Abstract: An apparatus and method for continuously monitoring and detecting an open ground connection which may occur anywhere between the chassis of an electrical appliance and the grounding terminal of a receptacle. The apparatus includes a plug having a grounding blade and a sensing blade which together form an assembly adapted for insertion into the grounding terminal of the receptacle. When inserted into the grounding terminal, the grounding and sensing blades complete a closed current path formed by a sensing conductor connected to the sensing blade and a grounding conductor connected to the grounding blade. The sensing conductor is connected to an inverter and the input of the inverter is also connected through a resistor to the DC power source so as to place the small current on the sensing conductor at the input of the inverter.

Abstract: In an AC electric power system including a voltage source having a live conductor and a neutral, a grounding and ground fault detection circuit connected between the neutral and ground potential and comprising, in series, a current limiter, a rectifier, and a signal generator for providing a control signal in response to a ground fault current.

Abstract: The present invention relates to a ground detection arrangement for an A.C. generator in which positive and negative D.C. voltage are alternately applied to the neutral point of an armature winding so as to detect voltages proportional to ground currents corresponding to the respective D.C. voltages, and a ground resistance is obtained with the sum of the absolute values of both the detected voltages, whereby the existence of grounding can be correctly detected regardless of the grounding position.

Abstract: The present invention relates to a ground detection arrangement for an A.C. generator in which positive and negative D.C. voltages are alternately applied to the neutral point of an armature winding so as to detect voltages proportional to ground currents corresponding to the respective D.C. voltages, a ground resistance is calculated using the sum of the absolute values of both the detected voltages, while a grounding position of a field winding is calculated using the relative sum, the calculated results being displayed, whereby the existence of grounding can be correctly detected regardless of the grounding position, and the grounding position of the field winding can be correctly known.

Abstract: The present invention relates to a ground detection arrangement for an A.C. generator in which positive and negative D.C. voltages are alternately applied to the neutral point of an armature winding so as to detect voltages proportional to ground currents corresponding to the respective D.C. voltages, and the average of the sum of the absolute values of both the detected voltages is compared with a reference value thereby to detect the existence of grounding, whereby the existence of the grounding can be detected without being affected by the grounding position of a field winding.

Abstract: A system is provided for early detection of leakage currents through ground connections of loads such as three-phase motors connected to isolated secondary windings of supply transformers. An alarm device is energizable when leakage current is a small fraction of a predetermined value which might present a potential hazard, the point of energization being adjustable by an operator until the predetermined value is reached. Thereafter, it is adjustable only by a supervisor, after operation of a key switch. Circuitry is provided to obtain sensitive, stable and reliable operation.

Abstract: A system to prevent a dangerous contact voltage in a welding apparatus by providing a protective device for cutting off the power for welding. The welding system has a power source including a primary circuit and a secondary circuit. An electrode receiving the power welds workpieces which are successively inserted and removed into electrical contact in the welding system. A protective ground is provided between the housing for the power source and ground. To prevent dangerous grounding during the welding operation, there is connected between the workpiece lead in the secondary and the housing a device which monitors both the current to the protective wire ground and the voltage between the workpiece lead and the housing. This monitor device controls a power cut-off switch. The current is monitored through a current sensor which is connected to the monitor device and the current sensor is also connected in series between the housing and the protective ground.

Abstract: A bi-directional system for ensuring that a ground connection is made in a three-wire conductor system including a line "hot" conductor, a line neutral conductor, and a ground conductor includes a circuit for generating direct current potential related to the potential difference between the line "hot" conductor and ground and a second circuit for generating a direct current potential related to the potential difference between the line "hot" conductor and ground. A circuit including a male plug for insertion into a female receptacle includes a first prong for coupling alternatively to the line "hot" conductor or the line neutral conductor, a second prong for coupling alternatively to the line "hot" conductor or the line neutral conductor, and a third prong for coupling to the line ground conductor.

Abstract: A protective circuit arrangement for sheathed heating elements which interrupts ground fault conditions by effectively decoupling the power line from the heating element regardless of the polarity of the power supply connections. A fusible link couples each side of the heating element to the power supply. A normally open switch responsive to current in the ground path switches a relatively low resistance shunt current path across the heating element when the ground current exceeds a predetermined threshold level. Closure of the shunt path enables sufficient current to flow in the power supply lines to actuate the fusible links. Circuit parameters are selected such that the current in the fusible link coupled to the hot power line is sufficiently greater than that in the fusible link coupled to the neutral line to cause the hot power line fusible link to be actuated first, thereby interrupting the fault condition and decoupling the hot power line from the heating element.

Abstract: An electrical safety switch for protecting an electrical appliance requiring a ground, an on/off switch disposed in series with a resistor and primary coil of a transformer between the ground line and the B+ line of the appliance, and a triac connected in series with the load of the appliance between the B+ line and the neutral line with the gate triggering the triac connected to the transformer to be energized thereby upon a current being present through the on/off switch.

Abstract: A ground isolation monitoring apparatus having a protective circuit is provided for use between an AC power source and a utilization device, such as an electronic instrument. The protective circuit permits operation of the utilization device with earth ground disconnected, automatically reconnecting earth ground if a hazardous voltage or current appears on device chassis or exposed metal parts. The protective circuit also monitors neutral-to-earth ground continuity and shuts off AC power to the utilization device if the ground path opens or if the impedance thereof increases. Various other features may be provided to ensure safe operation of the device.

Abstract: A personnel protection circuit for electrical supply systems comprises a normally closed switch connected between a source of electric power and a load. Two parallel conductors are connected between the switch and the load, and include a control circuit having a current unbalance detector for detecting current unbalance between the two conductors. Upon detection of such current unbalance, the normally closed switch is opened thereby disconnecting the electrical supply. Such control circuit devices may be included in both lines of the electrical supply system between the source and the load, or alternatively, further control circuit devices may be provided at both the source end and the load end of the parallel conductors.

Abstract: A circuit breaker, having a latching mechanism and a solenoid senses current through a circuit. The sensed current is converted to a proportional voltage. A current rating plug and receptacle system, responsive thereto, provides a standardized voltage. The proportional voltage is applied across a resistor in series with parallel connected permanent shunt resistor and replaceable plug resistor. The standardized voltage is obtained across the parallel connection. A peak detector provides an approximate true peak value voltage of the standardized voltage. An instantaneous trip circuit, a ground fault detector, and both short term and long term delay circuits provide trip signals upon certain conditions. Upon the presence of any trip signal, an OR circuit provides a control signal to gate an SCR having a thermal switch coupled across its anode and cathode. A supply voltage is applied across a serial connection of the anode, the cathode, and the solenoid.

Abstract: A safety circuit prevents shocks, and is particularly useful with a television camera head and processing unit that are connected by a triaxial cable. The circuit applies power to the triax at the processing unit. If the current is interrupted, the power is no longer applied and a selected impedance is applied to the triax at the camera. If said impedance can be detected at the processing unit, power is reapplied to the triax. The impedance can comprise a diode, which has different effects upon different alternating signal polarities.

Abstract: An improved discriminating circuit breaker system for use with an electrically grounded direct current power distribution system. A three-tier safeguard system is provided to insure proper operation of the breaker should a fault occur. The basic components include the electrically operated circuit breaker and a control circuit therefor. The control circuit sends a control signal to the breaker to operate it depending on whether a illegitimate load is detected on the power distribution system. This detection process utilizes: a pilot wire through which any control signal flows; an alternating current (a.c) signal generator to superimpose such a signal on the transmission line; a current detector to sense the a.c. level and produce a control signal if its current value exceeds a maximum level; a voltage detector to sense the voltage level of the a.c.

Abstract: A device for sensing current flow in an electric conductor employs a ferromagnetic core coupled to the conductor and a control winding on the core for applying a periodic magnetic flux to a part of the core of a magnitude to vary the core permeability, preferably driving a part of the core in and out of saturation. The periodic flux interrupts any flux circulating in the core due to current flow in the conductor. An output winding on the core has a signal voltage induced therein whose amplitude is determined by the rate of change of the interrupted circulating flux. The device effectively amplifies a small current input signal to a relatively high output level. A bias winding may be wound on the core to compensate for stray magnetic fields in the vicinity of the device.

Abstract: In one embodiment, a sheathed electrical resistance heating unit is operated from a 120 volt unbalanced-to-ground household power line. The heating unit sheath is grounded. In order to interrupt a fault between the actual resistance heating element and the outer sheath of the heating unit, regardless of where along the length of the heating unit the fault occurs, a fuse is connected in series with the "hot" side of the power line, and, by means of at least one unidirectional current conducting device, the two terminals of the heating element are effectively connected, through the fuse, to the "hot" side of the power line during alternate AC half-cycles.

Abstract: A ground fault circuit interrupting (GFCI) device of the type utilized in low voltage, residential type circuits for personnel protection against ground faults is connected in circuit with a high voltage, high current source so as to trip in response to ground fault current returning to the source via a conductor path solidly connecting the source to ground.

Abstract: Disclosed is a system for monitoring the resistance in the pilot and ground conductors of a power cable and for interrupting power if the resistance exceeds a predetermined limit established for the particular cable. Novel circuit arrangements are employed to reset and calibrate the system.

Abstract: A safety protection circuit for controlling the operation of electrically-powered tools including a switching device. In one application, the power tool is a drill which is utilized in drilling a hole through electrically non-conductive material such as a concrete floor and an electrically conductive material such as a grounded metallic conduit having electrical cables therein disposed directly below the floor. The switching device automatically discontinues the drilling operation when the drill bit contacts the metallic conduit after passing through the concrete floor thereby avoiding any damage to the cables within the metallic conduit or causing a safety hazard. Subsequently, the drill can be reactivated to penetrate the metallic conduit. The switching device will again automatically discontinue the operation of the drill after breaking contact with the metallic conduit.

Abstract: An electric hospital bed system including a conducting frame and movable parts, an electric device for controlling the movements of the movable parts and a ground circuit monitor operatively connected between a power supply source and the electric device. The monitor continuously senses the integrity of the ground connection between the hospital bed system and the building ground bus-bar, including the ground line in the wall outlet. In the event the ground connection is broken or disconnected for any reason, the power supply to the electric device will be interrupted and switched to a warning device mounted in the hospital bed system or at a remote central monitoring station. The hospital bed system remains inoperative until the ground fault is located and the ground connection restored.

Abstract: A ground-fault circuit interrupter has normally open relay contacts connected in series between an incoming hot line and an outgoing hot line. A coil of a detector relay is connected between the outgoing ground line and the outgoing cold line and closes when even a slight voltage differential appears between the outgoing ground line and outgoing cold line. Closing of the detector relay illuminates a short-indicating lamp and causes a further relay to latch on and disconnect the relay whose contacts are connected between the incoming hot line and outgoing hot line so that the device connected to the outgoing hot line is open-circuited. A reset button is provided for placing the circuit back in operative condition with a green OK lamp lighted.

Abstract: An a-c power supply for a load such as a household appliance, including a line wire, a neutral wire and a ground wire, has a safety switch and an overload-sensing resistor inserted in its line wire and also comprises a ground-fault detector in the form of a differential transformer with a toroidal core traversed by the line and neutral wires. The safety switch, which may be a manually resettable circuit breaker or an armature of a self-locking relay, has an operating winding in series with an SCR connected between a positive and a negative terminal, one terminal being connected via respective diodes to the line and neutral wires, the other terminal being connected via respective diodes to the neutral and ground wires.

Abstract: A vaporizer having an improved electrode-type steam generator structure to control the amount of steam generated and to maintain the power requirements for generating the steam constant. The generator is particularly adapted for portable room humidifiers where the steam is generated in a confined chamber within a large reservoir of water. The generator comprises a pair of concentric electrodes disposed in the bottom of the steam chamber. The surface areas of the electrodes are in spaced relationship and a perforate cap is placed over the electrodes or the radially outer electrode is an inverted cup-shaped member the end of which is perforated to determine the amount of steam which is allowed to escape off of the electrodes. A fan mixes the steam with air and the unit is provided with an electrical circuit to prevent shocksfrom the unit and to prevent operation without a properly wired and grounded outlet.

Abstract: An electrical protection unit having a plurality of main leads for respectively interconnecting a plurality of lines of an electrical power source to at least one electrically operated unit. At least one main lead has a device therein for opening the respective lead when the device is activated. The one main lead has one side of an electrical circuit interconnected thereto with the other side of the circuit being adapted to be interconnected to ground, the circuit having means for activating the device when the circuit is operatively interconnected to ground. Control means are provided for operatively interconnecting the circuit to ground.

Abstract: An autotransformer having the same polarity impedance, series and tertiary windings as defined by an equivalent three-terminal network of said autotransformer. Autotransformers are often protected against phase-to-ground faults by ground fault relays and such devices require this type of impedance relationship for proper operation; especially during phase-to-ground fault conditions.