| 摘要 |
A safety device for use in conjunction with a delta-connected three-phase electric appliance. The electric appliance is supplied in a delta connection so that the loads ( 100, 101, 102 ) of the appliance with their respective control switches ( 100 a , 101 a , 102 a) are connected over the phase legs (L 1 , L 2 , L 3 ) 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 loads and a control unit for controlling the switch unit on the basis of the sensed load current. The control unit incorporates a timer and a switch unit control block, the timer having a nominal operating time of the load, at the lapse of which the switch unit 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.
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