VFD-rated motor cable
Price this when overcurrent or overload faults trace to damaged output wiring.
Allen-Bradley PowerFlex Fault F012 — What It Means
Allen-Bradley PowerFlex fault F012 is an output phase-to-phase overcurrent fault. The drive’s current sensing detected output current exceeding 200–300% of drive rated current — a condition that indicates a very low impedance path across the output phases, such as a motor winding short, an output phase-to-phase cable fault, or a power factor correction capacitor improperly connected to the drive output. F012 trips instantaneously via hardware protection and cannot be inhibited through software. This makes it distinct from the software-adjustable overload faults (F005, F007) and indicates a genuine power circuit fault.
Common Causes
- Motor winding short circuit (phase to phase) — The motor has developed an inter-turn or phase-to-phase short in the windings, creating near-zero impedance between two output terminals.
- Short circuit in output cable — Physical damage (pinching, abrasion, rodent damage) to the output cable between the drive and motor creates a direct conductor-to-conductor short.
- Power factor correction capacitors on output — PF capacitors installed on the load side of the drive cause massive current transients when the drive’s switching frequency excites them. Never install PF capacitors between a VFD and its motor.
- Wrong motor connected or wired incorrectly — A delta-wired motor connected in wye, a wrong-voltage motor, or wiring errors in the terminal box can create low-impedance conditions that trip F012 on startup.
Step-by-Step Fix
- Disconnect the motor and output cable from the drive — Remove all wiring from T1, T2, T3. Attempt to clear the fault with the output disconnected. If F012 clears (and doesn’t return on a run command with no motor), the fault is external to the drive.
- Measure resistance between output phases — With the drive output disconnected and all power off, measure T1-T2, T2-T3, and T1-T3. All three should be equal (matching the motor winding resistance). Any near-zero reading indicates a short in the motor or cable.
- Megger test motor and cable separately — Disconnect the cable at the motor terminal box. Megger each cable conductor against ground and against each other. Megger each motor terminal against the others and against ground.
- Inspect motor terminal box for wiring errors — Open the motor junction box. Verify the correct connection pattern (wye or delta) for the supply voltage. Look for accidentally bridged terminals.
- Remove any PF capacitors from the load circuit — If PF capacitors are present in the circuit between the drive and motor, remove them immediately. Relocate any PF correction to the input side of the drive if required.
Parts Often Needed
| Part | Notes |
|---|---|
| Motor (replacement) | If winding short is confirmed; compare repair cost vs. replacement |
| Output cable | Replace complete run if cable short is found |
| Drive output power module | If drive’s internal current sensing or IGBT triggered incorrectly; verify externally first |
Technician Tips
When diagnosing VFD faults, always check the drive’s fault history before resetting. Modern drives store the last 5-10 faults with the drive state at the time (running, accelerating, decelerating, stopped). An overcurrent fault that occurs only during acceleration points to incorrect motor data or mechanical binding. The same fault during deceleration suggests regeneration issues. A ground fault that clears after disconnecting the motor and returns when reconnected means the motor or cable insulation has failed.
Prevention: Schedule annual infrared scanning of drive cabinets. Loose power connections and failing capacitors produce heat long before they cause faults. A 5-minute scan can prevent hours of unplanned downtime.
Need Replacement Parts?
Before ordering, match the drive part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
If the drive itself trips F012 with nothing connected to the output terminals, the fault is internal to the drive’s power electronics. This requires a Rockwell-authorized service technician or a drive repair depot — do not attempt to clear this condition by parameter adjustment.