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I have a projector I plan on mounting to the ceiling in my basement. It just so happens that I have an unused light fixture receptacle which had been covered with a plate, right next to where I am tying to mount it. I know how to replace an electrical outlet, but I had a few questions:

  1. Is light fixture wiring capable of handling the 350 Watts the projector consumes (the additional 3A shouldn't be a problem, I don't think)
  2. There are 4 wires of each color (white, black, and bare). Why so many? Which ones do I use?
  3. I have yet to measure whether or not this receptacle is on the same circuit as the lights, but if so, how do I get this outlet off of the switch? Since I would like to use the projector with the lights off, I need this circuit to always be hot. This is my biggest question. I would prefer not to have to run additional wiring to that spot on the ceiling.

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Since it always comes up, I live in Maryland (USA).

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    Do you have a multimeter or a non-contact voltage tester? With one of those, you can figure out whether the box is always hot or switched.
    – Aloysius Defenestrate
    Dec 14, 2015 at 14:35
  • Yes, I have a pretty nice multimeter. As I said, I have not yet poked around. I was just surprised when I saw 4 wires in each nut - thought there might be a reason for it.
    – dberm22
    Dec 14, 2015 at 17:38

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  1. Light wiring is no different than outlet wiring in terms of capacity. The breaker should already be sized appropriately.

  2. Could be that the switch and/or home run (source) wires come into that box, and that two pairs go out to the other light boxes. Some tracing or testing would be necessary.

  3. If the source comes into the box, you're golden. You can connect the new outlet to that and leave the rest of the circuit as-is. If not, You'd probably need to find a way to make changes elsewhere in the circuit to isolate that box. You probably can't bring additional cabling into that box as it's very full already.

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  • As it turns out, the box had source going to it. I had my grandfather (retired licensed electrician) add an extender to the box and put a fifth wire (pigtail) in each nut. The fifth wires went into the new outlet. The box sticks a bit out of the ceiling due to the extender, but It's not a big deal since it's in the basement. The new wire nuts are rated for up to 5 #12 wires, so this should be fine.
    – dberm22
    Dec 21, 2015 at 13:56
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Without poking around in there with a probe, there's no way to tell what's going on. There might be an always hot power source, but there also might not be. You'll have to run some tests.

The other issue, is that the box is potentially too full to add a receptacle. You'll have to do a box fill calculation, but it looks fairly stuffed.

If it is too full, you'll have to install a separate box, or install an extension ring on this box.

Lastly. There's no way to know the capacity of this circuit, without knowing the breaker size, and everything else that's on the circuit.

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