I have purchased a 12x20 shed. Now I need to get power to it. It will be a work shop so I am going to use 8/3 UF cable buried in conduit until I get to the house.
OK. Have you ever done conduit running before? Why are you selecting cable for running inside conduit? I can't speak for your case, but 90% of the time it's a novice, who knows nothing about conduit, knows only cable and does not know/trust THWN wire. There's nothing wrong with that; it's just a knowledge gap; but it'll lead you to a blunder.
Just to fast forward, other common novice errors are:
- Scrimping on the electrical panel, saving pretty much the cost of *a pizza* and then running out of breaker spaces soon after, and having do an expensive re-do.
- going with copper when they should be using aluminum (now you have the worst case; wasted money on wire AND a future panel-space crisis).
- Insisting on using cable and then failing to buy the *ginormous* conduit cable requires. 8/3 UF requires 1-1/2" conduit. 6/3 UF requires 2" conduit.
- getting so frustrated with pulling the balky uncooperative cable through the too-small conduit that they assemble the conduit pipes around the cable - nope, that's illegal.
- Burying too shallow (you need 18" *of cover* unless you're using very pricey Rigid conduit).
To fast forward to the right answer, since you state later you want 8" burial depth... SO. 3/4" Rigid conduit at $2/foot, or 1" Rigid conduit at $3/ft. That's because of your shallow burial depth; it's your only choice. The Rigid connects your new subpanel to a steel junction box inside the house. This will involve actual pipefitting, thus a trip or two to the hardware store to have them cut and thread your pipe. Then, into the pipe goes ONE of the following:
- 3 x 8 AWG copper THWN or XHHW wire ($.33/foot/wire) -- 50A
- 3 x 6 AWG aluminum THWN or XHHW wire ($.20/foot/wire) -- 50A
- 3 x 6 AWG copper THWN or XHHW wire ($.52/ft/wire) -- 70A
Unfortunately colors must be 1x white and 2x non-white. If you bumped to 1" Rigid and use 4 AWG wire (aluminum, say) you would be able to just get one spool of wire and mark the wires with tape.
Notice there is no ground. The Rigid pipe *is* the ground.
Now, the 2nd half of this is getting from the main panel to this junction box. You can use any of these:
- 6/3 w/g copper NM-B cable (regular Romex)
- 4/3 w/g aluminum cable
- PVC conduit - in which case you must run a #10 Cu or larger ground wire from main panel to junction box.
- EMT metal conduit - no ground wire needed if you do this
If you use either type of conduit, then the 3 wires can *run straight through* the junction box and not even stop there. In fact, if it's EMT metal conduit, you can skip the junction box altogether and just use a "pulling point" e.g. a conduit body. You want to put as many pulling points in as you can, at or between bends.
That's how I'd do it, and I do a lot of conduit work, and I'm cheap, and I'm lazy.
"cheap" may not seem compatible with paying $2/foot for conduit, but that's because I'm too cheap to rent a ditcher and too cheap to pay for the damage to the other utilities that I slice through. Rigid only requires 6" cover, so you can trench it with a garden trowel