Abstract: A solid state load protection system whereby the current supplied to a load is monitored enabling ground fault sensing to be used. A current sensor is utilized so as to produce an output current which is proportional to the current in the electrical circuit. Attached to the current sensing function is a resistive load which converts the current produced by the current sensing function to a voltage which is also proportional to the current utilized by the motor. Attached between two resistors which comprise the resistive load is a ground fault resistor which has its remaining end connected to the neutral leg of the current transformers of the current sensing function. The ground fault sensor monitors the voltage across the resistors in the resistive load and the current in the neutral leg of the current sensors.

Abstract: Solid state relay system which includes a break-before-make function on both the opening and closing operation thereof is taught. The system may be utilized in conjunction with an "on" delay module or an "off" delay module or with a module that is generally instantaneous in operation.

Abstract: A phase imbalance logic module for a solid state motor protection system for a three-phase motor. Three-phase line currents are converted to corresponding voltages and rectified. The resultant output voltage is a poorly regulated DC voltage having a ripple of approximately 4% during normal operating conditions. In the event of a phase failure, even if not total, the corresponding ripple percentage increases. The phase imbalance logic network senses ripple and provides an output signal to trip a protective circuit breaker if the component of ripple becomes significantly large.

Abstract: An electrical control system which is utilized for opening a circuit breaker which is connected to a load to be protected. The control system comprises a unitary current sensor module which senses current flowing in the load to be protected. The sensor is adapted to have connected at the output thereof a load resistor which is capable of cooperating with the sensed current to provide a range of voltage over which a set of plug-in modules are operable to either provide an indication of characteristics associated with the current or the load or to provide an output function which is adapted to open the circuit breaker. The load resistor is replaceable with other load resistors so that the voltage range may be maintained even though the expected value of currents to be sensed by the sensor may change depending upon the load and other circuit characteristics.

Abstract: A long acceleration module is provided for use with a current sensor which provides an output voltage which varies with load current. There is also provided an inverse time overload logic module which controls the tripping of a circuit breaker to protect the lines in which the load current flows in relationship to the output voltage of the current sensor. The long acceleration module allows motor startup when a motor is connected to the lines to be protected. The long acceleration module purposely simulates a relatively low voltage for the input to the inverse time overload logic module during the motor startup time when high but generally non-dangerous currents are drawn by the accelerating motor.

Abstract: An indicator light circuit utilizing a single lamp and providing continuous illumination during normal operation and on and off flashing during an emergency condition. The circuit can also provide an indication wherein the lamp is continuously on but pulsating bright and dim. The indicator light circuit can thus provide four visual indications: (1) Off; (2) Normal on; (3) Flashing on and off; and, (4) On, but pulsating bright and dim. The invention is particularly adaptable for use to provide motor running and relay trip indication.

Abstract: The utilization of a Zener diode long acceleration module in conjunction with a inverse time overload module for a motor starter control system. The long acceleration module prevents the quick opening of the motor starter during the acceleration mode of an electrical motor when overload currents of relatively high magnitude are present for short periods of time in the electrical system connected to the motor. Other protective devices in the circuit will protect the system should an overload occur other than the type of overload associated with the long acceleration of a motor or similar electric device.

Abstract: A timing device utilizing a transistor and silicon controlled rectifier to provide a momentary relatively high voltage for the solenoid coil of a tripping device which is part of an undervoltage detecting and tripping circuit to thus energize the coil to allow closing of a circuit breaker which is controlled by the undervoltage device when low voltage which originally caused the circuit breaker to trip is no longer present on the line to be protected by the circuit breaker. The relatively high voltage changes to a normal value shortly thereafter.