my electrical box EXPLODED!!!

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I was in the process of rewiring over 60% of my house and finally all rewiring are done. Yesterday was the finishing aspect for the electricians to do an electrical panel schedule - I have two separate panels A & B and they needed to mark all the circuit breakers existing and new as well as mark on each box/device which panel/circuit they belong to.
So as we were labeling one of the junction boxes were opened with some old wires in them, they had it all "stretched out" in order to figure out which wire goes where.
When one of the walked by the hallway where the box is with wire sticking out, he brushed his shoulder against some wires and suddenly BOOM!!! I heard a small explosion. The junction box is now partially black and this is what he called a "home run" connecting wire to the panel and running to another box.
The wires in the box "appears" to be ok to me. The electrician told me I should consider changing all "old wires" since they are old (1972) and may be the cause of the problem.
Replacing ALL old wires are cost prohibitive. What is the best way to determine why I had an explosion? I cannot see a wire being messed up as a result of the explosion...
and I could not tell if he said it just for me to hire him for another few weeks.
Thanks,
MC
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MiamiCuse wrote: ...

There must be an arc mark on the wire where it came in contact w/ the panel to cause the short to determine where the problem came from.
The root cause could have been anything from an exposed end, a nicked spot from previous work or a break from having become brittle either by age or perhaps some overheating w/ time.
I'd examine several of the old wires and see if there are any signs of cracking and whether the insulation does break w/ flexing and whether it is hard and breaks when stripped.
If these guy(s) are reputable (as one would assume they would be since you hired them based on qualifications and reputation, right? :) ), you're paying for advice as well as service.
The additional cost of rewiring would be minor in comparison to the cost of a fire later, though. The age you're talking isn't _that_ long, but w/ as much as you're investing already, cutting corners here isn't real smart, either. It's a tough call remotely...I have no "up/down" call here, only to not make the decision purely on trying to save a buck but on what seems the right thing based on what you can determine.
There's always the outside consultation of another electrician not associated w/ these contractors route if you're uncertain...
--
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Thanks, I guess my uncertainty came from the fact that it happened at 5pm yesterday and close to the end of the day, I would expect them to at least investigate which wire caused the problem and then offer an informed recommendation.
But he just glanced at it and said "these are old wires they do things like this if it were my house I will rewire all old wires just to be sure..." I mean this new wiring lasted about several weeks and part of what they told me they would do is to replace old questionable wires as they go, but they never did and now at the end of this they recommend that I replace ALL old wires because of this, so why didn't they recommend this along the way?
May be I need to hire another electrician for a second opinion. The problem is the answer to "should I rewire all my old wires" is probably going to be "of course new wires will be better than old wires" and "I cannot tell you unless I pull them all out..."
MC
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MiamiCuse wrote: ...

I'd not put too much into the first off-the-cuff comment--as you say, it's more reaction than analysis.
I'd definitely go inspect the wiring myself -- one should be able to tell where the arc happened and perhaps see why as noted.
If the insulation is extremely brittle (cracks simply w/ a bend, for example) that's pretty self-determinant that it's a potential problem down the road. Then you can have the discussion of why they didn't do what they said.
The hard part is if it isn't so clear-cut as it probably will be...I'd still do the investigation and at least know whether I thought it was a fluke, something as clearly expected because an exposed end did contact the panel or an obvious nick that was mechanically caused, or the insulation does actually crack/break easily. If it's a clear cause, you can probably relax. If it's clearly that the insulation is failing, well, it's only money. If it's in between, again, you're needing a decision that nobody here can really help...
That's repeating the same answer in different (or sometimes the same, even) words, I know... :)
--
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dpb wrote: ...

The one thing (obvious, probably, but...) is if you're not sure and they're still saying "replace", ask them/him to show you what, specifically, it is he sees that indicates to him it needs replacing.
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I examined the wires in that box closely, and I did not see any exposed copper at all, which is troubling. What is even more troubling is that there is no wire that is charred, only the box.
Of course, there are three boxes near to each other, one box on the left, one box on the right connected with a box coupling, then behind the box on the right is another box facing the other side of that same wall, so those are three walls with wires running into out of each...120v, 220v both. I will take another look at it again tomorrow.
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MiamiCuse wrote: ...

I wouldn't expect "charring" from a momentary arcing but there's definitely something in the vicinity that could have touched at the point indicated on the box.
Not being able to see it, no real specific ideas but is it possible the electrician was carrying something (like a roll of wire) and it brushed a hot point rather than it being the wire in the box at all?
--
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Well I looked and looked and could not find the wire that is responsible. I expected one wire that has the copper part exposed but after looking very closely I was unable to identify anything. Here is a pic:
http://i173.photobucket.com/albums/w67/143house/garage/P1020195.jpg
The box to the right, on the upper left corner see the blackened area? That was caused by the spark. A closer look:
http://i173.photobucket.com/albums/w67/143house/garage/P1020196.jpg
I examined each wire there, and did not see anything. Is it possible the exposed wire is actually inside the pipe behind the box and when pulled caused the spark?
Thanks,
MC
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Anything is possible..it looks if the black wire has been "burned". What I'd do is shut off the power, then remove the right hand box and all it's conduit connections and the box also. You'll get a lot better look at the wires that way.
Can you access the wires at the "other end" of that conduit coming from the back of the box ? You might be able to get some "slack" so you could pull them out a couple of inches to better inspect them.
Make notes to go with your digital pic to ensure you get it all back together correctly
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MiamiCuse wrote:

upper far right conduit, assuming those head upstream toward the incoming power. the charring looks like that is where the arc was. A nick or fatigue crack in the insulation being opened by the wire flexing would do it. Do those conduit ends have any sort of bushing on them? With the power off, stick your finger in there and feel for burrs. They were working the box with a hot feed coming in to it?
When I replaced the outlets in this place, several boxes had minute stripping-knife nicks in the leads, from where the last guy had cut away the outer sheath of the romex. They showed up as copper glints under my flashlight. Luckily, they weren't deep, and a little electrical tape solved the problem.
-- aem sends...
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MiamiCuse wrote: ...

Well, from just looking my first suspect point would be the red/black/white set coming from the upper right across to the other box. It looks like they have been pulled tight leaving no slack at all and are possibly rubbing against the connector. I can't tell for sure even where they're going--they're hidden behind the other bundle too much to trace.
I don't think in that configuration you can see enough to tell.
It does look to me like all three there show signs of heat--particularly the white, of course. Don't know where they're coming from, but I'd be for getting some slack in there so could really tell--just don't think it's possible as is.
It also looks like there could be a potential problem brewing at the upper right where they come into the box--they're pulled tight at that corner, too.
I'd say the other potential culprit might be the yellow going out.
I'd surely like to have known what was actually going on when it occurred--I still can't rule out from the looks of it that a hot end from somewhere else entirely got flipped across there from the way it looks--
I agree you have a problem that needs investigation to unravel what happened--I don't think the whole house wiring would need redone but I'd surely be doing some fairly major effort to get enough slack in that box to investigate it and to leave some slack in that one set that don't have enough.
It's useful to see the picture, but certainly not conclusive other than there definitely was an event at that point.
--
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dpb wrote: ...

As a solution, one might at least consider pulling the branch circuits from the two upper entrances at this end and making new runs from here to the next box. Depending on where they're going, that might not be particularly difficult or expensive.
As noted, I do not at all like that cross-box pull that certainly appears in the picture to have been pulled really tight (unless, of course, it's been pulled on only temporarily for some reason during the rework, perhaps, but if so, it needs the slack back). If it really is as tight as it looks and there is no slack while I was in major rework I'd surely consider it a candidate for a new run to forestall a problem. Depending on what I saw w/ "hands on", I might be satisfied w/ a non-metallic bushing to protect the insulation on the corners if inspection indicated it isn't damaged already.
--
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dpb wrote:

I'm delaying some office work and that is delaying mowing... :)
I looked at the wider-view picture again...that was actually quite a spark it seems when I realize the marking covers the full quadrant essentially.
It is, however, essentially symmetric around the SE of the conduit and also seems as though there's a concentrated mark on the NW edge of the center knockout plug. Behind that section is where it happened almost certainly imo, now. Notice how it appears to be evenly spread behind the wires and the clean spot where the red protected the surface and looks as though it has been moved in your investigating. The discoloration of the three wires there is telling too, I think. Will it come off? The white certainly seems to show a couple of at least knicks although don't look to be serious kinda' looks like been handled w/ pliers or pushed on w/ screwdriver or similar abuse...
I'm still thinking you're going to have to have more slack to be able to see what's behind there than can as it is in order to find the actual point unless, as I keep harping on, it was a bare hot end from somewhere else that just got lucky and hit the connector/box at that area.
Did it trip a breaker? That would give a circuit, too.
My prime suspect is still that diagonal run through although I can't get past the idea of the electrician holding a hot end...
This will be most interesting when you do finally track it down...
--
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Thanks dpb for all your comments. I am going there tomorrow again to untangle the boxes and see if I can get some slack in the wires in order to see what I needed to see. I will report back with good news hopefully or bad news.
Now go mow your lawn!
MC
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OK repair is done. You are right dpb, the spark came from an old wire going to the conduit in the back of the box, it was a solid wire going to a well pump, and as I loosen and untangle all the wires it literally broke off.
I believe my electrician when he tried to figure out which wire goes where, he used the "pull" technique to pull a wire hard and see which wire moves on the other end, and that caused a big strain on some wires, especially with that conduit having so many wires going through,
So here is the box taken apart we can see the charring:
http://i173.photobucket.com/albums/w67/143house/garage/P1020223.jpg
and the connector around that hole see it's totally broken by the spark:
http://i173.photobucket.com/albums/w67/143house/garage/P1020222.jpg
and now, I have two new boxes, with two connectors between the boxes instead of one and there are more slack to the wires.
http://i173.photobucket.com/albums/w67/143house/garage/P1020224.jpg
Thanks for all your help dpb.
MC
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MiamiCuse wrote: ...

It pretty much had to be there based on the markings -- that chunk it vaporized out of the connector was a pretty good hit...bigger than I expected, even.
But, all's well (so to speak :) ) that ends well and there's no mystery in the end (and old wires _don't_ just do that :( ).
--
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I concur with dpb. 1972 wires are not that old. There are plenty of houses wired in the 40's and 50's that are still using the original wiring. One of the hot wires may have had the insulation nicked and by moving it the exposed copper may have shorted to ground. You should take a look yourself with a magnifying glass and a flashlight. Look at the individual wires and try to determine at what point along the wire did it short out. Was it close to where it entered the box or at the end of the wire? Did it short to the box, the neutral, another hot wire, or to a ground wire? You should also check to see how pliable the insulation is on all of the wires. If the insulation is brittle and cracks or breaks off, then you should consider having that circuit replaced.
I am assuming that your house has copper wiring and not aluminum. Aluminum conductors can easily break after bending a few times.
If the wire shorted out close to where it enters into the box, the conductor may have been damaged to the point where copper may arced off of it and there is not enough slack to strip it back to splice further down. It is remotely possible that there may be slack in the wall that can be pulled into the box, but the clamp or connector will need to be loosened and staples may have to be removed which will involve making a hole in the wall.
What brand of circuit breakers are you using?
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Circuit breakers are all GE.
I cannot see the nick, but I will take a closer look tomorrow with a flash light as you suggested. Thanks.
I have twisted, bent those wires myself, does not look like there is any danger of breaking off.
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It seems to be broken.
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MiamiCuse wrote:

MAY be the problem? A several-thousand dollar renovation for something that MAY be a problem?
What if you run all new wires and the boxes STILL explode? What if it turns out that a twenty-five cent mousetrap would keep the critters from gnawing the insulation?
No, find out the CAUSE before you invest in an expensive cure.
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