IEEE Std C37.13-2008 IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures

IEEE Std C37.13™-2008(Revision of

IEEE Std C37.13-1990)

IEEE Standard for Low-Voltage ACPower Circuit Breakers Used inEnclosures

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

20 March 2009

IEEE Power & Energy SocietySponsored by theSwitchgear Committee

C37.

13TM

IEEE Std C37.13™-2008 (Revision of

IEEE Std C37.13-1990)

IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures

Sponsor

Switchgear Committee of the IEEE Power & Energy Society

Approved 10 December 2008

IEEE-SA Standards Board

Acknowledgments

The Working Group especially acknowledges the contributions of Shaun Slattery, Member of the Working Group and Chair of the Low-Voltage Switchgear Devices Subcommittee, who passed away during the development of this revision.

Abstract: The following enclosed low-voltage ac power circuit breakers are covered in this standard: a) stationary or draw-out type of two-, three-, or four-pole construction, with one or more rated maximum voltages of 635 V (600 V for units incorporating fuses), 508 V, and 254 V for application on systems having nominal voltages of 600 V, 480 V, and 240 V; b) unfused or fused circuit breakers; c) manually or power operated; and d) with or without electromechanical or electronic trip devices. Service conditions, ratings, functional components, temperature limitations and classifications of insulating materials, insulation (dielectric) withstand voltage requirements, test procedures, and application are discussed in this standard. Keywords: circuit breaker, fused circuit breaker, low-voltage ac power circuit breaker, open-fuse trip device, unfused circuit breaker

•

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 20 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. National Electrical Code and NEC are both registered trademarks of the National Fire Protection Association, Inc. PDF: ISBN 978-0-7381-5885-3 STD95869 Print: ISBN 978-0-7381-5886-0 STDPD95869 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 C37.13-2008, IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures.

The revisions to the 1990 version of this standard include the following:

⎯ Clarification of the differences between fused circuit breaker including intergrally fused and nonintegrally fused circuit breakers and separately fused circuit breakers as covered in IEEE Std C37.27™ [B7].a The revisions of IEEE Std C37.27 [B7]b were made concurrently with the revision of this standard.

⎯ All units were updated to reference metric units.

⎯ Review was made concerning lightning impulse withstand voltage (BIL) requirements. No BIL requirements were added to the standard.

⎯ Update of the requirements associated with demonstrating circuit breaker capabilities with consideration of operation at 50 Hz, 60 Hz, or for dual-rated 50 Hz/60 Hz circuit breakers.

⎯ Update of the requirements associated with the classification of insulating materials was made to the material definitions of UL 746A [B9].

The factors in Table 4 are based on the power frequency of 60 Hz. For 50 Hz circuits, the values in Table 4 can be used, but are conservative.

There was discussion concerning the service condition for the minimum temperature. The issue is that there are two references provided: 1) reference to the temperature inside the enclosure housing of −5 °C for the air surrounding the circuit breaker and 2) reference to the temperature of the air surrounding the enclosure as specified in IEEE Std C37.20.1™ (which is −30 °C).c In order not to hold up the publication of this standard, the original text in IEEE Std C37.13-1990 was used with one addition. Text was added to the application section that clarified that heaters should be used for low ambient temperature conditions. This issue will be reviewed in the next revision of this standard.

Notice to users

Laws and regulations

Users of these documents should consult all applicable laws and regulations. Compliance with the provisions of this standard does not imply compliance to any applicable regulatory requirements. Implementers of the standard are responsible for observing or referring to the applicable regulatory requirements. IEEE does not, by the publication of its standards, intend to urge action that is not in compliance with applicable laws, and these documents may not be construed as doing so.

a The numbers in brackets correspond to those of the bibliography in Annex A. b IEEE Std C37.27-2008 will be available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA, in April 2009. c Information on references can be found in Clause 2.

v Copyright © 2009 IEEE. All rights reserved.

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vi Copyright © 2009 IEEE. All rights reserved.

Participants

At the time this standard was submitted to the IEEE-SA Standards Board for approval, the C37.13 Working Group had the following membership:

Doug Edwards, Chair Paul Barnhart Donald Colaberardino Keith Flowers

Albert Livshitz Charles A. Morse Ted W. Olsen Robert J. Puckett

Carl Schneider Michael D. Sigmon Paul Sullivan

At the time this standard was submitted to the IEEE-SA Standards Board for approval, the Low-Voltage Switchgear Devices Subcommittee had the following membership:

Doug Edwards, Chair Keith Flowers, Secretary

Paul Barnhart S. (Dave) Gohil Nancy Gunderson Albert Livshitz Jean-Claude Maurice

Deepak Mazumdar Nigel P. McQuin Jeff Mizener Charles A. Morse George R. Nourse

Ted W. Olsen Robert J. Puckett Michael D. Sigmon Alan Storms Paul Sullivan

The following members of the individual balloting committee voted on this standard. Balloters may have voted for approval, disapproval, or abstention. William J. Ackerman Saber Azizi-Ghannad Paul Barnhart Wallace Binder Thomas Bishop Anne Bosma Steven Brockschink Chris Brooks David Burns Ted Burse Eldridge Byron Donald Colaberardino Tommy Cooper J. Disciullo Gary L. Donner Doug Edwards Gary Engmann Keith Flowers Rabiz Foda Marcel Fortin Randall Groves

Nancy Gunderson Kenneth Hanus David Horvath Dennis Horwitz David Jackson James Jones Joseph L. Koepfinger Boris Kogan Jim Kulchisky Solomon Lee Boyd Leuenberger Jason Jy-Shung Lin R. Long William Lumpkins G. Luri Frank Mayle Nigel P. McQuin Steven Meiners Gary Michel William Moncrief

Georges Montillet Charles A. Morse Jerry Murphy Dennis Neitzel Michael S. Newman Ted W. Olsen Lorraine Padden Ralph Patterson Robert J. Puckett Michael Roberts Vincent Saporita James E Smith Alan Storms Paul Sullivan S. Telander William W. Terry S. Thamilarasan Terry L. Williams James Wilson Larry Yonce Donald Zipse

vii Copyright © 2009 IEEE. All rights reserved.

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

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

Victor Berman Richard DeBlasio Andy Drozd Mark Epstein Alexander Gelman William Goldbach Arnie Greenspan Ken Hanus

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

Ron Petersen Chuck Powers Narayanan Ramachandran Jon Walter Rosdahl Anne-Marie Sahazizian Malcolm Thaden Howard 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

Lisa Perry

IEEE Standards Project Editor

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

viii Copyright © 2009 IEEE. All rights reserved.

Contents

1. Scope .......................................................................................................................................................... 1

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

3. Definitions .................................................................................................................................................. 3

4. Service conditions ...................................................................................................................................... 3

5. Ratings ........................................................................................................................................................ 4

5.1 General ................................................................................................................................................ 4 5.2 Rated maximum voltage ...................................................................................................................... 4 5.3 Rated power frequency ........................................................................................................................ 4 5.4 Rated continuous current ..................................................................................................................... 4 5.5 Rated short-time current ...................................................................................................................... 5 5.6 Rated short-circuit current ................................................................................................................... 5 5.7 Rated control voltage ........................................................................................................................... 7

6. Functional components ............................................................................................................................... 7

6.1 General ................................................................................................................................................ 7 6.2 Nameplate(s) ........................................................................................................................................ 7 6.3 Contact position indicator .................................................................................................................... 8 6.4 Stored energy indicator ........................................................................................................................ 9 6.5 Locking ................................................................................................................................................ 9 6.6 Primary disconnecting devices ............................................................................................................ 9 6.7 Circuit breaker ground connection ...................................................................................................... 9 6.8 Fused drawouts .................................................................................................................................... 9

7. Temperature limitations and classification of insulating materials .......................................................... 10

7.1 Temperature limits ............................................................................................................................. 10 7.2 Limits of temperature rise .................................................................................................................. 10 7.3 Classification of insulating materials ................................................................................................. 10

8. Test procedures ......................................................................................................................................... 12

8.1 Test specimen .................................................................................................................................... 12 8.2 Test values ......................................................................................................................................... 12

9. Application guide ..................................................................................................................................... 13

9.1 General .............................................................................................................................................. 13 9.2 Short-time current .............................................................................................................................. 19 9.3 Application of circuit breakers for selective tripping ........................................................................ 19

ix Copyright © 2009 IEEE. All rights reserved.

9.4 Application of circuit breakers to full-voltage motor-starting and running duty of three-phase motors ................................................................................................................................................ 21

9.5 Application of circuit breakers for capacitance switching ................................................................. 21 9.6 Service conditions affecting circuit breaker applications .................................................................. 22 9.7 Repetitive duty operations and normal maintenance ......................................................................... 23 9.8 Application of circuit breakers in cascade ......................................................................................... 24 9.9 Application of circuit breakers without enclosures ............................................................................ 24 9.10 Application of circuit breakers with dependent manually closing mechanisms .............................. 24 9.11 Application of fused circuit breakers on corner-grounded delta system .......................................... 24

Annex A (informative) Bibliography ........................................................................................................... 25

1 Copyright © 2009 IEEE. All rights reserved.

IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures

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. Scope

The scope of this standard includes the following enclosed low-voltage ac power circuit breakers:

a) Stationary or drawout type of two-, three-, or four-pole construction with one or more rated maximum voltages of 635 V (600 V for units incorporating fuses), 508 V, and 254 V for application on systems having nominal voltages of 600 V, 480 V, and 240 V

b) Unfused or fused type

c) Manually operated or power operated, with or without electromechanical or electronic trip devices

d) Fused drawouts consisting of current-limiting fuses in a drawout assembly intended to be connected in series with a low-voltage ac power circuit breaker to form a nonintegrally fused circuit breaker

NOTE—In this standard, the term circuit breaker shall mean enclosed low-voltage ac power circuit breaker, either fused or unfused. The term unfused circuit breaker shall mean a circuit breaker without either integrally or nonintegrally mounted fuses, and the term fused circuit breaker shall mean a circuit breaker incorporating current-limiting fuses.1

This document applies to both integrally and nonintegrally fused circuit breakers.

1 Notes in text, tables, and figures of a standard are given for information only and do not contain requirements needed to implement this standard.

IEEE Std C37.13-2008 IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures


2. Normative references

The following referenced documents are indispensable for the application of this document (i.e., they must be understood and used, so 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 C37.16, American National Standard for Low-Voltage Power Circuit Breakers and AC Power Circuit Protectors—Preferred Ratings, Related Requirements, and Application Recommendations.2, 3

ANSI C37.17, American National Standard for Trip Devices for AC and General Purpose DC Low-Voltage Power Circuit Breakers.4

ANSI C37.50, American National Standard Switchgear Low-Voltage AC Power Circuit Breakers Used in Enclosures—Test Procedures.

ASTM D 229, Standard Test Methods for Rigid Sheet and Plate Materials Used for Electrical Insulation.5

IEC 60417, Graphical symbols for use on equipment.6

IEEE Std 1™, IEEE Recommended Practices—General Principles for Temperature Limits in the Rating of Electrical Equipment and for the Evaluation of Electrical Insulation.7, 8

IEEE Std 141™, IEEE Recommended Practice for Electric Power Distribution for Industrial Plants (IEEE Red Book™).

IEEE Std 241™, IEEE Recommended Practice for Electric Power Systems in Commercial Buildings (IEEE Gray Book™).

IEEE Std 242™, IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems (IEEE Buff Book™).

IEEE Std C37.20.1™, IEEE Standard for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear.

IEEE Std C37.100™, IEEE Standard Definitions for Power Switchgear.

NEMA CP 1, Shunt Capacitors.9

NFPA 70, National Electrical Code® (NEC®).10

2 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/). 3 This standard is currently under revision as IEEE PC37.16. 4 This standard is currently under revision as IEEE PC37.17. 5 ASTM publications are available from the American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, USA (http://www.astm.org/). 6 IEC publications are available from the Sales Department of the International Electrotechnical Commission, 3, rue de Varembé, P.O. Box 131, CH-1211 Geneva 20, Switzerland (http://www.iec.ch/). 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. 7 IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA (http://standards.ieee.org/). 8 The IEEE standards or products referred to in this clause are trademarks owned by the Institute of Electrical and Electronics Engineers, Incorporated. 9 NEMA publications are available from Global Engineering Documents, 15 Inverness Way East, Englewood, Colorado 80112, USA (http://global.ihs.com/).



3. Definitions

The definitions of terms in this standard or in other standards referred to in this standard are not intended to embrace all legitimate meanings of the terms. They are applicable only to the subject treated in this standard.

For the purpose of this standard, the following terms and definitions apply. The Authoritative Dictionary of IEEE Standards Terms [B3]11 and IEEE Std C37.10012 should be referenced for terms not defined in this clause. An asterisk (*) following a definition indicates that the definition in this standard is not contained in IEEE Std C37.100, while a dagger (†) indicates the definition differs from that in IEEE Std C37.100.

3.1 low-voltage fused power circuit breaker: An assembly of an ac low-voltage power circuit breaker with either integrally mounted or nonintegrally mounted current-limiting fuses that function together as a coordinated protective device. †

3.2 low-voltage integrally fused power circuit breaker: An assembly of an ac low-voltage power circuit breaker with current-limiting fuses integrally mounted to the circuit breaker and that function together as a coordinated protective device.*

3.3 low-voltage nonintegrally fused power circuit breaker: An assembly of an ac low-voltage power circuit breaker and a close-coupled fused drawout assembly that function together as a coordinated protective device.*

3.4 open-fuse trip device: A device that operates to open (trip) all poles of a circuit breaker or definite purpose switching device in response to the opening, or absence, of one or more fuses integral or nonintegral to the circuit breaker with which the device is associated. After operating, the device shall prevent closing of the circuit breaker until a reset operation is performed. †

NOTE 1— Since some open-fuse trip devices may operate by sensing the voltage across the fuses, if they are reset with an open or missing fuse, they may not prevent closing of the circuit breaker. In most cases, if this type of operation is performed, it will cause an immediate trip. There is a practical limit of load impedance above which the device (sensing voltage across an open or missing fuse) will not function as described.

NOTE 2— See IEEE Std C37.13.1™ [B5] for definite purpose switching devices.

4. Service conditions

A circuit breaker conforming to this standard shall be suitable for operation up to and including all of its standard ratings, provided that

a) The temperature of the air surrounding the circuit breaker is not below −5 °C.

NOTE—When properly applied in metal-enclosed switchgear or individual enclosures, a circuit breaker will operate within the limits of ambient temperature of the air surrounding the enclosure as specified in IEEE Std C37.20.1.

b) The altitude does not exceed 2000 m (6600 ft).

c) The relative humidity of the air surrounding the circuit breaker is such that there will be no condensation on the circuit breaker parts at any time.

d) None of the service conditions as listed in 9.6.3 prevail.

10 The NEC is published by the National Fire Protection Association, Batterymarch Park, Quincy, MA 02269, USA (http://www.nfpa.org/). Copies are also available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA (http://standards.ieee.org/). 11 The numbers in brackets correspond to those of the bibliography in Annex A. 12 Information on references can be found in Clause 2.



For application of circuit breakers under service conditions other than those in item a) through item d), see Clause 9.

5. Ratings

5.1 General

The rating of a circuit breaker is a designated limit of operating characteristics based upon service conditions in Clause 4 and shall include the following, as applicable:

a) Rated maximum voltage(s)

b) Rated power frequency(s)

c) Rated continuous current

d) Rated short-time current

e) Rated short-circuit current at each rated maximum voltage

f) Rated control voltage(s)

The designated ratings in ANSI C37.16 are preferred, but are not considered to be restrictive.

5.2 Rated maximum voltage

The rated maximum voltage of a circuit breaker is the highest rms (root mean square) voltage, three-phase or single-phase, at which it is designed to perform. The circuit breaker shall be rated at one or more of the following maximum voltages: 635 V, 508 V, or 254 V. For fused circuit breakers, the 635 V rated maximum voltage becomes 600 V to match the fuse rating.

5.3 Rated power frequency

The rated power frequency of a circuit breaker is the frequency at which it is designed to operate. Preferred frequencies are 50 Hz and 60 Hz. Application at other frequencies should receive special consideration.

5.4 Rated continuous current

The rated continuous current of a circuit breaker is the designated limit of rms current at rated power frequency that it shall be required to carry continuously without exceeding the temperature limitations designated in Clause 7. The continuous current ratings of the various frame sizes are listed in ANSI C37.16. The rated continuous current of a circuit breaker equipped with direct-acting trip devices or fuses of a lower rating than the frame size of the circuit breaker is determined by the rating of those devices.

The circuit breaker rated continuous current capabilities are demonstrated by compliance with the applicable test requirements in ANSI C37.50.

a) Circuit breakers with rated power frequency of 50 Hz shall be required to meet the temperature rise limits of Table 3 when tested in accordance with the continuous current test requirements of ANSI C37.50 at either rated power frequency of 50 Hz or 60 Hz.



b) Circuit breakers with rated power frequency of 60 Hz or 50 Hz/60 Hz shall be required to meet the temperature rise limits of Table 3 when tested in accordance with the continuous current test requirements of ANSI C37.50 at rated power frequency of 60 Hz.

5.5 Rated short-time current

5.5.1 Unfused circuit breakers

For an unfused circuit breaker, the rated short-time current is the designated limit of available (prospective) current at which it shall be required to perform its short-time current duty cycle (two periods of 0.5 s current flow, separated by a 15 s interval of zero current) at rated maximum voltage under the prescribed test conditions. This current is expressed as the rms symmetrical value of current measured from the available current wave envelope at a time one-half cycle after short-circuit initiation.

Unfused circuit breakers shall be tested to and be capable of performing the short-time current duty cycle with all degrees of current asymmetry produced by three-phase or single-phase circuits having a short-circuit power factor of 15% lagging or less (X/R ratio of 6.6 or greater). Short-time current ratings are listed in ANSI C37.16.

5.5.2 Fused circuit breakers

Fused circuit breakers do not have a rated short-time current rating.

NOTE—The nameplate of a fused circuit breaker does not include a short-time current rating. However, the circuit breaker element of the fused circuit breaker assembly may have a short-time capability. The manufacturer should be consulted for details as needed.

5.6 Rated short-circuit current

5.6.1 General

The circuit breaker rated short-circuit current capabilities are demonstrated by compliance with the applicable test requirements in ANSI C37.50.

5.6.2 Circuit breaker (50 Hz or 60 Hz)

A circuit breaker with rated power frequency of 50 Hz shall be required to perform its short-circuit current duty cycle at rated power frequency of 50 Hz.

A circuit breaker with rated power frequency of 60 Hz shall be required to perform its short-circuit current duty cycle at rated power frequency of 60 Hz.

5.6.3 Circuit breaker (50Hz/60 Hz)

A circuit breaker with rated power frequency of 50Hz/60 Hz shall be required to perform its short-circuit current duty cycle as follows:

a) When the published tolerance bands of the time-current curves of the circuit breaker direct-acting trip system (see ANSI C37.17) at 50 Hz do not fall entirely within the published tolerance bands of the time-current curves at 60 Hz, the short-circuit current tests shall be conducted at each rated power frequency.



b) When the published tolerance bands of the time-current curves of the circuit breaker direct-acting trip system (see ANSI C37.17) at 50 Hz falls entirely within the published tolerance bands of the time-current curves at 60 Hz:

1) For an unfused circuit breaker with clearing time of less than one power-frequency cycle,13 the circuit breaker shall be required to perform its short-circuit current duty cycle at both 50 Hz and 60 Hz rated power frequency.

2) For an unfused circuit breaker with clearing time of one power-frequency cycle or more, the circuit breaker shall be required to perform its short-circuit current duty cycle at power frequency of 50 Hz.

3) For a fused circuit breaker, the circuit breaker shall be required to perform its short-circuit current duty cycle at both 50 Hz and 60 Hz rated power frequency, if the clearing time of the circuit breaker element (without fuses) is less than one power-frequency cycle.

4) For a fused circuit breaker, the circuit breaker shall be required to perform its short-circuit current duty cycle at power frequency of 50 Hz, if the clearing time of the circuit breaker element (without fuses) is one power-frequency cycle or more.


The rated short-circuit current of an unfused circuit breaker is the designated limit of available (prospective) current at which it shall be required to perform its short-circuit current duty cycle of an opening operation followed by a close-open operation (O–15 s–CO) at rated maximum voltage under the prescribed test conditions and at the rated power frequency corresponding to the short-circuit rating. This current is expressed as the rms symmetrical value of current measured from the available current wave envelope at a time one-half cycle after short-circuit initiation.

When short-time delay tripping devices are used, the tripping on each opening shall be delayed by these tripping devices, except when equipped with instantaneous tripping elements effective only during closing.

Unfused circuit breakers shall be tested to and capable of performing the short-circuit current duty cycle with all degrees of current asymmetry produced by three-phase or single-phase circuits having a short-circuit power factor of 15% lagging or less (X/R ratio of 6.6 or greater).

Unfused circuit breakers with direct-acting instantaneous phase trip elements shall have short-circuit current ratings at each rated maximum voltage as listed in ANSI C37.16. When not equipped with direct-acting instantaneous phase trip elements, the short-circuit current ratings shall be as listed in ANSI C37.16.

When unfused circuit breakers are equipped with direct-acting short-time-delay phase trip elements in addition to direct-acting instantaneous phase trip elements, they may have the short-circuit current ratings listed in ANSI C37.16 provided that the maximum instantaneous trip setting does not exceed the short-circuit current ratings listed in ANSI C37.16.


5.6.5.1 Integrally and nonintegrally fused circuit breakers

The rated short-circuit current of a fused circuit breaker is the designated limit of available (prospective) current at which it shall be required to perform its short-circuit current duty cycle at rated maximum voltage under the prescribed test conditions and at the rated frequency corresponding to the short-circuit

13 For clarification of the term “one power-frequency cycle,” for circuit breakers operating at 50 Hz rated power frequency, the one power-frequency cycle equates to 20 ms and for circuit breakers operating at 60 Hz rated power frequency, the one power-frequency cycle equates to 16.7 ms.



rating. The short-circuit current duty cycle consists of an O–T–CO operation, where T is the time necessary to replace fuses and reset the open-fuse trip device. This current is expressed as the rms symmetrical value of current measured from the available current wave envelope at a time one-half cycle after short-circuit initiation.

Fused circuit breakers shall be tested to and capable of performing the short-circuit current duty cycle with all degrees of current asymmetry produced by three-phase or single-phase circuits having a short-circuit power factor of 20% lagging or less (X/R ratio of 4.9 or greater).

The circuit breaker element of a fused circuit breaker shall have a short-circuit current rating as listed in ANSI C37.16 for the particular frame size for a system nominal voltage of 600 V. The fuses are required to operate in their current limiting region for short-circuit currents at or below the short-circuit current ratings in ANSI C37.16.

5.6.5.2 Nonintegrally fused circuit breakers—Fuse drawout

A fuse drawout unit shall be tested in combination with the specific circuit breaker with which it is intended to be used.

5.7 Rated control voltage

The rated control voltage is the voltage at which the mechanism of the circuit breaker is designed to operate when measured at the control power terminals of the operating mechanism with the highest operating current flowing. Preferred rated control voltages and their ranges for low-voltage power circuit breakers are listed in ANSI C37.16.

6. Functional components

6.1 General

The required functional components are listed in Table 1. Additional accessory devices may be available. The manufacturer should be consulted for specific information.

6.2 Nameplate(s)

The following minimum information shall be given on the nameplate(s) of all circuit breakers:

a) Manufacturer’s name

b) Type of circuit breaker

c) Rated continuous current of trip devices (where applicable) and type designation

d) Frame size

e) Rated maximum voltage(s)

f) Rated short-circuit current at each rated maximum voltage

g) Rated short-time current (where applicable)

h) Suitable fuse type and sizes (where applicable)

i) Rated power frequency(s)



j) Rated control voltage (where applicable)

k) Year of manufacture, by date

l) Identification number (e.g., serial number)

m) Manufacturer’s data sheets or instruction book reference

Table 1 —Functional components

Functional component Operating mechanism type

Manual Power

(1) Direct-acting trip device(s). See ANSI C37.17. Xa Xa

(2) Manual trip device X X

(3) Contact position indicator in accordance with 6.3 X X

(4) Independent, manually operated mechanism, trip-free, with attached operating handle

X ⎯

(5) Power-operated mechanism, trip-free, with anti-pump feature and maintenance closing device

⎯ X

(6) Shunt trip device with necessary control auxiliary switches ⎯ X

(7) Stored energy indicator in accordance with 6.4 Xb Xb

(8) Nameplate(s), with markings in accordance with 6.2 X X

(9) Fuses, one per pole, complying with ANSI C37.16 Xc Xc

(10) Open-fuse trip device Xc Xc

(11) Locking provisions in accordance with 6.5 X X

(12) Primary disconnecting devices in accordance with 6.6 Xd Xd

(13) Circuit breaker ground connection in accordance with 6.7 X X

(14) Secondary disconnect device(s) Xe Xd, e

(15) Fused drawout in accordance with 6.8 Xf Xf a As required by the application. b Required only on closing mechanisms that provide for stored energy operation when the mechanism can be left in the charged position. c Required on fused circuit breakers only. d Required on drawout circuit breakers only. e Required for drawout circuit breakers with external secondary connections. For stationary circuit breakers, an alternative method, such as terminal blocks or an umbilical cable, may provide the method of connection to the circuit breaker. f Required as part of nonintegrally fused circuit breaker construction only.

6.3 Contact position indicator

A reliable mechanical contact position indicator, which can easily be read by the local operator, shall be supplied. The following colors shall be used:

a) Red background with the word “CLOSED” in contrasting letters to indicate closed contacts

b) Green background with the word “OPEN” in contrasting letters to indicate open contacts



In addition to the required mechanical contact position indicator word, a symbol may also be provided in accordance with IEC 60417.

6.4 Stored energy indicator

A stored energy indicator that can easily be read by the local operator shall be supplied. A reliable indicator with the following colors shall be used:

a) Yellow background with black lettering to indicate ”CHARGED” mechanism

b) White background with black lettering to indicate “DISCHARGED” mechanism.

In addition to the required stored energy indicator word, a symbol may also be provided in accordance with IEC 60417.

6.5 Locking

Provisions shall be made for padlocking the circuit breaker in the open (trip-free) position. Other locking provisions may be provided to address specific applications.

6.6 Primary disconnecting devices

Any replaceable or renewable component(s) of the primary disconnecting device assembly shall be located on the circuit breaker.

6.7 Circuit breaker ground connection

Circuit breakers shall be provided with a ground connection. The ground connection shall be sufficient to provide an effectively grounded condition to all conductive circuit breaker parts that can be touched by an operator in the normal course of his or her duties. In addition, the ground connection shall also ground any other conductive parts of the circuit breaker that are intended to be grounded.

Ground connections shall be provided for all removable elements to ensure that the frame and mechanism are grounded, unless the primary and secondary circuits are disconnected and the removable element is moved a safe distance. (See IEEE Std C37.100 for definitions of test and disconnected positions.)

Safe distance, as used here, is a distance at which the circuit breaker will meet its withstand ratings between line and load stationary terminals and phase-to-phase and phase-to-ground on both line and load stationary terminals with the circuit breaker in the closed position.

6.8 Fused drawouts

Access to the fuses on a separate removable element of a nonintegrally fused circuit breaker shall meet the requirements stated in IEEE Std C37.20.1.



7. Temperature limitations and classification of insulating materials

7.1 Temperature limits

The temperature limits on which the rating of circuit breakers is based are determined by the characteristics of the insulating materials used and the metals that are used in current-carrying parts and springs.

7.2 Limits of temperature rise

The temperature rise of the various parts of the circuit breaker above the temperature of the air surrounding the circuit breaker test enclosure, when subjected to temperature tests in accordance with this standard, shall not exceed the values given in Table 3. This table applies only to a circuit breaker having all contacts silver-surfaced, silver alloy, or equivalent, and in addition, having all conducting joints, moving or fixed, including terminal connection, either:

a) Silver-surfaced and held mechanically

b) Brazed, welded, or silver-soldered

c) Fixed rigid mechanical joints surfaced with suitable material other than silver

7.3 Classification of insulating materials

7.3.1 Flame-resistant capabilities

7.3.1.1 Insulating materials in contact with primary voltage parts

Insulating materials shall be flame-resistant.

Sheet, molded, or cast insulating materials shall not be classified as flame-resistant unless they have a minimum average ignition time of 60 s and a maximum average burning time of 500 s when tested in accordance with Method II of ASTM D 229.

7.3.1.2 Insulating materials not in contact with primary voltage parts

7.3.1.2.1 Polymeric materials

Polymeric materials that are not in contact with primary voltage parts shall have a minimum flame rating of 94HB. Polymeric materials that are closer than 0.8 mm (1/32 in) to uninsulated live primary voltage parts shall also have ignition resistance performance-level characteristics (PLCs) based on the material flame rating given in Table 2. This includes (but is not limited to) items such as the contact position indicators, stored energy indicators, direct-acting trip device, manual trip device, and spring changing handle.

7.3.1.2.2 Non-polymeric materials

Non-polymeric materials shall be qualified to have equivalent capabilities as 7.3.1.2.1.



Table 2 —Required material properties

Performance-level characteristic (PLC) (See NOTE)

Flame rating of material 94V-0 94-5VA 94-5VB

94V-1 94V-2 94HB

High-current arc resistance to ignition 3 2 2 1 Hot wire ignition 4 3 2 2

NOTE—Material properties and PLC levels are defined in UL 746A [B9].

7.3.2 Thermal capabilities

The temperature limits on which circuit breaker ratings are based depend on the character of the insulating materials used.

For the purpose of establishing temperature limits, insulating materials are classified in IEEE Std 1.

7.3.3 Tracking capabilities

Insulating materials in contact with primary voltage parts shall have a comparative tracking index of PLC level 3 or lower. If the material is subject to contamination by the by-products of arcing parts, it shall have a PLC level of 2 or lower.

NOTE—Material properties and PLC levels are defined in UL 746A [B9].

Table 3 —Limits of temperature

Limit of temperature

rise over air surrounding enclosure (°C)

Limit of total temperature (°C)

Class 90 insulation 50 90 Class 105 insulation 65 105 Class 130 insulation 90 130 Class 155 insulation 115 155 Class 180 insulation 140 180 Class 220 insulation 180 220 Circuit breaker contacts, conducting joints, and other parts, except the following:

Fuse terminals Series coils with over Class 200 insulation or bare

85 (See Footnote a) (See Footnote a)

125 (See Footnote a) (See Footnote a)

Terminal connectionsb 55 95 a No specified limit except to minimize damage to adjacent parts. b Terminal connection temperatures are based on connections to bus in low-voltage metal-enclosed switchgear. If connections are made to cables, recognition must be given to possible thermal limitations of the cable insulation and appropriate measures taken.



8. Test procedures

8.1 Test specimen

See ANSI C37.50.

Tests shall be performed in minimum-dimension enclosure with the smallest electrical spacing recommended by the manufacturer for the particular frame size unfused circuit breaker, fused circuit breaker, and fuse drawout unit. The enclosure shall be equipped with the maximum number of mechanism-operated contacts and truck-operated contacts. The circuit breaker and fuse drawout unit combination shall be tested together for simultaneous qualification of both devices in accordance with 5.6.5.2.

The revision of this standard imposes changes in the requirements that affect the test requirements detailed in ANSI C37.50-1989 (R1995, R2000). Circuit breakers that have been qualified or certified do not require immediate retest but shall be retested based on the latest revision of ANSI C37.50 upon reaching the retest interval as defined by ANSI C37.50.

8.2 Test values

8.2.1 General

Circuit breakers, when tested in accordance with 8.1, shall be capable of withstanding without damage the following power-frequency test voltages (dry test) for a period of 60 s.

8.2.2 Test frequency values

8.2.2.1 General

Circuit breakers with rated power frequency of 50 Hz shall be tested at either 50 Hz or 60 Hz.

Circuit breakers with rated power frequency of 50Hz/60 Hz or 60 Hz shall be tested at 60 Hz.

8.2.2.2 Direct-acting trip system calibration

When the published tolerance bands of the time-current curves of the circuit breaker direct-acting trip system (see ANSI C37.17) at 50 Hz fall entirely within the published tolerance bands of the time-current curves at 60 Hz, the calibration tests may be conducted at either 50 Hz or 60 Hz.

When the published tolerance banks of the time-current curves of the circuit breaker direct-acting trip system (see ANSI C37.17) at 50 Hz do not fall entirely within the published tolerance bands of the time-current curves at 60 Hz:

a) Circuit breakers with rated power frequency of 50 Hz shall be tested at 50 Hz.

b) Circuit breakers with rated power frequency of 60 Hz shall be tested at 60 Hz.

8.2.3 Test voltage values

The test voltages shall be essentially sinusoidal with a crest value equal to 1.414 times the specified values.

a) Primary circuit of a new, completely assembled circuit breaker, 2200 V.

b) Secondary control wiring [except for item c), item d), and item e)], 1500 V.



c) Motors shall be tested at their specified dielectric withstand voltage but not less than 1000 V.

d) Control devices and circuitry operating at 80 V (ac) rms [110 V (dc)] or less and not directly to primary or external secondary control circuits, 500 V.

e) For undervoltage trip devices operating at a voltage above 250 V (ac), twice rated voltage plus 1000 V.

f) After interruption of a short-circuit current duty cycle and before servicing, the withstand test voltage shall be 60% of the values listed in item a) through item e).

g) After storage or installation in the field, a circuit breaker that has not been subjected to a short-circuit current interruption or has been serviced after interruption shall withstand 75% of the values listed in item a) through item e).

NOTE—Field tests are recommended after field modifications. The circuit breaker should be put in good condition prior to the field test. It is not expected that circuit breaker shall be subjected to these tests after it has been stored for long periods of time or has accumulated a large amount of dust, dirt, moisture, or other contaminants without first being restored to good condition.

9. Application guide

9.1 General

This clause covers the application of circuit breakers on low-voltage ac systems and applies to circuit breakers rated in accordance with Clause 5.

Other applicable codes, such as the National Electrical Code® (NEC®) (NFPA 70), should also be consulted.

Circuit breakers should be applied within their assigned voltage(s), power frequency, continuous current, short-time current, and short-circuit ratings as defined in this standard with proper consideration given to the service conditions stated in Clause 4. They should be selected to provide the protection required by the other components of the circuit. For other applications not covered by this standard, the manufacturer should be consulted.

9.1.1 Voltage

9.1.1.1 Rated maximum voltage

The voltage of the system to which circuit breakers are applied, including any possible variations, should not exceed the rated maximum voltages listed in 5.2. For application voltages between those listed, a circuit breaker should be selected on the basis of the next higher rated maximum voltage. See ANSI C37.16.

9.1.1.2 Control voltages

The control voltages applied to the circuit breaker should be within the tolerance range specified in ANSI C37.16.

For applications with control voltage quality issues, either ripple for dc circuits or harmonics for ac circuits, the control devices may not function over the entire voltage range specified in ANSI C37.16 and may thus require specific attention. The manufacturer should be consulted.



Device control components, in some applications, may be exposed to control voltages exceeding those specified in ANSI C37.16 due to abnormal conditions such as abrupt changes in line loading. Such applications require specific study, and the manufacturer should be consulted.

Application of control components containing solid-state devices, exposed continuously to control voltages approaching the upper limits of ranges specified in ANSI C37.16, requires specific attention, and the manufacturer should be consulted.

9.1.2 Power frequency

The rated power frequency for circuit breakers is typically 60 Hz (see 5.3). Application at nominal power frequencies other than 50 Hz or 60 Hz may require that consideration be given to the performance of the circuit breaker itself.

For application at 50 Hz, the circuit breaker, including the complete direct-acting trip system, must be rated for operation at 50 Hz (see 5.3).

9.1.3 Continuous current

9.1.3.1 General

The circuit breaker should be applied to a circuit having a maximum continuous-load current no greater than the continuous current rating of the circuit breaker. Direct-acting trip devices should be selected so as to provide the trip settings required, and should have a continuous current rating equal to, or greater than, the maximum current rating of the circuit to which they are to be applied.

Pickup setting of the long-time-delay elements may be provided above the continuous current ratings of the trip device for the purpose of maintaining circuit continuity during overload conditions. Supplemental overload current protection should be applied to prevent long-term operation with currents above the lesser of either the direct-acting overcurrent trip device current rating or the continuous current rating of the circuit breaker.

For electromechanical long-time-delay elements, the trip device may be able to carry currents for short periods of time above the direct-acting overcurrent trip device current rating to meet the application requirements for overload conditions. However, the trip device and circuit breaker frame combination cannot be expected to carry continuously more current than the lesser of either the direct-acting overcurrent trip device current rating or the continuous current rating of the circuit breaker.

For electronic long-time-delay elements, the trip device may be able to carry current continuously above the direct-acting overcurrent trip device current rating to meet the application requirements for overload conditions. However, the trip device and circuit breaker frame combination cannot be expected to carry continuously more current than the lesser of either the direct-acting overcurrent trip device continuous current capability or the continuous current rating of the circuit breaker.

9.1.3.2 Forced-air cooling

It is recognized that a circuit breaker may continuously carry current in excess of its continuous current rating if the circuit breaker is forced-air cooled by means such as a blower or a fan. The manufacturer of the assembly in which the circuit breaker and forced-air cooling means are to be installed should be contacted to obtain information about the increased capability. Suitable protection schemes should be utilized to assure that excessive temperatures do not result from necessary air filters becoming clogged or from failure of the forced-air cooling means to provide sufficient cooling. Settings of direct-acting trip devices should also be reevaluated in this circumstance.



9.1.3.3 Lower than 40 °C ambient temperature

If the ambient temperature outside the circuit breaker enclosure is maintained at less than 40 °C, the circuit breaker may be capable of carrying current in excess of its continuous current rating. However, since the long-time performance and useful life of the circuit breaker may be affected by such an increase in continuous current, the circuit breaker manufacturer should be consulted concerning any increased capability. Settings of direct-acting trip devices should be reevaluated in this circumstance.

9.1.3.4 Installation location

The installation of the circuit breaker shall consider the cumulative loading and minimal enclosure size. See IEEE Std C37.20.1.

9.1.4 Short-circuit current

9.1.4.1 General

Circuit breakers may be applied on a system when the calculated maximum available short-circuit current on the source side of the circuit breaker, modified by the power factor considerations in 9.1.4.4, is not more than the short-circuit current rating of the circuit breaker.

For three-phase ac circuits, the available current calculated is the maximum rms symmetrical value of the three phases at an instant one-half cycle after the short circuit occurs. This value is the total available current from all sources, including synchronous and induction motors.

For single-phase ac circuits, the current should be calculated using the same considerations as used for three-phase circuits. When a circuit breaker is applied in such a way on a single-phase circuit that the system voltage impressed across a single pole is no greater than 58% of any one of the rated maximum voltages, the maximum available short-circuit current may be equal to 100% of the corresponding three-phase short-circuit current rating.

When a circuit breaker is applied in such a manner on a three-phase system that the voltage impressed across a single pole exceeds 58% of the rated maximum voltage, the maximum available short-circuit current shall be limited to 87% of the corresponding three-phase short-circuit rating as listed in ANSI C37.16.

In determining the suitability of a circuit breaker for the short-circuit current conditions of a system, consideration should be given to the following:

a) Source contribution

b) Motor contribution

c) Effects of power factor

d) Types of operating mechanism

e) Duty cycle

f) Direct-acting trip devices

g) Effect of remote protective devices

Recommended guidance in calculating short-circuit currents is given in IEEE Std 141 (IEEE Red Book), IEEE Std 241 (IEEE Gray Book), and IEEE Std 242 (IEEE Buff Book).



9.1.4.2 Source contribution

The symmetrical short-circuit current, consisting of the sum of all sources, should be calculated by taking into account all impedances up to the source side of the circuit breaker but not including any of the circuit breaker impedance. Small impedances, such as cable impedances, should be taken into account, since they may greatly affect the result.

9.1.4.3 Motor contribution

The part of the symmetrical short-circuit current due to motor contributions should be calculated as follows: Induction and synchronous motors, connected to the bus, act as generators, and at one-half cycle after the short circuit occurs, contribute current that may be calculated from the subtransient reactance of the motor plus the impedance of the interconnecting cable. Where the impedances for the installation are not known, it should be assumed that the induction motors contribute 3.6 times their full-load current and that synchronous motors contribute 4.8 times their full-load current.

When the motor load of the installation is not known, the following assumptions should be made:

a) For nominal system voltages of 120 V and 208Y/120 V, it should be assumed that the connected load is 50% lighting and 50% motor load. This corresponds to an equivalent symmetrical contribution of approximately twice the full-load current.

b) For nominal system voltages of 240 V to 600 V, it should be assumed that the load is 100% motor load and, in the absence of exact information, that 25% of the motors are synchronous and 75% induction. This corresponds to an equivalent symmetrical contribution of approximately four times the full-load current.

9.1.4.4 Power factor considerations

Normally the short-circuit power factor (X/R) of a system need not be considered in applying circuit breakers. This is based on the fact that the power factors on which the ratings of the circuit breakers in this standard have been established amply cover most applications. Unfused circuit breakers should be applied at power factor of 15% lagging or more (X/R ratio of 6.6 or less). Fused circuit breakers should be applied at power factor of 20% lagging or more (X/R ratio of 4.9 or less), which is consistent with the standards established for fuses. The high short-circuit current rating of fused circuit breakers makes the need to consider power factor even more unlikely. There are, however, some specific applications when the available short-circuit current approaches 80% of the circuit breaker short-circuit current rating, which may require additional consideration because of lower short-circuit power factors. These considerations are as follows:

⎯ Local generation at circuit breaker voltage in unit sizes greater than 500 kVA

⎯ Gas-filled and dry-type transformers in sizes 1000 kVA and above; all types 2500 kVA and above

⎯ Network systems

⎯ Transformers with impedances higher than those specified in the ANSI C57 series of standards

⎯ Current-limiting reactors at circuit breaker voltage in source circuits

⎯ Current-limiting busway at circuit breaker voltage in source circuits

To determine the short-circuit current rating of the circuit breaker required for these applications, two approaches are possible:

a) If the short-circuit X/R ratio of the power system is known, the appropriate multiplying factor can be selected from Table 4 and multiplied by the calculated value of rms symmetrical current.



b) If the short-circuit X/R ratio of the power system has not been determined, a ratio of 20 should be assumed and the calculated value of rms symmetrical current should be multiplied by the appropriate multiplying factor selected from Table 4.

c) The multiplying factors for unfused circuit breakers are based on the highest peak current calculated in accordance with Equation (1):

[ ]29.2

1 2MF)/( RXe π−+= (1)

d) The multiplying factors for fused circuit breakers are based on total rms current (asymmetrical) calculated in accordance with Equation (2):

25.121MF

)/( 2 RXe π−+= (2)

Table 4 —Selection of multiplier factor

System short-circuit power factor (%) System X/R ratio

Multiplying factor for calculated short-circuit current

Unfused circuit breakers

Fused circuit breakers

20 4.9 1.00 1.00 15 6.6 1.00 1.07 12 8.27 1.04 1.12 10 9.95 1.07 1.15 8.5 11.7 1.09 1.18 7 14.3 1.11 1.21 5 20.0 1.14 1.26

9.1.4.5 Short-circuit duty cycle application

The applicable short-circuit current duty cycle for circuit breakers consists of an opening operation followed by a close-open operation. For unfused circuit breakers, the time between the open and the close-open operations is 15 s (O–15 s–CO). For fused circuit breakers, the time between these operations is the time necessary to replace the fuses and to reset the open-fuse trip device.

As soon as possible after performance at or near its rated short-circuit current, a circuit breaker should be removed from service and inspected, cleaned and, if necessary, otherwise maintained before being returned to service. After maintenance, field dielectric test should be conducted per 8.2.

9.1.4.6 Direct-acting trip devices

9.1.4.6.1 General

See ANSI C37.17.



9.1.4.6.2 Circuit breakers with instantaneous phase trip elements

Circuit breakers with instantaneous phase trip elements should be applied in accordance with the short-circuit current ratings. The settings of the instantaneous phase trip elements should not exceed 13 times the continuous current rating. Values are listed in ANSI C37.16.

9.1.4.6.3 Circuit breakers without instantaneous trip elements

Circuit breakers with long-time-delay and short-time-delay phase trip elements, but without instantaneous phase trip elements, should be applied in accordance with short-circuit/short-time current ratings. Values are listed in ANSI C37.16.

9.1.4.6.4 Circuit breakers with phase trip elements

Circuit breakers with phase trip elements may use instantaneous or short-time-delay ground trip elements in coordination with the normal phase trip element combination as required.

9.1.4.6.5 Circuit breakers without phase trip elements

Circuit breakers without phase trip elements may use instantaneous or short-time-delay ground trip elements, in coordination with the remote protective devices as required.

9.1.4.6.6 Circuit breakers with only long-time-delay or ground trip elements

Circuit breakers are generally not applied with long-time-delay phase trip or ground trip elements only. Such applications are considered unusual, and the manufacturer should be consulted.

9.1.4.7 Effect of remote protective devices

Circuit breakers not equipped with direct phase trip elements should be applied in accordance with their assigned short-circuit current ratings. The values are listed in ANSI C37.16. They should not be subjected to a time delay in tripping of more than 0.5 s duration at their short-circuit rating. Protection afforded under these conditions should be equivalent to that provided for the circuit breaker by a direct-acting phase trip device.

9.1.4.8 Protection of connected equipment when fused circuit breakers are applied

When applied on high short-circuit current capacity systems, the effects of the let-through characteristics of the fused circuit breakers on the connected equipment must be considered. The presence of the current-limiting fuse as part of the fused circuit breaker does not necessarily imply that the connected equipment can adequately withstand these effects.

It should be noted that the fused circuit breaker does not have any current-limiting effect until the current associated with the fault exceeds the current-limiting threshold of the fuse. When fuses of relatively low continuous current rating and relatively low peak let-through current rating are selected to give protection to downstream equipment, there is increased likelihood that they will open at currents much below the circuit breaker element short-circuit current rating.

If the full coordination study for the protection of connected equipment is made known to the manufacturer, then the best combination of direct-acting trip devices and fuses may be selected. Non-optimum combinations can lead to needless fuse opening.

In no case should combinations of trip devices and fuses that are not approved by the manufacturer be installed.



Where fuses of different manufacture are being considered for the same system, the characteristics of all the fuses and circuit breakers in the system should be evaluated, since both the melting time current characteristic and peak let-through current of a given fuse rating may vary substantially between manufacturers.

9.1.5 Surge protective devices

Protection against lightning surges should be considered for all equipment (see IEEE Std C37.20.1) having exposed circuits. Exposed circuits are those outside of buildings or those that do not have adequate surge protection connected to limit voltages to less than the dielectric capabilities of the equipment.

9.2 Short-time current


Unfused circuit breakers without direct-acting phase trip devices should not be applied to a circuit having a maximum symmetrical current available at the point of application that is greater than the short-time current rating of the circuit breaker. The ratings are listed in ANSI C37.16.

Short-time current duty cycle application. The applicable short-time current duty cycle for unfused circuit breakers consists of two periods of 0.5 s current flow, separated by a 15 s interval of zero current.


Fused circuit breakers have a rated short-circuit current rating but do not have a rated short-time current. If the circuit breaker element (without fuses) has a short-time current rating, as provided by the manufacturer, then the fused circuit breaker may be applied with remote relays instead of with direct-acting phase trip elements. The tripping delay for currents that do not cause fuse operation is to be no longer than it could be when using long- and short-time-delay direct-acting phase trip elements. The maximum fuse element rating for this delayed tripping condition may be less than that allowable with instantaneous trip elements, or the same maximum fuse element rating may result in a lesser short-circuit current rating. The manufacturer should be consulted regarding the maximum fuse element rating. For currents that cause fuse operation, tripping will occur by means of the open-fuse trip device.

9.3 Application of circuit breakers for selective tripping

9.3.1 General

Where continuity of service is desired, selective tripping arrangements should be used. A selective tripping arrangement is the application of circuit breakers in series so that, of the circuit breakers carrying overcurrent, the one electrically nearest the overcurrent condition should trip to isolate this circuit condition.

9.3.2 Phase-selective tripping arrangements

9.3.2.1 General

When circuit breakers are applied to low-voltage circuits in phase-selective tripping arrangements, the requirements of 9.3.2.2, 9.3.2.3, and 9.3.2.4 should be observed:



9.3.2.2 Short-circuit current ratings

Each circuit breaker should have an assigned short-circuit current rating equal to, or greater than, the available short-circuit current at the point of its application.

9.3.2.3 Time-current characteristics

The time-current characteristics of each circuit breaker, at all values of available phase overcurrent, should be sufficient to ensure that the circuit breaker nearest the cause of the overcurrent should open to isolate this circuit condition. Those nearest the source of power should remain closed and continue to carry the remaining load current.

It should be noted that continuity of service requires coordination of the low-voltage circuit breakers with the rest of the system. For example, circuit breakers on the low-voltage side of a transformer bank should properly coordinate with relays or fuses on the high-voltage side of the transformer, as well as with downstream protective devices.

9.3.2.4 Short-time-delay phase trip elements

Each circuit breaker, except the one farthest from the source of power, should be equipped with short-time-delay phase trip elements. The circuit breaker farthest from the source of power should normally be equipped with instantaneous phase trip elements if selective coordination with downstream devices is possible.

9.3.3 Ground-selective tripping arrangements

When circuit breakers are applied to low-voltage circuits in ground-selective tripping arrangements, the following should be observed:

⎯ For three-wire grounded systems, the application and coordination methods closely parallel those used for phase coordination.

⎯ For four-wire grounded systems, ground coordination is more complex and varies with the method and location of grounding. Application information should be obtained from the manufacturer.

9.3.4 Time-current characteristics coordination

To permit the circuit breaker in any selective arrangement function to meet these requirements, the time-current characteristics of associated circuit breakers should not overlap. To accomplish this, the pickup settings and time-delay adjustments of all trip elements should be properly selected.


9.3.5.1 General

For fused circuit breakers, the requirements of 9.3.5.2, 9.3.5.3, and 9.3.5.4 should be observed to ensure selective overcurrent tripping.

9.3.5.2 Short-circuit rating

Each fused circuit breaker should have a short-circuit current rating greater than the available fault current at the point of application. Trip functions should be applied as described in 9.2.2.



9.3.5.3 Time-current characteristics coordination

The time-current characteristics of each fused circuit breaker and all values of available overcurrent should be such that the fused circuit breaker electrically nearest the fault will function to remove the overcurrent. The fused circuit breakers electrically nearer the source of power should remain closed and continue to carry the remaining load current.

9.3.5.4 Circuit breaker and fuse coordination

To assure that each circuit breaker and fuse combination will function to meet these requirements, the time-current characteristics of associated fused circuit breakers should not overlap for values of current up to the maximum available fault current at the fused circuit breaker element nearest the fault. The fuse time-current characteristics and direct-acting trip device pickup settings and time-delay bands of both the long-time- and short-time-delay elements, and the pickup settings of the instantaneous devices, should be properly selected.

9.4 Application of circuit breakers to full-voltage motor-starting and running duty of three-phase motors

Trip element settings for motor applications shall be in accordance with the NEC.

The trip device should include long-time, short-time, and instantaneous trip elements except as exceptions are allowed by the NEC. Ground-trip elements may be desirable based on the application.

9.5 Application of circuit breakers for capacitance switching

The continuous current rating of the circuit breaker should be at least 135% of the capacitor bank-rated current. (See NEMA CP 1.)

Short-circuit current contributions and inrush currents during switching of isolated capacitor banks do not generally influence the selection of the circuit breakers, except that they should be considered for proper fuse selection for fused circuit breakers. When parallel capacitor banks are involved, circuit breaker as well as fuse selection may be influenced. If desired, one or more of the following steps may be taken to reduce the effect of the inrush currents:

a) Space the parallel banks far enough apart, or insert reactors to obtain sufficient impedance between the banks.

b) Reduce the size (kVAr) of the banks.

c) Select a circuit breaker of increased short-circuit current rating.

The circuit breaker should be equipped with a direct-acting trip device for short-circuit protection. Instantaneous phase trip elements should be set sufficiently high to prevent tripping on inrush currents.

Capacitance switching ratings are under consideration and the manufacturer should be consulted for specific applications.



9.6 Service conditions affecting circuit breaker applications

9.6.1 Application at low ambient temperatures

For ambient temperatures below −5 °C, heaters should be used to raise the temperature to meet the −5 °C condition as described in service conditions of Clause 4.

9.6.2 Altitude correction

Circuit breakers, when applied at altitudes greater than 2000 m (6600 ft), should have their dielectric withstand, continuous current, and rated maximum voltage ratings multiplied by the correction factors shown in Table 5 to obtain values at which the application is made. The short-time and short-circuit current ratings are not affected by altitude. However, the short-circuit current should not exceed that of the voltage rating prior to derating in accordance with ANSI C37.16.

Table 5 —Altitude correction factors

Altitude Rated continuous current

Rated voltage (m) (ft)

2 000 and below 6 600 and below 1.00 1.00 2 600 8 500 0.99 0.95 3 900 13 000 0.96 0.80

NOTE—Values for intermediate altitudes may be derived by linear interpolation.

9.6.3 Other service conditions

Certain service conditions may require unusual construction or operation, and these conditions should be brought to the attention of those responsible for the application, manufacture, and operation of the circuit breaker. Wherever possible, steps such as inclusion of heaters, placement in controlled atmosphere areas, or others, should be taken at the site of the installation to nullify the deleterious effect of the following:

a) Exposure to damaging fumes or vapors, excessive or abrasive dust, explosive mixture of dust or gases, steam, salt spray, excessive moisture, dripping water, radiation, and other similar conditions

b) Exposure to abnormal vibration, shocks, seismic occurrences, or tilting

c) Exposure to excessively high or low temperature

d) Exposure to unusual transportation or storage conditions

e) Exposure to extreme solar temperatures

f) Unusual operating duty, frequency of operation, and difficulty of maintenance

g) Load currents of nonsinusoidal waveforms

h) Temperature of circuit breaker parts that falls below the dew point of the surrounding air, causing moisture condensation on the parts



9.7 Repetitive duty operations and normal maintenance

9.7.1 General

Power-operated circuit breakers, when operating under service conditions listed in Clause 4 can be expected to operate the number of times specified in ANSI C37.16.

These numbers of operation apply to all parts of a circuit breaker that function during normal operation. They do not apply to other parts, such as direct-acting trip devices, open fuse trip devices, or fuses that function only during infrequent abnormal circuit conditions.

9.7.2 Operating conditions—Unfused circuit breakers

The following paragraphs reference ANSI C37.16 and are applicable to the number of repetitive operations listed:

a) Servicing consists of adjusting, cleaning, lubricating, tightening, etc., as recommended by the manufacturer. When current is interrupted, dressing of contacts may be required as well. The operations listed are on the basis of servicing on an annual interval, or less.

b) When closing and opening no-load.

c) With rated control voltage applied.

d) Frequency of operation not to exceed 20 operations in 10 min or 30 operations in 1 h. Rectifiers or other auxiliary devices may further limit the frequency of operation.

e) Servicing at no greater intervals than shown in ANSI C37.16.

f) No functional parts should have been replaced during the listed operations.

g) The unfused circuit breaker should be in a condition to carry its rated continuous current at rated maximum voltage and perform at least one opening operation at rated short-circuit current. After completion of this series of operations, functional part replacement and general servicing may be necessary.

h) When closing and opening current up to the continuous current rating of the circuit breaker at voltages up to the rated maximum voltage and at 85% power factor or higher.

i) When closing current up to 600% and opening currents up to 100% (80% power factor or higher) of the continuous current rating of the circuit breaker at voltages up to the rated maximum voltage.

j) When closing currents up to 600% and opening currents up to 600% (50% power factor or less) of the continuous current rating of the circuit breaker at voltages up to rated maximum voltage, the number of operations shown shall be reduced to 10% of the number listed.

k) If a fault operation occurs before the completion of the listed operations, servicing is recommended and possible functional part replacements may be necessary, depending on previous accumulated duty, fault magnitude, and expected future operations.

9.7.3 Operating conditions—Fused circuit breakers

The following paragraphs reference ANSI C37.16 and are applicable to the number of operations listed:

⎯ Paragraph a) through paragraph f) are as specified in 9.7.2.

⎯ Paragraph g). The fused circuit breaker should be in a condition to carry its rated continuous current at rated maximum voltage and perform at least one opening operation at any current not exceeding rated short-circuit current. The ability of the fuses to limit fault current should be



unimpaired. After completion of this series of operations, functional part replacement and general servicing may be necessary.

⎯ Paragraphs h), paragraph i), and paragraph j) are as specified in 9.7.2.

⎯ Paragraph k). If a fault operation occurs before the completion of the listed operations, servicing is recommended and possible functional part replacement may be necessary, depending on previous accumulated duty, fault magnitude, and expected future operations. Replacement of unblown fuses should be considered when continuity of service is critical because the time-current characteristic of the fuse could be affected.

9.8 Application of circuit breakers in cascade

Application of circuit breakers above their short-circuit ratings in cascade is not recommended.

9.9 Application of circuit breakers without enclosures

Application of circuit breakers without enclosures is not recommended.

9.10 Application of circuit breakers with dependent manually closing mechanisms

Application of circuit breakers with dependent manual mechanisms is not recommended.

9.11 Application of fused circuit breakers on corner-grounded delta system

When a fused circuit breaker is used on a corner-grounded delta system, a shunt shall be installed in place of the fuse for the phase with the grounded conductor.



Annex A

(informative)

Bibliography

[B1] ANSI/IEEE Std C37.14™, IEEE Standard for Low-Voltage DC Power Circuit Breakers in Enclosures.

[B2] IEC 60947-2, Low-voltage switchgear and controlgear—Part 2: Circuit-breakers.14

[B3] IEEE 100™, The Authoritative Dictionary of IEEE Standards Terms, Seventh Edition. New York: Institute of Electrical and Electronics Engineers, Inc.15, 16

[B4] IEEE Std 1015™, Recommended Practice for Applying Low-Voltage Circuit Breakers Used in Industrial and Commercial Power Systems.

[B5] IEEE Std C37.13.1™, IEEE Standard for Definite Purpose Switching Devices for Use in Metal Enclosed Low Voltage Power Circuit Breaker Switchgear.

[B6] IEEE Std C37.18™, IEEE Standard Enclosed Field Discharge Circuit Breakers for Rotating Electric Machinery.

[B7] IEEE Std C37.27™, IEEE Application Guide for Low-Voltage AC Power Circuit Breakers Applied With Separately Mounted Current-Limiting Fuses.

[B8] IEEE Std C37.100.1™, IEEE Standard of Common Requirements for Power Switchgear.

[B9] UL 746A, Standard for Polymeric Materials—Short Term Property Evaluations.17

[B10] UL 746C, Standard for Polymeric Materials; Use in Electrical Equipment Evaluations.

[B11] UL 1066, Low-Voltage Power Circuit Breakers Used in Enclosures.

14 IEC publications are available from the Sales Department of the International Electrotechnical Commission, 3, rue de Varembé, P.O. Box 131, CH-1211 Geneva 20, Switzerland (http://www.iec.ch/). 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. 15 IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854, USA (http://standards.ieee.org/). 16 The IEEE standards or products referred to in this annex are trademarks owned by the Institute of Electrical and Electronics Engineers, Incorporated. 17 UL standards are available from Global Engineering Documents, 15 Inverness Way East, Englewood, CO 80112, USA (http://global.ihs.com/).

IEEE Std C37.13-2008 IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures

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Transcript of IEEE Std C37.13-2008 IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures