Abstract: When there are single-phase grounding faults happening somewhere in the apartment buildings and the protection devices can not effectively cut the fault circuit,the fault voltage will pass along the mutual PE conductor and then transfer to all apartments,making the metal shell of electric appliances alive and causing electric shock accidents.Through the analysis of the feature of the circuit of various common protective grounding system with single-phase grounding faults,the author finds no matter what kind of grounding system is employed,the voltage between L and PE conductors will turn significantly low or close to zero in each family distribution box after the grounding faults happen.Therefore,an effective way to solve the problem is to stall undervoltage tripping device between L and PE conductor in each family distribution box as a monitoring device to find fault voltage on PE conductor.Finally,the paper introduces the design principle and application of the PE-conductor fault voltage monitoring devices.

Key words: PE-conductor, residence, fault-voltage, monitoring