Applicable Systems
Okken
Symptoms
The ground fault relay has detected current leakage to ground exceeding 30mA. The main breaker trips to prevent electrical shock hazard and equipment damage.
Possible Causes
- Motor winding insulation breakdown causing current leakage to the frame
- Cable insulation damaged by abrasion, heat, or chemical exposure
- Moisture or condensation inside a junction box or motor terminal box
- Failed surge protector or capacitor leaking current to ground
Troubleshooting Steps
- Step 1: Disconnect power and use a megohmmeter to test motor winding insulation to ground
Insulation resistance should be above 1 megohm per kV of rated voltage - Step 2: Disconnect the motor cables and test each cable for continuity to ground
Replace any cable with insulation resistance below 1 megohm - Step 3: Inspect all junction boxes and motor terminal boxes for moisture or contamination
Dry with a heat gun and apply desiccant if moisture is found - Step 4: If the motor insulation is below 1 megohm, the motor needs reconditioning or replacement
Dry the windings using a bake oven or low-voltage heating method
How to Reset
Reset: After the ground fault is cleared and insulation resistance is verified above 1 megohm, reset the ground fault relay and close the main breaker.
Common Replacement Parts
- Ground fault relay: Core-balanced type, 30mA trip (Verify CT window size matches cable)
- Megohmmeter: 500V or 1000V test voltage (Select based on motor rated voltage)
Frequently Asked Questions
- Q: What is acceptable motor insulation resistance?
Minimum 1 megohm per kV of rated voltage plus 1 megohm. For a 480V motor, the minimum is approximately 1.5 megohms.
- Q: How do I dry a wet motor?
Use a low-voltage heating method: apply 10-15% of rated voltage to the windings and allow the resistance heating to evaporate moisture over 12-24 hours.
- Q: Can I reset a ground fault relay without fixing the fault?
No. Repeated tripping without repair will cause further insulation damage. Always identify and fix the root cause before resetting.
Source: OEM Technical Manual
Category: Electrical