Fried wiring

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  #1  
Old 03-21-16, 07:12 PM
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Fried wiring

I've got a question I'm hoping you all can help me with. I'll try to keep this as brief as possible.

Tonight while replacing an outdated outlet, we wound up with some toasty insulation. There are also two switches that were replaced just before the outlet in the circuit.
After replacing the outlet and two switches, but before pushing everything back into the receptacles, I flipped the breaker back to test all of the devices. The outlet and lights all functioned properly, so I flipped the breaker again, folded the wires into the receptacles, and tested again. As soon as I flipped the circuit back on I heard the outlet pop. Upon examination it was easy to find where the arc had occurred, due to the blackened spot on the box. I was able to trace this to a nick in the insulation I had missed earlier, which made contact with the box. I was able to snip off the burnt insulation and connect a new outlet, to ensure the previous unit wasn't fried, but it still didn't work. I checked the wires in the receptacle with a voltage detector and found that none of the wires were live any longer.

The switches upstream in the circuit work fine, and none downstream work, which makes sense given that the wires in this box seem to be fried. What I can't make sense of is how the circuit seems to interrupted halfway between two receptacles. I am not an expert, but I would have thought a short in the circuit somewhere else would cause the breaker to continually flip and no devices on this circuit would function.

The only uneducated guess I have is that the short caused damage to the light switch that is upstream, and caused the circuit to stop there. I haven't yet had time to test this theory by swapping out that switch though, and I would love any input!

Thank you all
 
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Old 03-21-16, 07:19 PM
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I checked the wires in the receptacle with a voltage detector and found that none of the wires were live any longer.
Non contact testers are useless for real testing. You need a multimeter, preferably analog (or a neon test light or solenoid tester). If there are any back stabs they need to be moved to the screws. Any wire nuts need to be redone.
 
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Old 03-21-16, 07:20 PM
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Welcome to the forums.

Sometimes when you create a dead short..... an iffy/weak connection opens from the high current. The problem is at the last working device or at the first non working device.

If you have any devices that are backstabbed.... where the wires are just stuck into the back of the device..... check them first and move the wires to the screw terminals.
 
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Old 03-21-16, 07:36 PM
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Thank you both for the input, I really appreciate it.
No back stabs, but I will double-check my connections and wire nuts. I'll also dust off my multimeter and give that a go, as I was previously testing with a non-contact tester.
 
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Old 03-21-16, 07:42 PM
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What I can't make sense of is how the circuit seems to interrupted halfway between two receptacles.
It may appear that way but it's more likely bad at one end. Cable rarely goes bad in the wall.
 
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Old 03-22-16, 05:00 AM
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In most cases, if you see burned insulation on wires in the outlet box, the reason was a loose connection with the switch or receptacle or wire nut. Loose connections generate heat, and more so when more power is drawn either there or at a downstream receptacle.

Usually only a few inches of wire in the box will be fried while the wire back inside the wall is okay. But after snipping off the burned insulation the wire end is too short and you have to splice on an additional short piece.
 
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Old 03-22-16, 03:18 PM
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Thank you all for your input, it's great to have helpful folks like you.
I had a chance to do some testing with my digital multimeter this evening, and I am hoping the results will mean more to all of you than to myself. I know basic wiring, but I don't pretend to be anything near proficient.
Behind the now defunct outlet is the standard 5-wire configuration, with 2 blacks, 2 whites, as well a ground. I tested all for continuity with the wiring (deenergized) in what I believe to be the next receptacle upstream in the circuit. I found continuity between the functioning receptacle and one of the white wires in the defunct box, but no others.
I have also double-checked all connections and redid the wire nuts, to no avail.

Thanks again for the help folks
 
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Old 03-22-16, 03:53 PM
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When we discuss wiring... we leave the grounds out of the count. They are there and should be connected properly.

So you have two cables there. That means one cable is the feed in and one is the feed out.
With the receptacle and wiring pulled out of the box.... you need to check from the black to ground to see if you have hot there. If you do.... check from black to white. If no voltage now... you've lost a neutral connection.
 
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Old 03-22-16, 03:53 PM
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One more thing, and again I am not an expert with a multimeter, but I did find 500 Ohms resistance between a black and a white wire in the non-functioning box. I wasn't able to find resistance between any of the other wires. Don't know if that helps much, but thought I'd share anything that could help in a diagnoses.
 
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Old 03-22-16, 03:58 PM
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Checking resistance of the wiring is not terribly helpful. What happens is that you can read the resistance of anything attached to that circuit.... like lights or appliances.

With AC power off..... you should see 0 ohms between white and ground.
 
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