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My understanding is that feeder wires need to be in conduit for the whole run, but running schedule 40 through my basement joists seems awful and maybe impossible. I’m wondering if I can use a more flexible conduit from the main panel in my basement, then switch to schedule 40 where it leaves my basement and goes underground to the garage.

Additional info: Aiming to add a 100A sub panel from a 200A main. The run through my basement is maybe 50’ and about 20’ underground to the garage. Based on threads here I think I’ll need #1 aluminum THWN feeder wires. Would be thrilled to get any other advice. Planning to use the garage mostly as a workshop.

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  • What type of "more flexible" conduit are you thinking? With that wire size I think you'll need 1-1/4" or 1-1/2" conduit, and your options for flexible conduit will be few and expensive.
    – JPhi1618
    Nov 4 '21 at 13:45
  • What about running PVC conduit through joists is "awful and maybe impossible"? You can run the conduit below your basement ceiling joists and avoid the fuss, anyway. You can also use metal conduit which gives a more 'finished' look if that's what you care about.
    – TylerH
    Nov 4 '21 at 14:08
  • "feeder wires need to be in conduit for the whole run" - That's not really true, in general. Feeders can be fed like any other circuit as far as the wiring goes, so e.g. a 50 amp subpanel can be fed with 6/3 romex. However, in your specific case you'll need conduit because the largest NM-B is 2 AWG, to my knowledge, which won't cut it for 100 amps. Nov 5 '21 at 4:38
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Use 1½" ENT for the run in the basement

While running rigid conduit thru existing joists is indeed a pain one's better off avoiding, fortunately for you, there is an easy alternative. Electrical Nonmetallic Tubing (ENT/"smurf tube") is listed to mate with same-sized PVC conduit bell-ends and fittings, so you can use ENT of the appropriate size for the run through the basement, then transition to rigid PVC where you exit the basement. You simply have to be careful to obey the 360° limit on accumulated bending between pull points.

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  • Out of curiosity, since ENT is flexible, I would presume it will naturally sag between joists/studs when it is run. Do those sags count toward the 360° bend limit, or are you supposed to pull it tight and anchor it so it doesn't sag in the first place?
    – FreeMan
    Nov 5 '21 at 14:29
  • I’m not familiar with the 360 degree rule, I’ll have to look into that. Another commenter suggested running conduit along the bottom of joists - is that viable? I’d be happy to avoid drilling such large holes through my joists, but I do want to do this correctly.
    – c_C
    Nov 5 '21 at 14:48
  • @c_C -- I would not run it along the bottom of the joists if I were you (you'd need supports almost as often, and it would block folks from finishing the space in the future) Nov 5 '21 at 22:42

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