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This is covered all over and hoping I have everything correct. Im planning on doing a sub panel in a detached garage, from panel to panel is 210ft. My plan is to bury 2" PVC 18" deep (from top of PVC), run three 2/0 Alum xhhw-2 feeders for hot-hot-neutral, one 4AWG alum xhhw-2 ground, to the unbounded 30 space 200amp (rated) sub panel. Upstream breaker will be 125amp, down stream will leave the 200 (just a disconnect really). Adding 2 ground rods to earth ground the panel 8ft apart.

Permit and inspection will happen but just making sure I'm on track.

Let me know if this sounds on track or if anything isn't to code.

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  • Welcome to Home Improvement. What does your first sentence mean? What is an "unbounded" 30 space panel, is that supposed to be "ungrounded"? You might want to edit it for clarity.
    – FreeMan
    Commented Aug 16, 2023 at 21:06
  • Everything sounds good (pending the edit suggested by FreeMan). But one key issue: load calculation. Have you done a load calculation of the existing (main) panel vs. utility service to see how much you can send to the subpanel, and a load calculation on the planned subpanel loads to make sure they're OK? FYI, if you don't have enough in the main panel then look at your subpanel loads - if a large part is EV charging then there are some things you can do to solve it - just ask, with details.
    – manassehkatz-Moving 2 Codidact
    Commented Aug 16, 2023 at 21:11
  • @FreeMan That's presumably supposed to be unbonded since we have here a questioner who is actually running the required separate grounding wire for a sub-panel. Questioner - you can edit your question to correct such typos.
    – Ecnerwal
    Commented Aug 16, 2023 at 21:59
  • 125A in a garage? Please tell me it's not for two EVs. There are so many better ways to do that, which won't create huge safety issues with your main panel, and won't require a service upgrade. Ask.
    – Harper - Reinstate Monica
    Commented Aug 17, 2023 at 4:37

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Other than some typos, and little details like the earth grounding portion of the grounding system needs to be copper (aluminum is fine through the conduit, but when you get into the dirt with the local grounding rods you need copper for better corrosion performance) this seems on track and like you did your homework.

If, by any chance, you have concrete work yet to be done on the garage, try to get a "concrete encased electrode" (aka an Ufer ground, after the guy that invented it) installed instead of (or in addition to) one of your ground rods. Since it's simply making use of the reinforcing steel it costs very little extra, and is one of the best grounding electrodes you can get.

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  • I appreciate the response! I will defiantly do bare copper wire to earth and for sure look into the Ufer ground since they will start concrete work in the next couple weeks. It will only be a 4" slab, which I'm told will only be fiberglass reinforced so that may cause a snag in that idea. The concrete guys say anything 4" or less no longer gets rebar.
    – Sean Elliott
    Commented Aug 17, 2023 at 19:04

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