Electrical Troubleshooting Quiz, July 12, 2011

July 12, 2011
Maintenance is buying too many of a particular circuit board as a replacement part

Maintenance is buying too many of a particular circuit board as a replacement part. During your initial fact-finding, you discover the following:

  • The four main production lines each use this board in six places.
  • About 90% of the failures occur in the same two particular places in each line.
  • At each cabinet using this board, the 120V supply power waveform is severely distorted.
  • At one line, you measure 2,917 ft of wire run to its supply panel.
  • Each cabinet is grounded per the manufacturer's installation manual.
Armed with just these facts, what should you recommend?

That is a long run, making excess voltage drop an obvious issue. After verification with an AC resistance tester, you should recommend:

  1. Moving the supply transformer/panel closer to the load.
  2. As part of this move, upsize the conductors from the NEC minimums.
This should fix the voltage distortion problem. But if not, this needs to be done anyhow. Perform waveform analysis at each affected cabinet, before and after.

Are the production cabinets actually "grounded" (per NEC Art. 100 definition)? These must be bonded, not grounded. Grounding here allows undesired currents to circulate.

Next, do a survey to identify high harmonic sources for mitigation and/or isolation from these cabinets.

Voice your opinion!

To join the conversation, and become an exclusive member of EC&M, create an account today!

Sponsored Recommendations

Electrical Conduit Comparison Chart

CHAMPION FIBERGLASS electrical conduit is a lightweight, durable option that provides lasting savings when compared to other materials. Compare electrical conduit types including...

Fiberglass Electrical Conduit Chemical Resistance Chart

This information is provided solely as a guide since it is impossible to anticipate all individual site conditions. For specific applications which are not covered in this guide...

Considerations for Direct Burial Conduit

Installation type plays a key role in the type of conduit selected for electrical systems in industrial construction projects. Above ground, below ground, direct buried, encased...

How to Calculate Labor Costs

Most important to accurately estimating labor costs is knowing the approximate hours required for project completion. Learn how to calculate electrical labor cost.