A conveyor motor that will not start is one of the most common — and most disruptive — faults on a production line. The cause can be electrical, mechanical, or a safety/permissive interlock, and chasing the wrong one first wastes time. This guide gives a structured sequence you can apply consistently rather than jumping to a conclusion.

Safety first

Before any testing, follow your site's safe isolation and lock-off procedures and prove dead. Safety devices must never be bypassed, defeated or overridden as part of fault finding. These resources are for general engineering information and do not replace site-specific risk assessments, safe isolation procedures, manufacturer instructions, competent engineering judgement or applicable legislation.

Symptoms to record first

  • Does the motor hum, trip, or do nothing at all?
  • Is there a drive or VFD fault code, or a PLC or HMI alarm?
  • Did it stop suddenly, or fail to start after a changeover or reset?
  • Are other conveyors on the same panel affected?

The answers point the diagnosis: a hum suggests mechanical load or single phasing; an immediate trip suggests a short or ground fault; nothing at all usually points to a missing command or permissive.

A structured diagnostic sequence

Work top-down from safety to mechanical so each step logically depends on the one before it:

  1. Emergency stop / safety circuit — is it healthy and reset?
  2. Guards and interlocks — are they satisfied?
  3. PLC permissives — does the PLC have the inputs it needs to allow a start?
  4. PLC command — is the PLC actually issuing a start command?
  5. Contactor or VFD — is the output device being driven, and is it healthy?
  6. Motor supply — is the motor receiving the correct voltage on all phases?
  7. Mechanical load — is there a jam, obstruction or seized component?

Illustrative decision tree

This is an illustrative structure, not a substitute for site procedures:

  • START
  • ↓ E-stop / safety circuit healthy? → No → reset or repair safety circuit
  • ↓ Guards and interlocks satisfied? → No → close guards / fix interlock
  • ↓ PLC has required permissives? → No → check sensors and inputs feeding the permissives
  • ↓ PLC commanding the drive? → No → check logic, HMI and auto mode
  • ↓ Contactor/VFD healthy and driving? → No → check output, auxiliary contact and VFD fault code
  • ↓ Motor receiving correct supply? → No → check cabling, connections and phases
  • ↓ Mechanical load free to turn? → No → clear jam, inspect gearbox and bearings
  • ↓ Investigate the motor itself

Common causes mapped to symptoms

| Symptom | Likely area | |---|---| | Nothing happens, no alarm | Safety circuit, PLC permissive, command path | | Motor hums, draws current | Single phasing, mechanical overload, jam | | Trips immediately | Short/ground fault, VFD fault, overload setting | | Intermittent | Loose connection, thermal trip, intermittent sensor |

Key points

  • Do not jump straight to the motor — most "will not start" faults sit upstream in the command or safety path.
  • Capture the fault code and the sequence of checks each time, so repeating faults are recognised rather than re-diagnosed from scratch.
  • A consistent order beats memory under time pressure.