FIELD: electrical engineering, specifically, relay protection. SUBSTANCE: invention can find use in protection of bus bars of lowest level of voltage against various faults in bushing, suspension or supporting insulation, leads-in of transformers, switches and so forth accompanied by various types of short-circuits. Signal of alternating current characterizing summary current of all lines feeding bus bars and alternating current characterizing summary current of all lines outgoing from bus bars are converted to first and second signals of direct current which are supplied to input of polarized threshold element. First D C signal is supplied in positive direction with reference to input of threshold element and second D C signal is supplied in negative direction with regard to same input. When current across input of threshold element exceeds specified level protection disconnecting all lines from bus bars operates. Sensitivity of protection using direct current rises thanks to employment of threshold element. Possibility of employment of current transformers in circuits of protection of outgoing lines leads to reduction of mass and size of proposed gear. Freedom from necessity to match polarity of connection of windings of current transformers in lines outgoing from bus bars and in lines supplying bus bars results in increased reliability of protection and in decreased labor input to installation, adjustment and operation of gear. EFFECT: enhanced sensitivity, reduced mass and size characteristics, increased reliability and decreased labor input to installation, adjustment and operation of gear. 11 cl, 2 dwg
