Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1983-02-14
1985-05-28
Salce, Patrick R.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 49, 361 87, 340652, 219507, 219510, H02H 333
Patent
active
045204179
ABSTRACT:
Electrical systems, especially elongate heating systems, include means for monitoring circuit continuity and/or absence of ground faults. The systems comprise a switching device, e.g. a thermostat, as well as a circuit breaker. When the switching device is on, a relatively high current passes through the circuit and when it is off, little or no current passes through the circuit. In one embodiment, a small controlled residual current flows in the circuit even when the switching device is off, and a current-detecting device signals when a discontinuity causes the current to drop below the expected value for the residual current. In another embodiment, the switching device is placed so that the heater (or other electrical load) is at a positive potential with respect to ground even when the switching device is off, and a ground fault indicator is used to compare the currents in the two legs of the circuit and to signal when a ground fault causes the currents to differ. Preferred circuits make use of both these embodiments. Preferably the fault circuits are powered by the same power source as the circuit which is being tested, but the fault indicators continue to signal faults even when the circuit is no longer powered, and both correction of the fault and powering of the circuit are required to cancel the fault indication.
REFERENCES:
patent: 2999189 (1961-09-01), Gerrard
patent: 3548398 (1970-12-01), Strimling
patent: 3766434 (1973-10-01), Sherman
patent: 3800121 (1974-03-01), Dean et al.
patent: 3997818 (1976-12-01), Bodkin
patent: 4068276 (1978-01-01), Pintell
patent: 4421976 (1983-12-01), Jurek
Burkard Herbert G.
Kaufman Stephen C.
Raychem Corporation
Richardson Timothy H.
Salce Patrick R.
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