Electrical Testing
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Tip of the Week: Motors and Vibration, Part 1

Vibration monitoring, if done correctly, will alert you to an increase in vibration.

The vibration signature of a motor can tell you a lot about what’s going on. Entry level vibration testers can tell you the magnitude. If you have the training, you can use more sophisticated testers to know more about the situation than just the fact the total vibration is excessive.

Vibration monitoring, if set up correctly, will alert you to an increase in vibration over the baseline vibration level—and so does periodic vibration testing as part of the routine preventive maintenance (PM) procedure.

Among the changes that may cause vibration to increase:

  • Motor bearings starting to fail or gall.
  • Alignment is deteriorating.
  • A coupling is going bad.
  • Lubrication problems exist somewhere in the motor system.
  • Something got bent; for example, a support bracket on a pipe connected to the pump the motor drives.
  • The motor pedestal is damaged.
  • Soft foot has occurred.
  • Mounting bolts have come loose.


Vibration testing is so valuable that there is almost no justification for excluding any motor from a vibration testing program. Yet, you never want to use vibration testing to take the place of other testing you should be doing. For example:

  • Motor bearings starting to fail or gall. By the time vibration shows up, you may not have much time left to intervene. Use ultrasonic testing to detect bearing problems super-early.
  • Alignment is deteriorating. Alignment issues may exist without boosting vibration over the alarm level. Periodically perform motor alignment per recommended intervals for a given application. Rely on vibration testing to alert you when something unusual knocks alignment out, not when alignment changes over time.
  • A coupling is going bad. Couplings should be inspected at each PM (and as part of the alignment procedure).
  • Soft foot has occurred. The No. 1 cause is improper tightening of the motor feet. You don’t just tighten motor mounting bolts to “make sure they’re tight” or to “correct” a higher than normal vibration reading. You need to replace the locking hardware and torque the bolts to the recommended torque.
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