Industrial motors are the workhorse of almost every production line, and motor faults come in a recognisable set of patterns. This guide covers the common ones and a structure for working through them safely.
Safety first
Electricity is dangerous. Follow site safe-isolation and lock-off procedures and prove dead before any electrical testing. Safety devices must never be bypassed, defeated or overridden as part of fault finding. This guide does not provide live-electrical working instructions.
The common fault patterns
The motor will not start
Check the supply (all phases present and correct voltage), the contactor/VFD output, the overload protection, and the command path (PLC output, safety circuit). A motor that sits silent usually has no command or no permissive; one that hums usually has a mechanical load or single-phasing issue.
Nuisance tripping
Recurring trips need the cause, not just a reset. Common drivers: overload setting too tight for real load, a driveside protection parameter, a degrading motor (winding or bearing), or a mechanical load that has increased (worn gearbox, seized bearing, blocked conveyor).
Overheating
Overheating often comes from overload (too much mechanical load), poor ventilation or cooling, frequent starting, voltage imbalance, or bearing failure. Check loading against the nameplate duty, cooling fans and filters, and the bearing condition (temperature, noise, vibration).
Abnormal noise and vibration
New noises are useful data. Bearing rumble, whine from a gearbox, a hum from the motor, and knocking all point to different things. Vibration can indicate misalignment, imbalance, a worn coupling, bearing wear or a structural resonance. A vibration analyser or even a simple screwdriver-to-ear check (with appropriate care) can localise the source.
Overload and drive-related faults
Where a motor is driven by a VFD, the drive's fault history is your friend — many "motor" faults are actually drive trips (overcurrent, overtemperature, following error). Always read the drive diagnostics before condemning the motor.
A structure to apply
- Define the symptom clearly (won't start, trips, overheats, noisy, vibrates).
- Check the electrical supply and protection (with safe isolation).
- Check the command and control path (PLC, safety, VFD status and fault code).
- Isolate electrical vs mechanical: rotate the motor by hand where safe — is the load free?
- Check loading against the nameplate and the application.
- Inspect bearings, coupling, alignment and cooling.
- Capture what you found.
Key points
- Most "motor faults" are either a missing command or a mechanical load issue, not the motor itself.
- The drive's fault history is often the fastest clue — read it before replacing anything.
- Record the symptom, the checks and the cause so the next occurrence is quick to resolve.