NEMA publishes SG 4 for AC circuit breakers
By Anthony Capkun
The National Electrical Manufacturers Association (NEMA) has published SG 4-2009, “Alternating Current High-Voltage Circuit Breakers”. Published under license from IEEE, the standard was revised by the High-Voltage Power Circuit Breaker Voting Classification of the Switchgear Section of NEMA.
The previous revision of SG 4 was published in 2000 and reaffirmed in
2005. The material in the 2000 revision of SG 4 dealt with two areas,
the first relating to construction and test issues for high-voltage
circuit breakers, and the second with recommendations for handling and
maintenance of high-voltage circuit breakers.
The material in the second area was removed from the 2009 edition of SG
4, and published separately as SG 11-2008. This was done to keep the
information available to those interested in high-voltage circuit
breakers while the IEEE Switchgear Committee working groups consider
this material for possible incorporation into revised editions of IEEE
C37.04 and IEEE C37.09.
SG 4 applies to all types of high-voltage circuit breakers, with the
exclusion of those used in metal-enclosed or metal-clad switchgear, and
automatic circuit reclosers. High-voltage circuit breakers are most
frequently installed in outdoor switchyards, used in utility
transmission and distribution substations, and in large industrial
Among the areas covered by the revised SG 4 (not covered in existing IEEE standards) are:
• Requirements for circuit breaker operating mechanisms
• Bushing terminal connector requirements
• Ground terminal requirements
• Current transformer thermal and short-time capabilities, and accuracy classes
• Multi-ratio current transformer tap connections
• Current transformer lead identifications and polarity conventions
• Radio Influence Voltage (RIV) tests and limits
• Noise levels for outdoor circuit breakers located in switchyards
• Repetitive duty requirements for special purpose arc-furnace switching circuit breakers
The material in SG 4 has been offered to IEEE for inclusion in
revisions of C37.04 and C37.09 (presently not addressed in those
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