Gate-controlled phase failure protection circuit

Claim 1

In a protective circuit for a three phase load circuit, wherein the protected circuit includes an actuable bypass device and means to break the load circuit upon actuation of the bypass device, the combination therewith of a phase failure-responsive protection circuit, said phase failure-responsive circuit comprising: trigger circuit means to provide an actuating signal to the bypass device; exclusive OR gate means in the trigger circuit means comprising two-part AND gate interposed in the trigger circuit means, a three-part NOT AND gate that is adapted to trigger one of the parts of the AND gate, and a three-part OR gate adapted to trigger the other part of the AND gate; and a plurality of separate signal means, one associated with each phase of the load circuit and adapted to provide a signal when the associated phase is operative, each of the respective signal means being connected to a respective part of the NOT AND gate and to a respective part of the OR gate means so that the exclusive OR gate is conductive when any one or any number less than all of the phases is operative but not when none or all of the phases is operative.