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I have a question very similar to How to attach to electrical subpanel?. I'm in Washington State, Jefferson County. PoCo is Mason PUD 1. AHJ is WA state L&I.

I want to run at least 70A, but future proof for 100A. Both panels are flush mounted, so their backs are against the exterior sheathing. I think for 100A, I want 3@2 AL XHHW-2 and 1@8 AWG bare copper. I think that fits (with spare room) in 1-1/2" Sched 40 PVC. I have (at least?) 4 90-degree elbows, as shown in the picture below. #1 is a transition from down from the main panel to run in the ground. #2 is a bend around the main building. #3 is a bend towards the outbuilding. #4 is a bend back up the wall of the outbuilding toward the panel.

First question: I've seen comments about expansion joints. Are those a must? A suggestion? We do get snow in WA, but not a lot.

Second question: I've seen comments about using Schedule 80 above grade? A must or a suggestion? There is foot traffic between the buildings (between angle 3 and 4), but that's about it. I had one inspector I talked to say 40 is fine. Might another inspector say something different?

Third question: I saw a comment in another question that XHHW-2 must be in a conduit. Does that mean I can't go straight from conduit into the panel boxes? If not, is there a wire I can use that can? I'd prefer no splices.

Fourth question: At each panel, I'll have a transition between the panel and the conduit. Is that included in the "bends"? If so, any thoughts on how I deal with the 360-degree bend limit? Moving panel placement isn't a viable option (if needed, I can go into details why).

Fifth question: What is the best transition fittings between the panels and conduit? In the question I referenced above, the suggestion was an LB (like https://www.homedepot.com/p/Carlon-1-1-2-in-Schedule-40-and-80-PVC-Type-LB-Conduit-Body-Case-of-6-E986HR/202380271). My concern with that is the building walls are thin (the outbuilding is probably 1/2" plywood - nothing else). With the panels flush-mounted inside, the back of the LB would extend maybe an inch into the box. I then saw a suggestion to add a nipple. Before I'm done, I am almost to the front of the box. And I still don't think I have a mechanical connection between this fitting and the box. Hence my question... Should I transition from PVC to metal and use something like https://www.mcmaster.com/rigid-conduit-fittings/shape~90-elbow/connectors-for-medium-wall-imc-and-thick-wall-rigid-steel-conduit/ or does that also push me over 360 degrees and again after adding a nipple, push me either far from the exterior wall or far into the box?

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  • I'm pretty sure more than 360° of bend between pull points is a no-no. Also, when laying conduit, go big or go home. Get a huge size, so your "I think it'll fit" has more confidence. And run another, for data lines, down the road. – whatsisname Aug 30 '20 at 22:43
  • Sorry. Let me be more precise. According to southwire.com/calculator-conduit, based on the wires I mentioned and the PVC size, I'm at 17% fill. I could use 1 1/4 at 23.24% fill, but as a novice, I want more "wiggle" room. – Tom Getzinger Aug 30 '20 at 22:53
  • By "no-no", I assume you mean "can fail an inspection". What qualifies as a "pull point"? Is that a term I can find in the NEC? And are you saying that any method of going from the vertical conduit into the panels in the wall will add at least some degree of bend, so with my 4 90s, I'm not going to be able to do what I want? If so, any suggestions for solutions? Perhaps I could run a conduit on the side of the main building from point 1 to 3, then do a buried U between the buildings. Problem is, I think there is a downspout at the building corner plus ugly looking fix. – Tom Getzinger Aug 30 '20 at 23:00
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    Pull points are boxes, ""conduit bodies**, or similar, that permit access to the conduit so you can yank wire through. Yes, no-no means can fall inspection, or worse, leaving a situation where you can't feed cable through from one side to the other. – whatsisname Aug 30 '20 at 23:20
  • By that definition, wouldn't both an LB and the rigid conduit piece I mentioned above both be pull points? Both permit access to the conduit so you can yank wire through. – Tom Getzinger Aug 30 '20 at 23:53
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Conduit

Is there any way you can move that east-west pipe north two grids (I'm assuming up is north) so it hugs the house? That would reduce you to three 90s including the stub-ups.

  • You need Schedule 80 PVC for the stub-ups at both ends (bottom of vertical curve to conduit body).

  • Expansion joints, I just don't glue my PVC conduit except where I need to, e.g. within 10' of a stub-up or corner because I don't want it coming apart or moving from pull forces. You won't keep water out; that's a lost cause.

  • Speaking of pull forces, make sure that pipe is good-and-buried and tamped down well, before you start pulling. The pull force would much rather move the whole pipe than just the wire.

  • The conduit body does not count as a 90, because it is accessible.

  • The stub-ups don't have to be dead vertical. If you're parallel to the building you can use a 45 degree at the bottom of the stub-up and come up the wall at a slant. The conduit body doesn't care. Two 45s like that and an extra-broad 90 underground wouldn't be terrible to pull, given your favor for extra large conduit. I would use Rigid for the exposed slanted part, because idiots.

  • If this seems like a lot of digging near the foundation, consider that Rigid conduit only requires a 6" burial depth. It's hella expensive, but it doesn't look like far, and you can trench it with a garden trowel. The only downside to Rigid is it must be cut and threaded, so it'll take a few runs to a hardware store that cuts and threads pipe (and shoplifters).

By the way, that stuff is all much cheaper at the electrical supply.

When you're at the electrical supply, mention your "thin wall" problem. I bet the person will disappear in the back and come back with a couple of iron or aluminum 1-1/2" 90 conduit bodies that have nice stubby ends. That plus a metal "close nipple" and a metal nut, should get it done.

If you can't solve it any other way, I'd thicken the wall in that immediate area with some plywood so the geometry works. Probably help with the conduit entering the ground also.

Wire

I don't know where people get the idea that #2 aluminum is rated for 100A. Table 310.15(B)(16) plainly states 90A in the 75C column, which you usually get to use. (60C if dealing with UF or NM). I suspect they are stealing the friendly derate from 310.15(B)(7), which is only for whole services not subpanel feeder.

You need #1 aluminum for 100A feeder. (or #3 copper). That with a #8 copper will fill your Sch 80 conduit to 26% which ain't so bad. You can use #6 aluminum for your ground, as long as it's insulated. Only copper can be bare in a wet location.

THWN or XHHW wire can't just be loosy-goosy flopping around in your walls. But it sounds like you are running straight out the back of the panel via a conduit body into conduit runs, then back out the same way. That is all conduit or raceway which is fine.

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  • Re: Eliminate bend 3 - yes! Only downside is there is a downward slope from 2 to 3. so now conduit heading back to to outbuilding won't be rue vertical, but you already said that's okay. Re: Sched 80 and exp joints, Okay, I'll add two joints and just do Sched 80 the whole way, or I'll look at rigid pipe. – Tom Getzinger Aug 31 '20 at 2:59
  • @Tom Once you're past the stub-ups Sched 40 is OK in the middle. The issue is somebody's carrying a workbench and they drop it and it smacks into the Sched 40, crunch... Sched 80 handles that better. – Harper - Reinstate Monica Aug 31 '20 at 3:03
  • As long as I'm buying some Sched 80, I'll buy it all. This is all pretty short stuff. – Tom Getzinger Aug 31 '20 at 3:05
  • Re: #2AL, I got that from 310.12(B) and Table 310.12. Rereading, does this not apply since it is a feeder to an outbuilding and not a dwelling? Okay, so #1AL it is.. – Tom Getzinger Aug 31 '20 at 3:06
  • @TomGetzinger Yeah, I knew it was short, that's why I tossed Rigid out there. Why trench to 20" when you only need to trench to 8"? I see in NEC 2020 they brought the table back. They got rid of it in NEC 2014 precisely because it kept misleading people like that. People search for the "what wire size for my ampacity" and there's simple little 310.12 that seems like it's exactly what they're after. So they stop their search and don't dig for the byzantine 310.15(B)(16). – Harper - Reinstate Monica Aug 31 '20 at 3:23

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