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My older home is currently grounded with what looks like two lengths of old rebar driven vertically in the ground. I know that the last time the grounding was touched was over 20 years ago, and I suspect it's older than that (home was built in the '30s and additions made in the '60s).

The previous owner rewired the former knob-and-tube in the original building with Romex about 20 years back. There is the service entrance panel plus two sub-panels for the garage/apartment and laundry/porch additions. The subpanels are connected to the service entrance with wiring run through EMT but there's no dedicated equipment grounding connector in the conduit, just the EMT itself.

I've seen elsewhere that the useful life of a ground rod is only about 35 years, and that old rebar looks suspect to me anyhow. What I'm contemplating is driving two new copper-coated ground rods, at least six feet apart, at the service entrance and bonding them to the ground/neutral bus with green #6. I also thought I might drive an additional ground rod at each of the two subpanels and bond them to the subpanel ground bars (neutrals isolated outside of the service entrance). Would this be proper practice? If not, how can I improve my plan?

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  • Your new copper-coated ground rods will effectively become the new main grounding electrodes, so the wire connecting at least the first one to the service panel ground can't have any reversible splices in it. It's now called the "Grounding Electrode Conductor".
    – Armand
    Jun 7 at 19:56

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The old ground rods are probably fine, which means I would suggest not putting your new ground rods in places totally redundant to the old ones. (i.e. not right on top of them).

Generally the farther apart you can spread the rods, the better they protect. All 4 corners of the building is ideal. You do want 1 rod quite close to the panel as this will be the least impedance for lightning protection.

There is no need to use insulated green wire for grounds, ground doesn't need insulation unless it's aluminum, and aluminum isn't allowed for this GEC (Grounding Electrode Conductor: the wire between panel and ground rods). They sell bare ground wire in several sizes specifically for GEC use. The wire cannot be broken or spliced between panel and first rod (though rods can be daisy-chained).

Note that subpanels prior to 2008 were allowed to be wired "3-wire" lacking a ground wire, and with subpanel ground bonded (read: bootlegged) off neutral. This means no ground at all, really. Thus, your subpanels are ambiguous: Do they have neutral and ground separated? Or did they ignore the EMT's ability to be ground and wire it bonded/bootlegged? I would check and correct that as a higher priority.

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  • The subpanels were originally wired 3-wire. One has been replaced and the grounds and neutral separated; I have plans to replace the other subpanel in the near future and it will be separated as well. I'm looking at doing the work on the grounding system as part of these upgrades.
    – ehbowen
    Jun 7 at 22:15
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When I did mine I put in a total of 8 rods as a grounding array. They were at least 8' apart. They were all eutectic bonded to a #2 copper then went to the main entrance point where it joined the service ground and from there went to the sub panels then to the water and gas lines. Yes this was one piece of wire and gas lines were required to be bonded a few years back.

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