Im preparing and researching about a conduit installation. I have a shed that is 100ft away from the main panel which is located inside the garage. I would like to bury 1" PVC 40 Schedule from just outside the main panel which is located inside the yard area to the shed. I would like to run 3 - 10 gauge wire to the shed to feed three 20 amp circuits. Once inside the shed I would like to distribute the 20 amp circuits to various points in the shed. I have a workshop that I am currently running an extension cord to run devices one at a time.

Also, once the 20 amp circuits are inside the shed I would like to run 12 gauge wire inside to various outlets.

Will the idea of the three 10 guage wire inside the 1" Schedule 40 PVC going to the shed to feed three different 20 amp circuits work? If not how can I be able to run the three 20 amp circuits.


  • Use one circuit to a sub-panel in the garage. Conduit is cheap, trenches are expensive - consider larger conduit. You need schedule 80 at the ends anyway for damage protection where it comes out of the ground - consider just using schedule 80 the whole way, it's a small cost difference and better protection the whole way. Don't forget the buried electric line below tape.
    – Ecnerwal
    Mar 16, 2021 at 1:58
  • @Ecnerwal -- there are some decent fill reasons not to go sch80 for the underground run, and PVC XJs are sch40-equivalent in their damage resistance AIUI (they accept both schedules of conduit, but aren't as sturdy as schedule 80) Mar 16, 2021 at 2:06
  • The parts at the ends "exposed to damage" have to be schedule 80, so more space in schedule 40 is moot unless you are managing to not have any of the conduit "exposed to damage." If the fill is too tight then, go up a size on the whole run, IMHO.
    – Ecnerwal
    Mar 16, 2021 at 2:32

1 Answer 1


One circuit too far for your idea

You are only allowed to effectively run two circuits (one multiwire branch circuit, really) to an outbuilding, given single phase power, or else you'll fall afoul of NEC 225.30 (quote snipped as the rest of it doesn't apply to you):

225.30 Number of Supplies. A building or other structure that is served by a branch circuit or feeder on the load side of a service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit.

There is a silver lining though

The silver lining to your thinking though is that 1" PVC conduit is useful for more than just branch circuits; instead, you can run a feeder in it to provide power to a subpanel at your shed, allowing you to have more power and more branch circuits than your proposal would provide.

In particular, if your inspector permits Schedule 40 PVC for stubups, you can pull 3 2AWG Al XHHW-2 wires and a bare 8AWG stranded copper ground through that 1" Schedule 40 PVC (it uses just over 205mm² of the 214mm² of usable fill your 1" conduit provides), providing a 90A(!) feeder to your subpanel for less money than all that 10AWG copper would have cost you! Even if they require Schedule 80 where the conduit emerges from the ground, you still can run 3 6AWG THHN wires and a bare 10AWG ground in your conduit, giving you a healthy 60A feeder.

With that feeder squared away, we can then fit a 100 or 125A, 24 or 30 space, main breaker panel at the shed to provide the local disconnecting means, with matching 20A breakers and 12/2 NM for the branch-circuit wiring. You'll need GFCI protection for the receptacles, by the way, although it's best to keep the lights off GFCI, and put them on a separate circuit for that matter, even, so tripping a breaker or GFCI with a tool doesn't plunge you into the dark.

Don't forget to buy and install the appropriate grounding bar for your panel if it doesn't come with one fitted! You also need to ensure that the green bonding screw or strap is removed from it so that it can be safely used as a subpanel with a 4-wire feeder as per the NEC; once that's squared away, you can run more of that 8AWG bare copper from the subpanel's grounding bar to a pair of 8' ground rods driven 6-8' apart, so that your shed has a grounding electrode system that can return wayward natural electricity directly to Mother Nature.

With that and an appropriate 80 or 90A breaker for your existing main panel, you can enjoy all your shop tools and more without having to worry about Code issues or running out of power.

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