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Old 09-16-2012, 01:30 PM   #1
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Breaker Failure


Yesterday I accidentally closed a door on an extension cord. The insulation got damaged and it started sparking. The lights got very dim for several seconds and then the main breaker cut off the power to the entire house. I removed the offending cord and reset the main breaker.

I'm wondering why the breaker to the room wouldn't have blown first (or in addition). Does anyone know?
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Old 09-16-2012, 01:51 PM   #2
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Breaker Failure


The breaker on the circuit did not trip, because of the type of short you had on the circuit. It was low enough to not trigger the mechanism to trip, but long enough that it caused the Main breaker for that leg to sense that there was enough over current flowing to trip the larger protector of the panel.

Just feel lucky, otherwise you would have burnt the whole structure down, if it also had failed at the main breaker protection device.
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Old 09-16-2012, 02:46 PM   #3
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Breaker Failure


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Originally Posted by gregzoll View Post
The breaker on the circuit did not trip, because of the type of short you had on the circuit. It was low enough to not trigger the mechanism to trip, but long enough that it caused the Main breaker for that leg to sense that there was enough over current flowing to trip the larger protector of the panel.
Huh?

I would suspect the branch circuit breaker is bad and change it as a precaution.
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Old 09-16-2012, 02:55 PM   #4
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Breaker Failure


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Huh?

I would suspect the branch circuit breaker is bad and change it as a precaution.
Nope. Seen it happen with Shore power cable from our ship to the shore taps. We would have to physically throw the breaker, because the short would happen at a point, that it would heat the weak point in the jacket sheathing, but still not a high enough short, that it would cause a dead fault.

It is really cool at first when you see it, but a dangerous as hell situation if you let it create a run away situation. You also see this in the real world, when you have failure on POCO lines at the Ceramics. The line will arc and spark, either until a lineman goes out there to throw the switch to kill the line, or it burns itself up causing the line to fail at the arc point.
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Old 09-16-2012, 02:57 PM   #5
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Breaker Failure


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Huh?

I would suspect the branch circuit breaker is bad and change it as a precaution.
I've seen entire buildings taken out because someone shorted out a light fixture...
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Old 09-16-2012, 04:15 PM   #6
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Breaker Failure


Can anyone say FPE?
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Old 09-16-2012, 04:45 PM   #7
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Breaker Failure


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Can anyone say FPE?
Can anyone say Thermal Runaway. Would have nothing to do with FPE, more with Thermal Runaway.
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Old 09-16-2012, 04:51 PM   #8
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Breaker Failure


My point was FPE's are notorious for not tripping under a bolted fault.
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Old 09-16-2012, 05:19 PM   #9
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Breaker Failure


What's FPE?
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Old 09-16-2012, 05:34 PM   #10
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Breaker Failure


What brand of breakers do you have? FPE is an older brand which was known for not tripping under certain conditions. FPE was
federal Pacific Electric Co.
























electric
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Old 09-16-2012, 05:34 PM   #11
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Breaker Failure


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My point was FPE's are notorious for not tripping under a bolted fault.
I know what a bolted fault is but I don't know what a dead fault is.
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Old 09-16-2012, 05:41 PM   #12
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Breaker Failure


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My point was FPE's are notorious for not tripping under a bolted fault.
Assume much. Nothing was stated by the OP as this being a issue with a FPE panel. It does have a lot to do with Thermal Runaway, which the OP experienced.
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Old 09-16-2012, 05:45 PM   #13
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Breaker Failure


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Assume much. Nothing was stated by the OP as this being a issue with a FPE panel.
I was not assuming anything Greg. I was simply offering an option. I've seen it happen a thousand times.
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Old 09-16-2012, 05:47 PM   #14
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Breaker Failure


Quote:
Originally Posted by Speedy Petey
Can anyone say FPE?
Or Zinsco. Have seen a 15a hold and the 200a blow. Curious to know what make breaker panel.
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Old 09-16-2012, 05:49 PM   #15
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Breaker Failure


For the OP http://search.yahoo.com/r/_ylt=A0oGd...r%2520safe.pdf Read through this pdf, it kind of explains the differences between Arc Fault & Bolted Fault.

Basically if it was a Arc Fault, the first line of protection, being the Branch Circuit breaker should have tripped first. Due to the nature of the fault, it basically took "Thermal Runaway", due to having a "Bolted" fault, which took longer and was lower than the tripping fail of the breaker mechanism for the first line, the second line being the Main breaker, did its job by finally failing and closing like it should, but not until the damage was done from the first breaker to where you caused the fault.
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