Auto resetting circuit breakers.
Submitted: Tuesday, Feb 01, 2005 at 10:19
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Austravel
Hi, any idea how they work are they bimetalic or...?? If there is a dead short I'm guessing they will just remain open constantly.
Reply By: Member - Ross P (NSW) - Tuesday, Feb 01, 2005 at 12:31
Tuesday, Feb 01, 2005 at 12:31
I have a resettable circuit breaker mounted on the fire wall. During a recent trip in which I experienced overheating problems I noticed that the CB had tripped. I couldn't manually reset it. After checking the wiring and appliances connected to the circuit I determined the CB was at fault. I have fuses in the line as
well so as "work around" I by-passed the CB. In the morning I could rest the switch and it has worked fine ever since.
Moral of the story is keep the CBs as far as possible away from heat sources.
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Follow Up By: Austravel - Tuesday, Feb 01, 2005 at 12:55
Tuesday, Feb 01, 2005 at 12:55
Thanks for
the tip never thought about that.
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Reply By: drivesafe - Tuesday, Feb 01, 2005 at 17:26
Tuesday, Feb 01, 2005 at 17:26
Hi Austravel, a little warning about using auto reset Circuit Breakers.
If you decide to use them, you would be
well advised to use cable that is at least twice the current rating of the CB.
The problem with auto reset CBs is that if a short circuit occurs, current passing through the CB not only causes the circuit breaker to heat up but the cable also heats up. The circuit breaker goes open circuit and cools down. At this point, the cable also cools down but because the copper in the cable is insulated by plastic which is there to insulate the copper from the outside world, but in this case the insulation works in reverse and keeps the heat in.
As soon as the circuit breaker cools down enough it goes close circuit and both the circuit breaker and the cable heat up again only the cable is still hot from the last short and just gets hotter. Eventually the cable’s heat gets to a temperature where the cable’s insulation ignites.
Using thicker cable has two advantages, because the cable is thicker it takes longer to heat up and the thicker cable allows a higher current to get to the circuit breaker so it trips quicker, this again reduces the heat up time on the cable.
Cheers
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