Automatic reset circuit for GFCI
First Claim
1. In a ground fault circuit interrupter having a ground fault sensor means and load current switching means responsive to said sensor means to supply a load current from an alternating current source to a load circuit and to interrupt said load current when a ground fault current flow exceeding a predetermined magnitude in the load circuit is sensed by said sensor means, said sensor means being incapable of sensing faults between the ungrounded and grounded conductors of said load circuit, the improvement comprising ground fault detecting means for determining the presence of a ground fault after interruption of load current by said switching means and providing an output signal determined by the impedance of said ground fault so detected, controlled reset means operably connected by coupling means to said detecting means and being responsive to said output signal for automatically resetting said ground fault circuit interrupter to supply said load current to said load circuit when the impedance of a ground fault would limit a load current through said ground fault to a magnitude which does not exceed a predetermined non-hazardous level.
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Abstract
When equipped with this improvement, a Gound Fault Circuit Interrupter will continue to monitor its protected circuits after tripping and automatically reset itself to restore power when no fault conditions are detected or when detected faults do not exceed a predetermined conduction level and are determined to be non-hazardous. The reset circuit shunts the tripped GFCI relay to pass a safely limited test current into the otherwise disconnected circuits of electrical utilization devices to determine the absence or the extent of fault conditions and is substantially fail-safe in regard to its own function. Four of the embodiments show the circuit as incorporated into the circuitry of an electrically resettable GFCI and a fifth as contained within an attachable enclosure.
120 Citations
23 Claims
- 1. In a ground fault circuit interrupter having a ground fault sensor means and load current switching means responsive to said sensor means to supply a load current from an alternating current source to a load circuit and to interrupt said load current when a ground fault current flow exceeding a predetermined magnitude in the load circuit is sensed by said sensor means, said sensor means being incapable of sensing faults between the ungrounded and grounded conductors of said load circuit, the improvement comprising ground fault detecting means for determining the presence of a ground fault after interruption of load current by said switching means and providing an output signal determined by the impedance of said ground fault so detected, controlled reset means operably connected by coupling means to said detecting means and being responsive to said output signal for automatically resetting said ground fault circuit interrupter to supply said load current to said load circuit when the impedance of a ground fault would limit a load current through said ground fault to a magnitude which does not exceed a predetermined non-hazardous level.
- 15. In a ground fault circuit interrupter having a ground fault sensor means including a differential current transformer and having a load current switching means responsive to said sensor means to supply a load current from an alternating current source to a load current utilization device, the improvement comprising an other sensor means to determine ground fault conditions after interruption of said load current by said switching means in response to said sensor means, circuit means responding to said other sensor means for automatically resetting said interrupter whenever said other sensor means determines an absence of ground fault in the circuitry of said load current utilization device or determines that conductivity of a ground fault in said circuitry does not exceed a predetermined level generally recognized as non-hazardous.
- 17. In a ground fault interrupter system, having an electrically resettable ground fault circuit interrupter including a first ground fault sensor for supplying ground fault protected electrical power from a source to a load current electrical utilization device, the improvement including a second sensor for determining the magnitude or absence of a ground fault in said utilization device or the circuit connecting such device to said circuit interrupter, a controlled reset switch and a control coupling that enables said second sensor to control said reset switch so that said circuit interrupter will be automatically reset when said second sensor senses no fault or determines that a fault condition is non-hazardous, but will not be reset when said second sensor senses a fault condition which would allow a fault current flow exceeding a predetermined level.
Specification