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Old 05-10-2016, 05:31 PM   #1
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Default Fire in the attic and breakers didn't trip.


My company installed an electrical panel 2 years ago at a home and last week we got a call from the owner. Something was smoking in the attic. By the time we got there the Fire Dept had been called....

Long story short an old bx cable blew a hole in the side of its armor and started the hole thing. Fortunately we did 0 work in attic. I'm just curious as to why the breaker didn't trip.. We are suppose to get a Siemens rep out to the job and an electrical engineer. I'm hoping they don't try to been the blame on us.
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Old 05-10-2016, 05:43 PM   #2
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Bx doesn't have a ground usually except for the sheathe itself and the little wire, if you guys did work below and back fed it and happened to interrupt that ground (ie plastic box or 4 square that wasn't grounded) they might try to pin it on you guys saying you broke the ground that would have caused the breaker to trip, if you didn't mess with the entire circuit you should be fine.

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Old 05-10-2016, 05:45 PM   #3
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The physics are obvious: the current flow never exceeded the OCPD's threshold.

Plan B, it's defective.

A tiny arc that gets a blaze going may not necessarily impose enough of a load to trip the c/b.

Bad make-up along that circuit path could mean that current flow is choked -- prior to the fire zone. So the current flow never trips the breaker -- while still being plenty enough to get a fire started.

( Electrical arcs have local temperature peaks of 5,000 degrees and more -- they are plasmas -- tiny versions of your friendly arc welder. So even a tiny spark// arc can beat any match -- especially in a dried out wooden attic with local temperatures past 100F. )

Defective breakers -- they're out there, too.

Take your pick.
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Old 05-10-2016, 05:48 PM   #4
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Please say it was on an arc fault breaker, I think that would make many electricians days around here

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Old 05-10-2016, 06:15 PM   #5
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Ha I wish it was an arc fault. I was just doing some poking around in the home. I looked at our old junction box we used for the new wires, can't seem to find anything. I wonder if there's somewhere that there could be a combo of 14 and 12 wire in the attic.


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Old 05-10-2016, 06:16 PM   #6
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Default Fire in the attic and breakers didn't trip.

Just makes me incredibly worried


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Old 05-10-2016, 06:44 PM   #7
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Like tesla said as long as the breaker was sized right it probably just fell in the gap and didn't cause the breaker to trip because it didn't pull enough. Even if it had all it would take is a split second flash between flash and trip that would cause the fire

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Old 05-10-2016, 10:19 PM   #8
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I have never seen an undamaged BX explode mid-cable, in 30 years in NYC (the world capital of BX), unless the armor was damaged (armor nicked with screw, etc.). I did see, once, a long run of old double-armored BX that did not have a drain wire in it get super hot under a short circuit condition at the far end of the run and not trip the fuse (you could actually follow the BX route beneath the ceiling below from the heat). Did the fire inspector identify the failure point on the cable? I have seen dozens of BX cables in attics spliced without boxes with no armor continuity. Most were poorly spliced, taped, no wire nuts, etc. and the connections had failed.
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Old 05-10-2016, 10:29 PM   #9
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He thought he was able to identify the source. He wasn't sure. If you ask me, I thought it was the aluminum cloth covered oven wire..... That seems to be the hottest spot in the attic... The BX cable seemed to be casualties because they were in the same area.... But, I'm not fire inspector
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Old 05-10-2016, 10:56 PM   #10
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Did the fire inspector note any open boxes, splices, etc? Unless some physical damage event occurred prior to the fire, electrical fires almost always start at connections, a failure of which could start a fire without tripping a circuit breaker. Did the homeowner turn on a large electrical load before the fire? There's no shortage of combustible materials in attics that can ignite from hot spots at connections. Unless the fire damage was total, he should have been able to note open boxes, splices, etc. Either way, if you didn't do any work in the attic, I wouldn't lose any sleep over it.
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Old 05-10-2016, 11:02 PM   #11
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Default what breaker

was it on a federal pacific breaker ?
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Old 05-10-2016, 11:04 PM   #12
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Quote:
Originally Posted by khfiei View Post
Did the fire inspector note any open boxes, splices, etc? Unless some physical damage event occurred prior to the fire, electrical fires almost always start at connections, a failure of which could start a fire without tripping a circuit breaker. Did the homeowner turn on a large electrical load before the fire? There's no shortage of combustible materials in attics that can ignite from hot spots at connections. Unless the fire damage was total, he should have been able to note open boxes, splices, etc. Either way, if you didn't do any work in the attic, I wouldn't lose any sleep over it.
There were no open J boxes in the attic. Either way, I'm curious.
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Old 05-10-2016, 11:05 PM   #13
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was it on a federal pacific breaker ?
It's a Siemens panel
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Old 05-11-2016, 11:51 AM   #14
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Default Seen many sparks without trip

I have seen many sparks without tripping the breaker, and it only takes 1 spark and the right conditions. I just had a kickback with my circular saw and cut the cord, sparks no trip.
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Old 05-11-2016, 02:35 PM   #15
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Kind of interesting the fire inspector said none of the breakers were tripped.... But all the breakers were or in the off position when he did his inspection. After I explained that to him, he felt like he needed to "investigate" more.


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Old 05-11-2016, 02:36 PM   #16
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BX cable does not have an EGC and its armor acts like a heating element.
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Old 05-11-2016, 02:38 PM   #17
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I have seen many sparks without tripping the breaker, and it only takes 1 spark and the right conditions. I just had a kickback with my circular saw and cut the cord, sparks no trip.

Breakers work on a time current curve. A short circuit must last long enough to trip a breaker, especially if its outside of a breakers magnetic trip curve.
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Old 05-11-2016, 02:38 PM   #18
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BX cable does not have an EGC and its armor acts like a heating element.


Why do you say that?
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Old 05-11-2016, 02:42 PM   #19
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Why do you say that?

Because BX does not have a bonding strip. All new AC cable comes with a bonding strip.
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Old 05-11-2016, 03:03 PM   #20
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Kind of interesting the fire inspector said none of the breakers were tripped.... But all the breakers were or in the off position when he did his inspection. After I explained that to him, he felt like he needed to "investigate" more.


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That part kinda got my attetion ...

Did anyone touch the breakers before the fire inspector have look the panel?

I am not too suprise if someone did turn all the breakers to off postion..

If that was a fuse it maybe easier to show the evince of it..

If they cant find out why breaker did not trip ..

I know series arc fault as other mention .. All just take one right spot to light up...

Majoty of breakers and useally most fuses will not catch series arc fault ..


Did any chance that house have gas line in attic ?

That some case it can cause it ..

Keep us posted if you find more info on this one..
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