Sparks from bare wire on disconnected circuit?

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Old 06-09-10, 07:47 PM
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Sparks from bare wire on disconnected circuit?

I've been working on renovating my basement. It was on a single circuit breaker, which I of course "broke" before getting started. It's been that way ever since.

When I was first removing some old outlets, there was a loud spark on one of them. I confirmed there was no power being fed to this wire, both before and after. So I didn't think much of it.

Now a couple of weeks later, that same wire is hanging bare, not connected to the circuit breaker panel at all as best I can tell. I've confirmed it's not live, just in case there's a hidden feed somewhere. But when my g/f went down there for some laundry, she made the wire move, and it sparked, once for her, and once again for me when I went down to see. Still no power in there it seems. I just touched it this time, maybe I'll take a meter to it to double check.

In all cases I check that other outlets/lights on the same wiring path are indeed dead.

The first time, the wire was obviously wired into outlet boxes. The second time it was lying on the ground.

The first time I shrugged it off as possible static electricity, but now I'm not so sure.

For now I've elevated it, and wrapped it some electrical tape, and made sure the two normally-live ends will remain far apart from each other.

Presuming I am indeed correct and there is no power to that wiring (I'm quite confident about this), what might be causing this? Should I be concerned?

My first post here, and a new home owner looking to work on his house! Look forward to participating in the community!

Thanks,
J.F.
 
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Old 06-09-10, 08:08 PM
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Yes, you should be concerned. You likely have two cables going to that box and the whites are not hooked together. The sparks you are seeing is because there is a load on the neutral wire. When they touch (or touch a ground) there will be a spark. There is something not working in the home, you just haven't found it yet. If you take a meter from one white to the other I bet you will see 120 volts.
 
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Old 06-09-10, 08:23 PM
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Strange, because I'm pretty darn sure there's NO power to any of that circuit, I've completely removed the feed from the breaker panel, and I've followed and accounted for every wire!

But yeah, the energy for that spark has to be coming from somewhere.

I'll open up the other end of that wire to see what it looks like in that box. It's a box with 2 switches and 1 GFCI outlet (in the basement bathroom).

Thanks!
 
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Old 06-09-10, 08:28 PM
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You disconnected the hot but not the neutral in the panel. The circuit may be a multiwire circuit where two hots share one neutral so the neutral may still have a load on it.
 
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Old 06-09-10, 08:41 PM
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Actually I removed the power by completely disconnecting the wire that was bringing the power in to the bathroom, a couple of outlets, and a couple of lights in the hall.

I've traced every wire on the basement circuit, and where it goes and what it does (except for one that goes into the wall upstairs, but that'd be the wire to the light switch at the top of the basement stairs).

I actually disconnected the supply by taking a junction box apart, which is where the power was coming from. I'm pretty sure there is no white, black, or ground connected to anything that might be a source of power of any kind. I basically cut the previous circuit layout in half. The wire coming out of the circuit breaker box is also just sitting there bare ended, but it hasn't misbehaved at all.

But I can always be wrong, like you said, it's gotta come from somewhere. I'll open that box that basically acts as a "junction box" (2 light switches for the bathroom lights, 1 GFCI, and also used to feed 3 other outlet pairs!). Seems like a lot of things going through that one point ...
 
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Old 06-10-10, 01:59 PM
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A static or induced charge might cause a tiny little spark once... one of those sparks that unless you were looking at it really closely you wouldn't even notice it.

If it's any more of a spark than that, you're dealing with 'real' voltage. It could be a connected neutral as others have said, or possibly somehow fed through another light fixture, providing less than 120v, but more than you'd want to touch.

This is where the NEC rule about finding the other end of the wire and not only disconnect it, but cut it and push it out of the box so there's no possible way of it being re-hooked up.

It could also be on a switch leg, which is why it's intermittent.
 
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Old 06-10-10, 02:07 PM
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Thanks, I'll look at it.

So all these situations you guys describe would not result in my noticing current in the wires? at one point I grabbed hold of the white and black firmly in my fingers ... nothing. Never tried with the ground mind you.

When I was undoing the outlets that first time and got a loud spark, I then went on to work on the wire without ever feeling a jolt or noticing anything abnormal.

But then I tend to be careful about the whole thing in general, keeping wires separate, even if I know they're disconnected, maybe I was lucky to not get the 2 bits that matter near each other? Seems unlikely ... but possible.

Anyway, the message is clear, there's some juice flowing somewhere as of yet unidentified, where it shouldn't. I shall track it down.
 
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Old 06-28-10, 05:50 PM
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So I took one of those live wire detectors to the cable in question, and it didn't beep. I also plugged in a tester in the outlets attached to the same circuit and nothing showed (with the CB off).

This tester does seem to report on improper wiring though (based on the lights on it) ... could I power the circuit, plug in the tester, and see if anything abnormal shows up?

Thanks again!
 
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Old 06-28-10, 07:23 PM
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Originally Posted by Tolyn Ironhand View Post
You disconnected the hot but not the neutral in the panel. The circuit may be a multiwire circuit where two hots share one neutral so the neutral may still have a load on it.
There might be two hots sharing the neutral. In this case part of the circuit can appear to be be dead while the other part still functions. Can you tell if this cable has both a red and a black along with the white and ground?
 
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Old 06-28-10, 08:32 PM
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No, just white, black and ground.

But ... I seem ot have somewhat figured it out.

Turns out there was another circuit! and the cabling goes through the one box. And the feed for the other circuit comes out of an outlet box that is supposed to be alone (the washing machine).

Noticed that because today I ran the tester again, and it was registering as live! So I tracked it down and figured out.

I'm still confused as to how it registered as dead last time, since I never knew about that other circuit breaker until then.

Anyways, I opened the box in question, took out the wiring (not needed anymore) and made sure everything was "clean" in there. The only thing I saw is that they all shared the same ground ... there was no obvious "cross-contamination" between the circuits (except for the ground ...).

The symptoms are still not *fully* explained, since I always ever only popped the one CB, I don't know how the wire in question 9which it turns out was on another circuit) was showing dead. Maybe the CB had popped and I never noticed ... that may very well be ...
 
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