Electrical Fault — Ground Fault Relay Trip (50G/51G)

What This Fault Means

A 50G (instantaneous) or 51G (time-overcurrent) ground fault relay trip indicates current flowing through the ground return path, meaning insulation has failed somewhere in the protected circuit.

Common Causes

• Cable insulation failure (age, heat, mechanical damage)
• Motor winding failure to ground
• Equipment flooded or exposed to moisture
• Vermin damage to cable insulation
• Failed surge protector shorting to ground

Recommended Fix

1. Lock out / tag out the faulted circuit per NFPA 70E.
2. Megger-test each branch cable and motor on the circuit to isolate the faulted segment.
3. Visually inspect cables for obvious damage, burn marks, or moisture ingress.
4. Repair or replace the faulted cable/motor.
5. Before re-energizing, verify the ground fault relay resets and the megger reading is >1 MΩ.