Patent ID: 6999293

Claim:
A safety device for use in conjunction with a delta-connected three-phase electric appliance such an electric range supplied in a delta connection so that the loads of the appliance with their respective control switches are connected over the phase legs of a three-phase supply, whereby the safety device comprises a switch unit, a load current sense unit for monitoring the magnitude of current supplied to the said loads and a control unit for controlling the switch unit on the basis of the sensed load current, the control unit incorporating a timer and a switch unit control block, the timer having therein preset a nominal operating time of the load, at the lapse of which the switch unit under control from the switch unit control block shuts off current supply to the load with the provision that the current supply has not already been shut off by the load control switch proper, wherein the switch unit and the load current sense unit are coupled to operate between a first and a second phase of the current supply and, respectively, the first terminals of the first and the second load of the appliance fed from the current supply, while a virtual neutral is formed by the third phase to which said loads are coupled at their second terminals, and the third load is coupled between the first and the second phase, whereby the load current sense unit senses and monitors only the supply currents to the first and the second load of the electric appliance and, respectively, the switch unit shuts off current supply to the monitored load at the lapse of the preset operating time.