A GF (Ground Fault) will occur when the inverter output summation current exceeds 50% of the inverter (drive) rated current.

The possible causes are listed below:

• Motor lead(s) shorted to ground.
• Motor winding(s) shorted to ground.
• DCCT(s) (DC Current Transformer) in the drive is defective.

Follow the steps below when troubleshooting a GF (Ground Fault): 

1. Remove power to the drive.
   • Caution: It is recommended to verify 10VDC or less is present on the DC bus before performing any service work.
2. Disconnect the motor wiring (U/T1, V/T2, W/T3) from the drive. 
3. Power up the drive and run without the motor connected.
   • If a fault occurs, the problem is internal to the VFD, which will need to be repaired or replaced.   ​​
   • If no faults occur, check all connections, cabling, splices, and/or external devices between the drive and motor. Use a megohmmeter to check motor insulation between each phase and ground.
     • Refer to document: Performing an Insulation (Megohmmeter) Test on a Motor with a Short Video

Note:

• If a DCCT is suspect as defective, it may be easier to replace all the DCCTs or the entire drive instead of trying to identify the problematic DCCT. An oscilloscope is generally required to properly diagnose a bad DCCT.
• In 7-Series and 1000-Series drives, the parameter L8-09 can be used to enable (1) or disable (0) output ground fault detection. In 5-Series, the parameter L8-10 is used. It is never recommended to disable ground fault detection.