| 摘要 |
PURPOSE:To ensure an operating range of predictive earth leakage detection within the operating region of earth leakage detection. CONSTITUTION:An earth leakage decision circuit 13 receives current, detected by a zero-phase current transformer 5 provided in a load power supply path 3, through a voltage converting resistor 18. An alarm decision circuit 21 receives an amplified output from the earth leakage decision circuit 13. Amplification degrees of input stage amplifiers in the decision circuits 13, 21 are set, respectively, by means of first and second amplification degree regulating resistors 19, 26. Since decision level of the alarm decision circuit 21 depends on the amplified output from the earth leakage decision circuit 13 and can be set at a constant ratio to the decision level of the earth leakage decision circuit 13 regardless of the fluctuation of the first amplification degree regulating resistor 19, an alarm decision range requiring no maintenance can be ensured without requiring setting at too low level. |
