How to Troubleshoot a VFD That Won't Start

A VFD that will not start may be unpowered, disabled, faulted, in the wrong control mode, missing a permissive, or unable to respond to the commanded reference. Start at the drive status and work outward toward the PLC and process.

Power and status

Qualified personnel should verify incoming power, control power, display status, disconnects, fuses, and grounding under the site’s electrical safety procedure. Do not bypass safe-torque-off or guarding circuits to force a test.

Control source

Confirm whether the drive expects keypad, terminal, analog, or network control. A PLC run bit has no effect when the drive is in local mode or when a different command source is selected.

Enable and permissives

Check drive-ready, enable, safe status, external fault, motor overload, process permissives, and feedback. Verify the PLC is not intentionally holding the command off because another machine or safety condition is not ready.

Reference and motor

Confirm the speed reference is nonzero and within limits. Compare motor nameplate data with configured parameters and check the mechanical load. For networked drives, inspect connection status and command/reference mapping.

For a PowerFlex-specific workflow, see PowerFlex 525 troubleshooting. TechControl provides VFD programming and industrial troubleshooting.