Self-monitoring fault current safety switch

Claim 1

A fault current circuit breaker used in monitoring electrical circuits, comprising: a total current converter including a primary circuit having outgoing return leads disposed therethrough; a secondary winding; an electromagnetic retaining device controlled by an electronic limit value circuit and containing a coil, said electronic limit value circuit being connected to said secondary winding; and switch contacts controlled by said electromagnetic retaining device for switching off an electrical circuit being monitored when a predetermined fault current is exceeded, said electronic limit value circuit, said coil and an evaluation circuit forming an oscillator circuit that generates current pulses which are supplied to an additional winding of said total current converter for simulating a fault current, said current pulses being temporarily stored in said additional winding of said total current converter and causing voltage pulses corresponding to said current pulses at the output of said electronic limit value circuit, said voltage pulses controlling said electromagnetic retaining device such that during normal operation, which corresponds to a condition that no actual fault current appears, said current pulses causing a sufficiently short de-energizing of said coil to allow said oscillator circuit to continue oscillating, and such that during an actual fault operation, which corresponds to a condition that an actual fault current appears, said oscillator circuit is interrupted causing said coil to be permanently de-energized, causing said switch contacts to open so as to shut off said primary circuit.