I can't find a straight answer to this, and my dad was the electrician, not me. I have a finished shed 65 feet from the house (8x12). Three receptacles run off of 14/2, one overhead light box, and (1)5000 BTU window ac unit that says it's pulling 4 amps.

Just finished off the building and ran temporary power with an extension cord, but now running juice to it. I will not be running much of anything in there but the ac unit, computer, stereo, maybe a lamp, but nothing major. I'm running 10/2 UF with a 20 amp shut off at the house(code), then into the attic and down into the panel. Will I need to run 10/3 with (2)20 amp breakers because of the ac unit, or will (1) 20 amp breaker handle it?

Edit: I am running conduit since it's code here for 18" burial. Was running 10/2 because of the 70 feet by the time I was done, and wanted to mitigate any line loss.

I never... ever, use 14 ga wire, but I had a roll. Walls are up and finished so I'm stuck there. I get the two 15 amp breakers, makes a bunch of sense, especially with the 14 ga in there. Don't need comm, so I'm good there. Non-fusible pull-out is a good Idea.

As the last response before yours stated, the two legs would be future proof if I need it a couple of years down the road. Both of you mentioned the THHN, good idea and didn't think of that.

  • Does everything (you want to use) run off a single extension cord? Since the shed is wired with 14 ga, you can supply 20A to the shed, but must have 15A breakers in the shed, or upgrade the shed wire to 12Ga if running 20A to the shed. There is no "straight answer" becasue the answer is "it depends" - the AC may only need 4Amps running, but might cause nusiance trips on start if sharing with other loads - but might not if the other loads are low-power.
    – Ecnerwal
    Sep 12 '20 at 0:51
  • If it all ran off an extension cord, it will probably all run off one leg - but 2 legs will be more future proof if your use changes. Consider using conduit and THWN rather than UF - sometimes the price is better. Certainly the "if your use changes" options are better.
    – Ecnerwal
    Sep 12 '20 at 0:51

Run individual THWN wires in a fat conduit, you'll thank yourself later

For your situation, I wouldn't even bother with a direct burial cable; instead, I would run a conduit (or two, even) from the house to the shed, and run 4 THHNs (14AWG is fine since you're limited to 15A circuits and a 15A two-pole breaker anyway by the 14AWG wiring inside the shed, unless you put a subpanel and ground rods in) in one conduit, leaving the other spare for communications cables. If you want a precise size, I'd use 1" for the power conduit and a 1.5" for the spare; this lets you use a cheap non-fusible pullout disconnect on the outside of the shed as the shed's disconnecting means, and since you're powering this shed with a single multi-wire branch circuit, you don't need ground rods there.

  • Yes, conduit, my experience is that buried cables attract shovels. And "fat "conduit , I made he mistake of putting 2 12AWG,3 wire in a one inch conduit for a friend who put a ceramic kiln in a shed. Sep 12 '20 at 19:16

Since you ran #14 in the shed, you will need the breaker to be 15A.

The two breakers for the Shared neutral circuit (Multi-Wire Branch Circuit or MWBC) must be handle-tied. Or it can be a 2-pole breaker.

If all the #14 wire is on one leg of the MWBC and the other leg is all #12 or larger, then you can use a 15A and 20A breaker with a handle tie.

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