Output side earth (ground) fault overcurrent

What does E.GF mean?

This fault occurs when an earth (ground) fault is detected on the inverter's output side, typically in the motor or its connecting cables, specifically during startup. This protective function, active when Pr. 249 is set to '1,' immediately trips the inverter to prevent damage. An unresolved ground fault poses an electrical shock hazard and can severely damage the inverter or motor.

• Insulation breakdown in the motor windings, causing a phase-to-ground short circuit.
• Damaged motor cable insulation (U, V, W to ground) due to mechanical stress, aging, or moisture ingress.
• Water ingress or excessive moisture inside the motor or its terminal box, leading to a path to ground.
• Incorrect grounding or bonding practices leading to circulating ground currents being detected as a fault.
• Malfunctioning inverter current sensor or ground fault detection circuit providing false readings.

Click steps to track your progress.

1. 1

   Disconnect the motor cables (U, V, W) from the inverter's output terminals.

2. 2

   Perform an insulation resistance test (Megger test) on each motor phase winding (U-GND, V-GND, W-GND) and each output cable (U-GND, V-GND, W-GND) to check for ground faults (typically >5MΩ).

3. 3

   Visually inspect the motor cable jacket and conduit for signs of damage, pinching, or water ingress.

4. 4

   Check the motor's terminal box for moisture, loose connections, or carbon tracking indicating arcing to ground.

5. 5

   If the motor and cables pass insulation testing, re-connect only the motor and temporarily disable Pr. 250 (Output side earth fault protection) to confirm the fault location (re-enable after testing).