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Old 06-23-2015, 09:55 PM   #1
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Smoking outlet and compromised copper


I was replacing an old outlet with a new one. Wired everything correctly, flipped the circuit back on and it popped immediately. An air conditioner was plugged in when I flipped the circuit on, so I figured that was a Bad Idea, unplugged it, checked the connections then flipped it again (with nothing plugged in except an outlet tester)

This time the outlet started smoking around the neutral terminal after about ten seconds, so I removed the outlet until further investigation.

The outlet tester didn't show any shorting, reversed wiring, etc.

Looks like the hot wire melted at a single point (see photos) and there seems to be a small compromise in the copper.

With that small ding in the copper, is the hot wire still good to use if I strip the insulation and replace it with heat shrink tube? I don't think there's enough slack behind the box to cut the wire and pull out three or four more inches, and I'm not familiar with BX wiring to replace the whole run.

As for the underlying problem, my guess is that the hot wire somehow came into contact with the metal box, which is grounded. Not sure how because there's plenty of room and I was careful with the wires. Any other potential hazards I should know about?

I should note that I wired four other outlets identical to this one without incident

Smoking outlet and compromised copper-imageuploadedbydiy-chat1435111394.610964.jpgSmoking outlet and compromised copper-imageuploadedbydiy-chat1435111417.740105.jpg
Smoking outlet and compromised copper-imageuploadedbydiy-chat1435112459.562432.jpg
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Old 06-23-2015, 10:53 PM   #2
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Cut out the damageg section,
Then use a pig tail to reconnect to outlet
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Old 06-24-2015, 12:32 AM   #3
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Better would to use the Ideal connectors that are best to use in this case. Otherwise, use a couple of layers of Heat Shrink for that nicked spot. I keep a box of the Ideal push on units for just this type of situation. Same as with Heat Shrink tubing, if the nick is too far back, to use the Ideal or Wago on it.



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Old 06-24-2015, 05:14 AM   #4
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Quote:
Originally Posted by bvac View Post
I was replacing an old outlet with a new one. Wired everything correctly
Obviously not, if it let the smoke out.

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Old 06-24-2015, 05:22 AM   #5
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Quote:
Originally Posted by bvac View Post
As for the underlying problem, my guess is that the hot wire somehow came into contact with the metal box....
I learned from an electrician pal to always wrap those wires in electrical tape. He takes the tape and just goes around the outlet a couple times before inserting it in the box.
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Old 06-24-2015, 06:58 AM   #6
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Slice the wire off right at the nick. Then do what you have to do (Wagos (tm), pigtails, etc.) to get everything reassembled.

It is not safe to leave the nick in the middle of the wire with or without shrink tubing over the nick. The compromised copper is a little thin at that spot and could overheat when the circuit is used to its maximum amperage.

You were unlucky enough to have two unfortunate events hit you at the same time (1) the insulation on the wire got chipped, (2) that very spot on the wire touched something adverse causing a short circuit.
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Heat went off in the dead of winter? Excellent idea to be late or absent for work and to spend the day winterizing your house to keep pipes from freezing. Every house is different. For those of you not hit yet, think of what things you need to do.

Last edited by AllanJ; 06-24-2015 at 07:05 AM.
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Old 06-24-2015, 07:56 AM   #7
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Quote:
Originally Posted by AllanJ View Post
Slice the wire off right at the nick. Then do what you have to do (Wagos (tm), pigtails, etc.) to get everything reassembled.

It is not safe to leave the nick in the middle of the wire with or without shrink tubing over the nick. The compromised copper is a little thin at that spot and could overheat when the circuit is used to its maximum amperage.

You were unlucky enough to have two unfortunate events hit you at the same time (1) the insulation on the wire got chipped, (2) that very spot on the wire touched something adverse causing a short circuit.
I don't think it was two separate events. Most likely, the insulation got pinched and was too thin to protect and the hot arced to ground or neutral.

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Old 06-24-2015, 08:35 AM   #8
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Yes, you have to he careful folding the wire back in the box. I like to make them like an accordion. It doesn't look from the pic the nick is that bad. Just surface. A couple wraps of tape will fix it. No need to add more potential failure points with additional splices.
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Old 06-24-2015, 10:56 AM   #9
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Thanks for the replies all
@dmxtothemax would you pigtail behind the box and pull it through?
@gregzoll never used push on connectors before, will look into it
@busman yes I just meant the wires were going to the correct terminals
@craig11152 I did that on other outlets and not on this one, seemed like there was plenty of clearance but I guess not. Definitely a good practice
@AllanJ yeah looking at it closer I think the nick is deep enough where a couple more bends could break the wire, so it's getting replaced

So my next steps are: see if there's enough slack to cut the wire and pull it out another inch or two. Otherwise, pigtail the wire as securely as I can and rewire the outlet, insulating with electrical tape this time. Test everything thoroughly before turning it on.

On another note. 90% of the house uses this BX armored wiring with no dedicated ground wire, but the metal outlet boxes are grounded and in turn ground the outlets. All of the outlets are three prong and the outlet tester shows they're properly grounded. Probably doesn't meet current code but has been inspected and is grandfathered in. Any safety issues to be concerned with?
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Old 06-24-2015, 12:14 PM   #10
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the wire insulation melted? from conductor overload or from the local heat that the outlet fault was generating?
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Old 06-24-2015, 12:38 PM   #11
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Quote:
Originally Posted by InPhase277 View Post
Yes, you have to he careful folding the wire back in the box. I like to make them like an accordion. It doesn't look from the pic the nick is that bad. Just surface. A couple wraps of tape will fix it. No need to add more potential failure points with additional splices.
I hate to disagree with you, but the photo clearly shows that the conductor is compromised from the arcing. This isn't so much a current flow issue, as a mechanical one. Even the SLIGHTEST nick in a conductor creates a stress riser that will easily cause it to break at that point with only a few bends. It NEEDS to be spliced at that point.

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Old 06-24-2015, 12:43 PM   #12
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Spiral flexible conduit with no longitudinal ground strip or dedicated ground wire inside does not provide "adequate" grounding. While the cables themselves are probably grandfathered, it was not proper to install 3 prong receptacles except with ground fault interrupter protection upstream.

In this case there is a safety issue introduced in that a ground fault could cause the BX cable sheath to overheat since the latter is made up with a coiled up thin strip that is much longer (and therefore has a higher resistance than) a straight ground wire.

A tester may show proper grounding because it uses currents too small to overheat the cable sheath or to result in significant voltage drop in the test circuit.
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Heat went off in the dead of winter? Excellent idea to be late or absent for work and to spend the day winterizing your house to keep pipes from freezing. Every house is different. For those of you not hit yet, think of what things you need to do.

Last edited by AllanJ; 06-24-2015 at 12:48 PM.
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Old 06-24-2015, 12:58 PM   #13
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@concrete_joe the theory I'm running with is that bending the wire weakened the insulation and it arced, which melted the insulation and nicked the copper. The insulation isn't brittle to the point where it's crumbling to the touch, but bending it a few times isn't a good idea

As for the grounding issue I shouldn't speak too soon, I really don't know what's going on past the box where it's pigtailed. Could it be possible that there's a dedicated ground wire connected to the box? I'll find out.

Here are some of the old outlets I replaced. The house was rewired in 1965 and I believe these are from that era. Some had their brackets plastered over, even. If they were installed sometime after the rewiring, it was a pretty thorough job as every outlet is of this type.

Smoking outlet and compromised copper-imageuploadedbydiy-chat1435168611.065754.jpg
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Old 06-24-2015, 02:56 PM   #14
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Quote:
Originally Posted by busman View Post
I hate to disagree with you, but the photo clearly shows that the conductor is compromised from the arcing. This isn't so much a current flow issue, as a mechanical one. Even the SLIGHTEST nick in a conductor creates a stress riser that will easily cause it to break at that point with only a few bends. It NEEDS to be spliced at that point.

Mark
I would agree with you IF it were a nick. In the picture, it looks like the insulation is nicked and the conductor touched the box. There is a dark spot from the short but otherwise it looks intact. Perhaps I'm seeing it wrong. I would avoid a splice unless the conductor is physically compromised.
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Old 06-24-2015, 09:29 PM   #15
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Quote:
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Obviously not, if it let the smoke out.

Mark

And it will never work again !
UNLESS -
You can find every last bit of smoke that got out ?
And put them back in again.

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