Some previous owner of my house installed new lighting and receptacles in the attached garage, and these are all wired with 14/2 NM cable with ground on a 15A circuit that is otherwise ungrounded elsewhere in the house.
I eventually traced the origin of the new wiring portion back to a buried junction box in the garage wall, which has a separate ground wire joining with the original ungrounded hot and neutral to feed the new portion of the wiring. This ground wire appears to have at one point been connected to some plumbing, but I found the other end and it is no longer connected to anything.
It just so happens that I had the electrical panel replaced when I moved in, and my electrician ran a new system ground wire (bare copper) exposed along the same interior wall in the garage where the buried junction box is, on its way to the grounding rod. I'm planning to remove this buried box and instead install a larger box for a nearby outlet that is just upstream of it, and to relocate the connections into there.
In addition to replacing this outlet with a GFCI receptacle, I was thinking that while in the process I could restore the ground for this portion of the circuit by connecting a new grounding wire up to the nearby system ground. It would be trivial to get a wire from the box to the system ground, but a much bigger deal to get a separate ground wire all the way back to the panel, and a much bigger deal to replace the original ungrounded cabling all the way back to the panel.
I've found in other questions here that the most recent NEC says that you can provide a ground to circuit A by taking it from circuit B, as long as they both come from the same panel. But I'm not sure about this situation. There is only one panel involved, and I have verified that there is continuity between the neutral in the box and the system ground that I'm hoping to use.
- Is this an acceptable thing to do? Are there any downsides/risks?
- If it's OK, what would be the correct hardware to use to connect a 12 AWG wire to the middle of the 6 (I think) AWG system ground wire?