Danfoss FC 302 Alarm 14: Earth Fault after washdown or wet weather?
We have a Danfoss FC 302 VFD that trips on Alarm 14 (Earth Fault) only after washdowns or during periods of wet weather. It runs fine otherwise. What should I check first?
Alarm 14 on a Danfoss FC 302 indicates an Earth (Ground) Fault, meaning current is flowing from an output phase to ground. This typically occurs in the motor cable or the motor itself. The fact that it's triggered by wet conditions strongly suggests an insulation breakdown that becomes conductive when wet.
Likely causes and checks
1Damaged Motor Cable Insulation
- Points to it
- The fault appears after washdown or in wet weather, suggesting water ingress or a conductive path is created when wet. Damaged insulation on the motor cable, especially where it's exposed or routed, is a common culprit.
- Check
- Isolate and lock out power to the VFD. Visually inspect the entire length of the motor cable for any nicks, cuts, abrasions, or signs of wear, particularly at conduit entries, bends, and termination points. Pay close attention to areas that might collect water. Use a megohmmeter to test the insulation resistance of each motor phase conductor to ground. A low reading (below manufacturer specifications, typically <1 MΩ) when wet, but higher when dry, points to this issue.
2Motor Winding Insulation Breakdown
- Points to it
- Similar to cable insulation, the motor's internal winding insulation can degrade over time, creating a path to ground when exposed to moisture. This is especially common in older motors or those in harsh environments.
- Check
- Isolate and lock out power to the VFD. Disconnect the motor leads from the VFD. Use a megohmmeter to test the insulation resistance of each motor winding to the motor frame (ground). Compare readings taken when the fault is active (wet) versus when it's dry. A significant drop in resistance when wet indicates a problem with the motor's insulation.
3Poorly Sealed Motor Terminal Box
- Points to it
- If the motor's terminal box isn't properly sealed, water can enter and bridge the connections, creating a temporary ground fault. This would manifest specifically after washdowns or in very wet conditions.
- Check
- Isolate and lock out power to the VFD. Open the motor terminal box and inspect for any signs of water ingress, corrosion, or moisture. Check the integrity of the gasket and ensure all cable glands are properly tightened and sealed. Clean and dry the connections thoroughly, then re-seal the box correctly.
Next check: If the motor cable and motor insulation test good, or if the problem persists, consider checking the VFD's internal current transducers. The manual suggests performing a manual initialization or a complete Automatic Motor Adaptation (AMA) to reset any potential individual offset in the current transducers, especially after changing power components.
What it typically looks like in the data
Related questions
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