| 摘要 |
PROBLEM TO BE SOLVED: To display remaining time, until cutoff operation at a temporary overcurrent, when the overcurrent is admitted within the thermal tolerance of a circuit breaker. SOLUTION: A current effective-value computing means, in which the detection current of a wiring electric circuit 1 is converted into a digital signal by a current detection and conversion means 5 and by which a converted current value is square-averaged, so as to obtain an effective value is provided. A storage means (a ROM) in which an operation-timing characteristic, corresponding to the rated current of a circuit breaker is stored and retained is provided. A current effective-value integrating means, in which current effective value in a period in which a current flowing in the wiring electric circuit 1 exceeds the rated current, is integrated, and accumulrated is provided. The remaining time until a cutoff operation is calculated by a remaining-time computing means, on the basis of the current effective value at a time when an accumulated current effective value is subtracted from the relationship value between the current and the time of the operation-timing characteristic, and the remaining time, is displayed on a display part 9.
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