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Measuring Motor Temperatures
Tip written by: Infraspection Institute

Temperature can be an indicator of the condition of installed electric motors; however, the best location for measuring temperature is often debated. In this Tip we discuss the best location for measuring motor temperatures.

Measuring motor temperature is often a challenge since electric motors differ widely in their design and construction. 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 bellhousing within 1” of the output driveshaft consistently produced temperatures that were within 1 to 2 C of the motor windings and the output side bearing assembly. Temperatures taken at the bellhousing 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
• Motors with elevated temperature should be further investigated for cause and repaired or replaced accordingly

Temperature limits and trending are two of the many topics covered in the Level II Infraspection Institute Certified Infrared Thermographer^® training course. For more information on upcoming classes or to obtain a copy of our Cross Technologies Study, call 609-239-4788 or visit us online at www.infraspection.com.