While many have suggested measuring the motor casing along the stator, this method does not work well for motors that are fan cooled or exposed to external air currents.
For uncooled motors, this approach can produce varying temperature values depending upon the location of the subject temperature readings.
In 1997, a research project led by Infraspection Institute utilized instrumented motors in a controlled environment to determine the effect of excess force on installed motors.
One of the primary goals of this research was to identify a location for collecting reliable temperature data.
From our research it was found that measuring the exterior of the motor bell housing within 1″ of the output driveshaft consistently produced temperatures that were within 1 to 2 °C of the motor windings and the inboard bearing assembly.
Temperatures taken at the bell housing were especially useful for fan-cooled motors since this area was unaffected by convective cooling from the fan.
When measuring motor temperatures, keep the following in mind:
- Make certain that all thermometers are within calibration and used properly,
- Motor temperature will vary with load and ambient temperature. Be certain to record both along with motor temperature,
- Elevated temperatures can be caused by electrical or mechanical defects within the motor and/or defective installations, and,
- Motors having an elevated temperature should be further investigated for cause and repaired or replaced accordingly.
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