Abstract: A multi-function protection system (8) for protecting electrical equipment such as a screw compressor motor is shown having a housing (10, 20) mounting current sensing toroids (CT1, CT2, CT3) and associated circuitry as well as associated circuitry for temperature sensing PTC resistors (S1, S2, S3) adapted to be placed in heat conductive relation with respective windings of the motor. The circuitry is connected to an analog-to-digital converter or ADC (U6) which provides a binary coded input to a micro-controller (U5). The micro-controller performs protection sub-routines to control an output switch (Q4) which in turn controls the state of energization of a relay (K1) coupled to the screw compressor motor.

Abstract: An electronic motor protection system is shown having a power supply usable with multivoltage supplies and providing protection from over-temperature conditions caused by various fault conditions. The system also has optional features of a time delay for re-energization and for low voltage protection. The system is mounted on a circuit board and encased in potting material which also locks the two housing parts together. A miswiring feature is also provided to prevent connecting line voltage to the control circuit or sensor terminals.