Pump Myth #2: My Motor Must Be Bad – It Feels Really Hot

While feeling a person’s forehead to test their temperature might be a good indication of that person’s health, the “feel test” is not a good indication for the health of a pump motor, or any motor.

While motor manufacturers design their motor windings to certain operating temperature limits (to ensure long winding insulation life), there are many factors that contribute to the actual surface temperature of the motor housing. Factors include:

  • Type of motor enclosure (ODP, TEFC, etc.)
  • Whether surface is smooth or ribbed
  • How fully the motor is loaded vs. the motor rating
  • The motor efficiency rating (Note: Premium efficiency motors might exhibit a higher surface temperature than a standard efficiency motor, due to a smaller internal fan designed to consume less parasitic power.)

Depending on these and other factors, the surface temperature of a properly operating industrial motor may be 180-212 degrees F, so that even a quick touch test could result in a burn. An overloaded motor may run hotter, but who among us could leave our hand on the motor surface long enough to tell if the motor is hotter than 180-212 degrees?

Obviously, if a motor trips out on overload, smokes, or smells acrid (from “burning” insulation), these symptoms should not be ignored. A multi-meter can be used to see if the motor is drawing greater than name plate amps (improper flow balancing is the most common cause of high amp draws in pump applications ) and a megohmmeter can test insulation integrity. But the touch test does not provide a lot of useful information, may result in a burn, and give erroneous information about the health of the motor.