I replaced an old sub panel in my garage. The panel is fed by three wires from the main panel in the house overhead to the garage. Do I need a separate ground wire back to the main panel? There are no other sources of connection back to the house. No water, gas, or sewer lines.

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  • Is the garage attached to the house? I think all new sub panels need a ground wire to the main. Detached building also need ground rods.
    – crip659
    Commented Aug 17, 2023 at 0:16
  • No the garage is not attached. What are my options to retrofit a ground? Wires from house are exposed overhead
    – Jim M
    Commented Aug 17, 2023 at 0:20
  • Is there a messenger wire? The bare cable supporting the others? If so, are you certain it's not the ground?
    – FreeMan
    Commented Aug 17, 2023 at 1:03
  • There is a messenger wire but it feeds into what appears to be marked as a neutral wire. I posted a picture.
    – Jim M
    Commented Aug 17, 2023 at 1:24

2 Answers 2


You're grandfathered as long as the original installation was permitted prior to adoption of NEC 2008.

Merely upgrading the subpanel does not void the grandfathering.

You will need local ground rods, but it's still not the best situation and was banned in 2008. If you wonder why, see John Ward's video on broken PEN (Protective Earth + Neutral), which is what that bare wire is up on the pole.

If you want to retrofit ground, your best bet is probably to obtain a single wire similar to the triplex on the pole, probably XLP/USE-2/RHH/RHW-2 type. Then furl that onto the overhead service line, and also run an appropriate ground wire down the service riser. At this point, some rearrangement will be in order. The bare carrier wire should be re-tasked to be safety ground. The new insulated wire should be tasked to be neutral.

It looks to me like this pole line was thrown up by the power company, their use of triplex is typical. When you want a subpanel feeder you really need to lean on them to give you quadplex - and if they're doing it on the sly, that may not be possible since they can explain away 100' of triplex "evaporating" but quadplex not so much, since they didn't have any 3-phase jobs today.

  • So what’s the fix. Can I just run a ground wire between the two panels along the same overhead path and what type and size should the ground wire be.
    – Jim M
    Commented Aug 17, 2023 at 2:27
  • 2
    First you need to tell us the size of the breaker feeding the feeder in the main panel, and the sizes of the existing current-carrying wires in the feeder.
    – nobody
    Commented Aug 17, 2023 at 2:43
  • @JimM -- yeah, what is the size of the upstream breaker here? Commented Aug 17, 2023 at 2:51
  • 6 awg aluminum and 70 amp breaker
    – Jim M
    Commented Aug 17, 2023 at 2:58
  • 1
    @JimM there you go. The cable up the riser is not outdoors and does not get to use outdoor ampacity rules. There, #6AL is limited to 50A, with #4AL giving 65A (and a 70A breaker permissible there due to the "round up rule"). If this is for EV charging, just reduce charge rate - people grossly overestimate the power requirements of EVs. Commented Aug 17, 2023 at 4:33

Yes, the subpanel needs a safety ground. ANYTHING that isn't double-insulated needs a safety ground.

However, you should not bind/connect ground and neutral at the subpanel. That happens once, at the point of entry or main panel.

  • So what’s the best option to run a ground. The wires run overhead from the house to the garage and are exposed.
    – Jim M
    Commented Aug 17, 2023 at 0:18
  • Ground should run with the other wires. It can generally be a smaller gauge wire since ideally it never carries much current. But it needs to be there.
    – keshlam
    Commented Aug 17, 2023 at 0:21
  • Even if the wires are overhead and the neutral isn’t insulated
    – Jim M
    Commented Aug 17, 2023 at 0:24
  • @JimM Short answer is yes. Either separate ground away from neutral or use an insulated green ground wire.
    – crip659
    Commented Aug 17, 2023 at 0:30
  • What gauge can I get away with
    – Jim M
    Commented Aug 17, 2023 at 0:33

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