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Electrical Troubleshooting Quiz

A couple of years ago, one of your buildings was gutted, rewired, and refitted to accommodate a new, nearly 100% automated product line. The whole project was handled by the corporate office, which used an electrical contractor your plant never used before.

Since then, some really nutty things have been going on. For example, four motors and three drives have already failed and had to be replaced. One of the techs says he personally has changed out at least a dozen circuit boards for the robotic controllers. And there's that pesky static electricity problem.

Where do you start?

Document and photograph everything, so you may persuade corporate to pick up the tab for the repairs rather than hiding those costs in your maintenance budget.

Use a power analyzer to properly document the power quality problems. Be sure to look for signs of transformer core saturation.

The failure rates of the VFDs and motors indicate a drive/motor mismatch. Probably, the VFDs aren't properly power quality-corrected for the application. Ask the manufacturer for help in determining what's what.

The high rate of circuit board failures and the static electricity problem are signs that undesired current is circulating due to lack of a low-impedance return path and that dangerous potential exists due to lack of proper bonding.

As a first step in eliminating dangerous potential and the circulation of undesired current, ensure that all circuits and equipment comply with Sections 250.4, 250.24, 250.26, and 250.36 of the 2011 NEC. This may fix your transformer saturation problem.

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