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My garage has an electrical box with no receptacle in it, just wire-nutted wires. It came this way when I bought the house.

A non-contact voltage tester shows that the black wires are hot. I was about to shut off the breaker and install a receptacle in the box, but then I noticed the black marks around it which almost look like burn marks.

Should I be concerned that these marks tell the story of an electrical problem in the past, perhaps hinting that there's a good reason why there's no receptacle hooked up right now?

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    It's hard to say for sure, but it appears as though there may have been an issue with whatever was plugged in to the outlet that was removed. In your photo it doesn't appear as if the wire insulation is damaged so that's what is leading me to believe the cause of the smoke marks was external to the outlet box. – bigbull15 Nov 27 '15 at 20:26
  • Those black scorch lines look to be heated induced. Right above the box there are blister marks indicating heat from either the box or what was plugged into it. – ojait Nov 27 '15 at 20:36
  • I just noticed that the marks on the wall are symmetrical and perfectly arched (rounded). Also note the opening to the left of the upper box corner. It looks as though metal conduit (EMT) had been on the wall surface, but has been removed (maybe due to the accident?). That's a good guess though not a positive response! – ojait Nov 27 '15 at 20:41
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That does look as if it could be soot. The wires themselves don't look damaged (melted, charred).

So there may have been some kind of appliance or device plugged into an outlet there, which failed and caught on fire, which presumably also damaged the receptacle. Or the receptacle itself may have failed and started smoking. In either case, the receptacle was never replaced, possibly just because it wasn't convenient or the previous owner never got around to it, or didn't know how.

There wasn't necessarily an overcurrent condition. But if there was, it could have been due to all kinds of transient conditions.

However, there's also a chance that the overcurrent was due to something like a floating neutral in your panel, which can be really dangerous. As in appliances spontaneously catching on fire or blowing up, and so on.

Do you have any electrical problems anywhere else in the house?

The wires in this box are connected straight through, which indicates that you probably have healthy receptacles further "downstream," in which case there's no reason why this box should be a problem with a new receptacle in it.

For peace of mind, you may want to hire an electrician to check things out all the way back to your service panel, to make sure that all of the connections are tight and you don't have any intermittent failures (like a cracked wire that carries enough current 90% of the time, but then overheats and moves causing voltage fluctuations).

If you disconnect the wirenuts, only one of the black wires should be live, and it should only show current when connected to one of the white (grounded/neutral) wires, and it should also show current when connected to one of the ground wires. Those would be the three wires that lead back "upstream" to your service panel. The other wires carry current on to additional outlets. In both cases (grounded and grounding, or neutral and ground) the current should be a steady 120 volts give or take a few volts, with or without a load on the circuit.

  • No electrical problems anywhere else in the house. – iLikeDirt Nov 27 '15 at 20:34

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