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Electrical Troubleshooting Quiz — Sept. 5, 2017

Sept. 5, 2017
To help convince corporate of a necessary repair, first address issues that may be damaging perfectly good equipment.

Your plant’s 480V load-side distribution system is under a cable testing program for feeders and for branch circuits supplying motors over 30 hp. During each Thanksgiving shutdown, an electrical testing firm conducts cable testing and submits a report identifying suspect cables. During the Christmas shutdown, those cables get replaced.

The plant engineer put six years of results on a spreadsheet and noticed a pattern. About 80% of the “doomed” cables are in the same general area, and some cables have been replaced two or three times.

The electrical testing firm says they will troubleshoot only if allowed to perform baseline testing on the replacement cables, but corporate won’t pay for testing of new cables. Can you troubleshoot this problem?

The lack of baseline testing is a critical factor. It will tell you whether cables are damaged when installed as replacements and whether nearby existing cables are “collateral damage.”

To help convince corporate of the necessity, first address issues that may be damaging perfectly good replacement and existing cables. For example:

  • Bonding deficiencies. Ensure those motors have an uninterrupted bonding path to the equipment grounding conductor.
  • Power spikes, excess harmonics, lower power factor, etc. Rent or buy a power analyzer or power monitor, if you don’t have either.
  • Overheating. What is the raceway temperature at every place these cables are run, and are they rated for that service?

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