"This standard covers the test procedures for enclosed low-voltage ac power circuit breakers as follows: (1) Stationary or drawout circuit breakers of two- or three-pole construction@ with one or more rated maximum voltages of 635 (600 for units incorporating fuses)@ 508@ and 254 V for application on systems having nominal voltages of 600@ 480@ and 250 V. (2) (a) Unfused circuit breakers (b) Fused circuit breakers (3) Manually operated or power-operated circuit breakers with or without electromechanical or solid-state trip devices. NOTE: In this standard the words ??circuit breaker?? shall mean ??enclosed low-voltage ac power circuit breaker@?? either fused or unfused. The words ""unfused circuit breaker???? shall mean a ??circuit breaker without integral fuses?? and the words ??fused circuit breaker?? shall mean a ??circuit breaker incorporating current-limiting fuses as an integral part of the unit.??"
NEMA C37.50-1989 history
2012NEMA C37.50-2012 Switchgear - Low Voltage AC Power Circuit Breakers Used in Enclosures - Test Procedures
1989NEMA C37.50-1989 For Switchgear— Low-Voltage AC Power Circuit Breakers Used in Enclosures— Test Procedures