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We're just going to run a simple 120v 20amp branch circuit to a shed. 1/2" PVC conduit should be sufficiently large enough for #10/2 plus a #10 EGC. The shed is 140 ft away from a new 240v service panel that'll be installed in the house.

We'd like to run stranded through 1/2" conduit. It'll be a little more flexible for routing through bends. Pulling solid through bends potentially could fatigue them such that (potentially) a wire or two might break. We found fixtures for the shed (receptacle, toggle light switch, and a disconnect switch that'll accept #10 gauge. Stranded should be a little easier to connect I would think. I've never liked using the back-wired (push-in terminals) with solid and stranded 10/2 doesn't add that much more cost than solid for this run.

The grounding electrode conductor material in the NEC says the conductor shall be solid or stranded, insulated, covered, or bare.

We're just looking to avoid anything dumb that's being overlooked using stranded 10/2 THWN/THWN-2 plus a stranded #10 THHN/THWN-2 equipment grounding conductor. Unless there's some electrician who'll be installing the new main service panel and connecting the branch circuit who could take issue with it. (I can't think of what it might be)

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Well, if it's THWN wires it won't be 10/2 (which is a cable designation), it will be three individual strands of 10 AWG wire in conduit.

Stranded works fine and pulls easier than solid. Typically costs a penny or two more per foot.

Nothing wrong with using stranded, most people who know what they are doing, do. IIRC 10 AWG may also be the last size you can even get as solid wire, from which you can infer that stranded wire is very, very common.

If, at some future point, you need more power out there, an additional strand of 10 AWG will get you (at least) twice as much available power if you provision this as a MWBC, and actually could support a sub-panel fed 25 or 30A at the supply end quite reasonably. With 1/2" conduit there's no further upgrade path (but yeah, it's just a shed, so likely plenty)

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  • Thanks for your expertise @Ecnerwal . We just needed assurance we hadn't overlooked anything. We're having him do the cut through the wall for the LB body from the inside after the panel and metal box are removed. If the electrician said, sorry, I can't connect those wires to the panel because it violates some code regulation after we went through all that work of pulling the wires through, It would be a big setback. He'll connect the LB on the outside wall to where he wants it which will probably be somewhere close to the panel which is installed on the inside of the house. May 24, 2023 at 16:19
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Short answer: stranded. And though it'll fit in a 1/2" conduit, don't do that.. pay $30 more to get 3/4 inch PVC instead. It's really no more difficult to work with and the pulling will be easier. But before you rush out and buy that 10 gauge copper wire by-the-foot at your local home center.. do a little comparison.

This week I'm going out to directional bore a conduit for a feed to a backyard shed/shop. This one is only 100 feet, so a bit shorter than yours. The homeowner will be doing the electrical work himself but needed some guidance to figure out what size conduit I should install for him. The following is what I found. Although I know that pricing of materials will change over time and location, the relative cost between wire gauges and materials is what's of interest.

120 volt, 20 amp

This is the simple, easy, cheap option -- right?

By-the-foot 12 gauge stranded copper THHN at my local home center is going for $0.48/ft. Three lengths of 100 feet each (hot, neutral, ground) comes to $144.

120/240 volt, 20 amp

With just a single conductor added we can double the amount of power available at the shed-shop. Four lengths of that 12 ga stranded THHN comes to $192.

120 volt, 20 amp, 10 ga

Maybe you're concerned about voltage drop on the 12 gauge wire and want to upgrade it to 10 gauge. My local home center wants $0.68/ft on that -- three lengths will cost $204; a 42% increase in cost over the 12 gauge.

120/240 volt, 50 amp

This sounds crazy, right? But it gets us into the territory where we can use aluminum wire, and aluminum costs a lot less than copper. Check it out.

A local electrical distributor quoted me $0.27/ft on 6 gauge stranded aluminum XHHW wire. He only had it in black, though, which only works for the two hot conductors. So I got a price of $0.51/ft for 8 gauge stranded copper THHN with white insulation to use for the neutral, and $0.46/ft for stranded copper THHN for the ground. (Right off the bat, notice that he's asking 32% less than the home center per foot on the copper 10 gauge!)

So: two 100 foot lengths of the 6 ga aluminum comes to $54, plus 100 foot each of the 8 gauge and 10 gauge copper comes to $97. Total wire cost $151 -- and it still fits in a 3/4 inch conduit!

Summary

The 120/240 volt, 50 amp wiring costs only a few dollars more than the 120 volt, 20 amp wiring (and it would actually have been cheaper if I'd tracked down white-insulated aluminum 6 ga instead of taking white copper 8 ga). The 120/240 @50 amp is 26% cheaper than the 120 @20 amp with 10 gauge copper, and it leaves open all kinds of options for the future. Put a big air compressor in that shed? No problem. Get an RV and plug in its shore power here? All set. Insulate the shed and make a detached home office space with heating and air conditioning? Ready to go.

Caveats

The 20 amp 120 or 120/240 circuits can be wired directly to lighting and receptacles. To provision higher amperage you'll have to add a subpanel and ground rods. Those are going to push the all-in materials cost of the 120/240 @50 amp circuit maybe 10%-20% higher than the cost of the basic 120 @20 amp 10 gauge option -- but it's not often that one can have such a significant upgrade in potential for so little extra cost.

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    I'm not the owner of the property. I've offered my suggestions on a MWBC. However, he's made his mind up to just go with a simple 120v 20a circuit. I've already priced the materials and provided the cost to him. Being family related, he'll likely consider 3/4" for the added benefit of it being easier to pull the wire through. May 24, 2023 at 16:56
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    Or for $138 (at your prices and 100 foot length) you could just buy 3 lengths of 10 AWG from the electrical distributor, rather than the overpriced home store, if that's really all you need, rather than knee-jerking to overkill.)
    – Ecnerwal
    May 24, 2023 at 18:58
  • @Ecnerwal. . . hmm. can't imagine why you mentioned 100 ft lengths unless you mixed up Greg Hill's job with mine who is doing a conduit for a feed that's 100 ft. We're buying from an electrical distributor. Three THWN-2 stranded 10 gauge including plenty of length for drops - $77 USD (Houston Wire) May 24, 2023 at 20:45
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    @A.G.Bell while circuits like this may seem like a clever gig for a handyman, it must be done by a licensed electrician. The "homeowner-occupant exception" doesn't apply to you. You could only do this sort of work as a helper under the HO-O's supervision. That means you don't spec it, they spec it and you go "as you wish, sir". You can, of course, ascertain what is legal, and refuse to do what is illegal, i.e. "I won't help you bury this at 12" OF COVER unless there's a GFCI at the supply end; 18" would be fine by me." May 24, 2023 at 22:12
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    @Ecnerwal That's a fair point. I blended the "distributor may be cheaper than home center" thought with the "overkill doesn't actually cost that much more" thought. It's true, though: some sheds will never be more than a place to keep the garden tools and will never need more than a lamp and an outlet. There's no reason to overkill something like that.
    – Greg Hill
    May 24, 2023 at 22:16

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