I have an existing 40A circuit for my old window A/C. I plan to remove the outlet, pull wire back into basement and terminate to junction box. Then from J-box I'd run PVC conduit thru band joist and along the underside (outside) of porch, then within wall of breezeway, into garage overhead. I'd continue in the garage to the central place I want the outlet.

The porch is 18', breezeway is another 9', figure another 10-15 inside garage and existing length in basement is about 25'. I'd like to use 10awg individual wires within 1/2" ID conduit. Should I use Schedule 40 or 80?

The breezeway wall does not currently exist so that portion only will be new construction. Could other 120v or misc. wiring (gar door opener switch) wiring share the conduit or does it need to be exclusive? I suppose I could run up thru wall in house, thru attic of porch and breezeway but prefer not to have 240v in attics if I can avoid it.

  • Is there any power to the garage now, or is this going to be the power feed to the garage? If it's considered detached you can only have one circuit (or two if one is switched from the house, perhaps) but that rule may not apply if it's considered attached (via the breezeway.) Use aluminum wire. Your wallet will thank you. 8 gauge aluminum on 75C terminals (common for breakers and panels) will do, far cheaper than 10 gauge copper which is not large enough.
    – Ecnerwal
    May 2, 2022 at 15:49
  • 1
    I do have 120v out there, two lines actually pool, (switched) & everything else. I'm thinking this will be a dedicated circuit for car charger so hopefully no sub-panel. So switching to aluminum from j-box in house thru conduit is ok ? Are there special wire nuts to join copper & aluminum? Is that even allowed ? What are 75c terminals ? OK, my mistake I do actually have a 30a breaker & 10awg thru basement. So the new plan is to stay with 30amp OR a "re-wire" and bigger breaker to increase to 40a with 8awg. Is 8awg ok for 50a or even 60a breaker? (assuming my panel would be agreeable) ?
    – Ron C
    May 2, 2022 at 19:34
  • @RonC -- Cu to Al splicing for branch-circuit-sized wires is best done using Ilsco MAC Block connectors (they're a slightly beefier version of the AlumiConns commonly used for "pigtailing" repairs of aluminum house wire, and can even be used instead of AlumiConns for such repairs) May 3, 2022 at 3:39
  • Hmm, I was just looking at the WAGO connectors .. similar to the MAC Block .. I think. If I only have four (4) 10awg in conduit can I get away with a 1/2" ID OR would I have to go to 3/4" ? Not sure what the conduit-loading rules are or how to find out.
    – Ron C
    May 6, 2022 at 20:02
  • I think I found NEC where 10awg uses .0211 sq inches each and the inside of 1/2 sch 40 PVC has .114 sq inches avail at a 40% fill .. so I could actually use 5 wires (5.4) so 4 should be fine .. agree ?
    – Ron C
    May 6, 2022 at 20:19

1 Answer 1


You cannot put low voltage wires in the same conduit as AC power. Conduit is cheap, lay two.

You CAN have multiple circuits in a conduit. The only gotcha is if you do, you may have to "derate" the wire based on NEC 310.15(B)(3)(a). Assuming 3 circuits:

  • #12 gives 20A
  • #10 gives 30A
  • #8 aluminum THHN gives 32A
  • #8 copper THHN and #6 aluminum THHN wire give 44A
  • #6 copper THHN gives 60A

If you have 4 circuits,

  • #10 copper and #8 aluminum give 28A
  • THHN #8 copper and #6 aluminum give 38.5A
  • THHN #6 copper gives 52.5A

Having 5 or more requires a huge derate, and 2 conduits is cheaper in every case.

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