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Electrical Troubleshooting Quiz

Oct 26, 2009 1:48 PM

A new, highly automated production line was supposed to provide the competitive edge that justified not closing your plant. Now, upper management is reconsidering, because the line is unreliable and expensive to keep repairing. The spare parts costs for this line since startup have exceeded the spare parts costs of the rest of the plant. Last week alone required the replacement of three motors.

You've been tasked with getting this line out of the “frequent failure club” before the executive meeting next week. Are there some steps that could quickly lead to a solution? If so, what are they?

The problem most likely didn't originate with the system components, but with errors in the installation of the system. You can probably find the root cause(s) in less than half a day, by checking:

1. Grounding. A new installation with these particular symptoms is indicative of “separate ground” per the installation guide. If this NEC violation is what you have, fixing it will probably solve the entire mess. You'll find the requirements in Art. 250 and the theory in IEEE-142.
2. Bonding. Rather than ground (connect to earth) equipment, bond it to create a metallic path. Substituting Art. 250 Part III for Part V always ends badly. Thoroughly review your plant for conformance to Part V. In addition to presenting shock hazards, bonding deficiencies can result in flashovers and other problems that destroy equipment.
3. Neutral. Check every 277V feeder and branch circuit to ensure you don't have any open neutrals.
4. Voltage spikes. Spot voltage checks are unlikely to catch spikes. Use a recording DMM, power analyzer, or power monitor.
5. Power quality. Use a power analyzer to look for severe anomalies.

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