NEUTRAL-CONDUCTOR OPEN-PHASE DETECTING POINT EXTENSION UNIT IN SINGLE-PHASE THREE-WIRE SYSTEM

PURPOSE:To monitor the open phase of a plurality of branch circuits only by one breaker by inputting the voltage signals of the neutral conductors of a plurality of the branch circuits to a voltage line while only the maximum voltage signal in each voltage signal is input to the breaker with a neutral- conductor open-phase protective device. CONSTITUTION:When open phase is generated in one branch circuit in a single- phase three-wire type distribution line, abnormal voltage is input to the input terminals 2 of a single three-neutral conductor open-phase detecting point extension unit (hereinafter-called a unit-) 4 through open-phase detecting lines 14 from the open-phase detect ing point. A maximum voltage signal is detected by a maximum-value detector in the unit 4. The voltage signal is output to the external terminal 8 of a breaker 6 through a signal output line 13 from the output terminal 3 of the unit 4, and the breaker is operated in response to the voltage signal.