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I have 2 12/2 UF-B I’m running from my house to supply a double pole 20 in my shed to have 2 120v supplies out there I just dont know what size breaker I need in my main to supply the box in the shed and what size box in the shed to just hold a double pole 20 and maybe another spot if I ever want to add another one ( it will not use a lot of power only 3 led lights and 4 outlets the biggest thing will be a small window unit on one of the outlets

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  • I think (the experts will say for sure) you can only run one circuit of a given type to an outbuilding. If that is indeed the case, and to save money besides, instead of running 2 x 12/2, you could run 1 x 12/3 and install an MWBC. That will give you the same power, using a 20A double-breaker, but only one cable instead of 2 and technically counts as one circuit. Commented Jun 30, 2023 at 21:53
  • Instead of direct burial I had some 3/4 cpvc laying around so I used that for extra cover for the wire and the 12/3 wouldnt fit. Could I run braided THHN/THWN wire and just run an extra black for my second hot ?
    – Dalton
    Commented Jun 30, 2023 at 22:03
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    THWN in conduit is fine, but don't braid it. Four wires: white, ground, and your call for the remaining two colors, but whatever you do make them different for your future sanity. Black and red is the traditional pairing.
    – KMJ
    Commented Jun 30, 2023 at 23:30
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    This sounds like a detached shed. If so you probably also want two ground rods for it to be in code. If plans/materials not already bought, using larger gauge wire now will help to future proof work/cost later. Same with the panel in the shed.
    – crip659
    Commented Jul 1, 2023 at 0:06

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Depends on the pipe.

If you have proper PVC conduit and are willing to run it "end to end" from the panel to the outlets:

Then you can use THWN wires. You will need burial depth of 18" of cover. You cannot use the individual wires out of UF-B cable unless they have individual markings (they don't).

You can do a MWBC with THHN wires. You cannot do it with /2+gnd UF cable.

MWBC means a shared neutral circuit with two legs of 120V both feeding outlets and sharing a neutral. You do not need a subpanel in the shed for this use and that means you do not need ground rods.

If you have random PVC pipe of some kind:

Then you need to get proper PVC conduit for the stub-ups where it comes from above ground to depth, and the depth must be 24" of cover, since it's effectively not in conduit since it's not conduit at all. You cannot use individual wires and must use suitable direct-burial cable such as UF. Note UF is very flat and won't like to fit in normal sized pipe.

For the MWBC you would need 12/3 UF cable. Can't run 2 separate circuits to an outbuilding unless one is a different voltage or usage - for instance, it could be hooked into lights and controlled from a switch from the house. (no, the switch can't be the breaker).

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  • So I’m returning the 12/2 and getting the 12/3 I know it will be tight it shaved a thing layer off the end when trying to go through but still not sure what breaker I would need of my main to supply this and then what I would need in my shed on the other end of the 12/3 would I just Pull in and it goes straight to the outlets/ receptacles or is there some sort of junction I need to have a shut off on it?
    – Dalton
    Commented Jul 1, 2023 at 14:40

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