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I have this metal electrical box that has no ground wire. I was thinking that I could buy a ground screw and screw that into the side of the box. There's a wooden frame on all sides. Afterwards, I could simply hook a wire onto that and then connect it to the ground screw on my outlet.

I'm not entirely sure if this would work though or if it'd violate the NEC.

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    What's that bare wire entering the box along with the black/white wires if it's not a ground? – brhans Jan 11 '17 at 22:49
  • That particular wire is for grounding the box itself I believe. I'm not entirely sure what it's grounded to though. – TBSquare29 Jan 11 '17 at 22:51
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Yes, in most steel boxes, one of the holes is threaded 10-32 (specifically) for taking a ground screw. Sometimes it's risen above the bottom of the box so there's somewhere for the end of the screw to go.

If you can't find it, it would be legal to drill and tap your own hole. What you can't do is tap it any coarser than -32. That's because regulation boxes aren't thick enough to give proper thread engagement on any coarser threads. Obviously, sheet metal screws are Right Out.

Also, if the yoke (metal ends) of the receptacle are bottoming out hard against the box, then you can ground through the yoke instead of having to hard-wire one. This is not allowed if the ears are catching the wall and preventing it from bottoming out. It is also not allowed if any insulating material is between yoke and box, like those little bits of paper or plastic that hold screws to the outlets. So that leftover screw-catcher on the upper bolt would have to go.

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The clip on the edge of the box, with the wire attached to it (lower right in photo). That's a grounding clip. It's used to attach a grounding conductor to the edge of a metal box.

If that was not there, the two holes in the back of the box labeled GR, those should be threaded to accept a 10-32 ground screw.

Pointing out grounding point in box

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