Low-voltage power circuit breakers and molded case circuit breakers-a comparison of test requirements

This paper provides comparison tables between the test requirements for low-voltage power circuit breakers as specified in UL 1066 and the associated ANSI C37 standards, and those for molded case circuit breakers as specified in UL 489. The major differences in the performance characteristics of these circuit breakers are discussed with due reference to the tables. The paper also relates these differences to circuit breaker applications; with low-voltage power circuit breakers typically being located upstream from molded case circuit breakers in order to provide selective coordination. These upstream circuit breakers are typically bussed into the circuit, and can be withdrawn for circuit breaker maintenance. By contrast molded case circuit breakers are more typically wired directly into the circuit. Reference is also made to insulated case circuit breakers (UL 489) and to IEC circuit breakers (IEC 947-2).