TL;DR
A ground fault means one of the motor cable conductors or motor winding has broken down to ground. Megger the cable and motor separately to isolate the fault location.
What you might see
- F013 or GF fault on drive display
- fault trips immediately on start attempt
- motor cable insulation test fails
- fault appears after rain or condensation
Likely causes
Motor cable insulation failure from abrasion, pinching, or moisture ingress
Motor winding insulation breakdown from heat aging or moisture
Moisture or condensation inside the motor conduit box
Cable routing contacting sharp metal edges wearing through insulation over time
Required tools
- Megohmmeter (500V test voltage)
- LOTO kit
- True-RMS multimeter
- Compressed air
- Replacement motor cable (if needed)
Safety first
- VFDs retain lethal DC bus voltage after input disconnection. Always verify bus voltage below 50V DC before touching output terminals.
- A megohmmeter applies several hundred volts DC. Discharge leads to ground after testing before handling.
- Never bypass a ground fault alarm and attempt to run. A live conductor contacting ground is a shock and fire hazard.
Procedure
- 1
Read the fault code. F013 is the PowerFlex 525 ground fault.[1]
- 2
Lock out and tag out the drive input power. Wait 5 minutes for the DC bus to discharge.
Warning: Confirm bus voltage below 50V DC with a multimeter before touching any drive output terminals. - 3
Disconnect the motor cable at both the drive output terminals and the motor conduit box.
- 4
Megger the motor cable conductors to the cable conduit or shield. Set the megohmmeter to 500V. Any conductor reading below 100 MΩ to ground indicates cable insulation failure.[1]
- 5
Megger the motor windings from each terminal (T1, T2, T3) to the motor frame. Below 1 MΩ indicates a winding-to-ground fault and the motor needs rewinding or replacement.
- 6
Inspect the motor conduit box for moisture, condensation, or water ingress. Dry it with compressed air and inspect the conduit seal.
- 7
If the cable is at fault, locate the damaged section by visual inspection. Look for pinching points, conduit edges, or flex areas. Replace the damaged cable section or the full run.
- 8
After repair, re-megger the repaired cable before reconnecting. Confirm above 100 MΩ before restoring power and clearing the fault.
Sources
Allen-Bradley PowerFlex 520-Series AC Drives User Manual (Pub 520-UM001), Rockwell Automation (Allen-Bradley)
Allen-Bradley PowerFlex 520-Series User Manual, general ground fault diagnosis and insulation testing procedures (general)
View source
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