A mini-circuit breaker (UL 1077 supplemental protector) or supplemental fuses are suitable for motor branch-circuit short-circuit and ground-fault protection.

A mini-circuit breaker (UL 1077 supplemental protector) or supplemental fuses are suitable for motor branch-circuit short-circuit and ground-fault protection.

• A. True
• B. False
• C. Only for motor circuits under 50 hp
• D. They must be used with higher rated fuses

Answer: (B)

Protecting a motor branch circuit requires a device that can interrupt a high fault current with a suitable interrupting rating. UL 1077 supplemental protectors are designed as secondary or supplementary protection for equipment, not as the primary short-circuit or ground-fault protection for motor circuits. They generally have limited interrupting capacity and are not listed or suitable to interrupt the high fault currents that can occur in motor circuits. NEC 430.52 requires short-circuit and ground-fault protection for motor branches using devices rated for that purpose (such as inverse-time fuses or molded-case circuit breakers with appropriate interrupting ratings). So, a mini-circuit breaker or supplemental fuse, by itself, is not appropriate as the sole protection for motor branch-circuit short-circuit and ground-fault protection.

Protecting a motor branch circuit requires a device that can interrupt a high fault current with a suitable interrupting rating. UL 1077 supplemental protectors are designed as secondary or supplementary protection for equipment, not as the primary short-circuit or ground-fault protection for motor circuits. They generally have limited interrupting capacity and are not listed or suitable to interrupt the high fault currents that can occur in motor circuits. NEC 430.52 requires short-circuit and ground-fault protection for motor branches using devices rated for that purpose (such as inverse-time fuses or molded-case circuit breakers with appropriate interrupting ratings). So, a mini-circuit breaker or supplemental fuse, by itself, is not appropriate as the sole protection for motor branch-circuit short-circuit and ground-fault protection.