FIELD: electrical engineering; systems incorporating non-grounded power circuits, for example, protection of electrolyzer drive control circuits. SUBSTANCE: device has actuating element, dividing members inserted in star-connected circuit whose neutral point is coupled with resistor connected in parallel with comparison element. Common point is coupled through this resistor with electrolyzer anode bus. Introduced in device is double-pole switch one of whose poles is connected to ac circuit phase lead and other pole, to anode bus. Connected in series with switch are low-frequency filter and threshold element with two different-polarity comparison thresholds. Coincidence gate installed at input of actuating element has one of its inputs connected to output of threshold element and other input, to time delay output. Output of comparison element is connected to time delay input and to control input of double-pole switch. Capacitors are used as dividing members. EFFECT: provision for selective protection of ac circuit against current leakage to DC process bus system. 1 dwg
