US Patent 9391441 Zone selective interlocking for optical flash detection suppression

Nuisance tripping is reduced in a power protection and distribution system including an upstream circuit breaker, a power distribution bus, and one or more downstream circuit breakers. A signal indicative of a current or pending downstream circuit breaker tripping action, such as a Zone Selective Interlocking (ZSI) signal, normally used to delay tripping of the upstream breaker, is used to suppress an optical flash detection system from tripping the upstream breaker in response to an optical flash resulting from the tripping of the downstream breaker. In this way, nuisance tripping of the upstream breaker is avoided when the downstream breaker trips (and the ZSI function is preserved).