Electric Motor Failures: How to Diagnose

Small DC Motor rotor showing windings
File:Small DC Motor Rotor.JPG” by Jjmontero9 is licensed with CC BY-SA 3.0.

When your electric motor fails, it can be difficult to know why. But there are quick tests you can use to easily diagnose problems.

Make sure to disconnect power from your electric motor before beginning. Power is not required. This step protects you and the equipment.

Motor Identification

Electric motors have a metal nameplate or tag riveted to the outside of the motor housing. This nameplate usually includes a lot of useful information, including

Nameplate for a Reliance Electric Servo Motor
Nameplate for a Reliance Electric Servo Motor
  • Manufacturer Name. Who made the motor.
  • Serial Number or Model Number. The model number tells you the make of your motor. The serial number uniquely identifies it.
  • RPM. Revolutions Per Minute. The output capability of your motor.
  • Horsepower. A rating of motor performance.
  • Voltage. The motor’s voltage requirements.
  • Current. How many amps the motor requires.
  • Frame Style. The unit’s physical dimensions.
  • Type. This can include NEMA ratings, cooling indications, etc.

A wiring diagram may also be included on the nameplate. In some cases, this tag will include the unit’s manual identification number, too.

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