| 摘要 |
PROBLEM TO BE SOLVED: To prevent malfunction of a ground leakage breaker by surely detecting a ground fault in a large current region, in which a zero-phase current transformer outputs an unbalanced output. SOLUTION: Currents flowing through each phase of an AC electric wiring 1 by detecting voltage by phase-current detecting resistors 41-43, and an electromagnetic device 5 is driven by an overcurrent trip signal output 10a, in response to the detected voltage levels and the currents are interrupted by a breaker contact. The combined value of the currents flowing through each phase is detected by a phase-current detecting resistor 44, a CPU 10 derives a fluctuating threshold in response to the resultant value, while deciding the ground fault when the combined value exceeds the fluctuating threshold and a lock signal output 10b is released, the electromagnetic device 5 is driven by a leakage current detected by a zero-phase current transformer 2, and the currents are interrupted by the breaker contact. When the CPU 10 decides that it is not a ground fault, the leakage current detected by the zero-phase current transformer 2 is locked by the lock signal output 10b, and malfunction is prevented.
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