The ground trip relay with look ahead is designed for use with 120 VAC controlled under-voltage release breakers and contactor coils on circuits limitied to 25 amps or less ground fault current. It is factory adjusted to trip at less than 6 amps ground fault through a current transformer. This relay uses a breaker for tripping and indication. When a ground fault current occurs the breaker trips and must be manually reset. A resistor in series with the breaker under-voltage to limit current on a ground fault is not required.
What is look ahead? The relay has the feature to verify no fault is present before closing the contactor/circuit breaker. Typical molded case circuit breakers require at least 30 seconds prior to reclose to dissipate any ionized air. The relay has a minimum 30-second to allow this to take place in circuit breaker application. The time delay is scalable to 180 seconds for applications where inertial loads require more time to dissipate back emf from the motor circuit.
Look Ahead Mode
The purpose of this is to test the voltage circuit for a cable or motor ground fault. The Look Ahead circuit performs this function by connecting to the motor circuit through the high tension coupler. Internal circuitry will first test for any AC voltage on the motor circuit. If AC voltage is detected a constant DC current will be applied through the high tension coupler. A DC voltage will develop across any leakage resistance. This voltage is read, converted to a resistance value and compared to a pre-selected resistance threshold. If the measured resistance value is greater than the pre-selected threshold an internal register is set and the indicating RES LED will illuminate GREEN. If the measured resistance value is less than the pre-selected threshold a ground fault is detected, indicated by the blinking RED RES LED, tripping the relay circuit breaker, The high tension coupler is available in a single phase or three phase configuration depending on customer requirements.