FIELD: electrical engineering. SUBSTANCE: device has three resistors interconnected through some of their leads and connected to phase leads of supply mains through their other leads; connected in series with mentioned resistors are DC voltage supply and measuring circuit which is connected to ground; voltage supply is regulated device; measuring circuit is, essentially, resistive divider connected to inverted input of operational amplifier whose output is connected to input of comparator whose output is connected to inputs of two transistor switch amplifiers through diode isolator. Insulation resistance drop below permissible value energizes switch which initiates emergency condition and/or disconnects electric system from supply mains. EFFECT: simplified design, increased sensitivity due to improved measuring circuit arrangement. 1 dwg
