I have separate garage building that is fed by a 240v 50A circuit run through 1" schedule 40 to a sub panel in the garage. We are installing a hot tub off the main house but it will be located near where the garage feed exits the basement. The hot tub will be fed by 240v 60A circuits that run to the GFCI disconnect near the tub. Am I correct that I can run 6, #6 conductors (THHN) through 1" sch 40? Is it permitted to run both circuits to a junction box outside the main house through one conduit, then separate them to their respective destinations? Or should I run each completely separately of the other from the main panel?


  • I take it the existing garage feeder is a four wire feeder? Jul 4, 2019 at 15:43
  • Also, do you plan to mount the junction box on the outside of the house, or as a handhole in the ground somewhere? Jul 4, 2019 at 15:48
  • Yes. the feed to the garage is 4 wire.
    – Confundity
    Jul 4, 2019 at 21:45
  • I was planning on mounting the junction on the outside of the house.
    – Confundity
    Jul 4, 2019 at 21:46

1 Answer 1


Yes, you can fit six #6 stranded THWN-2 copper conductors into a 1" Sched 40 PVC conduit, along with up to two #10 ground wires.

Technically, if you use two stranded/insulated #10 THWN-2 ground wires, your conduit fill will be 40.03%. However I would disregard the 0.03%.

Yes, you are allowed to have all these wires stop at a junction box and get spliced to continue onward. If you split the ground wire to both the garage and hot tub, you only need one ground wire.

However, it will be a big box. Each #6 wire needs 5 cubic inches. You will have 6 from the house, 3 from the hot tub and 3 from the garage = 12. Plus 3 cubic inches for all the #10 grounds. So the box must be 63 cubic inches. Now you'd think you could get that beast at a big-box store, right? Nope. You'll need to go to an electrical supply for big boxes, and while you're there, check their prices on other stuff. I find big-box stores are only cheaper on the most popular commodities; on everything else they are a blatant ripoff.

You must use actual white or gray wires for neutrals. The upside of that is that black/colored tape markings on white wires have no meaning whatsoever. This means you can use colored tape to distinguish the two circuits. For instance I might use all black and white, and mark 2 hot tub hots and 1 hot tub neutral all with blue tape, and the garage circuit with red etc.

  • Thank you. If wires enter a junction box, do they have to be spliced? Since the junction is actually just where the conduit splits, it should be possible to run the wires continuously from the main panel to their termination uninterrupted. Does this change the requirement for the outside box?
    – Confundity
    Jul 5, 2019 at 14:43
  • No, you can passthru the box with no splices. That's why I mentioned 2 ground wires, in case you just wanted to have the garage panel's ground roll right through the box without stopping. In that case the box does not need to be as large. A box which only has thru wires is considered a "conduit body" and almost anything will suffice. They even make "T" conduit bodies. Jul 5, 2019 at 15:34

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