A no-load run can reveal wrong rotation, electrical asymmetry, rubbing, abnormal bearing behaviour or cooling problems before the motor is connected to the process. It cannot reproduce full-load temperature or prove driven-equipment performance. Its value comes from a controlled setup and a record that another engineer can compare with the factory test or a later maintenance run.
Freeze the test configuration first
Record the motor serial number, nameplate, winding connection, terminal links, supply source and whether the coupling half is fitted. Confirm that the shaft is safe to rotate and that lubrication, cooling, space heaters and auxiliary fans are in the required state. Remove transport restraints and complete the pre-start insulation and mechanical checks required by the project procedure.
Briefly “bump” the motor only under an approved safe method if rotation must be confirmed. Direction labels should refer to the agreed viewing end.
Use a time-based record
| Time or state | Electrical readings | Mechanical and thermal observations |
|---|---|---|
| Before start | Phase voltage, connection and protection settings | Bearing lubrication, free rotation and visible clearances |
| Immediately after start | Phase current and frequency | Direction, severe noise, rubbing or rapid vibration change |
| During run | Repeated voltage and phase-current readings | Drive/non-drive bearing vibration, noise and temperature trend |
| Stable condition | Final comparable readings and speed | Bearing/housing temperatures and cooling airflow |
| After stop | Supply isolated and run-down time if required | Coast-down noise, looseness, leakage or contact marks |
Use consistent measurement points and identify the instrument. A single final reading cannot show whether temperature or vibration was rising throughout the run.
Compare like with like
Before comparing with a factory report, check supply voltage/frequency, connection, coupling state, fitted fan and measurement locations. No-load current varies with design and supply conditions; a generic percentage should not replace motor-specific data and engineering review.
For vibration, use the project’s nominated standard, machine category, support condition and measurement method. Do not apply a limit copied from a different machine class without confirming that it fits this motor and installation.
Stop conditions belong in the procedure
Define the responsible person and immediate stop conditions before energisation. Examples include wrong rotation where it creates risk, rubbing, smoke, rapidly rising bearing temperature, unstable current or vibration above the agreed action level. The test record should state why a run was stopped and what investigation followed.
For an unusual current result, review high no-load current in an induction motor. Use the factory acceptance test checklist to connect this run with the wider inspection package.