A contractor called MIDWEST for a little free advice. His customer had a 400 amp molded case circuit breaker. This happened to be a 400 amp Westinghouse circuit breaker, but it could just as well have been Square D or General Electric. He was very worried because his customer’s 400 amp circuit breaker was rattling, making a terrible humming and rattling noise. He had never heard this before and didn’t know if the circuit breaker was going to blow up, fall apart or what. He said this was a very old breaker, 1960s. We recommended he measure the load on the feeder cables from the breaker, but to do this very safely. Measure the current at the load end of the feeder, if possible, not at the circuit breaker. It is not totally unusual for an old circuit breaker to rattle and hum away when the load is near or over the rating of the over current device. When the breaker’s internal over current device is picking up because of the load. It depends on the breaker. The noise might be an indication the over current device is picking up and may trip the circuit breaker if the load doesn’t drop down below pickup soon enough. Either way, it may be a good idea to replace the circuit breaker. Sometimes these breakers will nuisance trip at less than the pickup current level. If possible retrofit the old circuit breaker with a newer replacement model. Sometimes the rattling is from the metal arc dividers in the circuit breaker arc chutes. Either way, it is not a noise you want to hear. Check the load. If that is not the problem, change the circuit breaker. Safely.
Archive for August, 2011
August 12th, 2011 1 comment
Categories: Uncategorized 400 Amp Molded Case Circuit Breaker, arc chutes, circuit breakers, Feeder Cables, General Electric Breakers, Noisy Circuit Breaker, Over Current Device, replace circuit breakers, replacement circuit breakers, Retrofit Circuit Breakers, Square D Breakers, Westinghouse Circuit Breaker