A fail-safe ground fault receptacle circuit includes a ground fault circuit interrupter inductively coupled to a load, directly coupled to one potential source terminal, and coupled by way of a series connected solenoid winding and contacts of a circuit breaker shunted by a series connected impedance and indicating lamp to another potential source terminal whereby manually closing the circuit breaker causes current flow through the solenoid winding shunting the indicator lamp and preventing acti...

A sensing amplifier of half wave sensitivity has its trip level effectively changed without internal adjustment in the sensing amplifier by a circuit branch connected between respective points on the hot line conductor and the neutral conductor across the differential transformer core and containing a resistance for causing additional current flow vectorially added to differential current otherwise occurring between the primary windings.

A ground leakage relay circuit including a core balance transformer through which pass the supply and return line of the circuit to be protected and having a multi-turn secondary winding. A capacitor is connected to be normally charged from a d.c. source. A normally conducting transistor is connected across the capacitor. When the transformer secondary winding exceeds a preselected level, the transistor is switched "off" to permit a voltage build-up across the capacitor. When the voltage across ...

A ground fault circuit interrupter includes a differential current transformer sensing winding supplying input to an integrator which is reset to zero at the end of each half-cycle of AC line current. A line-to-ground fault current will cause the integrator output to exceed a predetermined limit value and produce a trip indication. A saturable neutral transformer supplies a voltage to the neutral line and a reference current proportional to the neutral voltage to a comparator. The peak value of ...

Ground fault interrupter apparatus of the differential transformer type is provided with a sensing amplifier and trip circuit that includes an operational amplifier operated in a manner so that the interrupter apparatus is less sensitive to capacitive ground faults than it is to resistive ground faults. The quality of less sensitivity to capacitive ground faults is preferably obtained by applying to the operational amplifier a biasing voltage that is a half-wave rectified, unfiltered, voltage wh...

The device detects "ground faults" (short circuits to ground) in electrical wiring systems such as those used in household or factory wiring. The device causes disconnection of power if the fault current exceeds a relatively low value such as 5 milliamperes so as to minimize shock damage to the human being or other object causing the short circuit. Means are provided for detecting the grounding of the "hot" wire and/or the neutral wire at a point between the device and the load. A transformer wi...

Ground fault protective system including means for detecting grounding of the neutral conductor independently of the means for detecting ground faults. The secondary winding of a transformer is connected in series with the neutral conductors, and the primary winding of the transformer is energized. Grounding of the neutral conductor is detected by an increase in the primary current.

A ground fault circuit breaker is disclosed in which a differential transformer used to sense ground faults is provided with feedback current for generating a magnetic flux which opposes the ground fault induced flux. The resulting flux nulling cancels out the effects of variable core permeability on the breaker trip signal. This permits the use of less expensive and smaller sensor cores together with more consistant and stable calibration. The feedback current is derived from the output signal ...

Highly sensitive ground fault protective system utilizing an operational amplifier, integrator and switching means for interrupting the flow of current in a distribution system when the amplified and integrated signal produced by a fault current reaches a sharply defined threshold value. The system can be built in highly miniaturized, modular form which can be incorporated in small circuit breakers and receptacle outlet boxes.

Ground fault protectors commonly use a differential current transformer for sensing ground-fault current, and a level detector causes opening of the load circuit in response to ground-fault current above a tripping level. A current loop develops around the core of the differential transformer in case a fault develops between the "white" or neutral load-circuit conductor and the ground-return current path, this loop having the effect of reducing the sensitivity of the ground-fault sensing means. ...