How Does Ground Fault Relay Work

Ground fault relays (or sensors) are used to sense low magnitude ground faults. When the ground fault current magnitude and time reach the G.F. relay pick up setting, the control scheme signals the circuit disconnect to open.

How does a ground fault detector work?

Ground fault current is sensed by passing all lines carrying current to and from a motor through the window of a special current transformer called a ground fault sensor. If all of the current to the motor returns through the lines in the sensor window, no significant current will be induced in the sensor secondary.

How do you test a ground fault relay?

Inject 80% or pickup value and raise the current until the relay picks up. Record this value. This test confirms continuity of the ground path from the ground bus to the neutral as well as proper operation of the relay. The timing test requires testing the time delay of the relay.