Variable frequency drives trip to protect themselves and the motor, and a VFD fault is rarely just "the drive is broken" — it is usually the drive telling you something about the supply, the load, the environment or the control. This guide gives a structured way to read the message.

Safety first

A VFD can store lethal DC-link voltage after power is removed. Follow the manufacturer's stated discharge time and site safe-isolation procedures before any internal work. Safety devices must never be bypassed or overridden. This is a diagnostic guide, not live-working instructions.

Common VFD fault categories

  • Supply faults — under/overvoltage, phase loss, supply imbalance.
  • Overload / overcurrent — the load exceeds what the drive can deliver.
  • Overtemperature — the drive or motor is too hot (cooling, ambient, duty).
  • Motor / load issues — loss of load, stall, broken belt, jam, motor winding fault.
  • Control signal faults — missing start/run command, reference lost, communication drop.
  • Parameter / configuration — wrong motor data, current limits, ramp times, control mode.

A diagnostic sequence

  1. Read and record the fault code and any sub-codes — they map to a category above.
  2. Supply: is incoming voltage correct and balanced on all phases? Is there recent history of dips?
  3. Environment and cooling: are the drive's fans and heatsinks clean? Is the enclosure temperature within rating?
  4. Load: has the mechanical load changed? Run the motor uncoupled where safe — does the fault clear?
  5. Control signals: is the start/run command present from the PLC or HMI? Is the speed reference healthy?
  6. Parameters: do the motor nameplate values match the drive's motor data? Have limits or ramps been changed?
  7. History: is this trip new, or recurring? What changed last (a changeover, a new motor, a cable repair)?

Interaction with the PLC

Many VFD "faults" are actually missing commands or references from the PLC. Before condemning the drive, confirm the run command and the reference are present at the drive terminals, and that the PLC is not holding a permissive off. See our guides on PLC input troubleshooting and PLC output troubleshooting.

Key points

  • The fault code is a category, not a cause — still work the checks in order.
  • Supply and cooling faults are as common as the drive itself; check them before replacing anything.
  • Always confirm the motor nameplate data is correctly entered in the drive.