Circuit breakers

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Old 05-29-06, 02:45 PM
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Circuit breakers

My neighbor had a scary situation today. A lamp cord got stuck in his vacuum cleaner wheels and it ripped the insulation off the cord. His wife didn't get a shock but the scary part was that the cord shorted and melted. So did the outlet cover. He ended up calling the FD afraid that there might be fire in his walls. The breaker did not trip. The overload was probably several minutes before he manually opened the breaker.
That got me thinking about circuit breakers. We all depend on them to protect us - in some cases from our own stupidity - but they just sit in our service panels, sometimes for years without ever being operated and never being tested. They are mechanical devices, often exposed to harsh environments yet there is no way to test them, no way to inspect their internals, and no maintenance on them.
Anyone know what the manufacturer's warrantee is on a typical residential breaker? How about after it has overload tripped. Will it trip at the same sustained overload time and again?
 
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Old 05-29-06, 03:00 PM
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First one has to realize that the common breaker is designed to trip under two different conditions.
1. current overload
2. short circuit (which may seem like current overload. it is but a different situaion.

under current o'load, a breaker is a thermal device. It requires a certain amount of heat build up to make the brreaker trip. Most breakers will carry more than the rated current for a period of time. A 20 amp breaker will often carry 20-25 amps for a long period of time. Over and hour is not totally unusual. It is a matter of heat build up. The greater the heat build up, the sooner it will trip. This makes the time and/or point of trip an in-exact point. I have also had breakers that were only 60- 80% loaded setting next to several other breakers that were a similarly loaded and producing copiuos amounts of heat. This caused some of them to trip while obviously below rating. Even when replaced with new breakers, it would continue. Simple fix; re-arrange the breakers to seperate the heat producers and all is fine.

A perfect examplle of this is a breaker used for HID lighting. They can get toasty even withought being taxed to their limit.

under short circuit conditions, a breaker requires many times the rating to make it trip "instantaneously". I can't give you the exact specs but I had a 250 amp breaker that had adjustable trip. The minimum setting was 1250 amps and the max. 2250. That is 5 to 9 times rating.

Another thing that most people NEVER do is exercise their breakers. They should be manually be switched on and off several times every year to do this. This is a manuf. recommended procedure. (at least as related to me)

Now you ask of warranty. Again, this is what was related to me;
If a breaker is tripped by a short circuit, it is no longer warranted and is to be replaced. It would seem the manuf. understand that damage can occur and should not be trusted after this point.
 
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Old 05-29-06, 04:21 PM
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Wayne, were the breakers "Federal Pacific" or "Zinsco" brand?
 
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Old 05-29-06, 06:56 PM
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I'm betting GE Nevertrips
 
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