TL;DR
Overcurrent faults most often come from an accel time that's too short for the load, a motor wiring fault, or a jammed load. Lengthen the accel ramp first and check motor lead insulation.
What you might see
- F002 or OC fault on drive display
- drive trips during acceleration
- current reading exceeds drive rating
- fault repeats after clearing
Likely causes
Acceleration ramp too short for the load inertia demanding peak current on every start
Motor overload from mechanical jam or driven equipment binding
Phase-to-phase or phase-to-ground short in the motor cable or motor windings
Motor parameters in the drive (motor NP amps, voltage) not matching the nameplate
Required tools
- Megohmmeter (500V test voltage)
- True-RMS multimeter
- LOTO kit
- HIM keypad
Safety first
- Never disconnect drive output terminals while the drive is powered. Always lock out input power first.
- VFDs retain DC bus voltage after disconnect. Wait at least 5 minutes and confirm bus voltage below 50V DC before opening the enclosure.
- Megger testing applies several hundred volts DC. Discharge leads to ground before handling.
Procedure
- 1
Read the fault queue on the PowerFlex 525 HIM keypad. Confirm the fault code is F002 (overcurrent).[1]
- 2
Check the accel time parameter (A441, Accel Time 1). Increase it by 50% and test a start.[1]
- 3
Check the load by uncoupling or unloading the driven equipment if possible. A start attempt with no load confirms whether the fault is in the motor or the load.
- 4
Lock out and tag out the drive. Disconnect the motor leads at the drive output terminals.
Warning: Do not disconnect drive output terminals while the drive is energized. The drive output has high-frequency switching voltage that will arc badly and damage equipment. - 5
Megger the motor cable and motor windings using a 500V megohmmeter. Confirm insulation resistance is above 100 MΩ phase-to-ground and above 50 MΩ phase-to-phase.
- 6
Verify the motor nameplate parameters are correctly entered in the drive: motor NP volts (P031), motor NP Hz (P032), motor NP amps (P033), motor NP RPM (P034), motor NP power (P035).[1]
- 7
Reconnect the motor, restore power, clear the fault, and run a test start while monitoring the drive current display.
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 overcurrent fault diagnosis and motor parameter setup procedures (general)
View source
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