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: An automatic circuit restoration device for polyphase lines, comprising a set of normally open circuit breakers connected in series to respective feed lines and controlled in unison by one coil, and an auxiliary movable contact controlled by means responsive to the presence of voltage on one or more of the feed lines so that said movable contact is opened and said circuit breakers are closed through said coil when one of said feed lines is deenergized.

Abstract: A protection circuit is provided which incorporates a reed relay whose contacts form the circuit breaker of an electrical appliance. The winding of the reed relay is supplied with a rectified alternating current derived from a current transformer coupled to the supply line to the appliance. In order to avoid periods of zero current in the winding, the winding is also supplied with a rectified alternating current from a source which is out of phase with that supplying the supply line. Failure of the current on the line will cause the contacts to open. Preferably the relay has a set of self latching contacts to prevent re-energization of the winding once de-energized. A manually operable reset switch is provided in series with the self latching contacts.

Abstract: A protection circuit for use with circuit breakers for electrical apparatus operated by multiple phase, alternating current power systems characterized by a plurality of electrical distribution lines for transmitting electrical energy, with the electrical energy in the lines having a spaced phase relationship. The protection circuit includes a first sensor coupled to the lines for detecting an undesirable phase imbalance between two or more of the lines, and for detecting a low voltage on one or more of the lines, and initiating a first signal responsive to either or both of these conditions. The protection circuit also includes a second sensor coupled to the lines for detecting a phase reversal between two or more of the lines and initiating a second signal responsive thereto. A circuit breaker operating circuit is coupled to the second sensor for operating the circuit breaker responsive to the second signal.

Abstract: A motor protector for three-phase electric motors includes two independent sensing transformers for simultaneously sensing the voltage across two phases of a three-phase power supply to detect failures in all of the power lines including either the primary or secondary side of a line transformer. A first relay is actuated by the electric power sensed across the one phase and a second relay is actuated by the electric power sensed across said other phase through a set of contacts of the first relay for disconnecting the second sensing transformer from the power supply when there is a failure that results in a reduction in voltage in the one phase to prevent production of feedback voltages through the phase windings of a line transformer. For a wye-delta line transformer configuration the one phase is a high leg and the other phase is the low leg.

Abstract: In a load-protection circuit operative with an alternating current voltage source and including circuit means for sensing an undervoltage conditon to control the voltage supplied to a load upon the occurrence of such a condition, the improvement includes a transformer which has input and output windings, and wherein the output winding has two output taps and at least one additional tap. The input winding is connected to the voltage source, and the load is connected across one of the output taps and the additional tap, the other tap and the addition tap being connected to the circuit means for causing the latter to switch the load from the additional tap to the other tap upon occurrece of the undervoltage condition. The voltage across the load is then substantially restored to a normal condition.

Abstract: A control circuit for a switching regulator comprised of silicon controlled rectifiers and inductive reactors is disclosed. The control circuit provides for fault detection and voltage regulation while using these output as control signals for a frequency variable gating mechanism to trigger the switching regulator so as to provide its maximum output capability.

Abstract: Circuitry for rapidly switching off the power to a universal motor upon sensing of overloading of the motor. Sudden motor overloading results in rapid speed reduction that is detected by measuring the voltage drop across the motor armature. The circuitry detects this drop and removes a gating signal to a triac switch in series with the motor to remove the power to the motor within one cycle of the applied AC.

Abstract: In a protection circuit for a device such as a motor, the unused half or a dedicated half of an AC signal on the secondary of an isolation transformer is sensed to disconnect the AC line from the device if the line voltage is abnormal, such as being too low. Conveniently the protection circuit is employed in a complete motor protection system which may include a thermal protection circuit, a low oil pressure protection circuit, and/or a time delay circuit to prevent start-up too soon after shut-down.

Abstract: A circuit breaker including a solid-state circuit for providing regulated current to operate a holding coil for an undervoltage release mechanism. An alternating current control line feeds a full wave bridge rectifier in the control circuit to provide pulsating direct current to a reference voltage supply circuit, a current regulating circuit, and the holding coil of an undervoltage release mechanism. The current regulating circuit comprises two series connected units of an integrated circuit quad current differential operational amplifier. The output of the second unit controls the base current of a regulating transistor which is series connected to the holding coil. The reference voltage supply circuit includes a transistor connected as a variable resistor to provide operation of the circuit over a wide range of input voltages without excessive heat generation.

Abstract: A phase loss detector for detecting and responding to voltage loss or failure in a polyphase electric power supply to disconnect the load or motor in the event of such loss, which is adapted to serve in conjunction with either a delta or wye power configuration and is characterized by an internally generated AC common line such that a common line of the power source is unnecessary.

Abstract: A multipole circuit breaker including a latch release actuator having a trip coil and a hold-in coil coaxially surrounding a plunger and mounted within a hollow cylindrical actuator support frame. The actuator is mounted in association with a latch mechanism and includes a spring biasing the plunger toward release of the latch mechanism. The hold-in coil is responsive to voltage conditions on an external control line and serves to oppose the action of the bias spring and maintain the plunger in a position to prevent release of the latch mechanism when the voltage on the control line is above a predetermined level.

Abstract: An undervoltage circuit having a power supply voltage level detector, a reset circuit, and a hold-in circuit. The level detector of the circuit causes an undervoltage coil to trip a circuit breaker when the power being supplied falls below a predetermined voltage level. When power is restored, an automatic reset circuit resets the circuit breakers undervoltage coil at a preset voltage level by applying a repetitive pulse to the coil. The hold-in circuit applies a continuous current to the same coil of the undervoltage circuit to hold it in once it has been reset.