Electrical Troubleshooting Quiz, Nov. 22, 2011

On a critical production line, a motor stopped working and would not restart

On a critical production line, a motor stopped working and would not restart. You and another electrician responded to the trouble call. It didn't take you long to see that the insulation was cooked. Fortunately, a replacement was in the stockroom. While you were aligning the motor, the operator commented that the motor had been replaced three times this year and he'd never seen anyone using a laser before. Your boss came by to check progress, and when you asked him for the emergency work order, he said he already filled it out.

What are some problems that contribute to the recurring failure? What steps can you take to reduce the likelihood of a fourth failure?

This high failure rate for a critical motor indicates poor maintenance practices, and you've just seen two of them:

  1. Your boss filled out your work order, losing valuable information from the field.
  2. Previous installers didn't use the shop's laser alignment tool. So how exactly did they align the motor?
These administrative issues can easily be fixed. Diagnosing the cause of failure is a bit trickier. Take these steps:
  1. Send the motor out for motor shop analysis.
  2. Determine whether the motor is temperature-rated for the location.
  3. Compare the motor's NEMA design to the application.
  4. Monitor its supply power with a power analyzer.
  5. Ensure the installation meets NEC Art. 250, Part V bonding requirements.
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