A motor can pass its factory temperature test and still run hot after installation. One common site cause is recirculation: heated outlet air cannot escape and returns to the cooling inlet. The motor then operates in a hotter local environment than the temperature measured across the room.
Read the airflow path, not just the clearance
Stand back and trace where cool air enters, where the motor discharges it and where that air can go next. Check the arrangement in the plant’s normal state, with acoustic covers, weather hoods, belt guards, filters, nearby motors and process ventilation operating as intended.
| Observation | Possible mechanism | Evidence to collect |
|---|---|---|
| Inlet temperature rises after start | Discharge air is returning to the inlet | Time trend at inlet and discharge |
| One side runs hotter | Wall, duct or neighbouring machine blocks flow | Layout, clearances and temperature map |
| Temperature changes when a door opens | Enclosure ventilation is insufficient or unbalanced | Fan states and enclosure pressure/air path |
| Heat increases after a guard change | New panel traps or redirects hot air | Before/after photos and readings |
| VFD motor heats at low speed | Shaft fan airflow is reduced | Speed, torque, duration and auxiliary-fan state |
| Outdoor unit heats in still weather | Hot air collects under a canopy or wind screen | Wind condition and local inlet temperature |
The table guides investigation; it does not replace the motor manufacturer’s clearance and cooling requirements.
Measure the air the motor actually uses
Place the temperature sensor where it represents incoming cooling air without touching a hot frame or obstructing the inlet. Record motor load, speed, process state, room ventilation and nearby equipment status. Compare the local inlet reading with a remote ambient point and track both over time.
Smoke or airflow visualisation may help when permitted by site safety rules. Avoid makeshift materials near rotating equipment, hot surfaces or hazardous areas.
Correct the path without creating another risk
Possible actions include increasing separation between inlet and discharge, adding a properly designed baffle, moving a heat source, revising enclosure ventilation or providing ducted/independent cooling approved for the motor. Any change must preserve guarding, ingress protection, hazardous-area compliance, access and noise controls.
After modification, repeat measurements under comparable load and weather or room conditions. A lower frame temperature without a recorded operating case is weak evidence.
Use ambient and altitude derating guidance when the inlet condition exceeds the rating basis. Also verify motor fan rotation and airflow before blaming the room layout.