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I bought a new single-bulb light fixture. It's going in a small animal cage, so the wall plug comes in through the ceiling of the cage. I connected white to white, black to black, and green to a green grounding screw in the fixture. When I plugged it in and switched it on, the light worked but withing a half-second there was a pop and the ground wire blew off. The light stayed on and works. My questions:

1) What did I do wrong? I'm admittedly a real newbie on this.

2) Is it at all unsafe to keep running it now?

3) My first guess is that maybe some of the live wire (black or white) touched the ground? I have them all wound up in plastic wire connectors, but they are admittedly pretty close together where they come out of the plug. Is that a possible cause, and if so, would it be safe to strip some more of the green wire coming from the wall plug, connect that to the ground screw, and try again?

4) Am I about to electrocute myself and/or start a fire and therefore should cease and desist?

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    #2 and #4 are both a definite YES
    – jsotola
    Apr 18, 2020 at 0:29
  • Gotcha. Already turned off, deciding on next step. =)
    – bobobob
    Apr 18, 2020 at 0:32
  • It'd help to see pictures of it.
    – Harper - Reinstate Monica
    Apr 18, 2020 at 0:55
  • Added 2 pics. Plug wires coming down from top. I've already detached from the fixture and separated a longer length of the wires from the plugs to try to keep them separate, in case #3 in my original post was correct. But, I'm waiting for good guidance before I decide to do any more. You can see the ground wire is basically gone from the green screw on the fixture now.
    – bobobob
    Apr 18, 2020 at 1:09
  • You'll probably find that the insulation on the hot wire has been nicked or pinched somewhere it's not easy to see and the conductors have touched the metal fixture.
    – brhans
    Apr 18, 2020 at 1:34

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I don't see in the photos what type of plastic connectors you are using, but if they are the typical twist-on wire nuts, then the amount of exposed copper you have is much too long. As mentioned in the comments, it also looks like you've nicked the insulation on the hot (black) and ground (green) wires, right after they are separated out from the outer sheath. If that is true, you should cut it back to remove the damaged part. If that's absolutely impossible, what you should definitely not do (but some people might do this anyway....) is carefully cover the nicked portion with scotch 33 electrical tape (not cheap no-name brand).

It should be easy enough to figure out where the problem is: on the inside of the junction box, right over the screw mounting hole, it looks charred due to the arcing that happened. If the box is charred, there is going to be an equally charred wire that was on the other side of the arc.

Also, where it appears the arc occurred (right under a screw mount) could be a hint about what you might have done that caused this (did you drive a screw through there when installing the cover and inadvertently drill through a wire?).

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  • So, the white and black wire from the fixture (not the plug) are charred where the arc happened. And, yes, it does appear I nicked the insulation on all three wires coming out of the plug, though none enough to visibly expose wire. Is that enough to cause a problem? I naively assumed it only mattered if the different wires could touch each other. I can certainly cut back the plug and reattach some copper wire to the ground screw on the fixture, then try again, a bit more carefully; probably in the AM. Thanks for your help!
    – bobobob
    Apr 18, 2020 at 3:07
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    yeah, if you can tell that you got a bite out of the insulation on any of those wires, it's best to treat it like exposed copper (since there's a good chance that the stress of assembly + any tension over time will help it along). The same applies to the copper itself: when you strip it back, don't take off any strands (or nick it if solid copper). Good luck, stay safe.
    – Z4-tier
    Apr 18, 2020 at 4:09
  • just to add, if the black/white wires going to the light socket are burned, those need to be fixed too. That black char material is carbon, which is a pretty good conductor (better than salt water).
    – Z4-tier
    Apr 18, 2020 at 17:27

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