An electronic module for ground fault circuit interrupters (GFCI) in both circuit breaker and receptacle configurations includes a signal processor having a plurality of fault signal threshold stages for differentially charging an integrating capacitor in accordance with the magnitude of the fault signal...http://www.google.ca/patents/US3953766?utm_source=gb-gplus-sharePatent US3953766 - Ground fault circuit interrupter and electronic module therefor
