Electric Motor Failure

Electric motor failure stems mostly from damaged bearings or stator windings. However, there are a number of other reasons they can fail.

The most common failures in order are:

  1. bearing failure
  2. stator winding failure
  3. overheating
  4. power supply anomaly
  5. humidity
  6. contamination
  7. unusual mechanical loads

Bearing Failure

The main reasons for bearing failure are:

  • improper lubrication
  • electrical discharge across the bearing

Stator Winding Failure

Electrical insulation deteriorates at a rate that doubles for every 10°C increase in temperature.


The reasons for overheating are numerous and include:

  • overloaded
  • too many starts
  • high ambient temperature
  • coolant failure
  • low or unbalanced voltages

Power Supply Anomaly

  • harmonics
  • over-voltage
  • under-voltage
  • voltage unbalance
  • voltage spikes


If the motor is stopped and cools down it may drop below the dew point. Moisture weakens the insulation and contributes to bearing corrosion.


This results in: abrasion, corrosion and overheating. Small particles in the windings can gradually wear the insulation away as the wires flex during operation.

Electric motor failure is a large subject area with specialist knowledge required in a number of disciplines to enable a robust design to be made. We would welcome contributions from hobbyists, researchers and commercial organisations alike. Drop us a line at editor@glue-it.com

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