Ground fault interrupters

A neutral-to-ground fault detector for a distribution circuit to supply alternating current at about 60 Hz to a load, where the circuit includes line and neutral conductors extending to load-connection terminals, and where the neutral conductor has a ground connection, said neutral-to-ground fault detector including a differential current transformer having a core, single turn primary windings forming current paths in series with said line and neutral conductors respectively, between said load-connection terminals and said ground connection of said neutral conductor, said primary windings being arranged to produce mutually concelling magnetic effects in the core due to load current carried thereby, and a multi-turn winding on the core, means including a capacitor connected to said multiturn winding for producing resonance therein at a frequency substantially higher than 60 Hz, said core and said resonated winding being formed to have a Q greatly in excess of unity at the resonant frequency, means for exciting said resonated winding within its pass band, and means for detecting the reduction of Q of the resonated winding resulting from a neutral-to-ground fault on the portion of said neutral conductor remote from said ground connection, and line-to-ground leakage detecting means having control means selectively responsive to 60 Hz signals exceeding a prescribed level and having input signal means coupled to said core.