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I want to re-locate our electrical vehicle charger (EVSE), which is now on the side of the house and located pretty inconveniently. I want to move it to the edge of the gravel parking area. To do that, I will need to bury about 20ft of conduit across an area of lawn and a gravel path. Unfortunately I'll be crossing the main power feed to the house, theoretically buried 24" deep, but I don't completely trust that and the penalty for failure is high; so I don't want to attempt the 18" burial depth for PVC conduit (never mind the grunt work).

So I'm looking to use intermediate metal conduit (IMC) or possibly rigid metal conduit (RMC). I am thinking I can get away with only burying it 6", although I'll probably do more like 12". I am basing this on NEC Table 300.5

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Using column 2, it looks like the top row ("All locations not specified below") would apply, allowing 6" burial. It seems like the only thing that could get me would be the next to bottom row ("One- and two-family dwelling driveways and outdoor parking areas, and used only for dwelling-related purposes"). But as long as the IMC only comes up the edge of my parking area, and perhaps follows the edge to the ideal location (and never crosses the driveway itself), I should be ok with 6" per the top column. In other words, that gravel path does not put me in the next-to-bottom row, as long as there is no motor vehicular traffic on that path.

Am I interpreting Table 300.5 correctly ?

I'm also thinking the vertical runs coming up at each end, to the house and to the EVSE, can be done in PVC. Simply to save having to buy all those expensive IMC fittings. So hopefully two 10-ft sections of IMC is all I need, the remainder can be PVC (assuming the transition can be gracefully done, with the threaded PVC fittings mating up with the threaded fittings at the ends of the IMC). Does this make sense ?

Obviously, since I'm planning to transition to PVC at the ends, I'm not intending to use the IMC for the grounding conductor. Given that all the IMC will be buried, do I need to connect it to the ground wire, using a grounding bushing ?

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I think you will need to connect the IMC to the grounding conductor.

An alternative (since you're planning on 12" anyway) would be to use PVC all the way, and pour 2" concrete on top of the conduit, as per the second row of the table. That might come out cheaper than buying IMC.

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  • Interesting idea. But it looks like 3/4" IMC is about $20 for a 10ft piece, and two of them is all I need, assuming it's ok for the elbows and risers to be PVC. I'm willing to pay $40 to not have to mess with pouring some concrete. Oct 15, 2023 at 18:03
  • It'd be allowable to use 1/2" (three 8awg conductors), but it's not much cheaper than 3/4". Oct 15, 2023 at 18:11
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    Definitely pick larger over smaller unless smaller saves you a lot of money. It's easier to pull and gives you more options, say when you decide a 120V outlet would be nice to have in the same location.
    – Ecnerwal
    Oct 15, 2023 at 18:18
  • So, is it ok to transition to PVC for the elbows and risers ? Oct 15, 2023 at 21:42
  • Yes, (using schedule 80 PVC) but I believe you'll need to use a handhole (below-grade "junction box") for at least one to facilitate the bonding. Or you could run one end up in metal to facilitate that.
    – Ecnerwal
    Oct 15, 2023 at 22:39

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