electricalwiring
I am trying to wire a dimmer in an old outlet box and need to attach a ground. All other holes are too big or small, except the two that are being occupied by what looks like a wire clamp. Is it safe to attach my ground wire to this clamp? Thanks for your help!
The simple answer is get "self grounding" duplex outlets. The typical design has a little spring plate meant to connect your grounded metal box to the outlet yoke, and thus to the third prong. Just install, test the ground with an inexpensive outlet tester, and feel lucky that the builder left you in such good shape:
If you are in the United States: surprisingly these are legal even in new construction. Beyond that, they're perfect for your retrofit. See the National Electric Code (NEC) section 250.146(b). Note that your ground wires may 16 guage rather than 14 or 12. That was OK at the time, and you're not required to change it now.
This is NOT okay.
Use a multimeter (or voltmeter) to test the grounded (neutral) conductor, to see if you're getting the proper voltage between it and the ungrounded (hot) conductor.
If it tests okay, wire the receptacle up the way it's supposed to.
If not, you'll have to trace back through the circuit, and try to figure out what's wrong.
Best Answer
That screw holds down the cable clamp, which is anchoring your BX cables into the box. I have seen it used for grounds but it's not ideal at all.
Push the wires around in the back of the box and look for a hole that is somewhat smaller than the others. This may be tapped #10-32, if so it is specifically for a ground screw. They sell #10-32 ground screws plated green, either with or without integrated pigtails.