Circuit for verifying correct connections to a three-wire dual voltage power distribution system and the absence of open circuit conditions therein

Claim 1

The combination of a logic circuit for use with a three-wire AC power distribution system to verify proper connections thereto or open circuit conditions therein and a ground fault sensing circuit, the power distribution system having two nongrounded lines and a neutral line, said logic circuit comprising: semiconductor switching means having conductive and nonconductive states for selectively interrupting current flow therethrough; polarity-responsive means for synchronizing the states of said switching means with conditions of opposite voltage polarities in the nongrounded lines relative to the neutral line, said polarity-responsive means rendering said switching means nonconductive when conditions of opposite voltage polarities fail to exist in the nongrounding lines of the power distribution system; said switching means having first and second main terminals and a control terminal, said polarity-responsive means having plural AC input terminals and plural DC output terminals, said control terminal coupled to one of said DC output terminals; a load series coupled to said main terminals between the other DC output terminal and the neutral line and receiving current by way of said logic circuit when the nongrounded lines are connected to said AC input terminals if no open circuit conditions exist in the power distribution system; means for indicating electrical conductivity coupled as said load to detect when proper connections are made to the power distribution system or open circuit conditions exist therein, said indicating means comprising first and second coils mounted in a circuit breaker, said breaker having breaker poles electromechanically linked with said first coil to open when the energizing voltage of said first coil is below a predetermined minimum level and said breaker poles being electromechanically linked with said second coil to open when energizing voltage is applied to said second coil; latching means for holding said switching means in a conductive state when open circuit conditions exist in one nongrounded line of the power distribution system; said latching means including an externally controlled switching means for interrupting current flow and means for dividing a voltage into equal magnitudes, said externally controlled switching means having wiring terminals across which electrical conductivity is interrupted, said voltage dividing means having input terminals and a center tap terminal at the divided voltage level, said input terminals being connected to said AC input terminals, said wiring terminals being connected between said control terminal and said center tap terminal, said center tap terminal attaining a voltage level relative to the neutral line when open circuit conditions exist in either nongrounded line of the power distribution system, said voltage level holding said switching means in a conductive state when said externally controlled switching means is closed to conduct current therethrough; and a ground fault sensing circuit connected to energize said second coil when current leakage to ground of predetermined magnitude occurs in the power distribution system.