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I've got a house in Chicago, which in Chicago residential construction is piped in 1/2" conduit.

I'm finishing up a remodel and still have the rough garage. The plan (back in September before it was cold), was to re-mud the garage, clean up the tape, paint, and then epoxy.

It's cold now, so... I have free reign to make some more holes and then patch and and finish in the spring.

I want to add a 10,000 watt, electric heater to the garage (no, the central vac is 120V too....).

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I have experience pulling 12 gauge with a nylon fishtape 20' feet in mostly clear conduit for small house runs. I've never tried a really long run from the panel (which I'm guessing is like 100 to 120 feet).

Ideally in this run, I would just put in a double pole breaker and pull 8 gauge from the panel all the way to a box in the garage and then add on an outlet + whip somewhere in the garage to finish up the run.

Theoretically that sounds great, but looking at the initial runs out of my panel, they are SUPER STUFFED. Intuitively, it seems like the pipe is too full (no idea on the code requirements for maximum conductors in 1/2 inch conduit).

I have also thought of branching of the 8 gauge as a new conduit run in my basement until I can find the last box that is not as full of wires and then trying to pull to the garage from there.

From someone with experience, would I better off just avoiding the main run (I think in Chicago we call those "home runs") and struggling to pull 8 gauge through there?

It's a huge pain because I don't have experience bending conduit, but if the alternative is wasting 3 hours trying to pull two huge 8 gauge wires through a hopeless scenario I'm can learn to bend some 45s' and offsets.

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    Bending 1/2" conduit isn't hard. You just need the right tool. Commented Oct 30, 2020 at 14:42
  • I did not follow the comment the central vac is 120v are you planning on both 120 and 240? Of so 1/2” pipe will not work because you would need a neutral. That would require a larger pipe size because 2 # 6 are the max for 1/2” rigid and emt.
    – Ed Beal
    Commented Oct 30, 2020 at 15:56
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    Spend more on the heater and less on running it? A cold-climate (usually mini-split) heat pump will provide the same heat on far less electricity - both size of wire needed and power to run it over time.
    – Ecnerwal
    Commented Oct 30, 2020 at 16:13
  • If you bite the bullet and add a subpanel, you can give yourself capacity for an electric car charger, too. You'll thank yourself if you add the conduit and up-size your feeder to 100A or so. Commented Oct 30, 2020 at 16:33
  • I would almost agree with a mini split except I have lived in that area and with months of 20 degree F temps and well into -20 a split will not provide heat, whole house heat pumps use heat strips and those are need the same or larger circuits for winter heat in extreme conditions.
    – Ed Beal
    Commented Oct 30, 2020 at 16:50

2 Answers 2

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First 10000w 240v heater is 41.6 amps to have wire large enough by code 41.6 x125% = 52.08 amps you need #6 wire rated at 55 amps.

You can put 3 ea Thhn #8 wires in 1/2” conduit but that is the max fill code table C.9 in the annex you said 2 wires so I assume you are using the conduit as a ground.

Since you need #6, 1/2” can still be used for 2 wires as that is the max fill same table.

Code allows 4ea 90 degree bends or a maximum of 360 degrees without a pull box.

To tell the truth if you don’t have sweeps for your 90’s you probably won’t make it even with lube at that length if you are at 360 in total turns it gets very tough. I add pull boxes quite often after 180 degrees especially if I am pulling by my self. (If you have someone pushing and at the other end pulling with lube it will normally work).

the pull boxes or conduit body’s can be one of your 90’s or, an inline straight type at a convenient location.

What is lube? Pull lube or soap is used to help the wire slide through the conduit. Years ago we used dish soap the cheap crystal clear stuff you purchased a 1/2 gallon for under 2$ today the lubes are much better and some don’t dry (lube that drys like soap make getting the wire out of the pipe almost impossible later).

I use ideal clear glide for small jobs like yours gob it on for the first 1/2 pull then only a light coat for the last 1/2.

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    It's in conduit and (almost certainly) 75C connections, so #6 copper is actually good for 65A - but you need it because #8 copper only gets to 50A in the 75C column. Obligitory note that you can't use that trick on 10,12 or 14Ga, though.
    – Ecnerwal
    Commented Oct 30, 2020 at 16:29
  • Do we need to have a non electrician training session? Sorry and I appreciate your answers but you are wrong. NEC 110.14.C.1.2. I will summarize, conductors 14 awg through 1 awg are to use the 60 degree table the conductors may have a higher rating but the ampacity is based on the 60 degree table, I never used to point out the little stuff that most non electricians don’t know but after enough down votes and no votes for code referenced and correct answers I have started using what I know and am licensed for.
    – Ed Beal
    Commented Oct 30, 2020 at 16:45
  • @EdBeal -- super appreciate the calculation on the wire gauge. I haven't fully noodled that out yet and checked the final amps on the garage heater. I was going to call them on the final wiring. I've never seen 6 gauge wire, but I bet it's beastly to pull. I can easily see 360 degrees of turns from the panel to the garage too.
    – Leroy105
    Commented Oct 30, 2020 at 16:52
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    @EdBeal -- haha, I'm sitting looking at Mendard's cost for 6 gauge. Wondering the same thing. How sad would you be 2' short of wire...
    – Leroy105
    Commented Oct 30, 2020 at 17:25
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    Yes you won’t find solid wire larger than #10 for the most part it would be impossible to pull. I use stranded exclusively with conduit (I rarely use 14 awg) if stranded Romex was the same price as solid I would use that but it is more expensive because not many use it. (Stranded won’t coil up as bad at the end of the roll also) to reduce coiling pull it off the spool so it unwinds not off the end this helps to straighten it out.
    – Ed Beal
    Commented Oct 30, 2020 at 23:49
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There are rules on how much you can stuff in a conduit. Part of it is based on heat, but part is simply based on basic physics - you can only squeeze so much stuff into a small space. The rule in Chicago (or anywhere that uses (required or not) conduit) is not 1/2" conduit, it is conduit that is big enough for the job. Here is a table (there are many available, Google is your friend):

Conduit Fill Table

It clearly shows you can get 3 or 4 #12 or #14 circuits into a 1/2" conduit. But you can only get 3 #8 wires into a 1/2" conduit, and that is if there is nothing else in the conduit.

The only practical options are:

  • Remove everything else and run just the #8 in the 1/2" conduit to a subpanel and connect everything that was connected directly instead to that subpanel. Note though that the #8 wires may not be big enough for a proper subpanel for both your heater and all the existing circuits, and according to the table I linked, you can't bump up to #6. But it does avoid new conduit.
  • Run a new conduit. To avoid being maxed out immediately, go up to at least 3/4", maybe even 1", so that you can add more circuits and/or upsize the wires later.

As noted in another answer, #8 wire isn't big enough. You could get 2 #6 in there to run a heater, but then you couldn't run a subpanel (because you wouldn't have a neutral). End result: New, larger, conduit.

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  • Oh man, even worse... 3, 8#. There's no way to use the existing run from the panel. That's off the table, so you need to pull the 8# in the basement to get whatever box and branch closests to the garage and then I need to check that. My guess is I'll find a 4 inch box with eventually or 4 12# for 2 20 amp circuits in the garage. (Though maybe 6 12#, 3 20 amp circuits - one for the central vac, and two for outlets).
    – Leroy105
    Commented Oct 30, 2020 at 15:04
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    3 ea #8 or 2#6 will go in emt or rigid but you need #6 wire see my answer.
    – Ed Beal
    Commented Oct 30, 2020 at 15:37

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