Applicable Systems
PowerFlex 753
Symptoms
The PowerFlex 755 drive trips on fault F38 (Ground Fault). The drive keypad displays F38 and the fault log records the magnitude. The output contactor opens if present.
Possible Causes
- Insulation breakdown in motor windings or cable to ground
- Moisture ingress into conduit or motor terminal box
- Damaged cable sheath causing phase-to-ground contact
- EMI filter capacitor failure creating a ground path
Troubleshooting Steps
- Step 1: Disconnect the motor cable at the drive and megger each phase to ground
Insulation resistance >10 MOhm at 1000V DC for each phase - Step 2: Inspect motor terminal box seals and conduit drains for water ingress
Box is dry, seals intact, and drain holes are unobstructed - Step 3: Check cable routing for abrasion points against tray edges or sharp bends
Cables are properly supported with no visible damage to sheath - Step 4: If the fault clears when the motor is disconnected, megger the motor separately
Motor windings show >5 MOhm to ground; if lower, rewind or replace motor
How to Reset
Press the Stop key to clear the fault after the ground fault is repaired. Verify zero ground leakage with a clamp meter on the PE conductor before restarting.
Common Replacement Parts
- 20G11NC8P0JA0NNNNN: Allen-Bradley PowerFlex 755 7.5HP drive (Verify voltage class, braking option, and communication module)
Frequently Asked Questions
- Q: How sensitive is the PowerFlex 755 ground fault detection?
The drive detects ground current as a percentage of drive rated current, typically tripping at >50% with a fast response.
- Q: Can a VFD output filter cause a ground fault trip?
Yes. Failed filter capacitors or reactors can create ground paths. Disconnect the filter and test to isolate the cause.
Source: Rockwell Automation PowerFlex 750-Series Installation Manual, Publication 750-IN001
Category: Electrical