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
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
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...
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
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..."
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... :)
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.
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.
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?
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:
The box to the right, on the upper left corner see the blackened area? That
was caused by the spark. A closer look:
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?
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
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.
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
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
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
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
It's useful to see the picture, but certainly not conclusive other than
there definitely was an event at that point.
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.
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
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...
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
Now go mow your lawn!
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:
and the connector around that hole see it's totally broken by the spark:
and now, I have two new boxes, with two connectors between the boxes instead
of one and there are more slack to the wires.
Thanks for all your help dpb.
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
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 :( ).
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?
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.
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
No, find out the CAUSE before you invest in an expensive cure.
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