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Background:

I'm updating an outdoor garage wall single gang electrical outlet that's 2-wire ungrounded installed perhaps 70 years ago. I only have access to the outside of the wall. My plan:

Remove existing faceplate and outlet, make sure incoming cable/wire is in satisfactory condition. Install one or two weatherproof extension rings with gaskets to provide depth, one with 1/2 inch threaded ports. Attach 1/2 inch liquidtite conduit carrying 8 gauge THHN grounding "bus" running along outside wall to port. Install weatherproof outdoor outlet shield. Install WR/TR GFCI outlet, connecting original hot/neutral and new ground wires.

Question:

What's a good robust code-compliant method to connect the 8 gauge stranded copper THHN EGC conductor to the two 12 gauge solid grounding pigtail wires in the box? Normally I would used a 3M blue/gray wire nut, but since there is an increased chance of moisture getting in there, should I use a split bolt instead, or something else?

To clarify - since these are grounds, I want to make sure the electrical connection remains solid but am not so worried about their exposure to water otherwise.

Update: I've just learned about weatherproof wire nuts, with skirts and pre-filled with (dielectric?) grease. Seems like those are a good default both mechanically and to minimize corrosion for these outdoor wet locations.

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  • This might be an XY question. I realize this comment doesn't directly answer your question, that's why it's a comment, not an answer. Instead of adding a ground wire, if you are desiring improved safety, that can also be accomplished with GFCI outlet. They work without a ground. Code requires a label "no equipment ground" on faceplate of the outlet. BTW a common misconception is GFCIs provide over-current protection, THEY DO NOT! They only provide ground fault protection. Commented Jul 15, 2022 at 22:34
  • @GeorgeAnderson Not XY I think. I did mention in my question that I am installing a GFCI outlet; since I have a ground wire running nearby on the wall, I thought it best to ground the outlet as well.
    – Armand
    Commented Jul 15, 2022 at 22:43
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    You called it a WR/TR GHCI outlet (probably a typo), so I missed that. You should edit your question to fix that. Yes, it's better to have a true ground, but remember ALL connections need to be permanently accessible. Commented Jul 15, 2022 at 22:59
  • your plan sounds good to me
    – Traveler
    Commented Jul 16, 2022 at 0:58
  • @GeorgeAnderson thanks for the typo catch; fixed now. All connections will be in this weatherproof box or in weatherproof junction boxes along the ground wire run. Accessibility is one big thing I've learned from reading your, Ed's and other comments here :)
    – Armand
    Commented Jul 16, 2022 at 3:07

1 Answer 1

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If you use 8 awg it the wire requires protection.

Using 12 for the grounding will also need protection but be less expensive.

I run #6 quite often as it doesn’t require protection and everything in the home can be attached to #6 so that might be a consideration.

A blue gray nut is fine, a 3 wire split bolt would be great (these are about 10x the cost of a blue/gray) also the split bolt for grounding and bonding are brass way more expensive than aluminum. Again note a standard split bolt is listed for 2 conductors. The blue/gray wins hands down

If you would be continuing on beyond this box with the electrode conductor it would require a compression splice. But as this is the termination and pigtail ground the box and your 2#12’s

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  • Actually this is a tap ground wire off the electrode conductor (split bolt connection to continuous electrode conductor) but for convenience is being run in 1/2 inch liquitight along the wall. Didn't realize standard split bolts were only listed for 2 conductors - thanks for that info.
    – Armand
    Commented Jul 16, 2022 at 3:08

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