| 摘要 |
<p>A residual current device comprises a circuit (CT, 10, 12) for detecting a current imbalance in an AC supply to a load indicative of a residual current and providing a corresponding output. A relay RLA has contacts SWl in the AC supply to the load. The relay contacts SWl automatically close when a closing current is passed through the relay and is thereafter maintained closed so long as a holding current, less than the closing current, passes through the relay. A capacitor Cl is connected to the AC supply in parallel with the relay RLA such that, upon application of power from the AC supply, current flows to the charge storage device. An electronic switch SCR2 in series with the relay is turned on when the voltage on the capacitor exceeds the breakover voltage of a Zener diode ZD2 to allow discharge of the capacitor through the relay to provide a current exceeding the closing current, the AC supply thereafter providing a holding current for the relay at least when the supply is at a certain minimum voltage. An output from the current imbalance detecting circuit opens contacts SW3 in series with the relay to interrupt the current flow through the relay.</p> |
