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Beginning Disclaimer - I am not a Serious DIYer. (I'm more of a Seriously Try to Avoid Paying Someone Else to Do Iter).

So anyways, I've been having trouble with lights flickering or not working in a room. I checked the voltage, and found that 3 out of the 4 outlets had quite low voltage (around 40 instead of the rest of the house outlets at 120).

After some investigation, I took out several outlets and found that the first problematic one appeared to have a wire that was corroded or burned. Didn't look really bad, but didn't look right.

enter image description here

I detached the outlet, cleaned up the wire with some steel wool, and installed a new outlet in there. Surprisingly that worked. This outlet and the 2 others in the room now have normal voltage and work fine.

So my question is - what would cause the wire to become corroded or burned like this? Is there anything I need to look out for?

Thanks.

  • 2
    It's probably worth inspecting all the outlets to see if any others have a similar class of workmanship, and replacing any dubious ones (or buy enough outlets and just replace them all, being careful to note the state of the original outlet, and tightening all connections properly. The good news is that you appear to have copper wiring, not aluminum. Keshlam's answer is spot-on. – Ecnerwal Jul 22 '16 at 13:57
  • The heat is generated at the point with a high electrical resistance where the connection is bad, i.e. somewhere inside the connector itself. The heat is then conducted back along the copper wire and "fries" the insulation from the inside outwards. Most materials that are electrical insulators are also thermal insulators, so the temperature of the wire will keep slowly increasing if the lights were left switched on for several hours at a time. – alephzero Jul 22 '16 at 17:26
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    This is a pretty common problem with "backstab" outlets. Many of them have a defective clamping mechanism inside of them which prevents the wire from getting locked in properly and over time the wire can get loose and arc, which causes the wires to burn and can eventually cause a full scale fire. Most licensed electricians will not use these type of outlets, so there is a pretty good chance it was installed by either the homeowner or a "handyman". If you have any more of these, it would be best to get them all replaced as a precaution. – Jason Hutchinson Jul 22 '16 at 19:54
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    @JasonHutchinson - It seems the other way around in my experience - I mostly see the backstabbed outlets in original home wiring (which would have been done by a licensed electrical contractor). For smaller projects (whether done by the homeowner, handyman or electrician), more often or not, they use the screw terminals. There's a significant time savings when using backstabs to install 50 outlets in a new home, but not that much savings when installing 5 outlets in a room remodel. – Johnny Jul 22 '16 at 20:16
  • Spring-loaded backstab failure in my experience is quite common early on in the daisy chain and typically in the first two sockets in a 4-6 outlet chain. The spring pressure just doesn't give good enough contact for the additive current passed, over time, relaxes from the heat generated and then fails. Not sure how newer backstab equipment ages, the above observation was in 20 year old housing, all copper. The straight in connections under the screw terminal plate have never given me this problem. – Fiasco Labs Jul 23 '16 at 17:29
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Loose connections can produce heat and cause this problem. The fix is to disconnect and reconnect properly. Spring-loaded "stab connections" are particularly likely to suffer this problem; screw terminals (or shove-in terminals that are clamped by tightening a screw) are more reliable. If in doubt, outlets are cheap and you might want to simply replace this one.

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    Also of note, the wire is wrapped around the wrong direction on the ground screw -- it should be wrapped clockwise. Though from that picture, it's not clear that it's wrapped around the screw at all, it might just be a straight segment of wire. – Johnny Jul 22 '16 at 18:10
  • @Johnny It looks like it was a "backstab" outlet that doesn't have screw terminals. Here is another textbook example of why these kind of devices should be banned by the NEC. – Jason Hutchinson Jul 22 '16 at 19:46
  • @JasonHutchinson - I was talking specifically about the ground terminal, which is visible in the picture. – Johnny Jul 22 '16 at 20:03
  • @Johnny oh, good catch, I didn't even really look at the ground. You're definitely right, the wire is not wrapped around the screw at all. I was referring to the slightly singed neutral wire ;-) – Jason Hutchinson Jul 22 '16 at 20:07
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The wires are made of copper, which is normal. It is a good conductor but it does corrode in time.

What may have happened: The copper wires were not screwed it very tight. It is also possible that an older, cheaply designed socket simply doesn't clamp in the wires as well as modern ones.

Over time, the copper corroded. The point of contact between the wire and the connector got a bit insulated by corrosion. The resistance increased. When the socket was used, the current through this resistance caused heat which caused the burnmarks.

Solution:

  • Clean the wires.
  • Screw them in tight.
  • If applicable, replace the socket by a newer one.
0

The sheathing on one of the ground wires appears to be melted. A faulty appliance plugged into the outlet could have overheated the outlet if the circuit breakers (or fuses) weren't working properly. The corroded look on the wires could also have been caused by high temperatures.

  • The heat is caused from using backstabs. I see this all the time. A space heater can cause this when backstabs are used or several items plugged in. The wire has a large safety margin built in with the proper sized 15a breaker. – Ed Beal Apr 4 at 16:16

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