Molded Case Circuit Breakers - Some Holes in the Electrical Safety Net

Test results presented in this paper demonstrate that some brands of residential molded case circuit breakers do not operate properly within the limits specified by the applicable standard. The samples tested are both used, from homes, and new, purchased at retail sources. The minimum trip current is determined for each breaker. The test procedure encompasses the basic overload trip requirements of the applicable standard. Breakers that do not open the circuit at or below 135% of rated current fail to meet the requirements of the standard. Test results vary substantially from brand to brand. The best brands are essentially failure free. The failure rate of the worst-case brands is in the order of 50% for both used breakers from homes and new breakers recently purchased. Some samples, primarily multi-pole breakers, do not open the circuit at any level of applied current. Failure of a circuit breaker in a home to operate properly when required poses an increased risk of fire and injury.