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I have a problem like Best way to make wiring to outbuilding legal. Unfortunately, the answers there weren't specific enough to tell me how to solve my problems.

I have an outbuilding that is 3' away from the main house. It has a main lug panel fed from a 50 Amp 240V breaker at the main panel. Wiring is NM 6-3 w/ 10 AWG Ground. From the panel, it goes 2' up behind the wall into the attic, 11' through the attic, unshielded except for the black plastic cover on the cable, 3' between the building through a 1.5" I.D. pipe (not sure if this is an approved metal conduit) which is 8' above grade, then 2.5' between studs in the outbuilding to the main lug panel. I know this is all wrong in so many ways. What I am unsure of is the best way to fix it all.

Q1: I want the outbuilding to have at least 70 Amps. I think I should switch the 50A breaker for a 70A breaker, change the main lug panel to a main breaker panel with a 70A or 100A breaker (just as a disconnect). I think I want to use #1 AL wires and an 8 AWG ground in case I decide to switch to 100A. I also want to add two grounding rods, at least 6' apart, all connected together at the outbuilding panel with 8 AWG bare copper, but not connected to neutral there. Does that sound right so far?

Q2: I believe that overhead of this walkway, I need to be 10' above grade. Where the conduit is currently is at the top of some cinder block steps. I can't go higher where it is (or it hits the roof), but I can move it laterally. If I pick a step where I can place the conduit 10' above it, is that sufficient, or do I need 10' between the edge of the higher step and the conduit (measured kinda diagonally)?

Q3: Can I use Schedule 80 PVC for the conduit between buildings? Or should I use EMT? What size for 70A? for 100A? Or is there a compliant way to skip the conduit? And if so, is it worth going that route?

Q4: What type wire(s) should I use for all this? I'd like to not have a junction anywhere in the middle (so ideally, one run of wires). Is there anything I have to do with the wire(s) in the attic? E.g., if I use AL XHHW-2, can I bury that inside insulated walls, and do I need to do anything special in the attic? Reading PVC electrical conduit connection to service panel, it sounds like I need two J-boxes, on either side of the conduit (if I use conduit). For three #1 AL wires, that sounds like some big J-boxes :(

Q5: Assuming I do need three sections of wire, one conduit, and two J-boxes, I may rethink trenching (it isn't that far...). If I do that, I think I can now use Schedule 40 PVC, go from an outdoor meter main combo box (so, after the service disconnect breaker), down, over, up, and into the outbuilding. Where I'd do it, I'd still want to run wire about 6' between studs to the indoor panel for the outbuilding. It sounds like I'd still need one junction box. Or perhaps I should have an outdoor panel with my disconnect breaker, and possibly breakers for each branch circuit in the outbuilding, each then having NM feeding into the outbuilding and going through studs to where they are needed. Any thoughts on this versus the overhead approach?

Here is a picture of the current pipe between buildings.enter image description here

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  • The 10’ height requirement is irrelevant because you are just running the wire through the breezeway. Also the breezeway means it is not an outbuilding, so no disconnect required. Grats on your new breezeway! Aug 16 '20 at 21:33
  • What defines a "breezeway"? There is a space to walk between the two buildings. Each building is separate, with independent roofs. NEC Art 100 has no definition for "breezeway", but defines "building" as "a structure that stands alone or that is separated from adjoining structures by fire walls." I would think, by the first def, these are separate buildings. So, doesn't 225.18 apply? If breezeway is defined in NEC, can you tell me where? I wish I had a searchable version :( Aug 16 '20 at 23:30
  • Imagine you had a linked passageway that would let you get between buildings without going outside. Now, imagine that passageway only had the roof and not the walls. That's a breezeway and it turns a detached building into an attached one for Code purposes. Aug 17 '20 at 2:17
  • I'm not sure what you mean by "linked" passageway. In any event, as I said, there is no roof connecting the two buildings. There are two separate roofs, each with some degree of overhang, but also with some gap not covered by either roof. I'll see if I can attach a picture to the original question, as I don't know how to add one to a comment. So, it still sounds like I'm back to the original problem, yes? Aug 17 '20 at 15:26
  • You can only add pics to Qs & As, not in comments (except as a link to elsewhere - just edit it into your post). It would be nice if you could include a daylight pic, as the lighting makes it difficult to see. Additionally, I think @Harper-ReinstateMonica is suggesting you might make a "breezeway" out of your 3' walkway, but I may be misinterpreting his comments.
    – FreeMan
    Aug 17 '20 at 16:46

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