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Electrical Troubleshooting Quiz

A few weeks ago, an 800A breaker tripped and could not be reclosed. So, it was replaced. The new breaker tripped several times, and a recording DMM left on it showed a maximum load of 620A. Each time, the investigating technician couldn't identify a fault before reclosing the breaker.

The plant manager had a tech place a bypass jumper around it. "We've got an instrument monitoring the current and if it gets too high someone can just pull the handle." He wants you to figure out why the breaker "doesn't hold." What should you do?

The plant manager's decision to jump around an 800A breaker is a severe safety violation that could result in an extended plant shutdown and considerable human tragedy. If there's a fault, you'd have to open the jumper not the breaker — under load.

You need another shutdown to remove that jumper. Before shutting down, photograph the existing breaker from as far away as your zoom lens permits, and examine its purchase documentation. Contact the manufacturer to determine whether there's been other reported problems with this make and model.

Before replacing the breaker during shutdown, have a qualified testing firm conduct a full battery of tests to look for possible faults or cable failures. Then test the replacement breaker and the existing one.

Send the replaced breaker to a qualified shop to examine it for damage and defects. If replaced breaker is OK and there's no fault causing the trips, you may have power quality issues. Prior to powering back up, set up power analysis on the feeder and the major supplied loads.

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