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Electrical Troubleshooting Quiz

Over the past couple of years, an overload or fault on one branch circuit or another has caused the feeder breaker to trip instead of the branch circuit breaker. Having to troubleshoot several branch circuits instead of just one means extended downtime, and the downtime is over a wider area.

The plant manager told you there was a breaker coordination study, so the problem must be with faulty breakers. Now he wants you to identify which breakers need replacement and submit a capital request. What should you do instead?

There's no way to identify which breakers are bad without individually testing each one. When were any of these breakers last tested? If breaker testing doesn't meet the schedule recommended by each manufacturer, your plant manager is accidentally on the right track.

Look at the date on that coordination study. If it's not recent, get the plant manager to agree to a new one.

Look at the fault clearance history. Is this problem occurring on only one or two feeders? Was every fault on a branch circuit? Did you have any feeder ground faults? Were faults even found? This may be a feeder breaker nuisance tripping problem rather than a branch circuit fail closed problem — especially if no faults were found.

A power event may have damaged several breakers. If you have a power monitor, see what power events it captured and compare that to when this problem started.

Also, see 3007.2-2010, "IEEE Recommended Practice for the Maintenance of Industrial and Commercial Power Systems" and NETA's Frequency of Maintenance Tests.

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