I realize this/these questions have been asked a million times before on this forum, but I appreciate any help that will help me drill down on exactly what materials I need and what I need to do.

Because I live on a rock pile, here in Washington, and it would take forever and a day to dig a trench, my goal is to run wire/cable in sch40 conduit that is mounted up under the eaves of my shop about a 100' from a junction box mounted next to my 200A service panel. The thought behind the junction box is to give extra room for bringing the wire/cable into the 2x4 wall before entering the service panel.

The conduit will go around my shop to a 125A sub panel located in an attached carport that will support a welder, car lift, large compressor, plasma cutter, and lights/outlets. For economic reasons, I would like to use aluminum wire/cable.

  • What size and type of wire/cable do I need?
  • What size PVC conduit can I run the specified wire/cable in?
  • Is it acceptable to use LB conduit bodies to get around the corners of the shop or would those bodies be too tight for the specified wire/cable?

I plan on using the long sweep elbows for other change of directions as needed. Thank you for all your help.

  • 1
    If you use metallic conduit, you need one less wire... As for LBs, realize that they are pulling points. You open them up and pull wire, then pull to the next point - you don't attempt to pull through one.
    – Ecnerwal
    Commented Feb 19, 2021 at 22:31
  • LB's are often labelled for a maximum size wire allowed that is smaller than what is allowed in the conduit of the same size. The specific condulet you are using would need to be consulted. Commented Feb 20, 2021 at 4:23
  • See also this discussion. Commented Feb 20, 2021 at 7:50

1 Answer 1


Most jurisdictions would allow 1/0 Al THWN or better wire rated at 120A (per 75°C terminations) to be rounded up to 125A protection, and a #4 Al ground if using non-conductive PVC conduit.

1.25" minimum conduit would be needed with Sch40 PVC. Long sweeps are probably not necessary. If you use Sch80 PVC you would need to use 1.5".

LB's are fine, you may need to upsize LB's to 1.5" with reducing bushings to accommodate the wire size used, consult the internal markings on the LB's.

You need to protect the feeder with a 125A breaker at the service, check the stab limits in your main panel, sometimes you can't install another breaker across from the 125A breaker.

Your subpanel needs to be rated 125A minimum. However, often for pennies more, you can get a big 200A panel with lots of extra breaker spaces, so do that if it can fit.

  • Please further explain what you mean by "typically you can't install another breaker on opposite side of panel". I like the 200A panel idea, thanks.
    – Rip
    Commented Feb 20, 2021 at 13:27
  • In many 100A+ panels the tabs that the breakers attach to are smaller than the full size of the bussing, and the total amperage of the two breakers attached to each tab can't exceed the rating of the tab. The stab limits aren't always clearly defined, sometimes the high amp breaker is built different to reject opposite breaker, sometimes it just seems to be limited by the specific list of compatible breakers. Commented Feb 20, 2021 at 15:32
  • Yeah -- some panels have kind of onerous stab limits. The good news is that they'll be stated on the label on the inside of the panel's door, so if your panel doesn't mention any, you're good to go Commented Feb 20, 2021 at 15:33

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