disseminated.

d) The ratio between successive current peaks (reversal) shall be between 0.8 and 0.95. This requirement shall be determined by replacing the fuse with a shorting link of negligible impedance compared with that of the test circuit. This calibration test may be made at a reduced voltage.

e) For fuses that do not provide an automatic isolating gap after operation, the voltage trapped on the capacitors shall be left on the fuse for a minimum of 10 min after the fuse operates. This may require that the capacitors used in the test circuit be without discharge resistors.

The test procedures for capacitor discharge current interrupting tests shall be as follows:

For current-limiting fuses belonging to a homogeneous series per 6.6.4, the fuse with the smallest current rating in that particular series and the fuse with the largest current rating in that series shall be tested. Any current rating of fuses within this series shall be deemed to comply with the interrupting requirements of this standard if these units operate satisfactorily. If a fuse does not perform satisfactorily, then it may be rejected from the homogeneous series and a new series should be selected.

For expulsion type fuses, the tests should be made on all fuse types where the bore of the fuse tube and/or its length changes, and on any fuses where the materials of the fuse tube are different from other tested devices. For fuses that use replaceable links, the tests should be made with the smallest and the largest link that is intended to be used in the particular fuse holder. A 6 A type K link may be used for the minimum size requirement.

Two tests are to be made on each size fuse. For expulsion type fuses, a complete new fuse shall be used for the second test.

The residual voltage across the capacitor(s) shall be measured immediately after discharge to determine the amount of energy dissipated in the fuse and the circuit resistance. This residual voltage shall be recorded in the test report.

The “joule rating” that may be assigned to the fuse being tested is the energy stored in the capacitor test bank prior to the time it is discharged through the fuse.





6.10.6 Criteria for successful interruption tests

a) Flashover to ground or adjacent components shall not occur during operation when the fuse is mounted in accordance with the manufacturer’s recommendations and per 4.7.7.

b) Following the interrupting of the test current, the fuse shall be capable of withstanding the recovery voltage of the test circuit, which may be as high as

fV×× 22

where

Vf is the rated maximum voltage of the fuse (rms volts)

c) After the fuse has operated, the components of the fuse (apart from those intended to be replaced after each operation) shall be in substantially the same condition as at the beginning of the test, except for erosion of the bore of the fuse tube of expulsion fuses. After completion of the interrupting discharge tests, however, the components of the fuse may be damaged and require replacement to restore the fuse to its operating condition.

7. Load-break tests

7.1 Procedures common to all load-break tests

7.1.1 General

Devices, unless they incorporate a load-breaking means, have no load-break rating. Load-break test procedures for devices with load-breaking equipment shall be as specified in Clause 4 and in Clause 7.


The device shall be mounted in all positions for which it is designed or for which it is recommended for load-break operation.

7.1.3 Test circuit

7.1.3.1 Test circuit power factor

The power factor of the test circuit shall be between 70% and 80% for lagging power factor tests and between 0% and 10% for leading power factor tests. If test laboratory limitations or special applications require a more severe test circuit, the lagging power factor may be reduced to less than 70% upon agreement with the device’s manufacturer. In special applications, the allowable limits for tests shall be as agreed upon by the manufacturer and the user.

7.1.3.2 Test circuit impedance

The circuit impedance Z shall consist of two components connected in series. The first component shall not be less than 10% or more than 20% of the total impedance of the test circuit and shall have an X/R ratio of 2 or more. This circuit component shall have its inductive and resistive elements in series relationship. The second component for lagging power factor tests shall consist of inductance and resistance in parallel relationship (see





Figure 4). The second component for leading power factor tests shall consist of capacitance alone. When tests are made line to ground, at least the second component of impedance shall be on the load side of the device.

TESTSPECIMEN

XL1R1

Z1 is > .1Z AND < .2Z

XL1 / R1 > 2

R2

XL2

Z is the total circuit impedance

a) Typical lagging power factor test circuit

XL1

TESTSPECIMEN

R1

C2

Z1 is > .1Z AND < .2Z

XL1 / R1 > 2

Z is the total circuit impedance

b) Typical leading power factor test circuit

Figure 4 —Test circuit for load-break tests

7.1.3.3 Test circuit capacitance

The total shunt capacitance of the test circuit (measured across the open switch) when breaking inductive loads shall not exceed the following.

Test voltage (kV)

Maximum capacitance (µF)

2.6 0.003 5.2 0.066 7.8 0.10 15.0 0.20 18.0 0.20 27.0 0.35 38.0 0.40

NOTE—These values apply only to devices designed for use on distribution circuits.





7.1.3.4 Power-frequency recovery voltage

The power-frequency recovery voltage across the terminals of the device shall be the rated maximum voltage of the device.

7.1.4 Measurement of test values

7.1.4.1 Measurement of test current

The current interrupted shall be the rms symmetrical current measured from the envelope of the wave at the start of arcing.

7.1.4.2 Calculation of test current and recovery voltage

The rms alternating test current and recovery voltage shall be determined. This may be accomplished by following the methods described in Annex A.


There shall be no failure to interrupt the circuit for any test condition, fuse link rating, and mounting position. Tests shall be made under a sufficient number of conditions to ensure meeting the requirements specified for the device or mechanism undergoing test. The condition of the device at the conclusion of any series of five load-break operations for distribution enclosed, open, or open-link cutouts, the device and the load-break mechanism, after renewing the fuse link if destroyed in the normal load-break operation, shall be as specified in 4.5.

7.2 Description of load-break tests for all fused devices

Load-break tests shall be conducted as follows.

One or more devices with the means for interrupting load currents, or one or more load-break mechanisms properly assembled on devices of the rating and type recommended by the manufacturer, shall be opened manually or automatically, at an equivalent speed, when carrying the specified load current. The test shall be repeated five times with an interval between tests of not less than 3 min.

8. Radio-influence tests

8.1 Procedures common to all radio-influence tests

8.1.1 General

Radio-influence test procedures shall be as specified in Clause 4 and in Clause 8. Radio-influence voltage is the result of electrical stress from an energized part to adjacent energized or grounded parts. Radio-influence voltage for a fuse by itself does not have any meaning. Any test of this type must be performed on the fuse in its mounting. The test should be configured so that the electrical stress on the fuse and mounting, created by mechanical structures of the mount, the spatial relationship between other phases, and sources of voltage and grounds, match the electrical stress that the device under test will experience in use. The manufacturer of the device under test should detail any restrictions on the location of





any adjacent structures or ground. Any test summary or report should detail the locations of these associated parts.


8.1.2.1 Ambient humidity and air density during test

Tests shall be conducted under atmospheric conditions prevailing at the time and place of the test; it is recommended, however, that tests be avoided when the vapor pressure of moisture in the atmosphere is below 680 Pa (0.2 in Hg) or exceeds 2030 Pa (0.6 in Hg). Since the effects of humidity and air density on radio-influence voltage are not definitely known, correction factors are not recommended at the present time. It is recommended, however, that the barometric pressure as well as dry and wet bulb thermometer readings be recorded so that, if suitable correction factors should be determined, they can be applied to previous measurements.

8.1.2.2 Ambient radio-influence noise during test

Tests may be made under the conditions prevailing at the time and place of the test. It is recommended, however, that tests be avoided when the ambient radio-influence voltage (including the influence voltage of irrelevant electrical devices with the device under test disconnected from the test equipment) exceeds 25% of the radio-influence voltage of the device to be tested.

8.1.2.3 Tests on fluid-immersed devices

The tanks of fluid-immersed apparatus shall be filled with the specified amount of fluid.

8.1.3 Proximity of other objects during test

No other grounded or ungrounded object or structure (except a mounting structure when required) shall be in closer proximity to any part of the device undergoing test than three times the longest overall dimension of the device, with a minimum permitted spacing of 0.9 m (3 ft). Where space limitations under test conditions do not permit the above clearance to be maintained, the test will be considered valid if the limits of radio-influence voltage obtained are equal to or less than those specified for the device. In such cases, it is desirable that a record be made of the object, structures, and so on, as well as their distances from the device under test. These data may be useful for future use in determining proximity effect. These clearance guidelines apply predominately to parts used on overhead systems, where maintaining a relatively large clearance between energized parts and grounded components controls the location of adjacent parts. On underground circuits or within fluid-filled devices, the ground or adjacent parts may be closer to parts of the device under test. In these cases, the manufacturer of the fuse and fuseholder shall specify the clearances for the part under test.


The conductors shall be arranged as specified in 4.6.2. The free end of all conductors shall be terminated in a sphere having a minimum diameter of twice the diameter of the conductor, or the free end shall be shielded in some other suitable manner to eliminate the effect of the end of the conductor as a source of radio-influence voltage.


8.1.5.1 Measurement equipment for test

The meter used for making radio-influence measurements shall be in accordance with ANSI C63.2-1987.





8.1.5.2 Measurement of test voltage impulses with low repetition rates

When making measurements on radio-influence voltage impulses with repetition rates so low that meter fluctuation makes reading of either the minimum or the maximum pointer deflection doubtful, the slow-speed indicating output meter listed in 16.2 of ANSI C63.2-1987 shall be used. The highest pointer deflection of the meter during a 15 s interval of observation shall be recorded as the radio-influence voltage, so that differences between various operators in recorded results for noise sources with low repetition rates may be minimized.

8.1.5.3 Test instrument calibration

Calibrations and adjustments of the radio noise meter shall be made as specified in the instruction manual for the radio noise meter.

8.1.5.4 Test instrument settings

The detector function selector switch shall be set to the quasi-peak position on the radio noise meter.

8.1.5.5 Characterization of radio-influence voltage during test

When it is desired to identify the character of the radio-influence voltage, measurements should be monitored using a headset, loudspeaker, or oscilloscope. Precautions should be taken to determine whether or not these devices affect the radio-noise meter indications during measurements.

8.1.5.6 Precautions in taking test measurements

The following precautions shall be observed when making radio-influence tests:

a) The device shall be at approximately the same temperature as the room in which the test is performed. It shall be dry and clean, and it shall not have been subjected to dielectric tests within 2 h prior to the radio-influence test.

b) In some cases, it may be found that the radio-influence voltage falls off rapidly after the rated- frequency voltage has been applied for a short time. In such cases, it is permissible to re-excite the test piece at normal operating voltage for a period not to exceed 5 min before proceeding with the tests.


The radio-influence voltage measured in the test is the total ionization voltage at the terminals of the device. Since this is conducted radio-influence voltage, the permissible maximum values specified for the device in the appropriate standard (see Clause 3) will add a negligible amount to the radio-influence radiated from an otherwise normal line to which the device is connected, even at short distances from the device.

8.2 Description of radio-influence tests on a single device

Tests at 1 MHz shall be made on the device with the fuse unit or fuse holder, including the conducting element (fuse link) or disconnecting switch blade, in the closed and open positions. When a test is made in the open position, the pole or group of poles not connected to the influence-measuring equipment shall be grounded and ungrounded, and the radio-influence voltage shall be determined for each condition.





8.3 Description of radio-influence tests on multiple devices

In the case of multiple devices, one pole or terminal (or groups of the same) may be tested at a time following the procedures specified in 8.2.

8.4 Description of radio-influence tests for assembled apparatus

In the case of assembled apparatus, the test shall be made without removing any component part, and the test voltage shall be based on the lowest rated voltage of any component part. The limiting radio-influence voltage shall be identical to the highest value specified for any of the component parts that determine the test voltage.

9. Short-time current tests

9.1 General

Short-time current test procedures shall be as specified in Clause 4 and in Clause 9. Tests consist of momentary, 15-cycle, and 3 s tests for disconnecting cutouts, and momentary and 3 s tests for distribution class enclosed single-pole air switches (called “air switches” in this clause for convenience).

9.2 Mounting and grounding of device for the momentary test

For distribution disconnecting cutouts only one mounting position (vertical or angle) is required for attaching the support to the devices mounting bracket. If some of these devices do not use a mounting bracket and are designed for other mounting arrangements that have various mounting positions only one position is required for this test. If air switches have various mounting positions provided, only one position is required for this test. Grounding of the mounting bracket or mounting structure of distribution class enclosed or open disconnecting cutouts and air switches is not necessary.

9.3 Test connections

The device shall have a bare conductor connected to each terminal that has the size and minimum length specified in Table 2. The conductors shall leave the terminals in substantially a straight line, parallel to the blade of the device. The minimum unsupported length of these conductors shall be the open-gap distance of the device.

9.4 Test circuit

9.4.1 Test circuit configuration

Short-time tests shall be made using a single-phase alternating current circuit. The circuit elements used to control the current and X/R ratio shall be in series with each other and with the device being tested. The test circuit frequency shall be the rated frequency of the device ± 2 Hz. If 60 Hz test facilities are not available, tests at (50 ± 2) Hz are acceptable for verifying 60 Hz ratings. The circuit for 15-cycle and/or 3 s tests shall be capable of providing the symmetrical current as specified for a particular device in its specification standard. The X/R for these tests may be any convenient value, except as specified in 9.4.4.





For disconnecting cutouts, the circuit for the momentary tests shall be capable of providing the symmetrical current specified for the device’s rated 15-cycle withstand current, as listed in the appropriate table in the device’s specification standard. The circuit X/R shall be equal to the value specified in this same table for the device being tested (if this is not listed for the disconnecting cutout, the value for the equivalent fuse cutout shall be used). For air switches, the circuit for the momentary tests shall be capable of providing the symmetrical current specified for the device’s 3 s rating and the X/R shall be as specified for that particular device.

9.4.2 Test circuit tolerances

For the manufacturer, tolerances shall be +5%, –0% for current, and where a specific X/R is required, it is a minimum value. See 3.4.1 for test parameters for testing performed by other than the device manufacturer.

9.4.3 Test circuit voltage

The test circuit voltage may be any convenient voltage that is capable of supplying the required test currents.

9.4.4 Test circuit X/R ratio for combined tests

For convenience, the momentary test may be combined with the rated 15-cycle disconnecting cutout test, or the rated 3 s air switch test. In this case, the momentary and the 15-cycle or 3 s requirements will be met if the X/R ratio is a value that will provide the rated momentary current specified in 9.7, and the rated 15-cycle or 3 s currents specified in 9.5 or 9.6.

Table 21 —Momentary (first peak) current for a specified 15-cycle or 3 s current and circuit X/R 15-cycle current

(disconnecting cutouts) or 3 s current (air switches) (kA rms symmetrical)

X/R Momentary current (peak kA)

4 8 9.46 4 12 9.97 5 15 12.7

6.25 25 16.5 6.3 5 13.7 7.1 8 16.7 8 12 19.9

8.6 8 20.3 10.6 12 26.4 11.2 5 24.4 12.5 25 33.0 13.2 12 32.8 15 12 37.3 16 5 34.8

9.4.5 Making angle

When conducting the 15-cycle and 3 s tests separately from the momentary test, the power is applied at the point on the voltage wave that minimizes offset in the first loop of current. For the momentary test, and for the 15-cycle or 3 s test when combined with the momentary test, the power shall be applied at the point on the voltage wave that produces the required preferred momentary current (first peak asymmetrical current), listed in Table 21. A making angle, related to voltage zero, from 0° to +10° and the proper X/R will provide the asymmetrical current that has a first peak value equal to, or greater than, that specified in Table 21.





9.4.6 Determination of short-time current

During testing of the circuit or the device, the currents involved shall be measured as follows. For momentary tests, the current peak of the first major current loop shall be determined. For 15-cycle and 3 s tests, the symmetrical current shall be determined. This may be accomplished by following the method shown in Figure A.1. For 3 s tests, the current value may be determined with an ammeter if the circuit characteristics are such that there is no decay in the current values after any initial transient. If current decay does occur, an oscillograph or equivalent metering methods should be used to determine the true rms current.

9.4.7 Determination of the circuit current

Prior to testing of the device, the circuit may be checked (if desired) for correctness and capability by using a reduced voltage check test or, in some cases, a reduced time check test. Normal ratio methods and engineering judgment are used to determine the voltage required for the device test. If the device has negligible impedance, another check method is to replace the properly connected device in the test circuit with a connection having a negligible impedance. If an alternative connection was used to check the circuit, remove it before testing the device.

9.5 Description of 15-cycle current tests

One sample of the device shall be tested in the circuit described in 9.4. The test rms symmetrical current shall be at least the rated 15-cycle current value during the test, with the final measurement taken at the end of the 15 cycles. The preferred values of the rated 15-cycle currents are specified in the specification standard for the device.

9.6 Description of 3-second current tests

One sample of the device shall be tested in the circuit described in 9.4. If the integrated heating equivalent of the 3-second rating has been obtained, the device shall be considered to have been properly tested. The tests may also be conducted at a reduced current if the integrated heating equivalent of the 3-second rating is obtained in a time period not exceeding 8 s. However, for momentary current tests on air switches, the full value of the 3-second current shall be used. The preferred values of the rated 3-second currents are specified in the specification standard for the device being tested.

9.7 Description of momentary current tests

One sample of the device shall be tested in the circuit described in 9.4. The current shall be maintained for a minimum of three cycles. The preferred rated momentary current is achieved when the first major current peak (peak asymmetrical current) meets or exceeds the preferred rated momentary current value specified for the device. This is listed in its specification standard, and in Table 21, based on a device’s preferred 15-cycle or 3-second current and X/R ratio. Momentary tests may be combined with the 15-cycle test or 3-second test (see 9.4.4) When this is done, the circuit shall be closed at the point on the voltage wave that will provide the required momentary current.

NOTE—Prior to the publishing of this standard, momentary currents were defined in terms of first loop rms asymmetrical current. In common with other standards, a change has been made to redefine momentary currents in terms of the value of the first peak of the asymmetrical waveform. Although the intention has been to change the definition of momentary currents, it has not been intended to change the actual method of testing or, indeed, the test currents associated with the





test. It is therefore anticipated that devices tested to earlier versions of the standard will meet the requirements of this standard.


After successful completion of the tests, the condition of the device shall be as specified in 4.5, except the tests may have resulted in some visual evidence of the device having passed current, such as slight contact markings. If this occurs, ratings shall be considered met when the device will withstand repeated mechanical operations without cumulative damage and is capable of carrying its rated continuous current as specified in 4.5.

10. Temperature-rise tests

10.1 Procedures common to all temperature-rise tests

10.1.1 General

Temperature-rise tests shall be as specified in Clause 4 and in Clause 10.


The device shall be mounted in a closed room substantially free from air currents other than those generated by heat from the device being tested. The ambient temperature shall be taken as that of the surrounding air, which should not be less than 10 ºC and not more than 40 ºC. Corrections shall not be applied to any ambient temperature within this range. The ambient temperature shall be determined by taking the average of the readings of three thermocouples (or thermometers) placed as follows:

a) One 30 cm (12 in) above the device

b) One 30 cm (12 in) below the device, 30 cm (12 in) above the floor, and 30 cm (12 in) to the side of the floor-mounted apparatus

c) One midway between the above two positions and 30 cm (12 in) from the side of the device

NOTE—For small devices, such as distribution cutouts or distribution-enclosed single-pole air switches, one thermocouple (or thermometer) at location c) is sufficient.


Grounding of the mounting bracket or base as specified in 4.7 is not required.






10.1.4.1 Method of determining temperature during test

The temperature of a device shall be determined by thermocouples or by mercury or alcohol thermometers. Any of these instruments shall be applied to the hottest parts of the device, excepting the conducting element of a fuse, while maintaining all parts in normal operating condition.

10.1.4.2 Use of oil cups

To avoid errors due to the time lag between the temperature of large devices or apparatus and the variation of ambient temperature, all reasonable precautions must be taken to reduce these variations and the errors arising from them. Thus, when the ambient temperature is subject to such variations that error in the temperature-rise might result, the thermocouples (or thermometers) for determining the ambient temperature should be immersed in a suitable liquid such as oil, in suitably heavy metal cups, or should be attached to suitable masses of metal. A convenient form for such an oil cup consists of a metal cylinder with a hole drilled partly through it. This hole is filled with oil, and the thermocouple (or thermometer with its bulb) is placed therein so it is well immersed. The response of the thermocouple (or thermometer) to various rates of temperature change will depend largely on the size, kind of material, and mass of the containing cup, and it may be further regulated by adjusting the amount of oil in the cup. The larger the apparatus under test, the larger should be the metal cylinder used as an oil cup in determining the ambient temperature. The smallest size of the oil cup employed in any case shall consist of a metal cylinder with 25 mm (1 in) diameter and 50 mm (2 in) height.

10.1.4.3 Use of thermometers

If thermometers are used for taking temperatures, the bulbs of thermometers shall be covered by felt pads cemented to the apparatus, by oil putty, or by cotton waste. Dimensions of felt pads for use with large apparatus shall be 40 × 50 × 3 mm thick (1½ × 2 × ⅛ in thick). The use of smaller pads is permissible on small devices.

10.2 Description of temperature-rise tests

The test current shall be applied continuously until three consecutive temperature readings taken at 30 min intervals show a maximum variation of 1 ºC in the temperature-rise above ambient.

10.3 Description of temperature-rise tests for air-insulated FEPs using expulsion type indoor power class fuses

Additional rated continuous current testing shall be conducted, as specified in the “Ratings” and “Rated continuous current” discussions in IEEE Std C37.20.3, using fuse links or fuse units of the maximum current rating permitted by the rating of the mounting. Connecting conductors and temperature limits for buses and connections shall be the same as specified for switches in IEEE Std C37.20.3. The reference ambient temperature of the fuse or F/C shall also be measured and related to both the ambient temperature surrounding the enclosure and the maximum reference ambient temperature specified by the fuse or F/C manufacturer.





11. Time-current tests

11.1 Procedures common to all time-current tests

11.1.1 General

Time-current test practices shall be as specified in Clause 4 and in Clause 11.


Only one position for mounting all devices is required. Grounding of the mounting bracket or base as specified in 4.7 is not necessary.


11.1.3.1 Measurement of current during tests

The measurement of current through the fuse during a time-current test shall be made as follows:

a) A current existing for 5 s or more may be measured with a standard indicating ammeter.

b) A current of less than 5 s duration shall be measured with an oscillograph or other suitable instrument, and the current wave (including the dc component of current and the ac decrement) shall be corrected to steady-state conditions for plotting both melting and total clearing time curves (see Annex B for method of correction).

NOTE—A standard ammeter equipped with an adjustable stop to reduce the movement of the needle during test will improve the accuracy of the measurement.

11.1.3.2 Measurement of time during test

The measurement of the time shall be made as follows:

a) A time longer than 10 s may be measured with a stopwatch, electric clock, or timer.

b) A time longer than 1 s may be measured with a synchronous timer.

c) A time shorter than 1 s shall be measured with an oscillograph or suitable instrument.

11.1.4 Description of time-current test parameters

11.1.4.1 Initial conditions

Tests shall be initiated with the fuse at an ambient temperature of 20 °C to 30 °C and without an initial load passing through the current-responsive element.





11.1.4.2 Test samples

The fuse links or fuse units shall be tested in the fuse cutout or fuse support with which they are designed to be used.

11.1.5 Presentation of time-current test data

The results of time-current tests shall be presented as time-current curves on log-log paper (preferably with current as abscissa and time as ordinate, and with the dimension of each decade as 5.6 cm). The curves shall show the following:

a) The relation between the time in seconds and the rms symmetrical amperes required either to melt and sever the conducting element or to interrupt the circuit.

b) The basis of time on which the curves are plotted; that is, only the melting time required to melt and sever the conducting element, or the total clearing time, which combines both melting and arcing time.

c) The voltage at which the tests are made when plotted on the basis of total clearing time.

d) The type and rating of distribution or power fuses for which curve data apply.

e) The time range for the fuses, as indicated in item a) through item e) in 11.1.6.

11.1.6 Time parameters of tests

Tests shall be made so that time-current curves are plotted in the time range of

a) 0.01 s to 300 s for power class fuses (except current-limiting fuses) and distribution fuse links, rated 100 A and below.

b) 0.01 s to 600 s for power class fuses (except current-limiting fuses) and distribution fuse links, rated above 100 A.

c) 0.01 s to 3600 s for general-purpose power class and distribution class current-limiting fuses.

d) 0.01 s to 10 000 s for full-range power class and distribution class current-limiting fuses.

e) 0.01 s to 1000 s for minimum-melt time-current characteristics for backup-type power and distribution current-limiting fuses and the time corresponding to the rated minimum interrupting current for total-clearing time-current characteristics. For motor-starter fuses, the minimum-melt time-current characteristics need only be presented for 0.01 s to 100 s.

NOTE—The total-clearing time-current characteristics for power class and distribution class fuse links covered under item a) and item b) will have minimum clearing times greater than 0.01 s due to the clearing time associated with these types of fuses.

11.2 Description of melting time-current tests

11.2.1 Application of test parameters

Melting time-current tests shall be made at any voltage, up to the maximum voltage of the unit being tested, with the test circuit so arranged that current through the fuse is held to essentially a constant value. For low-voltage tests, when testing fuses that change their resistance during the melting process, by element resistance change and/or having parallel elements that melt progressively (such as a fusible element and a strain wire),





the test circuit shall prevent a material change in the current during the melting process, either by having sufficient impedance, or by being capable of responding sufficiently rapidly to changes in the desired current.

11.2.2 Presentation of melting time-current test data

Melting time-current curves for all fuse links, fuse units, or refill units shall be plotted to minimum values on the current axis, and the value shall be determined by taking the manufacturer’s average test value, as determined by the test specified in this clause, and subtracting a value equal to the manufacturer’s allowable minus variation. The minimum melting time-current curves should be black.

11.3 Description of total-clearing time-current tests


Total-clearing time-current tests shall be made at the rated maximum voltage under the test circuit conditions specified for interrupting tests in Clause 6.

11.3.2 Presentation of total-clearing time-current test data

The total-clearing time-current curves for all fuse links, fuse units, and fuse refill units shall be as follows:

a) Be plotted to maximum values (using the current during the melting part of the total period), which shall include the minimum melting time plus the tolerance

b) Add the maximum arcing time as determined by the test specified in this clause

When arcing time factors are used in place of tests at rated voltage, the method used to arrive at the total clearing time shall be shown. The total-clearing time-current curves should be dark red.

12. Manual-operation, thermal-cycle, and bolt-torque tests (distribution cutouts)

12.1 Description of manual-operation tests

12.1.1 Test series

Three cutouts shall each be closed and opened 200 times per the manufacturer’s specifications.

12.1.2 Mounting of the device

The cutout shall be mounted and operated per the manufacturer’s specifications.


After testing the cutout shall be in the condition as specified in 4.5. There shall be no cracks in the insulators or loose hardware. A visual check for cracks may be used.





12.2 Description of thermal cycle tests


During the entire test, the cutouts shall be mounted in the service position(s) that would most likely permit water to enter any openings in the device.

12.2.2 Test series

The thermal-cycle test shall consist of consecutive water immersion, cold chamber, and hot chamber cycling of the cutouts. Separate cold and hot chambers may be used.

12.2.3 Number of devices to be tested

Five cutouts in new condition shall be tested. Open cutout fuse holders and disconnecting switch blades may be omitted from the test device for the convenience of testing.

12.2.4 Number of tests per device

Each cutout shall receive 10 thermal cycles.

12.2.5 Thermal cycle

Each cycle shall consist of the following:

a) The cutout shall be immersed in water for a minimum of 1 h. Water temperature shall be from 5 °C to 35 °C. The depth of immersion shall provide a minimum water level of 13 mm (½ in) above any porcelain cavity, filled or open, or any hardware.

b) The cutout shall be removed from the water. The temperature of the air surrounding the device shall be lowered from ambient room temperature to –40 °C at a rate controlled to prevent thermal shock. A temperature of –40 °C to –50 °C shall be maintained for a minimum of 2 h.

c) The temperature of the air surrounding the cutout shall be raised from –40 °C to 60 °C at a rate controlled to prevent thermal shock. A temperature of 60 °C to 70 °C shall be maintained for a minimum of 2 h. The device shall be permitted to return to room temperature before reimmersing it in water for subsequent test cycles.

NOTE—As a guide, thermal shock may be avoided by maintaining the rate of temperature change at less than 2 °C per minute. The transition time should be 2 h or less. Separate hot and cold chambers may be used, which may require movement of the cutout. The position of the cutout shall not change during transfer from the water or movement between chambers.


The condition of the cutout after test shall be as specified in 4.4. There shall be no cracks in the porcelain or loose hardware. A visual check for cracks may be used.





12.3 Description of torque tests

12.3.1 Test series

Torque tests shall be performed on cutouts that utilize threaded fasteners to attach the hardware to the insulator. Five new cutouts shall be tested.


A torque of 125% of the nominal values specified by the manufacturer shall be applied to the threaded fasteners that attach the hardware to the insulator.


The condition of the device after testing shall be as specified in 4.4. There shall be no damage to the insulators, thread failures, or loose components.

13. Liquid-tightness tests

13.1 Description of liquid-tightness tests

13.1.1 General

Liquid-tightness tests are required on certain types of current-limiting fuses used in FEPs. These tests apply to any fuse or fuse container that is used in a liquid environment, such as those described in 1.5 for Types 2C and 3C.


The fuse or fuse container shall be mounted or supported in the liquid as specified by the manufacturer.

13.1.3 Thermal cycle for test in air

The device shall be thermally cycled in air from –30 ºC to the rated maximum application temperature (as specified by the manufacturer) and back to –30 ºC. The rate of temperature change shall be controlled to prevent thermal shock. Each thermal cycle from one temperature extreme to the other shall be accomplished in not more than 8 h, with a holding period at each temperature extreme of sufficient duration for the temperature of the device to stabilize. Current may be used as a supplemental heat source during the heating cycle.

13.1.4 Thermal cycle for test in liquid

The device shall be thermally cycled in liquid with current passed through the fuse for part of the cycle. The device shall be immersed in liquid, and the liquid temperature shall be raised from room temperature to the rated maximum application temperature (specified by the manufacturer) in not more than 6 h. The rate of rise of liquid temperature should not exceed 0.5 ºC/min. When the liquid temperature reaches the maximum specified temperature, the fuse rated current (or the maximum permissible continuous current) shall be maintained through the fuse for a period of 2 h with the liquid temperature held at or above this maximum temperature. Current may be used as a supplemental heat source during the heating cycle.





At the conclusion of the 2 h current period, the liquid shall be allowed to cool to the cold-cycle ambient temperature of (25 ± 5) ºC.

13.1.5 Alternative test

The requirements of 13.1.3 and 13.1.4 may be met by a single test series made according to 13.1.4 with the following exceptions. The test device shall be cycled from –30 ºC to the rated maximum application temperature (specified by the manufacturer) in not more than 8 h, with a holding period at –30 ºC of sufficient duration for the temperature of the fuse or the device to stabilize. In addition, at the conclusion of the 2 h maximum-temperature period, the liquid shall be cooled to –30 ºC in not more than 8 h.

13.2 Test series

13.2.1 Number of tests

The test series shall consist of 10 thermal cycles over any convenient time period.

13.2.2 Number of samples

A total of five devices with the largest current-rated fuse in each of the physical fuse sizes manufactured shall be tested.


All five samples shall pass one of the alternative test criteria methods selected for determining whether or not a particular design passes the test for liquid-tightness. Alternative, but not necessarily equivalent, test criteria methods are as follows:

a) Maintain a minimum of 96 kPa (14 lbf/in2) positive pressure differential while the device is submerged in the appropriate liquid (or suitable equivalent liquid) over a 5 min period. There shall be an absence of bubbles.

b) Measure the leak rate using a helium-detecting mass spectrometer. The maximum permissible leak rate, both before and after exposure to the above specified test cycles, shall be 10–6 cm3 per second (1 atm pressure differential).

c) The test device shall be carefully inspected for liquid ingress using ultraviolet light, spectrographic analysis, or another equivalent, positive liquid-detecting technique. No liquid ingress shall be detected.

Note that the use of ultraviolet light, or another technique, for detecting the presence of liquid inside the fuse will require a quantizing of the test to provide a correlation with expected long-time service when submersed in liquid. The use of a fluorescent dye in the liquid, plus comparison with an unexposed fuse, are possible techniques that should be considered.

14. Description of expendable-cap static-relief pressure tests

The device shall be tested without a fuse link. It shall be mounted, and a means provided for exerting the prescribed test pressure through a medium of a liquid against the entire surface of the pressure-responsive area. (See ANSI C37.42 for test details.)





Annex A (informative) Recommended methods for determining the value of a sinusoidal current wave and a power-frequency recovery voltage

A.1 Current waves

A.1.1 Classification of current waves

The determination of the current interrupted by a circuit-interrupting device involves the measurement of the rms or effective values of sinusoidal waves. These waves may be divided into two groups: those that are symmetrical about the zero axis and those that are asymmetrical with respect to the zero axis.

A.1.2 Symmetrical sinusoidal wave

The symmetrical sinusoidal wave has an rms value equal to the peak-to-peak value divided by 2.828. To determine the rms value at a given instant, draw the envelope of the current wave, determine from it the peak-to-peak value at the given instant, and divide by 2.828. See Figure A.1 for an example.

tENVELOPE

ENVELOPE

RMS VALUE

ZERO LINE &AXIS OF WAVE

A

B

t

T is the time for which measurement was made A is the peak-to-peak value

B is the rms value = A2 828.

Figure A.1—Symmetrical sinusoidal current wave

A.1.3 Asymmetrical sinusoidal wave

The asymmetrical sinusoidal wave can be considered to be composed of two components—an alternating component and a direct component.

A.1.3.1 Alternating component

The alternating component has a peak-to-peak value equal to the distance between the envelopes, and it has an axis midway between the envelopes.





A.1.3.2 Direct component

The direct component has an amplitude equal to the displacement of the axis of the alternating component. See Figure A.2 for an example.

A is the peak-to-peak value of alternating component = │A’│ + │B’│ D is the direct component = A’ – (A/2) A’ is the major ordinate (peak asymmetrical current) B’ is the minor ordinate

The rms value of the sinusoidal component = A

2 828.

Figure A.2—Asymmetrical sinusoidal current wave

A.2 Power-frequency recovery voltage

The power-frequency recovery voltage shall be determined from the envelope of each voltage wave at a point in time coincident with that peak that occurs more than 0.5 cycle, and not more than 1 cycle, after final arc extinction in the last phase to clear. The power-frequency recovery voltage for a three-phase short circuit shall be taken as the average of the three values obtained in this manner for the three voltage waves. See Figure A.3.

AXIS OF WAVE

ZERO LINE

A A'

B'

ENVELOPE

ENVELOPE

D





Phase A is the first to open circuit OO is the instant of final arc extinction

G1 G1 is the interval 1

2f from OO

G2 G2 is the interval f

1 from OO

1

f is equal to 1 period at system frequency

2.8281E

is normal frequency recovery voltage, phase A

E22.828

is normal frequency recovery voltage, phase B

2.8283E

is normal frequency recovery voltage, phase C

Average normal frequency recovery voltage

= E1

2.828

E22.828

E32.828

3+ + ÷

Figure A.3—Determination of power-frequency recovery voltage NOTE—In phase B, a voltage peak occurs exactly at interval G1 G1. In such event, measurement is made at the later interval G2 G2.





Annex B (informative) Recommended method of determining the equivalent steady-state rms current for plotting time-current curves

The current that melts a fuse in less than 1 s may contain a number of transients in the wave. The magnitude of these transients varies with each fuse operation, and the equivalent steady-state rms value of the current wave can be obtained only by evaluating each case individually. The following methods are recommended for fuse tests that fall in this class:

a) When the fuse melts during transient conditions, the area under the melting part of the current wave is integrated to determine the root-mean-square value of the wave. This value is then multiplied by the scale of the oscillogram to give the rms current.

b) When the fuse melts after transient conditions subside, the transient part of the wave is integrated as described in item a), and the crest-to-crest height of the steady-state wave is measured. The two values obtained are combined as follows:

It may be noted that methods are now more commonly available to obtain equivalent steady-state rms current by electronic integration over longer periods of time. Combining transient and steady-state periods, using the formula above, is then unnecessary.

[ ]

melt to timetotal

part state-steady of Time22

part state-steady ofcrest -to-crestparttransient of Time

parttransient of valuerms

point melting to vecurrent wa of valuerms

22

+

=





Annex C

(informative)

Simplified fault-current calculation

C.1 Interrupting duty and rated short-time withstand current

To select the proper rating for a device, it is necessary to calculate the maximum symmetrical fault current on the load side of the device and compare this value with the interrupting capability of the fuse or the short-time withstand current capability of disconnecting cutouts and distribution class enclosed single-pole air switches. Most power fuses, distribution current-limiting fuses, and distribution cutouts are now rated by the manufacturer in terms of symmetrical current. A direct comparison can be made between the calculated values of fault current and the fuse rating. However, many power fuses and distribution cutouts of earlier manufacture (pre-1970) were rated on the basis of asymmetrical current. In addition, momentary currents for disconnecting cutouts and distribution class enclosed single-pole air switches have been defined in terms of asymmetrical current until the publishing of this standard. For those devices that used an asymmetrical current rating, the equivalent rms symmetrical current value can be obtained by dividing the asymmetrical value by an appropriate factor. Momentary current, now defined as an asymmetrical peak current, can then be obtained from an rms symmetrical current by multiplying it by another factor. The factors to be applied depend on the circuit X/R ratio used for the appropriate tests on the device, and they are shown in Figure C.1. The curve labeled “rms multiplication factor” is used to obtain the equivalent rms symmetrical current from a quoted rms asymmetrical current. The curve labeled peak multiplication factor then gives the value of the first peak of a fully asymmetrical waveform (peak asymmetrical current, i.e., the momentary current), when multiplied by the momentary rms symmetrical current.

Figure C.1— Relation of X/R ratio to multiplication factor





Annex D

(informative)

TRV parameters

Figure D.1 shows typical test circuits.

Typical circuit diagram for: Table 7—test series 1, 2, and 3 Table 8—test series 1, 2, 3, and 6 Table 11—test series 1, 2, 3 and 4 Table 14—test series 1 and 2 Table 17—test series 1

Typical circuit diagram for: Table 7—test series 4 and 5a Table 8—test series 4 and 5a Table 11—test series 5 and 6a Table 14—test series 3a Table 17—test series 2a

aFor these test series, C2 may be required, and its value is under consideration; R3 is not required across XL2. Also, TD may be used as an alternative to XL2 and R4 and may have impedance connected between secondary terminals. A is the removable link used for the calibration test CB is the circuit breaker protecting the source CS is the closing switch CT is the current transformer or noninductive current shunt CVD is the capacitance voltage divider C1 is the transient recovery voltage frequency control for source C2 is the transient recovery voltage frequency control for load (value under consideration) F is the fuse under test G is the generator I is the current measurement XL1 is the reactance for source XL2 is the reactance for load (see TD) R1 is the resistance to control X/R ratio of source R2 is the damping resistance to control peak factor of source R3 is the damping resistance to control peak factor of load R4 is the resistance to control X/R ratio of load TD is the distribution transformer with short-circuited secondary terminals (alternate to XL2 and R4) T1, T2 is the possible locations of transformers for tests at voltages higher than generator voltage VF is the recovery voltage measurement

NOTE—Damping circuits other than shown, for controlling the inherent TRV parameters of the test circuit, may be used by mutual agreement between manufacturer and test laboratory. Such use shall be noted and explained in the test report.

Figure D.1—Typical test circuits





D.1 Measurement of peak factor

The peak factor is the ratio of the first peak of the TRV to the instantaneous value of source voltage at the time of current zero, which is defined by

( ) ( )[ ]RX /arctan sinoltagerecovery vfrequency power 2

peak TRVfirst factor Peak

××=

This parameter is used in lieu of the amplitude factor (the ratio of the first peak of the transient recovery voltage to the peak value of the power-frequency recovery voltage) and is considered superior especially when testing in circuits with low X/R ratios. The peak factor may be measured by current injecting the test circuit or, alternatively, by conducting an actual fault-interrupting test using a low-arc-voltage interrupting device that does not distort the TRV. Either method, incidentally, can also be used to determine the frequency of the test circuit TRV. The characteristic and use of current-injecting equipment shall be such as not to alter the inherent TRV characteristics of the circuit during measurement. For further information on such equipment, see Annex F.

D.1.1 Measurement of peak factor by current injection

The peak factor is graphically determined from the TRV appearing across the open interrupting device when the circuit is current injected at the point (see Figure D.2).

1.6

35.957.5 factor Peak ==

Figure D.2—Peak factor determination from current-injection test record





D.1.2 Measurement of peak factor by fault interruption

The peak factor is determined from the TRV record of an actual fault-interrupting test on a circuit employing a low-arc-voltage device that does not distort the TRV. (The peak factor cannot be determined from the TRV record of a test that uses a fuse cutout as the interrupting device, since cutouts typically distort the TRV.) (See Figure D.3.)

1.611.52.8)1n38.2sin(ta

11.564.2A)1Csin(Tan

ABFactor Peak

=+−

+=

+−+

=RX

Figure D.3—Peak factor determination from the fault-interruption test record

For this case, the first peak of the TRV is measured from the extinction peak as its starting point, as is the measurement of the instantaneous power-frequency recovery voltage at the time of current zero. The following equation shows the calculation:

( ) ( )( )[ ]{ } ( )peak extinctionRXarctan sin x oltagerecovery vfrequency power x 2

peak extinctionpeak TRVfirst factor peak

+

+=





Annex E

(informative)

Criteria for determining It testing validity

E.1 Introduction

Fuses that require an It test are those in which, at different current levels, different series parts of the element perform most of the current interrupting duty. When the high current tests (series 1 and series 2) and low current tests (series 3) do not cover the transitional region between currents interrupted by the different parts of the element, the It testing is intended to demonstrate that there are no currents that cannot be interrupted, either by the different sections individually or in combination. Because of the wide variety of fuse designs, there are no simple rules for determining the validity of such testing, so it is the intent of this annex to give general guidance to those attempting to verify that the It testing that has been performed does indeed show what is intended.

E.2 Interrupting processes

Possibly the simplest illustration of the It phenomenon would be with a fuse having a single element consisting of a current-limiting section (strip with restrictions) in series with an expulsion section (element in a sleeve). At high currents, only the strip melts and arcs (with all restrictions melting virtually simultaneously), whereas at low currents, only the expulsion section melts and arcs. With such a design, the melting time-current characteristics (TCCs) of the two series sections will cross at some intermediate current where both the low current section and at least one restriction of the high current section will melt and arc. Such a crossover current can usually be determined relatively easily, and it is well defined if the TCC curves cross each other with a relatively large angle. The crossing current is the It current of the fuse. Tests at two current levels, a little above and below this It current, will therefore demonstrate that the fuse can interrupt the highest current that the low current section must interrupt (without help from the high current section) and the lowest current that the high current section must interrupt (without help from the low current section). It is then a reasonable assumption that the high current section can break all currents higher than It, and the low current section can break all currents lower than It. Conformance with the standard can be verified if each test current produces arcing only in the relevant section. This can be determined by techniques such as physical examination (that is opening the fuse), X-ray examination, or the equivalent. The above simple illustration shows the basic principle to be followed for all fuses. However, many fuse designs do not conform to this simple process. The melting TCC of the series sections may cross at such a shallow angle that there is not one distinct It value but instead a crossover zone that is larger than ±20% of any one current value. For other designs, the melting TCC may not actually cross at all, so it is possible for one section to melt for all currents, even when it is another section that is performing most of the interrupting function. With some designs that have many elements in parallel, the current value at which the high current sections begin to melt and participate in the interrupting process may be substantially below the apparent “crossover” value that corresponds to the intersection of the TCC curves for the different sections. This is caused by the phenomenon whereby, at some currents, parallel elements do not arc simultaneously but sequentially. In all of these cases, only the fuse manufacturer is in a position to specify the values of test current that will demonstrate compliance with the standard, and often, only the manufacturer is in a position to determine whether a particular test has demonstrated the desired result. This is because simply demonstrating current interruption is not a sufficient criterion to show that the crossover zone has been adequately explored. For this





reason, 6.6.11 permits the manufacturer to specify other test currents than 1.2 It and 0.8 It, if these values are not appropriate. It should be noted that without the expertise of the fuse manufacturer, it is not possible for a test station or user to assess the adequacy of testing to demonstrate compliance with the standard in regard to crossover testing.





Annex F

(informative)

Bibliography

[B1] ANSI/UL 347-2000, Standard for High Voltage Industrial Control Equipment.8

[B2] Hammarlund, P., Transient recovery voltage subsequent to short-circuit interruption with special reference to Swedish power system. Proceedings, Royal Swedish Academy of Engineering Sciences, no. 189, 1946.

[B3] IEEE Std C37.48.1™-2002 (Reaff 2008), IEEE Guide for the Operation, Classification, Application, and Coordination of Current-Limiting Fuses with Rated Voltages 1-38 kV.

[B4] IEEE Std C37.100.1™-2007, IEEE Standard of Common Requirements for High Voltage Power Switchgear Rated Above 1000V.9, 10

[B5] Jackson, R. L., Low voltage injection equipment for determining the transient response of power system plant. Internal Laboratory Report, No. RD/L/R 1782, Central Electricity Research Laboratory, Leatherhead, England, Feb. 1972.

[B6] Kotheimer, W. C., A method for studying circuit transient recovery voltage characteristics of electric power systems. AIEE Transactions, vol. 74, pp. 1083–1086, 1955.

[B7] Sing-Yui-King, Determination of restriking transients on power networks by a half-wave injection method. JIEE, Part II, p. 700, 1949.

8 ANSI publications are available from the Sales Department, American National Standards Institute, 25 West 43rd Street, 4th Floor, New York, NY 10036, USA (http://www.ansi.org/). UL standards are available from Global Engineering Documents, 15 Inverness Way East, Englewood, CO 80112, USA (http://global.ihs.com/). 9 IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA (http://standards.ieee.org/). 10 The IEEE standards or products referred to in this clause are trademarks of the Institute of Electrical and Electronics Engineers, Inc.


ANSI C 37.42 Cortacircuitos

Documents

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pole air switches

pole air switches

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ieee std c37

ieee std c37

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