【IEEE国际电工】IEEE Std C37.20.1-1993 IEEE Standard for Metal-Enclosed Low- Voltage Power Circuit Breaker Switchgear

【IEEE国际电工】IEEE Std C37.20.1-1993 IEEE Standard for Metal-Enclosed Low- Voltage Power Circuit Breaker Switchgear IEEE Std C37.20.1-1993 (Revision of IEEE Std C37.20.1-1987) IEEE Standard for Metal-Enclosed Low- Voltage Power Circuit Breaker Switchgear Sponsor Switchgear Committee of the IEEE Power Engineering Society Approved September 15,1993 IEEE Standards Board Abstract: Low-voltage metal-enclosed switchgear, which can contain either stationary or drawout, manually or electrically operated low-voltage ac or dc power circuit breakers in individual grounded metal compartments, in three-pole, two-pole, or single-pole construction is covered. Rated maximum voltage levels can be 254 V, 508 V, or 635 Vac and 300/325 V, 800 V, 1000 V, 1600 V, or 3200 Vdc. The continuous current ratings of the main bus in ac designs can be 1600 Al 2000 A, 2500 A, 4000 A, 6000 A, 8000 A, 10,000 A, or 12,000 A. The switchgear can also contain associated control, instruments, metering, protective, and regulating devices as necessary. The standard deals with service conditions, ratings, temperature limitations, and classification of insulating materials, insulation (dielectric) withstand voltage requirements, test procedures, and application. Keywords: common related terms, control, cumulative loading, current transformers, drawout, indoor, instrumentation, load current-carrying, metering, outdoor, protection, qualifying terms, stationary The Institute of Electrical and Electronics Engineers, Inc.345 East 47th Street, New York, NY 10017-2394, USA Copyright ? 1994 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published 1994. Printed in the United States of America. ISBN 1-55937-378-4 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 i IEEE Standards documents are developed within the Technical Committees of the IEEE Societies and the Standards Coordinating Committees of the IEEE Standards Board. Members of the committees serve voluntarily and without compensation. They are not necessarily members of the Institute. The standards developed within IEEE represent a consensus of the broad expertise on the subject within the Institute as well as those activities outside of IEEE that have expressed an interest in participating in the development of the standard. Use of an IEEE Standard is wholly voluntary. The existence of an IEEE Standard does not imply that there are no other ways to produce, test, measure, purchase, market, or provide other goods and services related to the scope of the IEEE Standard. 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Their approval by the Institute of Electrical and Electronics Engineers does not mean that using such technology for the purpose of conforming to such standards is authorized by the patent owner. It is the obligation of the user of such technology to obtain all necessary permissions. vi Introduction (This introduction is not a part of IEEE Std C37.20.1-1993, IEEE Standard for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear.) This standard has been revised to reflect needed technical changes that have been suggested since the original document was published in 1987. This standard includes the requirements for only metal-enclosed low-voltage power circuit breaker switchgear. These requirements were previously a part of IEEE Std C37.20-1969 (Reaff 1981), IEEE Standard for Switchgear Assemblies Including Metal-Enclosed Bus (1974 consolidated edition). Other types of equipment previously included in IEEE Std C37.20-1969 (Reaff 1981), will be incorporated in separate publications. 1 IEEE Std C37.20-1969 has for many years covered all switchgear assemblies, including metal-enclosed bus. Standards committees of the IEEE Switchgear Assemblies Subcommittee and the NEMA Power Switchgear Assemblies Technical Committee recommended that the document be further developed and, where appropriate, that the various sections be identified with their own standards. This approach also identifies with the Conformance Test Procedure Standards. The IEEE Switchgear Assemblies Committee, in cooperation with the NEMA Power Switchgear Assemblies Technical Committee, was responsible for this revision. NEMA is responsible for developing clauses 4. and 6.. The Switchgear Assemblies Committee of the IEEE Switchgear Committee is responsible for developing clauses 2., 3., 5., 7., and 8.. A Working Group of the NEMA Power Switchgear Assemblies Technical Committee revised IEEE Std C37.23-1970, IEEE Guide for Calculating Losses in Isolated-Phase Bus to include clause 8. of IEEE Std C37.20. The document updates the material for metal-enclosed conductors including cable bus. The IEEE Switchgear Assemblies Committee refined and expanded the document. This publication is one of a series covering Switchgear Assemblies as follows (see figure A): IEEE Std C37.20.1-1993 Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear (1000 V and Below) IEEE Std C27.20.2-1993 Metal-Clad and Station-Type Cubicle Switchgear (Above 1000 V) IEEE Std C37.20.3-1987 Metal-Enclosed Interrupter Switchgear (Above 1000 V) IEEE Std C37.21-1985 Control Switchboards IEEE Std C37.23-1987 IEEE Standard for Metal-Enclosed Bus and Guide for Calculating Losses in Isolated Phase Bus Through this joint effort over the many years, the switchgear assemblies standards have been of extreme value to the industry. Further suggestions for improvement gained in the use of this standard will be welcomed. 1IEEE Std C37.20-1969 has been withdrawn. This standard was delineated into the various branches of the IEEE Std C37.20 series. iii Figure A —Types of switchgear assemblies The Standards Committee on Power Switchgear, C37, which reviewed and approved this standard, had the following personnel at the time of approval: E. Byron, Chair M. Williams, Secretary M. Calwise, Program Administrator A. K. McCabe, Executive Vice-Chair of High-Voltage Switchgear Standards (vacant) Executive Vice-Chair of Low-Voltage Switchgear Standards D. L. Swindler, Executive Vice-Chair of IEC Activities iv Organization Represented Name of Representative Association of Iron and Steel Engineers (vacant) Electric Light and Power Group M. C. Mingoia D. J. Borchart T. E. Bruck J. H. Provanzana J. D. Stewart G. R. Brandenberger (Alt.) A. K. McCabe (Alt.) Institute of Electrical and Electronics Engineers D. F. Peelo L. B. Beard H. L. Bowles P. W. Dwyer D. Signon S. C. Atkinson (Alt.) D. G. Kumbera (Alt.) L. V. McCall (Alt.) Laubach Associates W. Laubach National Electrical Manufacturers Association R. Garzon G. Haynes W. Kracht H. L. Miller T Olson E. Byron (Alt.) G. T Jones (Alt.) G. Sakats (Alt.) S. Stone (Alt.) D. L. Swindler (Alt.) Tennessee Valley Authority D. N. Reynolds Testing Laboratory Group L. Frier W. T O’Grady U.S. Department of the Army, Office of the Chief of Engineers J. A. Gilson U.S. Department of the Interior, Bureau of Reclamation R. Arnold U.S. Department of the Navy, Naval Construction Battalion Center R. L. Clark Western Area Power Administration G. D. Birney The Switchgear Assemblies Subcommittee of the IEEE Switchgear Committee that prepared and approved this standard had the following membership: L. W. Gaussa, Sr., Chair S. C. Atkinson P Clickner G. R. Nourse J. A. Bishop J. J. Dravis G. O. Perkins C. Ball J. M. Jerabek G. Sakats C. G. Burland W. McCowan J. C. Scott T. Burse W. McKay S. H. Telander E. R. Byron W. E. Laubach A. Tomeo v The following persons were on the balloting committee: R. J. Alton P. L. Kolarik A. F. Parks D. F. Perkins G. J. G. Angelis D. G. Kumbera R. H. Arndt S. R. Lambert O. Perkins R. L. R. Beard D. M. Larson Ranjan H. L. Bowles W. E. Laubach J. C. W. Ransom M. T. Brown J. G. Leach J. E. Reed J. H. Brunke G. N. Lester A. B. Rishworth C. G. Burland D. L. Lott H. C. Ross R. L. Capra E. L. Luehring L. R. Saavedra A. Dixon J. A. Maneatis L. H. Schmidt J. J. Dravis C. R. Matulic C. A. Schwalbe J. Dvorak P. P. C. Mayo G. St-Jean W. Dwyer R. A. K. McCabe D. L. Swindler D. Garzon L. L. V. McCall S. H. Telander W. Gaussa K. W. C. McKay F. C. Teufel I. Gray H. W. Mikulecky E. F Veverka K. D. Hendrix D. C. Mills C. L. Wagner H. L. Hess W. R. Wilson G. F. Montillet W. F. Hoenigmann F. J. Muench R. B. F. Wirtz J. M. Jerabek P. O’Leary When the IEEE Standards Board approved this standard on September 15, 1993, it had the following membership: Wallace S. Read, Chair Donald C. Loughry, Vice Chair Andrew G. Salem, Secretary Gilles A. Baril Jim Isaak Don T. Michael* José A. Berrios de la Paz Marco W. Migliaro Ben C. Johnson Clyde R. Camp Walter J. Karplus L. John Rankine Donald C. Fleckenstein Lorraine C. Kevra Arthur K. Reilly E. G. ―Al‖ Kiener Ronald H. Reimer Jay Forster* David F. Franklin Ramiro Ivor N. Knight Gary S. Robinson Garcia Donald N. Leonard L. Tripp Joseph L. Koepfinger* Donald W. Zipse Heirman D. N. ―Jim‖ Logothetis *Member Emeritus Also included are the following nonvoting IEEE Standards Board liaisons: Satish K. Aggarwal Richard B. Engelman Stanley I. Warshaw James Beall David E. Soffrin Rochelle L. Stem IEEE Standards Project Editor vi CLAUSE PAGE 1. Scope and references ...........................................................................................................................................1 1.1 Scope .......................................................................................................................................................... 1 1.2 References .................................................................................................................................................. 1 2. Definitions...........................................................................................................................................................3 2.1 General ....................................................................................................................................................... 3 2.2 Qualifying terms ........................................................................................................................................ 5 2.3 Common or related terms........................................................................................................................... 5 3. Service conditions ...............................................................................................................................................6 4. Ratings ................................................................................................................................................................7 4.1 General ....................................................................................................................................................... 7 4.2 Voltage and insulation levels ..................................................................................................................... 8 4.3 Rated frequency ......................................................................................................................................... 8 4.4 Rated current .............................................................................................................................................. 8 4.5 Temperature limitations ............................................................................................................................. 9 4.6 Current transformer ratings ...................................................................................................................... 11 4.7 Current transformer accuracies ................................................................................................................ 11 5. Tests ..................................................................................................................................................................12 5.1 General ..................................................................................................................................................... 12 5.2 Design tests .............................................................................................................................................. 12 5.3 Production tests ........................................................................................................................................ 19 5.4 Conformance tests .................................................................................................................................... 20 5.5 Field dielectric tests ................................................................................................................................. 20 6. Construction ......................................................................................................................................................20 6.1 General requirements ............................................................................................................................... 20 6.2 Materials and finish .................................................................................................................................. 26 6.3 Barriers ..................................................................................................................................................... 26 6.4 Buses and connections ............................................................................................................................. 27 6.5 Access doors and covers .......................................................................................................................... 27 6.6 Closing and tripping ................................................................................................................................. 27 6.7 Indoor LV switchgear .............................................................................................................................. 27 6.8 Outdoor LV switchgear............................................................................................................................ 27 6.9 Pull box .................................................................................................................................................... 28 6.10 Arrangements with stationary circuit breakers ........................................................................................ 28 6.11 Arrangements with drawout circuit breakers ........................................................................................... 28 6.12 Primary cable space ................................................................................................................................. 29 6.13 Precautionary labels ................................................................................................................................. 30 6.14 Lifting devices.......................................................................................................................................... 30 7. Application guide for LV switchgear................................................................................................................30 7.1 Unusual service conditions ...................................................................................................................... 30 7.2 System characteristics—Voltage and frequency...................................................................................... 33 vii CLAUSE PAGE 7.3 Overvoltage considerations—Insulation levels ....................................................................................... 33 7.4 Continuous current rating and overload capability .................................................................................. 34 7.5 Short-circuit considerations ..................................................................................................................... 40 7.6 Nuclear power plant application .............................................................................................................. 40 7.7 Associated devices often used in LV switchgear ..................................................................................... 40 7.8 Protection and isolation of switchgear connected to other circuit protective equipment ........................ 42 7.9 Overcurrent protection ............................................................................................................................. 42 8. Guide for handling, storage, and installation ....................................................................................................42 8.1 General ..................................................................................................................................................... 42 8.2 Handling ................................................................................................................................................... 42 8.3 Preoperation check ................................................................................................................................... 44 8.4 Removable elements ................................................................................................................................ 44 8.5 Interlocks .................................................................................................................................................. 44 8.6 Energizing ................................................................................................................................................ 45 viii IEEE Standard for Metal-Enclosed Low- Voltage Power Circuit Breaker Switchgear 1. Scope and references 1.1 Scope This standard covers metal-enclosed low-voltage power circuit breaker switchgear assemblies containing, but not limited to, such devices as low-voltage power circuit breakers (fused or unfused); other interrupting devices; switches, control, instrumentation, and metering; and protective and regulating equipment. This standard is concerned with enclosed, rather than open, indoor and outdoor switchgear assemblies. It includes types of equipment that are part of secondary unit substations. It does not apply to equipment covered by industrial control standards, communication switchboards, communication switching equipment, switchboards for use on board ships, or dead-front distribution switchboards. In this standard, metal-enclosed low-voltage power circuit breaker switchgear shall be called LV switchgear. For ac LV switchgear, the voltage shall be 1000 V or below; for dc LV switchgear, the voltage shall be 3200 V or below. 1.2 References This standard shall be used in conjunction with the following publications. When the standards referenced in this document are superseded by an approved revision, the revision shall apply. 1Accredited Standards Committee C2-1993, National Electrical Safety Code (NESC). ANSI C37.16-1988, American National Standard Preferred Ratings, Related Requirements and Application2 Recommendations for Low-Voltage Power Circuit Breakers and AC Power Circuit Protectors. 1The NESC is available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, USA. 2ANSI publications are available from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036, USA. 1 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR ANSI C37.51-1989, American National Standard for Switchgear—Metal-Enclosed Low-Voltage AC Power Circuit Breaker Switchgear Assemblies—Conformance Test Procedures. 3ANSI/NFPA 70-1993, National Electrical Code. 4ANSI/UL 486A-1991, Wire Connectors and Soldering Lugs for Use With Copper Conductors. ANSI Z535.4-1991, American National Standard for Product Safety Signs and Labels. 5ASTM B117-90, Standard Method of Salt Spray (Fog) Testing. ASTM D229-91, Standard Method of Testing Rigid Sheet and Plate Materials Used for Electrical Insulation. ASTM D714-87, Standard Method for Evaluating Degree of Blistering of Paints. ASTM D1535-89, Standard Method of Specifying Color by the Munsell System. ASTM D1654-79a (R 1984), Standard Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments. ASTM G21-90, Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi. IEEE Std 1-1986, IEEE Standard General Principles for Temperature Limits in the Rating of Electric Equipment and 6for the Evaluation of Electrical Insulation (ANSI). IEEE Std 4-1978, IEEE Standard Techniques for High-Voltage Testing (ANSI). IEEE Std 100-1992, The New IEEE Standard Dictionary of Electrical and Electronics Terms (ANSI). IEEE Std 141-1993, IEEE Recommended Practice for Electric Power Distribution for Industrial Plants (IEEE Red Book). IEEE Std 142-1991, IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems (IEEE Green Book) (ANSI). IEEE Std 241-1990, IEEE Recommended Practice for Electric Power Systems in Commercial Buildings (IEEE Gray Book) (ANSI). IEEE Std 242-1986 (Reaff 1991), IEEE Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems (IEEE Buff Book) (ANSI). IEEE Std 344-1987, IEEE Recommended Practices for Seismic Qualification of Class 1E Equipment for Nuclear Power Generating Stations (ANSI). IEEE Std 446-1987, IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications (IEEE Orange Book) (ANSI). 3The National Electrical Code is published by the National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Copies are also available from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036, USA. 4ANSI/UL publications are available from Underwriters Laboratories Inc., Publication Stock, 333 Pfingsten Road, Northbrook, IL 60062. Copies are also available from the Sales Department, American National Standards Institute, 11 West 42nd Street, 13th Floor, New York, NY 10036, USA. 5 ASTM publications are available from American Society for Testing and Materials, 1916 Race St, Philadelphia, PA 19103, USA.61EEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, PO Box 1331, Piscataway, NJ 08855- 1331, USA. 2 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 IEEE Std C37.09-1979 (Reaff 1988), IEEE Standard Test Procedures for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis (ANSI). IEEE Std C37.2-1991, IEEE Standard Electrical Power System Device Function Numbers (ANSI). IEEE Std C37.13-1990, IEEE Standard for Low-Voltage AC Power Circuit Breakers Used in Enclosures (ANSI). IEEE Std C37.14-1992, IEEE Standard for Low-Voltage DC Power Circuit Breakers Used in Enclosures (ANSI). IEEE Std C37.24-1986 (Reaff 1991), IEEE Guide for Evaluating the Effect of Solar Radiation on Outdoor Metal- Enclosed Switchgear (ANSI). IEEE Std C37.26-1972 (Reaff 1976), IEEE Guide for Methods of Power-Factor Measurement for Low-Voltage Inductive Test Circuits (ANSI). IEEE Std C37.100-1992, IEEE Standard Definitions for Power Switchgear. IEEE Std C37.90.1-1989, IEEE Standard Surge Withstand Capability (SWC) Tests for Protective Relays and Relay Systems (ANSI). IEEE Std C37.90.2-1987, IEEE Trial-Use Standard Withstand Capability of Relay Systems to Radiated Electromagnetic Interference from Transceivers (ANSI). IEEE Std C57.13-1978 (Reaff 1986), IEEE Standard Requirements for Instrument Transformers (ANSI). 7NEMA CC1-1993, Electric Power Connectors for Substations. NEMA WC5-1992/ICEA S-61-402, Thermoplastic-Insulated Wire and Cable for the Transmission and Distribution of Electrical Energy. NEMA WC7-1991/ICEA S-66-524, Cross-Linked Polyethylene-Insulated Wire and Cable for the Transmission and Distribution of Electrical Energy. 2. Definitions The definitions of terms contained 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. 8 If a term is not defined in this standard, the definition in IEEE Std C37.100-1992 applies. An asterisk(*) following a definition indicates that the definition in this standard is not contained in IEEE Std C37.100-1992 while a dagger (†) indicates the definition differs from that in IEEE Std C37.100-1992 . 2.1 General 2.1.1 ambient air temperature: The temperature of the surrounding air that comes in contact with equipment. NOTE — Ambient air temperature, as applied to enclosed switchgear assemblies, is the average temperature of the surrounding air that comes in contact with the enclosure. (See 5.2.2.3 for method of measurement.) 7 NEMA publications are available from the National Electrical Manufacturers Association, 2101 L Street, NW, Washington, DC 20037, USA.8Information on references can be found in 1.2. Copyright ? 1998 IEEE All Rights Reserved 3 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 2.1.2 auxiliary compartment: That portion of the switchgear assembly that is assigned to the housing of auxiliary *equipment, such as potential transformers, control power transformers, or other miscellaneous devices. 2.1.3 circuit breaker compartment: That portion of a switchgear assembly that contains one circuit breaker and the *associated primary conductors and secondary control connection devices including current transformers. 2.1.4 conformance tests: Tests that demonstrate compliance with the applicable standards. The test specimen is normally subjected to all planned production tests prior to initiation of the conformance test program.† NOTE — The conformance tests may, or may not, be similar to certain design tests. Demonstration of margin (capabilities) beyond the standards is not required. 2.1.5 design tests: Tests made by the manufacturer to determine the adequacy of the design of a particular type, style, or model of equipment or its component parts to meet its assigned ratings and to operate satisfactorily under normal service conditions or under special conditions if specified, and may be used to demonstrate compliance with applicable standards of the industry.† NOTES: 1 — Design tests are made on representative apparatuses or prototypes to verify the validity of design analyses and calculation methods and to substantiate the ratings assigned to all other apparatuses of basically the same design. These tests are not intended to be made on every design variation or to be used as part of normal production. The applicable portion of these design tests may also be used to evaluate modifications of a previous design and to ensure that performance has not been adversely affected. Test data from previous similar designs may also be used for current designs, where appropriate. Once made, the tests need not be repeated unless the design is changed so as to modify performance. 2 — Design tests are sometimes called type tests. 2.1.6 field tests: Tests made after the switchgear assembly has been installed at its place of utilization. 2.1.7 metal-enclosed low-voltage power circuit-breaker switchgear (LV): LV switchgear of multiple or individual enclosures, including the following equipment as required: a) Low-voltage power circuit breakers (fused or unfused) in accordance with IEEE Std C37.13-1990 .† b) Bare bus and connections c) Instrument and control power transformers d) Instruments, meters, and relays e) Control wiring and accessory devices The low-voltage power circuit breakers are contained in individual grounded metal compartments and controlled either remotely or from the front of the enclosure. The circuit breakers may be stationary or removable (drawout) type; when of removable type, mechanical interlocks are provided for proper operating sequence.† 2.1.8 metal-enclosed power switchgear (ME): A switchgear assembly completely enclosed on all sides and top with sheet metal (except for ventilating openings and inspection windows) containing primary power circuit switching or interrupting devices, or both, with buses and connections. The assembly may include control and auxiliary devices. Access to the interior of the enclosure is provided by doors or removable covers, or both.† 2.1.9 production tests: Tests made for quality control by the manufacturer on every device or representative samples, or on parts or materials as required to verify during production that the product meets the design specifications and applicable standards.† NOTES: 1 — Certain quality assurance tests on identified critical parts of repetitive high-production devices may be tested on a planned statistical sampling basis. 2 — Production tests are sometimes called routine tests. 2.1.10 switchgear: A general term covering switching and interrupting devices and their combination with associated control, instruments, metering, protective, and regulating devices; also assemblies of these devices with associated interconnections, accessories, and supporting structures used primarily in connection with the generation, transmission, distribution, and conversion of electric power.† 4 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 2.1.11 switchgear assembly (see figure A in the introduction): An assembled equipment (indoor or outdoor) including, but not limited to, one or more of the following categories: switching, interrupting, control, instrumentation, metering, protective, and regulating devices; together with their supporting structures, enclosures, conductors, electrical interconnections, and accessories.† 2.1.12 vertical section: That portion of the switchgear assembly between two successive vertical delineations, and may contain one or more circuit breakers, auxiliary compartments, and associated primary conductors.† 2.2 Qualifying terms The following qualifying terms relating to types of enclosures, ventilation methods, etc., are defined in IEEE Std 100- 1992 and the user is referred to the definitions given therein: 2.2.1 accessible (as applied to equipment): 2.2.2 alive (live): 2.2.3 automatic (self-coupling): 2.2.4 dead front: 2.2.5 enclosed (inclosed): 2.2.6 enclosed ventilated apparatus: 2.2.7 insulated: 2.2.8 insulating: 2.2.9 isolated: 2.2.10 manual: 2.2.11 ventilated: The following qualifying terms are defined in IEEE Std C37.100-1992 and the user is referred to the definitions given therein: 2.2.12 electrical: 2.2.13 enclosure: 2.2.14 flame-resistant (retardant): 2.2.15 general-purpose enclosure: 2.2.16 indoor: 2.2.17 metal-enclosed: 2.2.18 outdoor: 2.2.19 resistant (used as a suffix): 2.2.20 secondary (used as an adjective): 2.2.21 ventilated enclosure: 2.3 Common or related terms The following common or related terms are defined in IEEE Std C37.100-1992 and the user is referred to the definitions given therein: Copyright ? 1998 IEEE All Rights Reserved 5 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 2.3.1 asymmetrical: 2.3.2 auxiliary switches: 2.3.3 barrier: 2.3.4 bus: 2.3.5 connected position (of a switchgear assembly removable element): 2.3.6 continuous current tests: 2.3.7 current limiting fuse: 2.3.8 disconnected position (of a switchgear assembly removable element): 2.3.9 drawout-mounted device: 2.3.10 ground bus: 2.3.11 live parts: 2.3.12 main (primary) switchgear connections: 2.3.13 mimic bus: 2.3.14 normal frequency: 2.3.15 primary disconnecting devices (of a switchgear assembly): 2.3.16 removable element (of a switchgear assembly): 2.3.17 secondary and control wiring (small wiring): 2.3.18 secondary disconnecting contacts: 2.3.19 silver surfaced or equivalent: 2.3.20 stationary-mounted device: 2.3.21 symmetrical: 2.3.22 terminal (terminal connector): 2.3.23 terminal block (terminal board): 2.3.24 test position: 3. Service conditions Standards for the design and performance of LV switchgear are based on usual service conditions as described below. The selection of equipment for a particular application can be based on the construction and ratings as defined in this standard provided that the following usual service conditions exist: a) The temperature of the cooling air (ambient air temperature) surrounding the enclosure of the LV switchgear is within the limits of 30 C and +40 C. b) The altitude of the installation does not exceed 6600 ft (2000 m). c) The effect of solar radiation is not significant. (The principles stated in IEEE Std C37.24-1986 may be used for guidance.) d) Unusual service conditions, such as those outlined in 7.1, do not prevail. 6 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 4. Ratings 4.1 General The ratings of a switchgear assembly are designations of operating limits under specified conditions of ambient temperature, temperature rise, etc. Where the switchgear assembly comprises a combination of primary and secondary circuits, each may be given ratings. LV switchgear shall have the following ratings: a) Rated maximum voltage b) Rated frequency c) Rated insulation level d) Rated continuous current e) Rated short-time current f) Rated short-circuit current The designated ratings in this standard are preferred but are not considered to be restrictive. In addition to these ratings, a switchgear assembly may have interrupting or switching capabilities, which are determined by the ratings of the particular interrupting and switching devices that are integral parts of the switchgear assembly. Refer to specific standards for the ratings of these devices. Table 1— Voltage and insulation levels ac LV switchgear Insulation levels (kV) Rated maximum *Normal frequency Reference voltage (rms) withstand (rms) dc withstand 254/508/635 2.2 3.1 9 Table 2— Voltage and insulation levels dc LV switchgear Insulation levels dc LV switchgear (kV) Rated maximum voltage Normal frequency (rms) * withstand (rms) Referencedc withstand 300/325 2.2 3.1 †800 3.7 5.2 1200 4.6 6.5 1600 5.4 7.6 3200 8.8 12.4 NOTE — For field test values see 5.5. *The column headed ―dc withstand‖ is given as a reference only for those using dc tests to verify the integrity of connected cable installations without disconnecting the cables from the switchgear. It represents values believed to be appropriate and approximately equivalent to the corresponding normal frequency withstand test values specified for each voltage class of switchgear. The presence of this column in no way implies any requirement for a dc withstand test on ac/dc equipment or that a dc withstand test represents an acceptable alternative to the normal frequency withstand tests specified in this standard, either for design tests, production tests, conformance tests, or field tests. When making dc tests, the voltage should be raised to the test value in discrete steps and held for a period of 1 min. †See footnote 9. 9The values followed by a dagger (†) will be updated pending on the next revision. Refer to the table in 8.1 a) of IEEE Std C37.14-1992 for updated ac dielectric withstand voltage requirements. Copyright ? 1998 IEEE All Rights Reserved 7 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 4.2 Voltage and insulation levels 4.2.1 Rated maximum voltage The rated maximum voltage of LV switchgear is the highest rms voltage for which the equipment is designed, and is the upper limit for operation. 4.2.2 Rated insulation level The rated insulation level of LV switchgear is equal to the normal frequency one-minute withstand voltage. 4.2.3 Voltage and insulation levels for ac LV switchgear The rated maximum voltages and corresponding insulation levels for ac LV switchgear are listed in table 1. 4.2.4 Voltage and insulation level for dc LV switchgear The rated maximum voltages and corresponding insulation levels for dc LV switchgear are listed in table 2. 4.3 Rated frequency The rated frequency of a device, or an assembly, is the frequency of the circuit at which it is designed to perform. (Ratings for ac equipment are based on a frequency of 60 Hz.) 4.4 Rated current 4.4.1 Rated continuous current The rated continuous current of LV switchgear is the maximum current in rms amperes at rated frequency or direct current that can be carried continuously by the primary circuit components, including buses and connections, without causing temperatures in excess of specified limits for the following: a) Any primary or secondary circuit component b) Any insulating medium, or structural or enclosing member The specified temperature limits applicable to switchgear assemblies are given in 4.5.1 through 4.5.6. 4.4.2 Continuous current ratings The preferred continuous current ratings of the main bus in ac LV switchgear are 1600 A, 2000 A, 3000 A, 3200 A, or 4000 A. In dc LV switchgear the preferred continuous current ratings are 1600 A, 2000 A, 2500 A, 4000 A, 5000 A, 6000 A, 8000 A, 10,000 A, and 12,000 A. The continuous current rating of the vertical section bus riser shall be equal to the frame size of the ac LV power circuit breaker used (see ANSI C37.16-1988 ) except as modified by the allowable cumulative loading of multiple ac circuit breakers in the same section (see table 13), or by lower continuous current ratings for current transformers, but in no case does it need to be greater than the rating of the main bus. 4.4.3 Rated short-time current The rated short-time current of a LV switchgear assembly is the designated limit of available (prospective) current at which it shall be required to withstand its short-time current duty cycle (two periods of 1/2 s current flow, separated by 8 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 a 15 s interval of zero current) at rated maximum voltage under the prescribed test conditions. This current is expressed in rms symmetrical amperes and is measured from the envelope of the available current wave at a time one-half cycle after current is established. This current also demonstrates the dc short-time current ratings. LV switchgear assemblies shall be capable of withstanding 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% or greater (X/ R ratio 6.6 or less). LV switchgear assemblies shall have preferred short-time current ratings equal to the short-time current rating of the smallest frame size circuit breaker used in the assembly as listed in ANSI C37.16-1988. 4.4.4 Rated short-circuit current The rated short-circuit current of an LV ac assembly is the designated limit of available (prospective) current at rated maximum voltage that it shall be required to withstand for a period of no less than four cycles on a 60 Hz basis under the prescribed test conditions. This current is expressed in rms symmetrical amperes and is measured from the envelope of the available current wave at a time 1/2 cycle after current is established. AC LV switchgear assemblies shall have preferred short-circuit current ratings equal to the short-circuit current rating of the smallest frame size circuit breaker used in the assembly as covered in ANSI C37.16-1988. Use power factor (X/R ratio) identical to that of 4.4.3 for this test. DC LV switchgear shall meet the ratings and test parameters required for LV dc power circuit breakers as covered in IEEE Std C37.14-1992 and ANSI C37.16-1988. 4.5 Temperature limitations 4.5.1 Limiting temperature The limiting temperature for LV switchgear is the maximum temperature permitted for the following: a) Any component such as insulation, buses, instrument transformers, and switching and interrupting devices b) Air in cable termination compartments c) Any non-current-carrying structural parts d) Air-surrounding devices 4.5.2 Temperature limits for insulating materials The total temperature to which insulating materials are subjected shall not exceed the values listed in table 3 for the various classes of insulating materials. 4.5.3 Temperature limits for buses and connections The total temperature of buses and connections shall not exceed the values listed in table 4. 4.5.4 Temperature limitations for air surrounding devices within an enclosed assembly The temperature of the air surrounding all devices within an enclosed assembly, considered in conjunction with their rating and loading as used, shall not cause these devices to operate outside their rated temperature range when the enclosure of the assembly is surrounded by air within an ambient temperature range of 30 C to +40 C. Copyright ? 1998 IEEE All Rights Reserved 9 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR Table 3— Temperature limits for insulating materials as used in switchgear assemblies Limit of Class of Limit of hottest- hottest-spot insulating spot total temperature material temperature ( C) rise ( C) Class 90 50 90 Class 105 65 105 Class 130 90 130 Class 155 115 155 Class 180 140 180 Class 220 180 220 NOTE — These temperature limits for insulating materials may not apply to insulation in circuit breakers or other devices. For temperature limitations on devices, refer to the appropriate standards for the devices. See also 4.5.4. Table 4— Temperature limits for buses and connections as used in switchgear assemblies Limit of Limit of hottest- hottest-spot spot total Type of bus or connection temperature temperature rise ( C) ( C) Buses and connections with 30 70 unplated copper to copper connecting joints Buses and connections silver 65 105 surfaced, tin surfaced or equivalent connecting joints Connection to insulated cables 30 70 unplated copper to copper Connections to insulated 45 85 cables silver-surfaced, tin- surfaced, or equivalent NOTE — All aluminum buses shall have silver-surfaced, tin-surfaced, or equivalent connecting joints. Welded bus connections are not considered connecting joints. 4.5.5 Temperature limitations for air surrounding insulated power cables The temperature of the air surrounding insulated power cables within any compartment of an enclosed assembly shall not exceed 65 C when the assembly is a) Equipped with devices having maximum current rating for which the assembly is designed b) Carrying rated continuous current at rated voltage and at rated frequency or direct current, whichever applies c) In an ambient air temperature of 40 C NOTE — This temperature limitation is based on the use of 90 C insulated power cables. Use of lower temperature rated cables requires special consideration. 10 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 4.5.6 Temperature limitations for external parts subject to contact by personnel a) External parts handled by the operator in the normal course of his or her duties shall have no higher total temperature than 50 C. b) External surfaces accessible to an operator in the normal course of his or her duties shall have no higher total temperature than 70 C. c) External surfaces not accessible to an operator in the normal course of his or her duties shall have no higher total temperature than 110 C. NOTE — For additional information on temperature limits, see IEEE Std 1-1986. 4.6 Current transformer ratings 4.6.1 Current transformer mechanical ratings The mechanical ratings of current transformers shall be such that they will successfully withstand the short-circuit current for which the associated circuit-interrupting devices are applied. When the primary circuit is protected by current-limiting fuses, the current transformers shall successfully withstand the maximum let-through current of the fuses. Unless specifically limited to a shorter time by the associated protective equipment, the duration of the short- circuit shall be considered as being four cycles. 4.6.2 Current transformer thermal ratings The thermal ratings of current transformers shall be such that they will successfully withstand the short-circuit current for which the associated circuit-interrupting devices are applied. When the primary circuit is protected by current- 2limiting fuses, the current transformers shall successfully withstand the maximum It of the fuses. Unless specifically limited to a shorter time by the associated protective equipment, the duration of the short circuit shall be considered as being 1 s. 4.6.3 Current transformer ambient temperature Current transformers for use in switchgear assemblies shall be rated on the basis of at least 55 C ambient temperature in accordance with 4.1.1.2 in IEEE Std C57.13-1978. 4.7 Current transformer accuracies Accuracies tabulated hereafter are the minimum that shall be supplied. The manufacturer should be consulted if higher accuracies are required by the purchaser. It should be recognized that current transformers with higher accuracies may not meet the requirements of 4.6.1 and 4.6.2. For installation in ac LV switchgear, the standard current transformer accuracies for metering are listed in table 5. Copyright ? 1998 IEEE All Rights Reserved 11 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR * Table 5— Standard accuracy class ratingcurrent transformers in ac LV switchgear Ratio B 0.1 B 0.2 †100:5 1.2 2.4 150:5 1.2 2.4 200:5 1.2 1.2 300:5 0.6 0.6 400:5 0.6 0.6 600:5 0.6 0.6 800:5 0.3 0.3 1200:5 0.3 0.3 1500:5 0.3 0.3 2000:5 0.3 0.3 3000:5 0.3 0.3 4000:5 0.3 0.3 5000:5 0.3 0.3 6000:5 0.3 0.3 *See IEEE Std C57.13-1978. †Not in IEEE Std C57.13-1978. 5. Tests 5.1 General This subclause establishes physical and electrical conditions for tests and methods of determining temperatures and test values. All apparatuses and devices in the power circuit shall be mounted in their normal locations during tests. No statement in this subclause is to be construed as modifying the test requirements for devices included in switchgear assemblies. Tests are classified as design tests, production tests, conformance tests, and field tests. These are generally defined in 2.1.6 to 2.1.9. NOTE — Except for the main switching or interrupting device, other devices such as voltage transformers that are mounted in the switchgear assemblies may be disconnected during the dielectric test. Such devices are individually tested in accordance with standards applying to them. 5.2 Design tests Design tests as applicable shall be made in accordance with 5.2.1 through 5.2.9. 12 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 5.2.1 Dielectric tests Normal frequency withstand tests on LV switchgear shall be performed to demonstrate the ability of the insulation system to withstand the voltages in accordance with tables 1 and 2. All voltages shall be measured in accordance with IEEE Std 4-1978. The voltage is to be increased gradually from zero to the required test value within 5 s to 10 s and shall be held at that value for 1 min. The ac test voltages shall be essentially sinusoidal and applied with a minimum crest value equal to 1.414 times the specified values. The frequency of the test voltage shall be within +20% of the rated frequency of the LV switchgear or 20% of 60 Hz for dc switchgear being tested. If a test transformer of less than 500 VA is used, a suitable voltmeter shall be provided to measure the applied output voltage directly. The applicable test voltage in accordance with tables 1 and 2, shall be applied for a period of I min to the primary circuit of the LV switchgear in the following manner: a) For equipment with stationary devices and for equipment with drawout-mounted devices with the removable elements in the connected position, apply the test voltage as follows: 1) With the circuit breaker contacts closed, between each phase of the switchgear assembly individually with the frame and the other phases and the neutral bus grounded 2) With the circuit breaker contacts open, between each terminal of the switchgear assembly with the frame and all other terminals grounded b) With the drawout circuit breaker in the test position and closed, apply the test voltage as follows: 1) Simultaneously to all the incoming terminals of the switchgear assembly with the frame and outgoing terminals grounded. Repeat tests by applying the test voltage to the outgoing terminals with the frame and incoming terminals grounded. 2) Simultaneously between all incoming and outgoing terminals of the switchgear assembly. This test shall be made with a value of voltage 10% higher than that specified in tables 1 and 2. NOTES: 1 — For the test across the open gap at 10% higher voltage, an intermediate point of the voltage source may, if practicable, be connected to ground and to the frame of the assembly so that the voltage between any live part and the frame will not exceed that specified in table 1. If this is not practicable, the frame may be insulated from ground. 2 — Successful completion of these tests does not necessarily provide assurance that with the circuit breaker in the test position, it will always flashover to ground instead of across the gap between line and load terminals. Switchgear insulation does not provide surge protection for the open gap. Where surge protection of the gap is required, suitable protective devices must be applied. 3 — Apply test voltage between neutral and ground, except at 1800 V instead of 2200 V (not applicable to dc LV switchgear). 5.2.2 Rated continuous current tests To determine compliance with continuous current ratings, it is necessary to determine that temperatures of the various components of the switchgear assembly are within the limits set forth in 4.5. Temperature measurements shall be made in accordance with 5.2.2.1 through 5.2.2.7. 5.2.2.1 Test area conditions Temperature tests shall be conducted indoors in a test room that is reasonably free from drafts. 5.2.2.2 Ambient air temperature limits Tests may be made at any ambient air temperature between 10 C and 40 C. Copyright ? 1998 IEEE All Rights Reserved 13 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 5.2.2.3 Measurement of ambient air temperature Indoor ambient air temperatures shall be determined by taking the average of the readings of three temperature- measuring devices, such as thermometers or thermocouples, placed as follows: a) One level with the top of the structure b) One 12 in (305 mm) above the bottom of the structure c) One midway between the two positions a) and b) All temperature-measuring devices shall be placed 12 in (305 mm) from the structure, not in front of ventilators, and in locations unaffected by drafts caused by the structure or appreciable radiation from the equipment. When the ambient air temperature is subject to variations that might result in errors in measuring the temperature rise, the temperature-measuring devices should be immersed in a suitable liquid, such as oil in a suitable container, or reliably attached to a suitable mass of metal. NOTE — A convenient form for such a container consists of a metal cylinder with a hole drilled partly through it. This is filled with liquid and the temperature-measuring device is placed therein. A glass bottle may also be used as a container. The size of the container should be at least 1 in (25.4 mm) in diameter and 2 in (50.8 mm) high. 5.2.2.4 Method of measuring temperature Thermocouples, when used for measuring the temperature of insulation, shall be located on the current-carrying member or other metal part at a point as close as practical to the accessible junction of the insulation and the current- carrying member or other metal part. Thermocouples used for measuring the temperature of the circuit breaker separable primary contacts shall be located approximately 0.5 in (13 mm) from the contacts on the current-carrying member. For cable terminations, the thermocouples shall be located at the junction of the conductor and its insulation. Thermocouples shall be held in intimate contact with the conductor surface by such methods as welding, drilling, and peening, or cementing. The thermocouples on a design test shall be located in a manner so as to measure the hottest spot even though it may involve drilling holes that destroy some parts. It is recognized that thermocouples cannot be located in the actual contact point of line or point contacts without destroying the effectiveness of such line or point contacts. Measurements shall be made at junction points of insulation and conducting parts to ensure against exceeding temperature limits of the insulation. 5.2.2.5 Duration of tests The continuous current test shall be made for such a period of time that the temperature rise of any monitored point in the assembly has not increased by more than 1.0 C during each of two successive 30 min intervals as indicated by three successive readings. If the temperature rise at the end of the second interval is equal to the established limits, and if the temperature rise has increased since the previous reading, the test shall be continued until the temperature rise is constant. 5.2.2.6 Frequency of test current The frequency of the test current shall not be less than the rated frequency of the assembly tested. A sine wave shape is recommended. The test shall be made with alternating current having a crest value equal to 1.414 times the rms test current. Direct current assemblies should be tested using a de power supply with an rms ampere output equal to the continuous current rating. 14 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 5.2.2.7 Copper conductors for use in continuous current tests Bus bars are to be used for the connections to the main bus per table 6 and cables or bus per table 7 for connection to the circuit breaker unit outgoing terminals. If test arrangement internal bus sizes are different than tables 6 and 7, then external bus sizes equal to internal bus sizes may be substituted at the option of the manufacturer. The conductors connected to the terminals shall be a minimum of 4 ft (1.2 m) long. 5.2.3 Short-time current withstand tests Short-time current withstand tests shall be made to demonstrate the electrical and thermal adequacy of buses and connections in switchgear assemblies to withstand the rated short-time current of the assembly without physical damage. The prospective current shall be the rms value calculated in accordance with IEEE Std C37.09-1979 and shall continue for two periods of 1/2 s separated by a 15 s interval of zero current. Single-phase testing is permitted. For short-time tests the alternating component of the current at the end of 1/2 s shall be no less than 80% of the alternating component measured at one-half cycle after initiation of the current. Table 6— Copper conductors for use in continuous current tests (main bus) *Main bus Copper bus per terminal rating (amperes) Quantity Size, inches (mm) 1600 2 1/4 3 (6.35 76.2) 2000 2 1/4 4 (6.35 101.6) 3000/3200 3 1/4 5 (6.35 127.0) 4000 4 1/4 5 (6.35 127.0) NOTE — Larger main buses and circuit breaker frame sizes are required in dc LV switchgear, and IEEE Std C37.14- 1992 and ANSIC37.16-1988 shall be utilized for guidance in testing. *Where multiple bus bars are used, they are to be spaced 1/4 in (6.35 mm) apart. The 4000 A group is to be two sets of two bars with not more than 4 in (101.6 mm) between pair centers. Vertical or horizontal configuration shall be the option of the manufacturer. 5.2.4 Short-circuit current withstand tests Short-circuit current withstand tests shall be made to demonstrate the mechanical adequacy of the structure, buses, and connections to withstand the maximum short-circuit stresses that could occur when the switchgear assembly is properly applied on systems when the available short-circuit current is equal to the short-circuit current rating of the circuit breakers in the LV switchgear with no breakage of insulation and the following: a) No permanent deformation of bus bar, or b) Some deformation that is insufficient to prevent the dielectric requirements from being met Copyright ? 1998 IEEE All Rights Reserved 15 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR Table 7— Copper conductors for use in continuous current tests (outgoing terminals) Size of copper conductor Circuit breaker † Bus per terminal frame size *Cable size (amperes) Quantity Size, inches (mm) 600 2–350 kcmil — — 800 2–500 kcmil — — 1600 4–600 kcmil — — 2000 5–600 kcmil — — 3000/3200 — 3 1/4 5 (6.35 0.127) 4000 — 4 1/4 5 (6.35 0.127) NOTE — Larger main buses and circuit breaker frame sizes are required in dc LV switchgear, and IEEE Std C37.14-1992 and ANSI C37.16-1988 shall be utilized for guidance in testing. *Tests based on cross-sectional area, not cable insulation classification. †Where multiple bus bars are used, they are to be spaced 1/4 in (6.35 mm) apart. The 4000 A group is to be two sets of two bars with not more than 4 in (101.6 mm) between pair centers. Vertical or horizontal configuration shall be the option of the manufacturer. The duration of current flow during the short-circuit current withstand test shall be for no less than four cycles on a 60 Hz basis (0.067 s), unless the bus is protected by a current-limiting device, in which case the duration shall be for the time permitted by that device. NOTE — Four cycles is the maximum duration of short circuit expected on 600 V ac systems on which this equipment is applied. The three-phase rms symmetrical value of current that verifies the short-circuit current rating shall be determined by calibrating the test circuit with the LV switchgear omitted and shall be measured one-half cycle after the inception of the current flow in the test circuit. This current in each phase shall be calculated in accordance with IEEE Std C37.09- 1979. For three-phase circuits, the symmetrical current value shall be the average of the phase current. The power factor of the test circuit shall be 15% lagging or less (X/R ratio of 6.6 or greater) with X and R in series connection. The power factor shall be determined in accordance with IEEE Std C37.26-1972 (power factor minus 20% or less, X/R ratio of 5 or greater for fused circuit-breaker equipment). The rms value of the alternating component of the current at the end of three cycles shall be no less than 90% of the value measured at one-half cycle after initiation of the current. The current shall be initiated in the test circuit in such a manner to ensure that the peak current available is no less than 2.3 times the single-phase rms symmetrical value for the single-phase test and 2.3 times the three-phase rms symmetrical value in one phase for three-phase tests (peak current 2.16 times for fused circuit breakers). The frequency of the test circuit shall be 60 Hz ? 20%. The test-circuit voltage prior to the inception of current flow shall be no less than the rated maximum voltage. Individual single-phase tests are also to be made to prove the strength of the ground bus and the neutral conductor design with respect to the nearest phase bus during the test. Line-to-neutral voltage is to be applied between the neutral and the nearest phase bus during the test. Line-to-line voltage is to be applied between the ground bus and the nearest phase bus during the test. 16 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 5.2.5 Mechanical endurance tests LV switchgear with drawout circuit breakers shall have mechanical endurance test cycles consisting of at least 100 operations between connected and test positions for each frame size and type of circuit breaker to demonstrate proper sequential operation and to establish satisfactory function of the following elements. All primary power, included in the following, should be disconnected during these mechanical tests: a) Separable primary contacts b) Separable control contacts c) Circuit breaker removable element position interlocks (every tenth operation to withdrawn position) d) Stored energy mechanism interlocks, as applicable (every tenth operation to withdrawn position) e) Structure mounted breaker position switches f) Auxiliary switches mounted on stationary structure (every tenth operation) 5.2.6 Flame-resistance tests Sheet-, molded-, or cast-insulating material used in a switchgear assembly 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 D229-91. 5.2.7 Rod entry test 5.2.7.1 Method for ventilated enclosures This test shall prevent the insertion of a straight rod having a diameter of 0.500 in (12.7 mm) into the opening, except that, if the distance between the openings and the nearest live part is greater than 4 in (101.6 mm), a rod having a diameter greater than 0.500 in (12.7 mm) shall be permitted to enter the opening, but a rod having a diameter greater than 0.750 in (19 mm) shall not be permitted to enter the opening. 5.2.7.2 Evaluation The enclosure is considered to have met the requirements of this test if the appropriate rod cannot enter the enclosure. 5.2.8 Paint qualification test The paint qualification test applies to all enclosures incorporating external ferrous parts. Nonferrous enclosures with no external ferrous parts need not be tested. The paint qualification test shall be performed to ensure the adequacy of finishes to inhibit the buildup of rust on ferrous metal materials used for enclosures. The following methods are used. 5.2.8.1 Test specimens Representative test panels of a 3 in 6 in (76.2 mm 152.4 mm) minimum size that can be accommodated by the test chamber shall be provided. Each specimen shall be uniformly processed in the standard production paint-finishing system. At least four panels shall be selected for the test. All the test specimens shall be of standard gauge ferrous metal equivalent to that used for the enclosure. The specimen shall be allowed to age for a minimum of seven days before being tested. 5.2.8.2 Test apparatus The test apparatus shall consist of a fog chamber, salt-solution reservoir, compressed-air supply, provisions for heating, and means of control. The conditions in the salt-spray chamber, including the positioning of the specimens, content of the salt solution, and temperature and pressure to be maintained, shall be as defined in ASTM-B117-90. Copyright ? 1998 IEEE All Rights Reserved 17 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 5.2.8.3 Preparation of test specimens Two of the test panels shall be suitably scribed for testing in accordance with ASTM D1654-79a. 5.2.8.4 Exposure of test specimens All test specimens shall be tested in the salt-spray chamber for a period of 200 h continuously except for the short daily interruptions necessary to inspect the test specimen or replenish the solution in the reservoir. 5.2.8.5 Procedure After completion of the exposure period, the scribed specimens shall be processed in accordance with ASTM D1654- 79a, either method A (tape) or method B (scraper). 5.2.8.6 Evaluation The scribed specimens shall then be evaluated for creepage from the scribe mark in accordance with ASTM D1654- 79a, rating schedule No. 1. The non-scribed specimen shall be evaluated for degree of blistering in accordance with ASTM D714-87. 5.2.8.7 Performance The scribed specimens shall be judged to have met the requirements of the test if their rating number is 5 or higher as determined by ASTM D1654-79a. The non-scribed specimens shall be judged to have met the requirements of the test if their blistering size is No. 6 or higher, and their frequency designation is F or M as determined by ASTM D714-87. 5.2.9 Rain test for outdoor LV switchgear The enclosure to be tested shall be equipped and complete with typical appurtenances, and placed in the area to be supplied with artificial precipitation. For multiple unit construction a minimum of two units shall be used to test the joints between units. A roof joint shall be included. The artificial precipitation shall be supplied by a sufficient number of nozzles to produce a uniform spray over the entire surface or surfaces under test. The various vertical surfaces of an enclosure may be tested separately or collectively, provided that a uniform spray is simultaneously applied to both a) and b) as follows: a) The roof surface, from nozzles located at a suitable height b) The floor outside the enclosure for a distance of approximately 3 ft (0.91 m) in front of the surface under test with the enclosure located at floor level. The nozzles used for this test shall deliver a square-shaped spray pattern with uniform spray distribution and shall have a 32 2capacity of at least 7.1 gal/min (450 cm/s) at a pressure of 60 lbf/in(41.4 N/cm), and a spray angle of approximately 75 degrees. The centerline of the nozzles shall be inclined downward so that the top of the spray is horizontal as it is directed toward the vertical and roof surfaces being tested. 2 2The pressure at the nozzles shall be a minimum of 60 lbf/in (41.4 N/cm) under flow conditions. (This is approximately equivalent to rain driven by a 65 mi/h [29 m/s] wind.) The quantity of water applied to each surface under test shall be at least 0.2 in (0.5 cm) per unit surface per minute, and each surface so tested shall receive this rate of artificial precipitation for a duration of 5 min. The spray nozzle shall not be more than 10 ft (3.05 m) from the nearest vertical surface under test. After the test is completed, an inspection shall be made promptly to determine if the enclosure meets the requirements of outdoor construction. More specifically, the equipment shall have satisfactorily met the requirements of this test if the visible inspection indicates the following: a) No water on primary or secondary insulation 18 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 b) No water on any electrical components or mechanisms of the assembly c) No significant accumulation of water retained by the structure or other noninsulating parts (to minimize corrosion) 5.3 Production tests Production tests for LV switchgear shall be normal frequency dielectric tests, mechanical tests, grounding of instrument transformer case tests, and electrical operation and control wiring tests. Drawout circuit breakers need not be tested in the assembly if they are tested separately. 5.3.1 Dielectric tests Normal frequency withstand tests shall be made on each LV switchgear in accordance with the general requirements of 5.2.1 with the exception that tests across the open gap are not required. Tests shall be made between each phase and ground with the other phases grounded. Apply a test voltage of 1800 V between neutral and ground. 5.3.2 Mechanical operation tests Mechanical tests shall be performed to ensure the proper functioning of mechanical interlocks, etc. These tests shall ensure the interchangeability of removable elements designed to be interchangeable. 5.3.3 Grounding of instrument transformer case test The effectiveness of grounding of each instrument transformer case or frame shall be checked by a low potential source such as 10 V or less using bells, buzzers, or lights. This test is required only when instrument transformers are of metal-case design. 5.3.4 Electrical operation and control-wiring tests 5.3.4.1 Control wiring continuity The correctness of the control wiring of a switchgear assembly shall be verified by either or both a) Actual electrical operation of the component control devices b) Individual circuit continuity checks by electrical circuit testers 5.3.4.2 Control wiring insulation test A 60 Hz test voltage shall be applied after all circuit grounds have been disconnected. Either 1500 V for 1 min or 1800 V for 1 s may be utilized. All wires shall be tested either individually or in groups. At the option of the manufacturer, switchgear-mounted devices that have been individually tested may be disconnected during the test. DC switchgear rated above 300 Vdc may require a test voltage higher than stated above. 5.3.4.3 Polarity verification Tests or inspections shall be made to ensure that connections between instrument transformers and meters or relays, etc., are correctly connected with proper polarities in accordance with circuit diagrams. Instruments shall be tested to ensure that pointers move in the proper direction. This does not require tests using primary voltage and current. Copyright ? 1998 IEEE All Rights Reserved 19 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 5.3.4.4 Sequence tests LV switchgear involving the sequential operation of devices shall be tested to ensure that the devices in the sequence function properly and in the order intended. This sequence test need not include remote equipment controlled by the switchgear assembly. However, this equipment may be simulated, where necessary. 5.4 Conformance tests Conformance test procedures for LV switchgear are given in ANSI C37.51-1989. 5.5 Field dielectric tests When normal frequency withstand tests are to be made on LV switchgear after installation in the field, the switchgear shall not be tested at greater than 75% of the test values given in tables 1 and 2. NOTE — Field tests are recommended when new units are added to an existing installation or after major field modifications. The equipment should be put in good condition prior to the field test. It is not expected that equipment 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. 6. Construction 6.1 General requirements 6.1.1 Buses and primary connections Buses and primary connections shall be of copper or aluminum, or both. For bus ratings see 4.4.2. 6.1.1.1 Phase or polarity arrangements Panel-mounted devices shall be mounted in the same arrangement as described in a) and b), as viewed from the front of the panel. a) The phase arrangement on three-phase assembled switchgear buses and primary connections shall be 1, 2, 3, (or A, B, C) from front to back, top to bottom, or left to right, as viewed from the front of the switchgear. Certain types of equipment may require other phasing arrangements and a neutral conductor. In these cases the phasing shall be suitably indicated. b) Polarities on dc assembled switchgear buses and connections shall be positive, neutral, negative, front to back, top to bottom, or left to right, as viewed from the front of the switchgear. Certain types of equipment may require other polarity arrangements. In these cases the polarity shall be suitably indicated. 6.1.1.2 Phase sequence The phase sequence on connection diagrams shall be such that when considering voltages to neutral on a polyphase system with respect to the element of time, the voltage of phase 1 will reach a maximum ahead of the voltage of phase 2, phase 3, etc. This sequence shall be designated as phase sequence in the consecutive numerical order starting with 1. 20 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 6.1.1.3 Cable terminations The LV switchgear shall provide space for the devices used for making electrical and mechanical connections to incoming and outgoing cables. Each cable terminal connection point shall meet the bolt hole requirements of NEMA CC 1-1984. 6.1.1.4 Bushings, potheads, or other terminators These devices are not ordinarily used in LV switchgear. 6.1.1.5 Main bus splices When bolts, nuts, and washers are provided for connecting through buses to other sections, the length of the bolts shall be such that the dielectric integrity is not impaired. 6.1.2 Grounding A ground bus shall be included which will electrically connect together the structures in a switchgear assembly in or on which primary equipment or devices are mounted. At all points of connection between the ground bus and the assembly, any nonconductive coatings, such as paint, shall be removed or penetrated to ensure good electrical contact. The ground bus for each group of vertical sections shall have facilities for connection to a station ground bus by suitable conductors. Circuit connections to the ground bus shall be made so that it is not necessary to open-circuit the ground bus to remove any connection made to the ground bus. Ground connections shall be provided for all removable elements to ensure that the frame and mechanism are grounded until the primary circuit is disconnected and the removable element is moved a safe distance. (See IEEE Std C37.100-1992 for the test or disconnected position definition.) When mounted on metal switchgear structures, cases of instruments, instrument transformers, meters, relays, and similar devices shall be considered as being adequately grounded when secured to these structures by metal mounting hardware with adequate provision for penetrating the paint film (see 5.3.3). The ground bus shall be capable of carrying the rated short-time current of the LV switchgear for 0.5 s. EXCEPTION LV switchgear having single polarity direct-current circuits, rated above 250 V, shall be ungrounded. It is recommended that they be connected to ground only by protective or indicating devices of relatively high resistance. 6.1.3 Control and secondary circuits and devices 6.1.3.1 Control, secondary, and logic level wiring Flame-resistant, 600 V insulated copper wire, with a cross-sectional area not less than AWG No. 14 stranded (4110 nominal cmil) shall be used on small wiring between component devices or parts of switchgear assemblies. Where wire is connected across a hinge, flexible wire (37 or more strands) shall be used. Copyright ? 1998 IEEE All Rights Reserved 21 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR For logic level wiring and for wiring from supervisory and annunciator devices to terminal blocks, smaller wire may be used provided it is adequately supported and meets the voltage and current requirements. Wire shall be Class C or D stranded and shall meet the surge requirements of IEEE Std C37.90.1-1989 and IEEE Std C37.90.2-1987. Smaller wire, when used, shall not run in the same wire packs with other control and secondary wiring. Bushings, grommets, or other mechanical protection shall be provided for the wiring where logic level, control, or secondary wiring is run through a metal sheet, barrier, or raceway. The internal wiring of component devices or parts shall be in accordance with the applicable industry standards. The insulated wire shall be Type TBS or SIS as listed in ANSI/NFPA 70-1993 or an equivalent and shall meet the requirements of the following standards publication as applicable: a) Type TBS NEMA WC5-1992/ICEA S-61-402 b) Type SIS NEMA WC7-1991/ICEA S66-524 6.1.3.2 Secondary-wiring terminals Stranded control wire shall have solderless terminals of the type wherein the body of the terminal is crimped or indented onto the conductor or where the wire is formed into an eye and confined within a crimp and flat washer assembly. Solderless terminals are not required for connection to devices that have integral pressure terminal connectors. The wire may be soldered into terminals or, where desirable, directly to devices, such as secondary disconnecting contacts, or to soldered terminals on supervisory control and annunciator equipment. NOTE — In the absence with this standard of definitive performance requirements, compliance with this subclause can be assessed by referencing ANSI/UL 486A-1991. 6.1.3.3 Terminal blocks Terminal blocks incorporating screw- or stud-and-nut-type terminals shall accommodate wire lugs or similar devices affixed to stranded wire. Screw or stud and-nut-type terminals intended for use with stranded wire shall be such that all strands of the conductor are confined. Terminal blocks incorporating pressure connectors shall not damage the wire and, when terminating stranded conductors, all strands shall be clamped within the connector. Terminal blocks for external connections shall be suitable to accept AWG No. 10 (10380 nominal cmil) stranded wire. The use of solid wire is not recommended. NOTES: 1 — Where long connections to the control battery are necessary the cable should be large enough to prevent excessive voltage drop. 2 — In the absence with this standard of definitive performance requirements, compliance with this subclause can be assessed by referencing ANSI/UL 486A-1991. 6.1.3.4 Designation of auxiliary switches and contacts The operation of auxiliary switches and contacts for circuit-interrupting and switching devices shall be designated as follows: a is open when the device is in the de-energized or nonoperated position b is closed when the device is in the de-energized or nonoperated position aa is open when the operating mechanism of the main device is in the de-energized or nonoperated position bb is closed when the operating mechanism of the main device is in the de-energized or nonoperated position e, f, h, k are special contacts and auxiliary switches other than a, b, aa, or bb 22 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 Auxiliary switches mounted on the stationary housing used to indicate the connected position of the removable element shall have the suffix TOC (circuit breaker truck-operated cell switch). The position of the removable element in which the contacts are closed or open shall be designated. The following are examples: 52 TO C ------------------ is open when the circuit breaker is not in the connected positiona 52 TO C ------------------ is closed when the circuit breaker is not in the connected positionb Auxiliary switches mounted on the stationary housing operated by the circuit breaker to indicate circuit-breaker open- closed position shall have a suffix MOC (circuit-breaker mechanism-operated cell switch). The open-closed position of the circuit breaker shall be designated for the contacts. The following are examples: 52 MO C -------------------- is open when the circuit breaker is opena 52 MO C -------------------- is closed when the circuit breaker is openb If several auxiliary switches and contacts are present on the same device, they shall be designated numerically consecutive starting at 1, when necessary. On diagrams of all types, contacts, and switches shall be shown in the de-energized position of the device. 6.1.3.5 Device function numbers Device function numbers shall be in accordance with IEEE Std C37.2-1991. 6.1.3.6 Voltage limits of instrument and control circuits Voltage and current transformers shall be used for all instruments, meters, and relays connected to ac circuits over 240 V so as to reduce the voltage on instrument wiring, which must necessarily be closely grouped. DC instruments, meters, and relays may be used directly on circuits up to 750 V if their cases are grounded to the switchgear structures in accordance with 6.1.2. DC instruments, meters, and relays together with their associated wiring and accessories, when used on circuits over 750 V, shall be connected through isolating transducers. EXCEPTIONS 1—Instruments, meters, and relays, along with their associated wiring and accessories may be connected directly to circuits over 750 V dc when the instrument, meter, or relay and its associated wiring and accessories are isolated from other instruments, meters, relays, and their associated wiring and accessories and where the cases of such devices are left ungrounded and are provided with suitable protective barriers, insulated covers, or guards. 2—Ground detectors may be connected directly to circuits up to 600 V ac if connected to ground through voltage dividing resistors. The resistors should not be mounted on the instrument panel and the wires should be isolated from other control wiring. Copyright ? 1998 IEEE All Rights Reserved 23 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 6.1.3.7 Polarity of dc connections to device coils Where coils on devices used in LV switchgear are connected to a dc supply and when de-energized, are not disconnected from both the positive and negative supply leads, such coils shall be so connected that, when de- energized, they will be left connected to the negative supply lead to minimize the possibility of corrosion. 6.1.3.8 Voltage circuit protection All voltage circuits used for control, relaying, or metering shall be protected within the LV switchgear as follows: a) All circuits supplied from external sources (ac or dc) shall have short-circuit protection within the control source incoming section. This may be provided by a single set of short-circuit protective devices. b) All circuits supplied from internal sources (ac or dc) shall have short-circuit protection within the same section as the supply source. If these circuits are supplied by a control power transformer, this protection may be in the primary circuit only. Overcurrent protection of voltage circuits may be provided in addition to the required short-circuit protection. Voltage transformers are required whenever the nominal primary voltage is greater than 240 V ac. Other circuits supplying loads such as heaters, receptacles, or lights shall have overload and short-circuit protection. 6.1.3.8.1 Control power transformers Short-circuit protection of control power transformers shall be provided in accordance with table 8. 6.1.3.8.2 Voltage transformers Voltage transformers shall be protected in the primary circuit with current-limiting fuses not larger than 10 A. 6.1.3.8.3 Isolation Switches, fuse pullouts, and molded-case circuit breakers used to disconnect devices from the primary circuits shall be of a dead-front design. 24 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 Table 8— Control power transformer short-circuit protection Primary maximum current-limiting fuses Single phase for control power transformers (A) (kVA) 240 V 480 V 600 V *** Up to 1 kVA 10 10 6 **2 20 10 10 3 30 15 15 5 50 25 20 7.5 80 40 30 10 100 50 40 15 150 80 60 NOTE — Voltage and control power transformer primary fuses are intended for use as a protective function only and are not intended to be used as disconnect devices. When a primary disconnect means is required, a dead-front design switch or fuse pullout should be used with these transformers. *Due to inrush current certain types of current-limiting fuses may require larger ratings than those shown, but shall not exceed 20 A. 6.1.3.9 Current transformer secondary circuit protection Overcurrent protection of current transformer secondary circuits shall not be provided. 6.1.4 Miscellaneous 6.1.4.1 Nameplate marking The following minimum information shall be given on switchgear assemblies nameplates: a) Manufacturer’s name and address b) Manufacturer’s type designation (optional) c) Manufacturer’s identification reference d) Rated maximum voltage (where applicable) e) Rated frequency (where applicable) 6.1.4.2 Wiring devices Lighting fixtures provided in outdoor switchgear shall be of a type and shall be so located that lamps may be safely replaced without de-energizing the primary equipment. Convenience outlets shall be of the two-pole, three-wire grounding type and protected by a ground-fault interrupter. 6.1.4.3 Ventilation openings and vent outlets Openings for pressure relief or ventilation shall be so arranged that the gas or vapor escaping during normal operation will not endanger personnel operating the switchgear. Copyright ? 1998 IEEE All Rights Reserved 25 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 6.1.4.4 Service disconnecting means Switchgear assemblies designated as the service disconnecting means shall be designed so that they can be installed in accordance with the applicable provisions of Section 230 in ANSI/NFPA 70-1993. 6.2 Materials and finish 6.2.1 Materials The materials for LV switchgear assemblies shall be sheet metal suitably supported. Barriers between compartments as listed in 6.3 shall not be less than MSG No. 11 (nominal thickness 0.1196 in or 3 mm). All other covers, barriers, panels, and doors shall not be less than MSG No. 14 (nominal thickness 0.0747 in or 1.9 mm). The minimum thickness of sheet metal used for LV switchgear is based on the use of steel. Where other metals are used the thickness shall be modified to provide equivalent strength and deflection. For example, if aluminum alloy 2sheet, having a yield strength of 20 000 lbf/in, is used in the place of steel to provide equivalent strength and deflection, it is required that the thickness specified above be increased by 50%. Doors or panels used to support devices shall be increased in thickness or otherwise strengthened, as necessary, to support the devices. 6.2.2 Finishes and color All steel surfaces to be painted shall receive a phosphatizing treatment or equivalent prior to application of paint. External and internal surfaces shall be coated with at least one coat of corrosion-resistant paint. The finish paint system shall comply with the requirement of 5.2.8. The under-surfaces of outdoor assemblies shall additionally receive either a corrosion-resistant undercoating or an additional thickness of corrosion-resistant paint. The preferred color for the finish on switchgear assemblies shall be light gray No. 61 in accordance with ASTM D1535-89, (MUNSELL NOTATION 8.3 G6.10/0.54). NOTES: 1 — Internal detail parts may have metallic plating or equivalent in lieu of paint finish. 2 — For conformance testing a recognized organic coating system that has been investigated and found suitable for use as protection against atmospheric corrosion of electrical equipment steel enclosures for outdoor use may be utilized. 6.3 Barriers Each circuit breaker shall be mounted in a separate metal-enclosed compartment ventilated as necessary. Ventilation openings between compartments within the LV switchgear shall be such that the gases produced by circuit breaker interruption shall not impair the operation of adjacent compartments. When a bus sectionalizing breaker (or breakers) is included, barriers shall be provided in the bus compartment to segregate the separate bus sections from each other. If no bus sectionalizing breaker is involved, no barriers are provided in the bus compartments. Where buses and connections penetrate internal barriers, suitable insulation or clearance shall be provided. 26 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 6.4 Buses and connections The bus and connections shall be bare except where close clearances may make insulation necessary. The buses shall be mounted on Class 105 or higher insulation. See table 3. 6.5 Access doors and covers A hinged door shall be furnished on the front of the structure to cover each circuit breaker compartment. Removable top and back plates shall also be provided in sufficient number to permit access to the bus and connection compartments. For stationary equipment, a bolted cover may be used in the front of the breaker compartment. For ease in handling, cover plates that are intended to provide access for inspecting and maintenance shall not exceed2 2 12 ft(1.12 M) in area or 60 lb (27 kg) unless they are equipped with lifting means or hinges. To prevent access to energized fuses in power-circuit protectors, means shall be provided to interlock the door, cover, or barrier so that it cannot be opened unless the circuit breaker or switch is in the open position. 6.6 Closing and tripping Mechanical means for closing and tripping manually operated breakers and for manually tripping electrically operated breakers shall be provided and shall be accessible without exposing the operator to live parts. See IEEE Std C37.13- 1990 for limitations on manually operated breakers. 6.7 Indoor LV switchgear LV switchgear for indoor applications shall be ventilated enclosures intended primarily to provide a degree of protection against contact with the enclosed equipment. 6.7.1 Requirements When completely and properly installed, these enclosures a) Shall provide a degree of protection against limited amounts of falling dirt; however, they will not prevent the entry of dust or liquids. b) Shall prevent the insertion of the end portion of a straight rod of the specified diameter into the equipment cavity of the enclosure. c) Shall not rust when subjected to the paint qualification test for 200 h. 6.7.2 Design tests The enclosures shall be tested and evaluated by a) The rod entry test in 5.2.7 b) The paint qualification test in 5.2.8 6.8 Outdoor LV switchgear LV switchgear for outdoor applications shall be housed in ventilated enclosures intended primarily to provide a degree of protection against falling rain, sleet, and external ice formations. When completely and properly installed, these enclosures Copyright ? 1998 IEEE All Rights Reserved 27 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR a) Shall not permit water to enter the equipment cavity at a level higher than the lowest live part except if constructed to divert water from live parts, insulation, wiring, and shall have provisions for drainage. b) Shall require the use of a tool to gain access to the equipment cavity or have provision for locking. c) Shall have doors that are equipped with latches and stops to hold the doors in the open position. d) Shall prevent the insertion of the end portion of a straight rod of the specified diameter into the equipment cavity of the enclosure. e) Shall not rust when subjected to the paint qualification test for 200 h. f) Shall have heaters or other effective means to minimize internal condensation. For the design tests, the enclosures shall be tested and evaluated by a) The rod entry test in 5.2.7 b) The paint qualification test in 5.2.8 c) The rain test in 5.2.9 NOTE — External icing tests are not required because LV switchgear has no external cavities to trap water when mounted in the normal position. 6.9 Pull box A pull box for cables is not included in the standard equipment, but it may be furnished as an option. 6.10 Arrangements with stationary circuit breakers Circuit breakers may be stationary mounted with or without disconnecting switches. 6.11 Arrangements with drawout circuit breakers Drawout circuit breakers shall be equipped with self-coupling disconnecting devices and have the following categories discussed in 6.11.1 through 6.11.6: 6.11.1 Interlocks Mechanical interlocks shall be provided in LV switchgear as follows: a) To prevent moving the circuit breaker to or from the connected position when the circuit breaker is in the closed position b) To prevent closing the circuit breaker unless the primary disconnecting devices are in full contact or are separated by a safe distance c) Circuit breakers equipped with stored energy mechanisms shall be designed to prevent the release of the stored energy unless the mechanism has been fully charged. Operators and service personnel shall be protected from the effects of accidental discharge of the stored energy by any of the following means: 1) Interlocks provided in the housing to prevent the complete withdrawal of the circuit breaker from the housing when stored energy mechanism is charged 2) A suitable device provided to prevent the complete withdrawal of the circuit breaker until the closing function is blocked 3) A mechanism is provided to automatically discharge the stored energy during the process of withdrawing the circuit breaker from the housing 4) Mechanisms as described above are not required provided the stored energy mechanism and contact assembly are isolated within the breaker element and service is not possible 28 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 6.11.2 Circuit breaker retention and locking Means shall be provided for positively holding the circuit breaker in place in the housing when the removable element is in the connected or test position. When breakers are left in the housing in the disconnected position, they shall be securely held in that position by suitable mechanical means. Additionally, means shall be provided for locking the circuit breakers in the disconnected position to prevent them or replacement breakers from being moved into the connected position. 6.11.3 Fuse accessibility Where the removable element consists of a fused circuit breaker, the fuses shall be accessible only when the removable element is withdrawn to the test, disconnected, or into the withdrawn position. 6.11.4 Removable element interchangeability All removable elements of the same type and rating on a given assembly shall be physically interchangeable in the corresponding stationary housings. This need not include electrical interchangeability of secondary control circuits. 6.11.5 Fuses on separate removable elements Current-limiting fuses may be mounted on separate removable elements. The requirements of 6.11.4 apply to these elements, and in addition, these elements must be only used in series with circuit breakers or switches. To prevent access to energized fuses on these removable elements, means shall be provided to interlock the door or cover so that it cannot be opened unless the associated circuit breaker or switch is in the open position. If the fuses are located on the line side of the associated circuit breaker, interlocking of the breaker shall be provided to prevent connection or disconnection under load. 6.11.6 Secondary disconnect devices Control wiring connections between stationary structure and the removable element shall be provided with automatic (self-coupling) contacts or manual plug and receptacle for disconnection. The manual control connector shall be either interlocked or inaccessible to prevent connection or disconnection of the control circuits when the removable element is in the connected position and the removable element shall be prevented from being installed in the connected position unless the manual control connector is connected. With the manual arrangement, all connections shall be group connectable simultaneously with the male contacts on the removable element and the female receptacles on the stationary structure. NOTE — The intent of this requirement is to ensure that the control connection is always made to the circuit breaker when the circuit breaker is in the connected position. 6.12 Primary cable space The clear cabling space independent of all projections, obstructions, or interference from moving parts, shall not be less in total area than 250% of the total cross-sectional area of the maximum number of cables that may be used in such space. Table 9 gives the minimum area for the more common multiple-cable connections. Copyright ? 1998 IEEE All Rights Reserved 29 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 6.13 Precautionary labels Each LV switchgear should be provided with appropriate precautionary labels to call the user’s attention to potential hazards that are inherent to the equipment and which cannot be eliminated by design. See ANSI Z535.4-1991 for recommendations. 6.14 Lifting devices Lifting devices may be provided to facilitate the insertion or removal of drawout circuit breakers from their individual compartments and consist generally of a wheeled hoist device or an overhead lift device attached to the switchgear itself. 7. Application guide for LV switchgear 7.1 Unusual service conditions It is strongly recommended that the usual service conditions, as described in clause 3., be provided for LV switchgear applications, if practical (artificially, if necessary). However, if unusual conditions exist and cannot be eliminated, the following considerations apply: 7.1.1 Ambient air temperature above 40 C When LV switchgear is applied where the ambient air temperature is higher than 40 C, its performance may be affected, and special consideration should be given to these applications. The total temperature limits for parts and materials as given in 4.5 should not be exceeded. Therefore, for the higher ambients, the equipment should be derated to a continuous current value that maintains the total temperature limits. 7.1.2 Ambient air temperature below 30 C Special consideration is also required when LV switchgear is applied where the ambient air temperature is less than 30 C. Space heating and thermal insulation to minimize the effects of exposure should be considered. If this is not possible, the effect of low temperatures on the functional performance of such materials as oils, plastic insulation on primary and secondary circuits, control wire insulation, and lubricants should be considered. 30 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 Table 9— Minimum areas for multiple cable connections 2 2Minimum areas required for multiple cables, [in (cm)] (based on factor of 2.5) Size of Two cables Three cables Four cables Five cables Six cables Seven cables cable AWG 1 (8.7) 1.35 (13.1) 2.03 (17.4) 2.70 (21.8) 3.38 (26.2) 4.05 (30.5) 4.73 0 (10.0) 1.55 (15.1) 2.33 (20.0) 3.10 (25.0) 3.88 (30.0) 4.65 (35.0) 5.43 00 (11.6) 1.80 (17.5) 2.70 (23.2) 3.60 (29.0) 4.50 (34.8) 5.40 (40.5) 6.30 000 (13.5) 2.10 (20.4) 3.15 (27.1) 4.20 (33.9) 5.25 (40.5) 6.30 (47.4) 7.35 0000 (15.5) 2.40 (23.3) 3.60 (31.0) 4.80 (38.7) 6.00 (46.5) 7.20 (54.1) 8.40 250 (19.0) 2.95 (28.6) 4.42 (38.0) 5.90 47.5 7.36 (57.0) 8.85 (66.6) 10.32 kcmil 350 (24.5) 3.80 (36.8) 5.70 (49.2) 7.60 (61.4) 9.50 (73.5) 11.40 (85.8) 13.30 kcmil 600 (31.7) 4.90 (47.4) 7.35 (63.4) 9.80 (79.0) 12.25 (95.1) 14.70 (110.6) 17.15 kcmil 2 NOTE — Numbers in parenthesis are in cmand are approximate. 7.1.3 Application at unusual altitudes Switchgear assemblies that depend on air for an insulating and cooling medium will have a higher temperature rise and a lower dielectric withstand capability when operated at altitudes above values specified in clause 3.. For applications at higher altitudes, the rated 1 min normal frequency withstand voltage and continuous current rating of the assemblies should be multiplied by the correction factors in table 10 to obtain the modified ratings. 7.1.4 Modification of equipment for unusual environment Successful performance of standard LV switchgear may be extended to unusual environments by special considerations when developing equipment specifications. Several construction modifications that will mitigate the effects of these environments may be made in accordance with 7.1.4.1 through 7.1.4.6, but the emphasis should be on eliminating such conditions if at all possible. However, if these undesirable conditions cannot be eliminated, more frequent maintenance may be required. 7.1.4.1 Exposure to damaging fumes, vapors, steam, salt air, and oil vapors Indoor and outdoor equipment should be provided with the following modifications: a) All structural parts should be covered with a minimum of two coats of paint, one of which should be a corrosion- or rust-resistant primer. b) All steel parts that are not painted or plated should be covered with protective grease. c) All current-carrying joints should be covered with a coating of nonoxidizing grease. Greasing of nonarcing contacts should only be done on recommendations of the manufacturer. d) All coils should be impregnated with insulating compound and covered with an appropriate protective coating. e) Heaters, in quantity and sufficient rating to minimize condensation in all compartments, should be furnished. Copyright ? 1998 IEEE All Rights Reserved 31 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR Table 10— Altitude correction factors Altitude (ft) Voltage Current 6600 (2000 m) and below 1.00 1.00 8500 (2600 m) 0.95 0.99 13 000 (3900 m) 0.80 0.96 NOTES: 1 — Intermediate values may be obtained by interpolation. 2 — For devices used in switchgear assemblies, standards covering the specific devices should be used to determine the specific altitude correction factors. 7.1.4.2 Exposure to excessive dust, abrasive dust, and magnetic or metallic dust Indoor or outdoor equipment should be provided with the following modifications. Totally enclosed non-ventilated equipment should be furnished with a current rating of 70% of the ventilated rating or as specified by the manufacturer. Condensation could be a problem and should be evaluated. For outdoor assemblies, ventilated enclosures may be furnished with the ventilating openings equipped with dust filters. The requirements for these filters vary over such a range that standard specifications for their application are not practicable. Filters are available in both the washable type and the disposable type. Where used, they must be cleaned or replaced at intervals, depending upon the amount of dust in the air. Filters that are not cleaned or changed when required can cause excessive equipment temperature or condensation. The type of filter used should be selected based on the size of dust particles encountered and the extent to which dust is to be excluded. Where very fine dust particles are to be excluded, disposable filters soaked in oil should be used. These must be changed at frequent intervals. Forced ventilation may be required depending upon the volume of air required for ventilation and the severity of the environment. When a blower and filter are furnished based on conditions of the environment, they should be installed on the intake to minimize the possibility of drawing dust or other foreign matter into and throughout the switchgear assembly. 7.1.4.3 Exposure to hot and humid climate Indoor and outdoor equipment intended for exposure to hot and humid climates should be made fungus-resistant by the following modifications: a) Heaters in quantity and sufficient rating to minimize condensation in all compartments should be furnished. b) Secondary wiring that is not inherently fungus-resistant should have fungus-resistant coating applied. Secondary wiring that has fungus-resistant insulation should not require further treatment. c) All impregnated coils should be given an external treatment with fungus-resistant coating. Encapsulated coils that are inherently fungus-resistant should not require further treatment. d) Paints such as alkyd enamels having a fungus and rust-resistant property should be used. e) Insulation that is not inherently fungus-resistant should have fungus-resistant coating applied. Insulation in switchgear assemblies that is inherently fungus-resistant should not require further treatment. Fungus- resistant coatings should not be applied where they will interfere with proper operation of apparatus. In such cases, the part should be inherently fungus-resistant. These coatings should not reduce the flame-resistant properties. f) The fungus-resistance of materials should be determined in accordance with ASTM G21-90. Materials to be classified as fungus-resistant should have a rating not greater than 1. 32 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 g) Materials that are made fungus-resistant by means of a coating should have the coating reapplied at periodic intervals. 7.1.4.4 Exposure to explosive mixtures of dust or gases Application of LV switchgear for explosion-proof requirements is not recommended. 7.1.4.5 Exposure to abnormal vibration, shocks, or tilting Indoor and outdoor equipment is designed for mounting on level structures free from vibration, shocks, or tilting. Since these conditions vary so widely, it is recommended that the manufacturer be consulted for each specific application where vibration, shocks, or tilting are to be encountered. It is important that the full nature of the abnormal motion be specified. The magnitude and frequency range of the dynamic motion is required so that resonances may be investigated. This is usually specified by means of an acceleration response spectrum curve for the mounting surface on which the LV switchgear is to be installed. The response spectrum is a plot of the maximum response of single-degree-of-freedom bodies, at a damping value expressed as a percent of critical damping of different natural frequencies. These bodies are plotted when they are rigidly mounted on the surface of interest (i.e., on the ground for the ground response spectrum or on the floor for the floor response spectrum) when that surface is subjected to a given abnormal motion as modified by any intervening structures. The response spectrum is useful in designing a test or in making an analysis of the performance of the LV switchgear equipment mounted on the same surface and subjected to the same motion. In the case of tilting, it is also important that the maximum angles of tilt, both transverse and longitudinal, be specified. The exact performance requirements should also be defined. It should be recognized that equipment specifically designed for a usual installation on a substantially level surface free from excessive vibration, shock, or tilting may be damaged and may not be able to function properly when subjected to excessive motion and displacement. Hence, the application should be carefully analyzed and the essential performance requirements should be precisely defined. 7.1.4.6 Exposure to seismic shock Because of the importance of adequate performance of equipment when applied as Class 1E equipment in a nuclear power generating station, IEEE Std 344-1987 was developed for this application. 7.2 System characteristics—Voltage and frequency LV switchgear is designed for use on three-phase, 60 Hz, grounded or ungrounded ac systems. Application on other types of systems such as the following should be reviewed with the manufacturer: a) DC b) Three phase, four-wire with insulated neutral c) Two phase d) Frequency other than 60 Hz or other than sinusoidal waveform LV switchgear is intended for application on systems where the maximum operating voltage of the system does not exceed the rated maximum voltage for which the equipment is designed. The voltages for various types of LV switchgear are listed in tables 1 and 2. 7.3 Overvoltage considerations—Insulation levels The insulation levels to which LV switchgear is designed are also listed in tables 1 and 2. Copyright ? 1998 IEEE All Rights Reserved 33 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 7.4 Continuous current rating and overload capability LV switchgear assemblies are designed for normal application where the sustained load current does not exceed the rated continuous current, the altitude above sea level does not exceed 6600 ft (2000 m), the ambient air temperature does not exceed 40 C, and the effects of solar radiation can be neglected. For unusual altitudes, derating factors should be applied in accordance with 7.1.3. If solar radiation is significant, continuous current capability is limited. Refer to IEEE Std C37.24-1986 . The rated continuous current is based on not exceeding the limits of the hottest spot total temperature of the various parts of the switchgear assembly when this value of current is sustained in an ambient air temperature of 40 C. When the ambient air temperature is greater than 40 C, the current should be reduced to less than rated continuous current to keep the total temperature of these parts within allowable limits. The application of switchgear assemblies should be based on avoiding operation at current higher than the rated continuous current of the assembly. However, since the criterion is total temperature, the following considerations are in order: a) It is permissible to exceed rated current 1) For short periods, such as in the starting of motors or when energizing cold loads. Generally, the short duration of this type of current increase does not raise temperatures significantly. 2) When operating at an ambient air temperature below 40 C (see 7.4.1). b) Since trip devices, current transformers, and cable current ratings are frequently less than the continuous current rating of the circuit breaker, their capabilities to carry more than rated continuous current must be verified. c) When several switchgear compartments are included in the same vertical section, consideration must be given to the allowable cumulative loading of the section (see 7.4.2). 7.4.1 Load current-carrying capabilities under various conditions of ambient temperature and load When ambient air temperature is other than 40 C, on which continuous ratings in 4.4.2 are based, the allowable continuous current can be calculated by the following formula: 1-- 2– max a ----------------------I= I a r r where Iis the allowable continuous load current, A, at the actual ambient temperature (Iis not to exceed two a a a times I) rIis the rated continuous current, A, on basis of 40 C ambient r is the allowable hottest-spot total temperature max is the actual ambient temperature expected (between 30 C and 60 C), C a is the allowable hottest-spot temperature rise at rated current, C r NOTE — The temperature rise of a current-carrying part is proportional to an exponential value of the current flowing through it. The exponent value of 1/2 in the formula observed has been found to be generally valid for overload capability of LV switchgear and is therefore used in this standard. The construction features of LV switchgear dictate the appropriate values of and . The major components have r maxseveral different temperature limits specified in the standards or clauses of this standard as listed in table 11. 34 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 Table 11— Switchgear component—Temperature limitations Component Reference Circuit breakers IEEE Std C37.13-1990 Current transformers IEEE Std C57.13-1978 Insulating material in switchgear Table 3 assemblies Buses and connections Table 4 Air surrounding insulated power Subclause 4.5.5 cables *Parts subject to contact by Subclause 4.5.6 personnel *When applying switchgear at higher than the standard 40 C maximum temperature, the limitations of this subclause may be exceeded. To assure that none of the temperature limitations specified in the standards or the sections of this standard as listed in table 11 are exceeded, the permissible load current based on the actual ambient air temperature is determined by using the values of and selected as follows: r max a) If the actual ambient air temperature is less than 40 C, the component with the highest specified limit of total temperature should be selected. b) If the actual ambient air temperature is greater than 40 C, the component with the lowest specified limit of total temperature should be selected. The use of this value in the calculation will result in an allowable continuous current that will not cause the temperature of any part of the assembly to exceed the specified limit. Table 12 lists the calculated values of I/Ifor each specified temperature limit for the various components of LV ar switchgear over a range of typical ambient air temperatures. The allowable current in any given situation can be estimated from table 12 or may be calculated directly from the stated formula. 7.4.2 Load current-carrying capability of ac LV switchgear For ac LV switchgear, which may include one to four compartments in a single vertical section, the following guidelines discussed in table 12 and 7.4.2.1 through 7.4.2.5 are recommended for estimating the allowable cumulative loading. Copyright ? 1998 IEEE All Rights Reserved 35 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR Table 12— Ratios of (l/l) for various ambient temperatures ar Limiting temperatures of different switchgear components Maximum 50 65 70 85 90 105 110 125 max ambient C 10 25 30 45 50 65 70 85 r *60 — — 0.45 0.58 0.75 0.77 0.83 0.85 0.87 *50 — — 0.77 0.82 0.88 0.89 0.92 0.93 0.92 40 — 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 † 30 — 1.41 1.18 1.15 1.11 1.10 1.07 1.07 1.08 †25 — 1.58 1.26 1.22 1.15 1.14 1.11 1.10 1.08 †20 — 1.73 1.34 1.29 1.20 1.18 1.14 1.13 1.11 †‡10 — 2.0 1.48 1.41 1.29 1.26 1.21 1.20 1.16 † ‡ 0— 2.0 1.61 1.53 1.37 1.34 1.27 1.25 1.21 †‡ 10 — 2.0 1.73 1.63 1.45 1.41 1.33 1.31 1.26 † ‡0— 2.0 1.61 1.53 1.37 1.34 1.27 1.25 1.21 †‡10 — 2.0 1.73 1.63 1.45 1.41 1.33 1.31 1.26 †‡20 — 2.0 1.84 1.73 1.53 1.48 1.39 1.36 1.31 †‡ 30 — 2.0 1.95 1.83 1.60 1.55 1.44 1.41 1.35 *For limiting current, use lowest and r max†For limiting current, use highest and r max‡Designated limit—not calculated 7.4.2.1 Determination of main bus load current-carrying capability The ampacity for the main bus is usually a function of the main circuit breaker frame size or the current output of the supply transformer. The ampacity of the main bus is based on the temperature limitations as described in 4.5. 7.4.2.2 Determination of vertical section load current-carrying capability The load current-carrying capability of a vertical section consisting of one, two, three, or four circuit breakers should be determined by the lesser of the following two considerations: a) The main bus continuous current rating b) The allowable cumulative circuit-breaker loading 7.4.2.3 The cumulative circuit-breaker load—AC LV switchgear The cumulative circuit breaker loading is the total current that all circuit breakers within a vertical section can carry simultaneously without exceeding the temperature limits in 4.5. In the absence of data from the manufacturer for a specific LV switchgear configuration, it is recommended that the values for the allowable cumulative loading given in table 13 not be exceeded for an indoor ambient temperature of +40 C. NOTE — The values of allowable cumulative load can be based on equal loading (as a percentage of rating) of all compartments in the same vertical section. If equal loading is not practical, the load distribution should be such that the heavier loads are connected to the lowest circuit breaker compartment. Typically, a section with multiple circuit-breaker compartments carrying load should be loaded as follows: 36 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 a) Four circuit breaker compartments Bottom compartment 90% of compartment rating Next to bottom compartment 75% of compartment rating Next to top compartment 60% of compartment rating Top compartment 50% of compartment rating b) Three circuit breaker compartments Bottom compartment 90% of compartment rating Middle compartment 75% of compartment rating Top compartment 60% of compartment rating c) Two circuit breaker compartments Bottom compartment 90% of compartment rating Top compartment 75% of compartment rating If other arrangements are required, such as forced ventilation, it is recommended that the manufacturer be consulted. When different ratings of circuit breakers are utilized in the same vertical section, the allowable cumulative circuit breaker loading should be determined based on the number of circuit breakers in the vertical section and the corresponding value for each circuit breaker. Copyright ? 1998 IEEE All Rights Reserved 37 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR Table 13— Circuit breaker loads Number of Allowable Circuit breaker cumulative load circuit breakers frame size (A) *carrying load (A) 600 1 600 600 2 1000 600 3 1400 600 4 1700 800 1 800 800 2 1300 800 3 1800 800 4 2200 1600 1 1600 1600 2 2600 1600 3 3600 1600 4 4500 2000 1 2000 2000 2 3200 3000/3200 1 3000/3200 3000/3200 2 4800/5200 4000 1 4000 *Without forced ventilation The following examples will illustrate the above: a) One 1600 A and three 800 A 1) Distributed Distributed Equal loading Compartment Equal loading *loading factor loading factor Top 800 A 2200/4 550 0.5 400 Next to top 800A 2200/4 550 0.6 480 Next to bottom 2200/4 550 0.75 600 800 A Bottom 1600 A 4500/4 1125 0.9 1440 Cumulative loading 2775 — 2920 *From table 13. 38 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 2) Distributed Distributed Equal loading Compartment Equal loading *loading factor loading factor Top 1600 A 4500/4 1125 0.5 800 Next to top 800 2200/4 550 0.6 480 A Next to bottom 2200/4 550 0.75 600 800 A Bottom 800 A 2200/4 550 0.9 720 Cumulative loading 2775 — 2600 *From table 13. b) One 1600 A and two 600 A 1) Distributed Distributed Equal loading Compartment Equal loading *factor loading factor loading Top 600 A 1400/3 467 0.6 360 Middle 600 A 1400/3 467 .75 450 Bottom 600 A 3600/3 1200 0.9 1440 Cumulative Loading 2134 — 2250 *From table 13. 2) Distributed Distributed Equal loading Compartment Equal loading *factor loading factor loading Top 600 A 1400/3 467 0.6 360 Middle 1600 A 3600/3 1200 0.75 1200 Bottom 600 A 1400/3 467 0.9 540 Cumulative loading 2134 — 2100 *From table 13. c) One 3200 A and one 1600 A Distributed Distributed Equal loading Compartment Equal loading *factor loading factor loading Top 1600 A 2600/2 1300 0.75 1200 Bottom 3200 A 5200/2 2600 0.9 2880 Cumulative loading 3900 — 4080 *From table 13. Copyright ? 1998 IEEE All Rights Reserved 39 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 7.4.2.4 Conductor temperature Cables connected to LV switchgear should be capable of withstanding the 65 C ambient temperature to which they may be subjected. 7.4.2.5 Conductor terminations Consideration should be given to the use of suitable connectors that are designed for use with the outgoing conductors and terminals in the switchgear units. 7.5 Short-circuit considerations LV switchgear should have short-circuit capability equal to or greater than the short-circuit capability of the system on which it is applied. The short-circuit capability of the LV switchgear is equal to that of the smallest frame size circuit breaker utilized. 7.5.1 Selective trip arrangement Low-voltage power circuit breakers are suitable for selective tripping arrangements when the following precautions are taken: a) All the requirements of IEEE Std C37.13-1990 shall be met. b) Selective tripping is usually accomplished with circuit breakers utilizing direct-acting series-tripping devices integral with the circuit breaker. Relay tripping may be used provided the total time to clear the circuit (including relay, shunt trip, and circuit breaker time) does not exceed the short-time rating of any of the circuit breakers. c) All other equipment shall be properly coordinated, including the protective equipment on the high-voltage side of power transformers, and also short-time ratings of current transformers, series reactors, cables, and buses. For further information on selective tripping, see IEEE Std 141-1993. 7.5.2 Application of circuit breakers in cascade Application of circuit breakers in cascade (above their short-circuit current ratings) is not recommended. 7.6 Nuclear power plant application LV switchgear applied in nuclear power generating stations, and particularly as Class IE equipment, shall meet the requirements of pertinent standards that have been developed for such applications. 7.7 Associated devices often used in LV switchgear 7.7.1 Current transformers Current transformers included in LV switchgear are in accordance with 4.6 and 4.7. The accuracies listed in 4.7 are the minimum supplied in the usual design of this equipment, and are adequate for most applications. If an application requires higher accuracies, it should be specified by the user. It should be recognized that current transformers with higher accuracies than those listed in 4.7 may not meet the requirements of 4.6. The manufacturer should be consulted for possible solutions to the problem of obtaining required accuracy without compromising on other requirements. 40 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 7.7.2 Surge protective devices 7.7.2.1 Rotating equipment Capacitors or surge arresters, or both, used to protect the insulation of rotating machines, shall be housed in a suitable enclosure as close as possible to the machine and connected without fuses or disconnecting devices. Cable connections to these devices should be short, have minimum inductance and should be able to withstand possible short-circuit current, both thermally and mechanically. 7.7.2.2 Exposed circuits Protection against lightning surges should be considered for all switchgear assemblies 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 switchgear. 7.7.2.3 Surge arresters in switchgear assemblies Surge arresters used in switchgear assemblies should have adequate discharge capability and be voltage limiting to keep voltage surges below the insulation level of the protected equipment. Special consideration should be given to the use of coordinated surge arresters for LV switchgear installed at high altitudes. 7.7.3 Ground detectors The following methods are recommended for ground detectors furnished on power switchgear assemblies: a) Application to nominal voltages up to and including 240 V ac—lamps or voltmeters connected from the power conductors to ground without the use of transformers. b) Application to nominal voltages above 240 V 1) Transformers connected wye-wye. For three-phase systems, use three transformers rated for line-to-line voltage connected wye-wye with primary neutral grounded and lamps or voltmeters connected across the secondaries of the transformers. The primary neutral of the transformers should be stabilized by either connecting resistors in parallel with the lamps or voltmeters across the transformer secondaries, or connecting a resistor between the primary neutral of the transformers and ground. 2) Transformers connected wye-broken delta. For three-phase systems, use three transformers rated for line-to-line voltage connected wye-delta with neutral of primary wye-grounded and with a voltage relay, to give indication of ground, connected in the broken-delta corner of the 3 transformer secondaries. The primary neutral of the transformers should be stabilized by either connecting a resistor in parallel with the voltage relay across the broken-delta corner of the three transformer secondaries or connecting a resistor between the primary neutral of the transformers and ground. The relay should have a minimum voltage rating of 1.73 times the nominal secondary line-to-line voltage of the transformers. 3) Lamps or voltmeters may be used for nominal voltages up to 600 V if connected to ground through voltage dividing resistors that will limit the voltage applied to a lamp receptacle (with bulb removed) or to a voltmeter during ground conditions to 240 V. NOTES: 1 — These ground detectors are useful only on normally ungrounded circuits. 2 — Due to variations in brilliance between lamps, voltmeters are preferred for ground indication. Copyright ? 1998 IEEE All Rights Reserved 41 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR 7.8 Protection and isolation of switchgear connected to other circuit protective equipment When LV switchgear is electrically connected to other power switching and circuit-protective equipment, tie-circuit protective equipment should be provided in the connection between the two so that a fault in one assembly will not result in the loss of the other assembly. NOTE — Where both assemblies supply power to an entire integral unit process, so that the shutdown of one part necessitates the shutdown of the entire process, tie circuit protective equipment is not required. For additional information and further study of switching arrangements see industrial and commercial power systems standards IEEE Std 141-1993, IEEE Std 142-1991, IEEE Std 241-1990, IEEE Std 242-1986, and IEEE Std 446-1987. 7.9 Overcurrent protection For ac applications, overcurrent protection is usually provided for each ungrounded phase conductor. However, alternately, the two-phase overcurrent, residual ground arrangement is acceptable protection. 8. Guide for handling, storage, and installation 8.1 General This subclause is a guide for the handling, storage and installation of LV switchgear, and emphasizes safety aspects and other considerations when working with this type of equipment. It supplements, but does not replace, the manufacturer’s detail instructions on these subjects. The objective is to furnish additional guidelines to promote and enhance a reliable installation. The manufacturers of LV switchgear include instruction books and drawings with their equipment, containing detailed recommendations for storage, handling, installation, operation, and maintenance. Personnel responsible for these functions should review these recommendations before handling the equipment. Particular attention should be given to recommendations for preparation of foundation and forms on which the switchgear is to be mounted. One set of manufacturer’s instruction books should remain with the LV switchgear when in storage or at the installation site. 8.2 Handling 8.2.1 Receiving LV switchgear should be carefully inspected and packed before leaving the factory. Immediately upon receipt, the equipment should be examined for damage that may have been sustained during transit. If damage is evident or indications of rough handling are visible, the carrier (transportation company) and the manufacturer should be notified promptly. Only authorized personnel should be permitted to handle the equipment. Care should be exercised in handling each piece of equipment (even if crated) because parts may be damaged. 8.2.2 Rigging Instructions for lifting and handling of the equipment are contained in the manufacturer’s instruction books and drawings. The rigging should be adequate for the size and weight of the equipment. 42 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 8.2.3 Storage Indoor switchgear that cannot be installed immediately should be stored in a dry, clean location and should remain protected during the storage period. The longer the period of storage, the greater the care required for protection of the equipment. During storage, the LV switchgear should be placed on a level surface to prevent unnecessary strain and possible distortion. During the construction period, protection should be provided against dust, dirt, falling objects, dripping water, excessive water, excessive moisture, and other possible causes of damage to the equipment. Any temporary covering should not restrict ventilation and should not be removed until the equipment is ready for installation. It is preferable to store indoor equipment within a heated building. If this is not possible, special precaution should be taken to keep the equipment sufficiently warm with adequate ventilation to prevent condensation during the storage period. If necessary, temporary heating should be installed in the equipment. If outdoor switchgear cannot be installed and energized, temporary power must be provided for the operation of the space heaters provided so as to prevent condensation of moisture within the housing. CAUTION — Disconnect normal supply source to prevent backfeed. Ventilation openings in LV switchgear should be left open to permit proper circulation of air. 8.2.4 Installation When installing LV switchgear a) Protect workers adequately from live parts with barriers, screens, etc. b) ANSI C2 NESC, Part 1, Rule 124, guarding live parts shall be observed. 8.2.5 Removal of shipping members Before installation of LV switchgear, a careful check should be made to ensure that all members included for shipping purposes have been removed. 8.2.6 Connections 8.2.6.1 Bus connections When the LV switchgear consists of several shipping sections, the main bus is necessarily disconnected before shipping. The main bus should be reconnected with particular attention to the cleanliness of and pressure between the contact surfaces. It is essential that the connections be securely bolted because the conductivity of the joints is dependent on the applied pressure. The manufacturer’s torque instructions and any other special instructions should be referenced. 8.2.6.2 Cable connections Before making up the cable connections, the phasing of each cable shall be determined in accordance with the connection diagram, and the cables tagged accordingly. The cable manufacturer’s instructions should be followed when forming cable terminations and during the installation of the cable. It is essential that the connections be clean and securely bolted, since the conductivity of the joints is proportional to the applied pressure. The terminating devices (where required) should be installed pursuant to the terminator manufacturer’s instructions. 8.2.6.3 Control connections Control wires between shipping sections should be reconnected as marked by the manufacturer. Connections that are to be connected to terminals in apparatus remote from the switchgear should be carefully checked against the Copyright ? 1998 IEEE All Rights Reserved 43 IEEE Std C37.20.1-1993 LOW-VOLTAGE POWER CIRCUIT BREAKER SWITCHGEAR connection diagram. When making connections to terminals, care should be exercised to ensure that the connections are properly made. 8.2.6.4 Grounding Sections of ground bus previously disconnected at shipping sections shall be reconnected when the units are installed. Make sure that all secondary wiring is connected to the switchgear ground bus as indicated on the drawings. The ground bus should be connected to the system ground with as direct a connection as possible and should not be run in metal conduit unless the conduit is adequately bonded to the circuit. The grounding conductor should be capable of carrying the maximum line-to-ground short-circuit current for the duration of a fault. A reliable ground connection is necessary for every switchgear installation. It should be of sufficient ampacity to handle any abnormal condition that might occur on the system and should be independent of the grounds used for other apparatuses. A permanent low- resistance ground is essential for adequate protection and safety. 8.3 Preoperation check Care shall be exercised to prevent the LV switchgear from being energized from the power system while preliminary tests are being conducted. If disconnecting means is not available, line leads should be disconnected. All internal connections should be examined to ensure that they have not been loosened or damaged during shipment or installation and all bolted connections and joints should be tightened to ensure good contact. If spring washers are used under bolt heads and nuts, they should be tightened in accordance with manufacturer’s instructions. All wiring connections should be checked for tightness, including those at instrument transformers and all terminal blocks. Current transformer shorting devices on all active circuits should be removed. All ties and blocking from the relay armatures or discs should be removed before the control energy is applied. Protective relays, overcurrent trip devices, and breaker attachments included with the LV switchgear should be tested for correct connections and operation at the factory. However, the protective device settings for current, voltage, or other quantities shall be made by the user in accordance with the manufacturer’s operating practices. The manufacturer’s instruction books should be studied carefully before setting the protective devices. It is recommended that the integrity of control buses be checked with an ohmmeter to ensure against short circuits in the control wiring. Control wiring should be given a high-potential test or be insulation-resistance tested and power circuits, such as buses and circuit breakers should be given a normal frequency withstand test as described in 5.2.1 and 5.5. After LV switchgear has been installed and all interconnections completed, any control schemes should be operationally tested and power connections given a final check for phase rotation/sequence before the switchgear is finally energized for service. 8.4 Removable elements All circuit breakers should be inspected for damaged parts and any loose connections pursuant to the manufacturer’s instructions. Check manual operation with the manual closing lever or with the maintenance closing handle on the larger size circuit breaker elements. Trip each circuit breaker by operating the manual trip device. Operation with maintenance handle and slow closing should be done outside the breaker cubicle. Power-operated circuit breakers should be checked for proper operation while in the switchgear cubicle test position for both closing and tripping at the normal control voltage. 8.5 Interlocks Interlocks should be checked for proper operation before power is applied to the switchgear. The interlock between removable element and housing should be checked to see that 44 Copyright ? 1998 IEEE All Rights Reserved IEEE STANDARD FOR METAL-ENCLOSED IEEE Std C37.20.1-1993 a) The element cannot be moved to or from the connected position when the circuit breaker is in the closed position. b) The circuit breakers cannot be closed unless it is in the fully connected position or in the test position. So as to maintain the integrity of key interlock systems, duplicate keys should be destroyed or retained in a place accessible only to authorized personnel. 8.6 Energizing After the removable circuit breaker elements and interlocks have been tested satisfactorily, the circuit breakers may be moved to the connected position. Each compartment door should be closed and latched before energizing the circuit. Copyright ? 1998 IEEE All Rights Reserved 45