Circuit breaker with protection against sputtering arc faults

Abstract

A circuit breaker includes an electronic trip device which responds to sputtering arc-type faults. Level detectors compare the current in the protected circuit to a plurality of threshold levels and timers time the intervals that the current remains above each threshold, with the threshold levels and intervals selected to generate a response envelope for a trip signal which approximates, with a selected margin, the response of the protected circuit to introduction of a selected inductive load such as the starting of a motor into the circuit. If the sensed current falls below a threshold level which was being timed, the associated timer is not cleared unless the current falls below the lowest threshold, so that if the sensed current increases above the associated threshold, timing resumes where it left off, and a trip signal will be generated sooner than for an initial excursion above the threshold. Both analog and digital timer implementations are presented.