R&M Tip: Determining Maximum Operating Temperature for MotorsR&M Tip:

Operating temperature can have a significant impact on the service life of operating electric motors. Accurately determining maximum operating temperature for motors is critical for setting temperature limits.

One specification for electric motors is maximum operating temperature. This temperature value is determined by several factors—including, but not limited to, the motor’s insulation class. Exceeding the maximum temperature for a motor will shorten the life of the motor’s dielectric materials and will result in decreased service life for the motor.

To calculate a motor’s maximum rated temperature, one must know the motor’s ambient temperature rating and its rated temperature rise above ambient. Both values are generally found on the motor nameplate located on the exterior of the motor casing.

To calculate a motor’s maximum operating temperature, add the ambient and rated rise temperatures. Their sum is the maximum operating temperature for the subject motor at 100 percent load.


  • Rated Ambient: 40°C
  • Rated Rise: 90°C
  • 40 + 90 = 130°C or 266°F

It is important to note that some motors specify insulation class rather than a numeric value for temperature rise. In such cases, it is necessary to know the temperature values associated with the insulation class of the subject motor.

The Infraspection Institute Standard for Infrared Inspections of Electrical Systems & Rotating Equipment provides temperature limits for several common insulation classes of AC and DC motors. In addition to providing inspection procedures, it also provides temperature limit data for lubricants, bearings, and seals. To order a copy of the standard, call 609-239-4788 or visit the online store at infraspection.com.

As always, if you are experiencing unusual difficulty installing your MTAP, share your validation data with PdMA Technical Support ([email protected]) for assistance.

Tip courtesy: PdMA.