Residual current device

Details Residual current device Residual current device

2011-03-29

2011-03-29

Leja, Ronald W (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Ground fault protection

Reexamination Certificate

active

07916438

ABSTRACT:
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 SW1in the AC supply to the load. The relay contacts SW1automatically 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 C1is 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 SCR2in series with the relay is turned on when the voltage on the capacitor exceeds the breakover voltage of a Zener diode ZD2to 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 SW3in series with the relay to interrupt the current flow through the relay.

REFERENCES:
patent: 4042967 (1977-08-01), Yamamoto
patent: 4707759 (1987-11-01), Bodkin
patent: 5661623 (1997-08-01), McDonald et al.
patent: 6052266 (2000-04-01), Aromin
patent: 6975191 (2005-12-01), Ward
patent: 7242557 (2007-07-01), Ward

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