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  1. My g/f's 1940's/50's house has a grounding clamp attached to her 3/4" cold water line. There's a bare copper wire that runs the length of the basement from it (via grounding clamp) to the 200A circuit breaker. The breaker box has the bare 3rd conductor main service line also connected to the ground and neutral bars. There might also be a connection to an outside grounding rod. [ie. I don't think the copper water line is the only source of ground.]

  2. There are some junction boxes where the original cloth 2 wire lines connect to newer 3 conductor romex. The ground wires are tied to together in the box, but I don't think those are tied to a real ground. One box is about 2' from the copper ground line, half-way down it's length. Can I run a bare copper wire from the center ground line, an attach it to the existing junction box grounds? That is, if I want to ground it, it doesn't have to go back to the grounding bar in the breaker box?

  3. If this is possible, what's the best type of connector to use to attach them? I'm familiar with grounding clamps for pipes. But even something like this: https://www.homedepot.com/p/NSi-Industries-Heavy-Duty-Direct-Burial-Ground-Clamp-with-Lay-In-10-2-STR-GLC-12DB/307286461 looks like the "clamp" size is for at least 10 gauge wire (or a small rod). I don't think the grounding wire is this large. [Plus at almost $8 per, it's sort of pricey (I'd need a few.)

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That copper wire is the Grounding Electrode Conductor.

If you are retrofitting grounds, that is a legitimate destination.

You don't need to clamp to it for every single retrofit ground, you can install a junction box and tie a bunch of grounds together and bring 1 line to the GEC wire. The shared ground needs to be as large as the largest ground. Grounds don't normally flow current, so you don't need to worry about combining (combining is something you must never do anyway).

The item you linked looks very fancy. Normally that inline splice is done with a "Split Bolt Connector". They're not costly if you're not paying the "big box tax".

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    I'd recommend a GTT-2-2 or equivalent lay-in capable T-tap type connector for tapping GECs because they're a bit easier to use/handle than a split bolt for this AFAIK Commented Feb 28, 2023 at 3:04

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