Patent ID: 7301739

Claim:
A ground-fault circuit-interrupter (GFCI) system for a separately derived three-phase electrical power supply system including a three-phase power supply and main bus circuit with a plurality of feeder circuits connected to the main bus circuit, comprising: a plurality of GFCI units respectively associated with said main bus and one of said feeder circuits and operative to monitor the capacitive charging currents or the fault current to ground flowing therethrough and to generate a fault signal commensurate with the degree of unbalance of the currents flowing through the several conductors of each said circuit; and a processor for continuously monitoring the fault signals generated by the GCFI unit on the main bus circuit and the GCFI unit on each feeder circuit connected to the main bus circuit, said processor being programmed to determine when a fault condition exists based on certain predetermined relationships between and among the fault signal generated by the GFCI unit in the main bus circuit and the fault signals generated by the GFCI units in the feeder circuits, to determine which circuit is experiencing a fault, to generate and transmit a trip signal to the GFCI unit in the faulted circuit causing that circuit to be interrupted, and to generate and transmit an inhibit signal to at least some of the other circuits causing those circuits to be inhibited from interruption.