Abstract: A portable ground fault circuit interrupting (GFCI) device includes a housing equipped with two sets of back mounted contact blades or prongs for insertion in a conventional duplex wall receptacle. One set of contact blades conveys current from one socket of the wall receptacle to a known GFCI receptacle via a relay, both mounted within the housing. The other set of blades are dummy blades frictionally engaged in the other wall receptacle socket to reliably retain the portable GFCI device in place. The GFCI receptacle is accessible through a front opening in the housing for plug connection with circuits for which ground fault protection is afforded.

Abstract: A ground fault circuit interrupter (GFI) in which a load circuit is energized through a normally closed magnetically latchable circuit breaker. When no fault exists that is of sufficient magnitude to actuate the GFI, the latching coil of the circuit breaker is ineffective, whereby the circuit breaker remains closed. The coil is connected to the amplified DC output of a ground fault sensing circuit and is energized in a certain sense to open the circuit breaker upon the occurrence of a fault, the circuit breaker then being magnetically latched open. A capacitor is continuously DC charged in a certain sense by the AC supply line through a rectifier. To reset the circuit breaker the capacitor is selectively connected across the coil to discharge a pulse of a sufficient magnitude in a proper sense to reversely energize the coil enough to release the magnetic latch and allow the circuit breaker to reclose. The GFI is tested by closing a circuit that simulates a fault of the low magnitude which is to be sensed.

Abstract: 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.

Abstract: 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 activation thereof and excessive current flow through the solenoid winding opens the circuit breaker to cause current flow through and activation of the indicating lamp.

Abstract: A circuit interrupter responsive to ground-fault conditions is disclosed that is rendered relatively immune to many possible failures of components and connections. A differential current transformer has a pair of differential primary windings in series with the conductors of the protected load circuit (or a ground-fault-current primary winding in a modification), and a secondary winding in control of an AC-energized SCR that controls a "hold-in" coil of a circuit interrupter, and an AC - excited biasing winding. The arrangement is such that, in the absence of ground fault current, the hold-in coil is energized, whereas in case of a ground fault the AC biasing flux is opposed so as to be cancelled or reversed, releasing the circuit interrupter for opening.

Abstract: In a ground fault interrupter in which the relay switch for interrupting current through a-c lines has its actuating coil selectively connected by a controlled rectifier to receive a-c line power, a tendency towards relay switch chatter is suppressed by preventing the initiation of controlled rectifier conduction during the rapidly collapsing portions of the a-c power cycle.

Abstract: An improved ground fault tester uses a magnetostrictive element or piezo-electric element, such as a multimorph, which changes dimensions upon being magnetized or electrically charged. The dimensional change is used to interrupt the power circuit in which the ground fault occurs. The existence of a ground fault is sensed by a sensor which supplies current to the magnetostrictive or piezo-electric element. In the case of the piezo-electric element, the charge is dissipated through a parallel discharge circuit whereby interruption of the power circuit is accomplished rapidly and is reclosed only after a time delay. Automatic time delay resetting may be easily accomplished by the addition of a single resistor and a rectifier.

Abstract: A conductive touch grid or plate incorporated in the handle portion of apparatus such as an appliance performs the on/off function of the appliance as well as sensing the impedance of the operator with respect to either the line or neutral side of an associated AC source. Whenever the sensed impedance indicates a potentially dangerous condition a switching element in series with the line conductor interrupts current flow to the appliance thereby protecting the operator.

Abstract: A two to three wire converter circuit is disclosed which provides a protective function for users when using power hand tools, appliances or any electrically operated device. Many alternating current electrical supplies provide a hot or high line and a neutral line. Many electrical devices, such as hand tools and appliances, are provided with a high line, neutral and a ground line connected to the housing of the device. The present invention enables the connection of the housing ground line or the housing to the neutral line. The neutral line of an alternating current supply is connected to ground. The present invention provides a circuit for sensing which line is the high line and which line is the neutral line of an electric supply and connecting these to the electrical device only if the neutral line of the supply is connected to the neutral line of the electrical device.

Abstract: Ground fault detection circuitry for sensing ground fault currents is dissed. If ground fault occurs in a line conductor(s) in a distribution system supplying AC power to a load, the circuitry senses this ground fault and provides a signal in response to the sensing of the ground fault. The circuitry also senses the grounding of a neutral conductor, or in some systems the shorting of a line conductor by a parallel conductive path and provides a signal in response to the grounding of the neutral or the parallel conductive shorting path. The signals provided by the circuitry in response to these sensed conditions may be used to provide a visual or audible alarm, or may be used to remove power from the load.

Abstract: To minimize nuisance tripping for spurious causes in ground fault protective systems, fault-characterizing signals derived from differential currents in alternating current supply lines are subjected to a variable integration automatically adapted to the magnitude of the fault-characterizing signal. Higher level signals are integrated at augmented rates, preferably with an antilog characteristic. The supply circuit is interrupted when the expanded and integrated signal exceeds a threshold value.

Abstract: Apparatus is disclosed for monitoring an alternating current circuit having a three wire connection, wherein alternating voltage power is applied between two wires and the third wire is a circuit ground. The apparatus detects an open ground circuit and opens a circuit breaker to disconnect the voltage over the two alternating current wires whenever an open ground circuit is detected.

Abstract: An apparatus for determining in the field where breaks or other failures in metal cable occur is provided having a dual electrical pulse generator means attached to a gate assembly wherein one generator means will send an electrical pulse down the cable and back to one of the gates and wherein the other generator sends pulses of same frequency but of a known delay to the same gate. Attached to the gates are means for detecting when pulses from both sources arrive simultaneously at one of the gates.

Abstract: A differential transformer having a core of low permeability ferromagnetic material, a pair of identical primary windings and a secondary winding of relatively few turns capable of producing a large voltage output for a small magnitude ground fault current. A cross-field winding is utilized to periodically saturate a portion of the flux path in the transformer core to produce sudden changes in magnetic flux, which flux changes vary in magnitude proportional to the amount of fault current. During the time interval when the cross-field portion of the sensor is not saturated by a pulse of sampling current, a second pulse of current is introduced into the sensor secondary winding for detecting a grounded neutral wire by sensing the output voltage produced in response thereto.

Abstract: This disclosure relates to a protective relaying system for a polyphase power transmission line in which at least two separate line operating conditions at a remote end of a protected line section are transmitted to a local end of the line section over a single communication channel. In the preferred illustrated embodiment, the operating conditions of three-line conductors are sequentially transmitted whenever a fault condition is sensed on any one or more of the three-line conductors. During the normal, non-faulted operation, a coded signal is continually transmitted to maintain the time derived signals at the receiver in substantial synchronism with the time derived signals of the transmitter. The coded signal also establishes a trip inhibiting or guard signal at the receiver.

Abstract: A ground fault detector for protecting an electrical power system against ground leakage currents. The detector is of the differential transformer type, in which the primary windings of the transformer are connected in series with the hot and neutral lines of the power system, any unbalance in the currents flowing through these lines being detected by sensing the unbalance voltage induced in the secondary winding of the transformer. The secondary voltage is amplified and employed to actuate a solenoid which trips the system circuit breaker in response to unbalance in line and neutral currents due to the flow of ground leakage current. A secondary winding on the solenoid is connected in the neutral line to cause the detector to operate in response to a neutral to ground fault, which might otherwise go undetected.

Abstract: The sensing and trip circuit electronics of a ground fault interrupter of the differential current transformer type is, in a two pole system, supplied with power from each of the line conductors through separate solenoid trip coils and zener diodes that together provide good transient suppression while the zener diodes together provide full wave rectification for the voltage supplied to the electronics.