Skip navigation

Electrical Troubleshooting Quiz, Sept. 11, 2012

A critical production line has had recurring problems with downtime


Electrical Troubleshooting Quiz

A critical production line has had recurring problems with downtime. The symptoms have included such things as transformer loss, seemingly random breaker trips, failure of electronic components, and the loss of several small servo motors. The response thus far has been to replace the failed components.

The plant manager suspects a root cause and has specifically requested you as the person to find it. The repair records show frequent downtime going back to about seven months ago, and then there aren’t any failures until four more years back. What should you look at next, and what are some likely issues?

Naturally, you want to use your power analyzer to look at the power quality. It won't be surprising if your analyzer shows high harmonics and/or distorted waveforms. It would be surprising if the failures aren’t due to power quality problems traceable to an error in that repair of seven months ago.

How can you find that error? Start by opening the disconnects to all the equipment on this line. If the power quality anomalies disappear, then the source of the PQ problems is in the equipment. Next:

  • Visually inspect for bonding errors and load side grounding; fix as needed to comply with Article 250 Part V.
  • If that repair involved a motor or drive replacement, a motor/drive mismatch is likely; contact the drive manufacturer.
  • If power factor correction capacitors are present, recalculate the size needed. Note that motor drives and PF capacitors typically are incompatible; get a PF-corrected drive.
Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.