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michaelson 09-16-2012 01:30 PM

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?

gregzoll 09-16-2012 01:51 PM

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.

rjniles 09-16-2012 02:46 PM

Quote:

Originally Posted by gregzoll (Post 1011038)
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.

gregzoll 09-16-2012 02:55 PM

Quote:

Originally Posted by rjniles (Post 1011060)
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.

stickboy1375 09-16-2012 02:57 PM

Quote:

Originally Posted by rjniles (Post 1011060)
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...

Speedy Petey 09-16-2012 04:15 PM

Can anyone say FPE? :whistling2:

gregzoll 09-16-2012 04:45 PM

Quote:

Originally Posted by Speedy Petey (Post 1011089)
Can anyone say FPE? :whistling2:

Can anyone say Thermal Runaway. Would have nothing to do with FPE, more with Thermal Runaway.

Speedy Petey 09-16-2012 04:51 PM

My point was FPE's are notorious for not tripping under a bolted fault.

michaelson 09-16-2012 05:19 PM

What's FPE?

bernie963 09-16-2012 05:34 PM

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

brric 09-16-2012 05:34 PM

Quote:

Originally Posted by Speedy Petey (Post 1011109)
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.:huh:

gregzoll 09-16-2012 05:41 PM

Quote:

Originally Posted by Speedy Petey (Post 1011109)
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.

Speedy Petey 09-16-2012 05:45 PM

Quote:

Originally Posted by gregzoll (Post 1011143)
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.

electures 09-16-2012 05:47 PM

Quote:

Originally Posted by Speedy Petey
Can anyone say FPE? :whistling2:

Or Zinsco. Have seen a 15a hold and the 200a blow. Curious to know what make breaker panel.

gregzoll 09-16-2012 05:49 PM

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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