I've been using 3/4" schedule 40 PVC for three 6-gauge THWN wires coming from the main house panel, exiting the house to the outside and into an 18-ft. deep trench, and leading to an EVSE (electric car charger) near a chain link fence about 30-ft. away from the house.

Do you think it's necessary to convert to schedule 80 for the vertical section coming out of the house down to the trench, and up from the ground to the EVSE at the end of the run? (I’m not sure if either location is subject to “physical damage.”) The only thing I can think of is possibly dinging it with my lawnmower.

I'd prefer, of course, to just continue with schedule 40 if I can.

And if I should use schedule 80, would it be wise to transition to 1” instead of 3/4” conduit for those vertical sections for wire pulling reasons?

  • 2
    The trench needs to be 19 to 20" deep. 18" is to the TOP of the conduit.
    – Ecnerwal
    Commented Aug 29, 2023 at 17:44
  • 4
    @Ecnerwal Don't worry - OP apparently dug this 18 feet down. Commented Aug 29, 2023 at 17:47
  • 1
    OOPS!! HA HA. Yes, 18 inches. But I hear what you mean about the TOP of the conduit. But back to my main questions...
    – tubaman121
    Commented Aug 29, 2023 at 17:52
  • 2
    But honey, I need a 50-ton excavator! That puny 20-ton won't dig more than 12 feet down!
    – Ecnerwal
    Commented Aug 29, 2023 at 17:52
  • Out of curiosity, what's your plan for mounting the EVSE?
    – Huesmann
    Commented Aug 30, 2023 at 12:46

1 Answer 1


If you can ding it with the lawnmower, it's subject to damage.

3/4" schedule 80 is adequate for 3 6AWG THWN. You could also save some fill by using a bare ground wire, but you don't need to.

"Subject to damage" is one of the less well defined (or left open to inspectors choice/opinion) phrases in the code. Most areas consider conduit sections that are less than 18" down in the ground and less than 7 or 8 feet above ground to be "subject to damage" if not enclosed in other construction. So the sweep up, and the vertical section along the wall or post should be schedule 80.

Your area may or may not also require expansion joints to deal with frost movement, particularly if the frost line is more than 18" - frost movement can and does break conduits without expansion joints.

Or, you could use 1/2" rigid or intermediate metallic conduit (RMC or IMC) with the conduit itself serving as ground, and two 6AWG THWN conductors, and only need 6" of cover or about a 7" trench (in non-driveway areas.) If that means not renting an excavator the more expensive conduit can still be a win.

  • Ecnerwal, thank you very much for your detailled answer!
    – tubaman121
    Commented Sep 4, 2023 at 5:08

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