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So, our house just suffered an electrical fire...

7K views 34 replies 16 participants last post by  Missouri Bound 
#1 · (Edited)
...and now we're putting all the pieces of the puzzle together, working backwards to determine a root cause. This is a pretty good example of what you should never work on electrical by yourself without knowing exactly what you're doing. I could use some help in identifying some issues from the pros here.









Met with the Fire Inspector today, who was extremely knowledgable. He focused on one junction in particular with at least two circuits feeding through it and some serious code violations. I know that nothing learned here will have bearing on the report he submits to the insurance company. However, I'd like to know if there are major code violations here or if I'm just overreacting as a result of the accident. Take a look:









In the junction box, I noted that there's no cover. Cellulose insulation is a factor, as the box was completely covered over, and insulation has worked it way down into the box. Box fill limits appear to have been exceeded. Connections appear to be made questionably, but can't say for sure without touching.

A 220v 600v romex line exits the junction, but I can't identify a 220v line entering. Is it possible they took a two 110v lines from different legs, joined the neutrals, and hacked it together?

Three separately insulated black 12g lines exit the box (the ones that are twisted), piled up in a rats next on top of the drywall, then proceed down into the fiberglass and cellulose to somewhere we can't identify without digging in. Fire investigator has never seen this before. Obviously not K&T, as this house is 30-40 years too modern and this conversion is probably 20 years newer than that. What could this be?
 
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#5 ·
And that's just the start of that mess.

This is kind a rare occurrence, but it does happen often enough. Especially considering how many messes like that I encounter...and that's just lil' old me.
 
#6 ·
If there were two separate 120 circuits entering a metal box at different knockouts and the two hots were used as a 240 circuit, there would be inductive heating of the box.

There is no limit as to how hot it can get, inductive furnaces melt iron using this principal.

The insulation makes this scenario even worse; the heat has nowhere to go.

Could be the cause, maybe not.

Rob
 
#7 ·
To me, it doesn't look like the JBox was the cause. I'm not a fire investigator, but I would expect the wires in the box to be much more damaged if the fire started there. If I were to guess by looking at the pictures, I would say that the fire started somewhere under that access hole. Maybe the wire was damaged there when stapling or rodents chewing, then the wire arced and lit the insulation. Again, the same could be said about the J-Box, but I wouldn't expect the wood under the JBox to look as bad as it does and the wire look as good as it does.
 
#9 ·
I tend to agree with this but would like to see a picture of the inside of the jbox. The visible connections are not the cause as they not even burnt up.

There is no problem with a junction box being buried in insulation but it must have cover like all junction boxes.
 
#8 ·
if there were two separate 120 circuits entering a metal box at different knockouts and the two hots were used as a 240 circuit, there would be inductive heating of the box.
huh??
 
#23 ·
In an AC system, if one current carrying conductor passes through a hole in a metal box and the return path is through another hole in the same metal box, the metal between the two conductors will heat up because of induction.

The same thing would happen if one conductor was installed in a metal raceway and its return was installed in another metal raceway.

This is the principal on which a clamp-on ammeter works. If the jaws are clamped around all wires, no current will be read because the induction is cancelled out. If the jaws are clamped around one wire, current can be read because induction is present.

This is addressed in the NEC; 300.20 which basically states that all phase conductors and the neutral of any given circuit need to be grouped together and pass through the same hole of a metal enclosure, or a slot cut between the two holes.

I've never seen a fire because of this but I have seen the paint burned off of a metal box between two holes.

Rob
 
#16 ·
Does that J-box appear to be missing clamps?
Nothing specifically to do with this fire, but I noticed that in a few spots my electrician used those black plastic "clamps" for NM in metal boxes. I'm guessing that a fire in a junction box that they are used on would make short work of them--they don't seem like they're terribly robust.
 
#12 · (Edited)
I do have an above shot, but it's taken with an iPhone which makes uploading it without a PC difficult. Regardless, the wire nuts are not melted.

Investigator didn't find signs of arcing, but finds the three twisted separately insulated 12g wires suspicious. They are bare where they enter/exit the box. He used the term pyratic... something (sorry). Also looks like its not the first time the beam has been burnt!

If the insurance company accepts his preliminary, the story ends here, we engineer a new beam solution, and start repairs. If they think they can recover from somebody (previous owner, inspector, electrician, manufacturer?) then they'll bring in an electrical engineer to check it out a bit more.

Yes, I was home (used a day off). Around 2am. I smelled it, then found the paint blistering off the ceiling. We even did most of the extinguishing. Nobody hurt, thankfully.
 
#13 ·
Where the joist has been burned away is where the highest heat/longest burning was but that may not be the exact point of origin. With so much damage it's hard to tell what started the fire. But you can eliminate areas by looking for intact insulation on the wires.

One code violation I see is 2x4 joists and rafters. If they skimped there, there's no telling where else they skimped.

Is your panel fuses or breakers? If they are fuses, you don't by any chance have one of those fuse panels with all 30A fuses in it, do you?
 
#22 ·
Yeah, I know they are standard... but what I was saying was that the apparent absence of a clamp after a major fire event could just indicate that the plastic clamp was burned away.

To clutchcargo, you know, the more I think about it, the more I believe that if it were a matter of a clamp being missing and the wire chaffing, you'd see some of the copper conductor missing a chunk due to it vaporizing when the arc occurred... so if that is present, you'd know you at least had an arc there--whether or not that was the CAUSE of the fire, or occurred as a symptom of the fire (i.e. it was the first energized conductor that had it's insulation melted off, and thus arc'd after the fire started) would not be clear.
 
#28 ·
zappa said:
I believe that most of this damage took place over a long period of time with the junction box being the hot spot. Ever have any buring smells that you could never find?

I hope you can let us know where those twisted singles are going. It seems like someone had a bunch of wire laying around and tripled them up instead of using larger gauge wire.
I hope I can too. Only burning smells a few hours before. Smelled of mesquite, so I thought a neighbor was smoking meat.

If the insurance company doesn't want an electrical engineer, we can probably start ripping it out shortly. Otherwise, it'll be a week wait or more for one to come out before I can touch anything.

Will open up whatever wall it runs into. Not going to risk missing anything else.
 
#30 ·
zappa said:
That sounds like a good plan. Ignore my twisted singles comment. Looking closer it appears to be melted Romex.
Its not Romex. Indeed single wires. Thought they were coax at first and was ignoring them but they definitely enters the box and are too thick to be Romex. The copper is about 12g. Didn't see any text on them at all.

You can see lots of it hanging in other images. And its only twisted for the first 6", after that just a huge rats nest of wire.
 
#31 ·
If there is some way to determine if the heat flow in the wire insulation was from outside in or from the inside out, uniformly heated from excessive current or local heating from a bad connection, you may have some clues as to the source, and some clues as to what was not the source.

Plastics/polymers people knowledgeable with PVC and whatnot would know this kind of thing.

Also, heating from electrical causes vs. heating from an open flame may leave a different signature on the insulation.
This is forensics in the extreme.
 
#32 ·
The fire investigator could visually tell from the insulation on modern Romex if it burned from the inside out o from the outside in. He could also tell when insulation had baked off instead of burned. He didn't explain how he could tell, unfortunately.

He said arcing leaves pit marks, like an arc welder on iron and will usually heat wires enough to fuse them at that location as well.

He could also tell tons of things about the fire by the burn mark shapes and colors on the wood that were way above my head.
 
#34 ·
"He used the term pyratic... something (sorry). Also looks like its not the first time the beam has been burnt!"

The word is pyrolysis which causes the properties of the wood to be altered. Through repeated heating and cooling of the wood the ignition temperature of the wood becomes lower than normal which allows it to be ignited at lower than normal ignition temperatures. It often happens with low temperature heat over a long period of time. That alone isn't what causes the fire but when several pieces of the ignition sequence come together at just the right moment in time you can have ignition and a fire.
 
#35 ·
"He used the term pyratic... something (sorry). Also looks like its not the first time the beam has been burnt!"

The word is pyrolysis which causes the properties of the wood to be altered. Through repeated heating and cooling of the wood the ignition temperature of the wood becomes lower than normal which allows it to be ignited at lower than normal ignition temperatures. It often happens with low temperature heat over a long period of time. That alone isn't what causes the fire but when several pieces of the ignition sequence come together at just the right moment in time you can have ignition and a fire.
Very well explained. This happens very frequently around the stovepipe of a furnace when the clearance is not adequate and the wrong pipe is used. I friend of mine lost his house to this exact cause.
 
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