Applicable Systems
FC-30
FC-51
FC-101
FC-202
FC-302
Symptoms
The drive trips. The display shows Alarm 14, indicating an earth (ground) fault. The drive has detected leakage current from an output phase to earth ground.
Possible Causes
- Motor cable insulation failure to ground
- Motor winding insulation failure to ground
- Moisture in motor junction box or cable glands
- Cable gland or conduit fitting damaged, allowing water ingress
Troubleshooting Steps
- Step 1: Disconnect the motor cable and megger the cable phase-to-ground
Cable insulation resistance is in the megohm range - Step 2: Megger the motor windings to ground
Motor insulation resistance exceeds the minimum requirement - Step 3: Inspect the motor junction box for moisture or water ingress
Junction box is dry and properly sealed - Step 4: Replace any cables or motors with failed insulation
System operates without ground faults
How to Reset
To reset: 1) Fix the insulation failure. 2) Press RESET. Caution: Ground faults are fire and safety hazards. Do not reset repeatedly without fixing the root cause.
Frequently Asked Questions
- Q: What is the minimum acceptable motor insulation resistance?
For 400V motors, insulation resistance should be above 1 megohm. Values below 1 megohm indicate degraded insulation that may cause ground faults. The IEEE 43 standard recommends >100 megohm for good insulation.
- Q: Can moisture in the motor cause earth faults?
Yes, condensation or water ingress in the motor junction box or windings can create a conductive path to ground, triggering an earth fault alarm. Install anti-condensation heaters in motors exposed to humidity.
Source: Danfoss VLT FC-302 Design Guide, 2023
Category: PLC & VFD