I have 1" conduit running out to a gazebo on my patio. I would like to install a 240 circuit for 2 infrared heaters and a 120 circuit for a ceiling fan. Based on the heaters I want to use (2 3000W heaters that each draw 12.5A), I need to run 8-gauge wire for them. Can I fit 2 8-gauge conductors, an 8-gauge ground, and 2 12-gauge conductors for the ceiling fan? I was intending to use the 8-gauge ground to also ground the ceiling fan.

EDIT: Conduit is SCH 40 Cantex

  • Which type of conduit? The inside diameter varies a little; it's possible that a set of wires meet the fill rules for one type of 1" conduit but exceed the allowance for another.
    – Greg Hill
    Jul 11, 2021 at 14:47
  • It's true there's a small difference in ID's @greghill, but they'd have to be using crazy-big wire before that would matter on 1". Jul 11, 2021 at 17:32
  • Do the installation instructions specify circuit size requirements? Instructions are part of UL/CSA/ETL Listing and by NEC take priority above general circuit requirements. Jul 11, 2021 at 20:42
  • @NoSparksPlease I have not received them yet but from the online documentation I have looked at Jul 11, 2021 at 21:05
  • Why not just put a small sub panel in the gazebo and feed it with #6 Al? Jul 11, 2021 at 21:10

2 Answers 2


4 circuits

Note that a Multi-Wire Branch Circuit counts as 1 circuit.

You are really very unlikely to overfill a 1" conduit, unless you get into some crazy-huge wire, maybe lol.

Get into some crazy-huge wire, maybe!

You'll go broke putting #8 copper in that pipe. So if you even needed wire that large, use #6 aluminum instead. It's perfectly fine for large feeder like this. It attaches directly to the circuit breaker on the breaker end. On the other end, use 2-port "MAC Block connectors" (which are halfway between an Alumiconn and a Polaris in size and cost. One port takes the #6Al wire, and the other port takes 2x #12 for going onward to your heaters.

Actually let's review the amperages for each size of wire that is THWN or XHHW wire inside conduit which is permitted 75C thermal.

  • #14 Cu = 20A 15A due to 240.4(D) limitations
  • #12 Cu = 25A 20A due to 240.4(D) limitations
  • #10 Cu = 35A 30A due to 240.4(D)
  • #8 Cu = 50A
  • #8 Al = 40A
  • #6 Al = 50A

But you probably don't need wire that large.

Not least, because the allowance for 4 circuits is a game-changer.

Look closely at the heater's rating. Here's what you thought: "it's a 240V heater and computing 3000/240V = 12.5. When we apply a 125% derate, we get 15.625, x2 = 31.125A." Look again.

You may find it is a 250V heater. Now compute 3000/250V = 12.000. When we apply a 125% derate, we get 15.000A. X2 = 30A. Wow, it's almost like they sized the heater for that.

And even if it's a long run, we don't really care about voltage drop on a heater. The heater doesn't care. It's certainly not going to be bothered by 10% voltage drop. So getting spendy on thick wire isn't constructive.

  • Thanks for the detail. The heater specs say 240V an 12.5A. Everything I have found says that due to derating, in order to support 2 of those heaters I would need 8GA wire and a 40A breaker. I am sure I could make it work with 10GA and a 30A breaker but trying to do it the right way. Jul 11, 2021 at 17:20
  • If this was attached to (or part of) your house, the easy solution would be 2 x 20A 12 AWG circuits. I suspect (Harper can confirm) that you can't do that because circuits to other structures are "one circuit of each type". Jul 11, 2021 at 17:24
  • @manassehkatz that's a good point. Jul 11, 2021 at 17:31
  • What is meant by the comment "one circuit of each type"? Jul 11, 2021 at 18:19
  • 1
    Type means a 120V circuit, vs. a MWBC, vs. a 240V circuit, vs. a 120/240V circuit. You can only have one of each voltage, unless there's something special about it like being switched from the house. Jul 11, 2021 at 18:21

To answer your question, yes 3@#8 and 2@#12 will fill in sch 40 pvc only 16%, which is less than half of the allowed 40%.

But your ground will be larger than required, #10 copper is good for 60A for ground.

But why not run two separate 20A circuits for the heaters and use all #12? 4 wires for two heater circuits, two wires for fan, and a ground. Would all fit in 1/2" pvc, no fancy wire connectors, 125% rating for fixed electric satisfied, derating for 6 current carrying is satisfied, voltage drop is good for 200', easier to work on if fault develops.

  • Why not just put a small subpanel in the gazebo? Jul 11, 2021 at 21:08
  • @Craig a subpanel might seem a bit out of place on a gazebo, though technically just fine. Jul 11, 2021 at 21:36
  • I don't know, I think a small outdoor-rated breaker box would probably fit nicely behind a rose bush or under a bench? ;-) homedepot.com/p/… Jul 13, 2021 at 0:39
  • @Craig (a) Panel needs to have workspace in front of it - so under a bench for sure won't and have to be careful about bushes/etc. too; (b) once you go to subpanel, you also need cutoff switch (which could probably be done with this little panel by using 2 spaces for a feed breaker) and (c) once you go to subpanel also need ground rods. All makes sense for a shed/workshop/garage, but perhaps a bit overkill for a gazebo - even though the subpanel itself costs very little. Jul 13, 2021 at 3:29
  • If it’s a bench that you can just scoot away from the wall, I don’t see what the problem is. If it’s built-in, it would be different. Aug 8, 2021 at 20:02

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