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The conduit and outside wire has already been run, it's 1.5" sch40 pvc with 2-2-2-6 xhhw-2 wire running from the shop panel to inside the house (A).

My plan was to splice it in a 12x12x6 junction box (A) to SER 1/0-1/0-1/0-2 in the finished closet (B) and run that up the wall inside the closet (exposed?) and try to fish it through the mudroom ceiling (C) to the storage room ceiling (D) and down the wall in the storage room to the main panel. Because of the door in the mudroom I can't go in the wall which would be easier.

Some questions:

  • The plan was to use a 100 amp panel in the workshop, I think I've sized my wire and connectors appropriately.
  • The junction (A) would be coming in from the back of the box so I should only have to worry about the depth of the box and not the width/height. I'm thinking 12x12x6 because more space is better and it's easily available.
  • 1/0-1/0-1/0-2 because if it's in the wall it needs to be rated for 60C so to keep the 100 amps I need 1/0?
  • Is it okay to leave the SER exposed on the ceiling of the closet in that storage room closet? I could also box it in as it's just the oil tank in there and it wouldn't be seen. I'm trying to make the fishing easier by keeping it exposed in that location and only going in the wall to get it over the mudroom ceiling.
  • The destination storage room is technically finished but has holes all over the drywall from various projects so I'm not opposed to poking more holes or even running it outside of the wall if it's easier.
  • I would be using polaris connectors for the splice, could I use 2 or would it be better to use a single 4 wire one?

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  • 1 - Why not use conduit (does not have to be the same type) the whole way? 2 - In case you don't already know a 100A breaker in the main panel feeding appropriate wires can have any panel >= 100A as a subpanel - i.e., does not have to be "exactly 100A panel", can be a 200A panel so you have more spaces for circuits, etc. Jan 6, 2022 at 17:02
  • Are you sure that the Al is 2-2-2-6 and not 2-2-2-4 (90A) or 1-1-1-3 (100A)? Also, can you get 1.5" ENT (smurf tube) where you're at? Jan 7, 2022 at 0:31

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It's fine to feed a 100A subpanel with that. In fact, it's fine to feed a 200A subpanel with that. The main criterion you want for a panel is "plenty of spaces" so you never need deal with the "out of spaces" problem.

However, #2Al wire is only good for 100A if you are attaching at both ends to lugs rated at 90C thermal, such as Polaris connectors. Breakers and subpanel lugs are rated 75C thermal. Except in rare instances, it is more economical to buy the next size up of wire, than do all the enclosures, couplers and fooling around needed to "pigtail" both ends in 90C enclosures with 90C splices. So we advise 90A/75C for #2Al, normally.

However, if the nature of your installation has afforded you the opportunity to "pigtail at both ends", and you have to have those enclosures and splices anyway, then you might as well take advantage of the 90C thermal limit.

Most large wire rated for in-wall use is rated 75C. The only exception is NM type. (UF isn't made this large, and TW is obsolete).

SE is an odd duck. It has been 75C rated for half a century. However last decade, a wire company submitted a proposal to NEC that SE should follow the same rules as NM. This happened late in the revision cycle, so it slipped through largely unnoticed. Once it was noticed, there was massive pushback from just about everyone else, and the consensus waffled from "75C except when packed in insulation" to "75C everywhere". So unless you are under that particular edition of Code and your AHJ takes it seriously, SE should be fine to 75C.

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  • 2-2-2-6 isn't a standard combo of wire sizes anyway Jan 8, 2022 at 2:14
  • @ThreePhaseEel I wondered about that. Perhaps OP is referring to individual XHHW wires. But #6AL ground is legal for 100A. #4 is useful when up-sizing to #2 for a long run with voltage drop concerns, e.g. a 300' 65A circuit (nominally #4AL conductors and #6AL ground) but you use #2 and need to bump ground in proportion. Jan 8, 2022 at 2:43
  • The wire in the conduit is XHHW-2 wire, the run is 50' so we left it at #6 for the ground. The SER i'm looking at is 2-2-2-4. I think I'll just use a 90 amp breaker then as the existing wire in the conduit will be connected directly to a panel with a 75c breaker. Jan 8, 2022 at 11:50

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