A 1,200A feeder breaker has tripped six times in the last month. Before resetting it, electricians checked for ground faults and didn’t find any. After resetting it, everything was fine for several days.
The production superintendent wants it replaced. He says he’s replaced breakers in his home and maintenance should just replace an obviously bad breaker.
The replacement costs just over $25,000 so the plant manager has a different opinion on breaker replacement. The plant engineer isn’t convinced there’s a problem with the breaker. He’s called upon you to investigate. Where do you start?
The most common failure mode for breakers is they fail to open when they should. A bad breaker is unlikely to remain closed for days at a time and then just open for no reason.
Put a power analyzer on that feeder so you can identify what event, if any, is tripping the breaker. Have a trained thermographer conduct a thorough thermographic survey.
If you can schedule a shutdown, hire an electrical testing firm with expertise on that breaker and have them perform a preventive maintenance procedure and operational testing. Use the shutdown to perform a full battery of tests on that feeder and the branch circuits it supplies.
