Problems with a metal box

19 years ago

After wiring a number of receptacles with plastic boxes, I was feeling pretty cocky, until...

Then I tried add an electrical outlet at the bottom of a metal conduit in my basement in an empty metal box that was there.

The box had a corresponding box outside of the walkout basement sliding glass door. Before I touched it, the wiring went down the pole and outside and worked fine.

First, I opened the box outside and noticed that there was a bare copper wire which attached to the metal box (rapped once) and then was connected also to the receptacles grounding screw (green). Nothing out of the ordinary.

I proceeded to remove the outlet (after cutting the power of course). I pulled the wiring back through to the inside of the basement wall. Next, I trimmed the wires down since did not have to run as far. I attached the black wire to the brass and white to the silver. The bare copper wire I hooked to the ground screw of the metal box and continued to the receptacle ground screw (just like the outside).

Finally, I covered the outlet with a metal face plate and closed in the box. I turned on the power and voila - - it did not work. After scratching my head and trying a few things I discovered that I had tripped the circuit and it had to be reset. So it was blowing out as soon as I switched the power on. I tried placing a plastic box in front of the metal one and wiring the receptacle again and it works fine.

I noticed that the outside outlet had a foam gasket and plastic face plate. Is that the problem?

What am I missing about the metal box?

Featured Answer

Ron Natalie

11 years ago

Electrical wires are NOT so designed. In fact a ground-to-neutral fault will likely leave no such evidence. You may find some evidence of a hot-to-ground fault, but then again you may not.

Wrapping devices with tape is a crutch for the incompetent worker.

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Comments (9)

joed
19 years ago
It should have worked.
Possibly the bare ground wire when stuffed back into the box came in contact with the hot side of the receptacle(gold screws). Or the the receptacle was not centered in the box and the gold screws were in contact with the side of the box.
justjames
Original Author
19 years ago
It sounds like having a bare ground wire is not a good idea inside of a metal box. The cable is NM14/2 which has a bare wire for the ground. It is very possible that this bare wire made contact with the receptacle. What if I connect the bare wire to the ground screw in the metal box and trim it back, then run a covered wire from there to the receptacle? I was concerned that I needed something between the receptacle and the metal face plate...
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joed
19 years ago
Bare wire is a used all the time for ground in metal boxes. Just need to watch when you push everything back into the box. It is very seldom a problem.
cobraguy
19 years ago
Just out of curiosity, why didn't you run wires from the outside box back to the inside box so you would have both receptacles operating? Outside box should have been GFCI protected too...so you could have had the inside box protected as well.
cebury
11 years ago
I've done the same as DIY'er with receptacle wiring, except it happened because I didn't tighten both unused side screws when I used the rear-push wire holes. So the bare copper ground hit the hot side screw that was sticking out which btw comes very close to the edge of the metal box. Pop, smoke, burnt ground ... I like circuit breakers.
Ron Natalie
11 years ago
Yes, look for anything that can touch the bare wire or the box itself. If this is a GFCI-protected circuit, it could even be that the neutral side is touching the ground somewhere.
ionized_gw
11 years ago
Electrical wires like this are designed to make smells and leave black marks where an inadvertent touching of two conductors or a conductor and grounded metal occurs. It is likely that you will be able to identify the location of the problem by a close inspection of the inside surface of the box, receptacle and the wires inside the box.
kudzu9
11 years ago
It's usually good practice to run a couple wraps of electrical tape all around the receptacle from top to bottom to cover the side contacts. This helps prevent problems like you described.