I want to run a new 240V eletrical line to the garage as in the picture below. The dark blue one is the panel and the light blue is the garage. The problem is the roof is very sloped so it is almost impossible to get to that corner through the attic. I do have a hole going up from the panel to the house, but how could I fish something from that corner? do I have to open an area of ceiling from inside to do so? I really don't want to patch drywall (and painting)..

There is also an existing conduit that carries a 240V from the panel to the kitchen. It's about 1" in diameter. It does have space to have another 8/3 wire, so one option is to somehow break the conduit in the attic, and separate the two lines with a junction box. Is this something safe?

Alternatively, I considered to let the wire:

  1. Go through crawlspace
  2. Go directly through outside
  3. Enter the attic from a vent, which is not far from the panel

They may work...but I still prefer to have it go through attic directly if possible. Any suggestions would be appreciated. Thanks!

Edit: I measure the conduit using caliper - the OD reads 1 7/32. It's plastic. There are 3 wires in it - 2x hot 8 TW, 1 neutral 10 TW, no grounding)

house attic view

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    What is the size of that existing conduit? Also, what wires are in it already, and how large are they? – Harper - Reinstate Monica Jul 22 at 17:20
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    Note that you almost certainly do not want to put an 8/3 cable in conduit - you want to put individual wires in there, and you hope that's what's already in it, or fill percentages may be violated. – Ecnerwal Jul 22 at 17:25
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    When I ask about conduit size, the best way to know that is either see which size of open wrench will barely slip over it, or measure its circumference with a sewing tape measure, and get back with us. From that info, we will be able to derive a trade size, and the trade size will tell us how many wires will fit in it. Also if you can find a fitting on the conduit and tell us if it's threaded or sleeved. – Harper - Reinstate Monica Jul 22 at 17:40
  • @Ecnerwal not least because #8 THHN wires in conduit are allowed 50A, and #8 cable is only allowed 40A. – Harper - Reinstate Monica Jul 22 at 17:42
  • Well, you might be able to fish down to the panel if there aren't any cross-braces between the studs in that wall. Or, if the panel is in some back closet or the like and you don't mind running a new conduit up the wall, then it's just a small hole in the ceiling to get the new conduit thru to the attic/crawlspace. – Carl Witthoft Jul 22 at 19:09

Easy peasy. This is what conduit is for.

I propose putting 2 circuits in it. However, there are strict rules on conduit fill, and putting 2 cables in a conduit is impossible to do legally. So don't even try - switch to THHN individual wires. Now you have plenty of room.

Yes, you'll need to find an appropriate point to install a junction box. Now, if you do any splicing in this junction box, any at all, you'll need to do the cubic inch math. However if all wires simply pass through the box, and never will be spliced, then you can treat it same as a conduit body and any common box with enough physical space will suffice. I'm a big fan of that one, so I advise running 2 separate ground wires - one for the range circuit and one for the garage circuit. That way you don't have to splice in the box.

If I wasn't splicing, I'd use a 4-11/16" square deep box. This box must remain accessible, it can't be mudded or plywooded over.

The oven circuit needs a #10 ground wire. It really should have been put in at the time, and you'll have a chance to fix that now. Its neutral also needs to be #8.

I know you're familiar with 8/3 cable, but you cannot use 2 cables in a conduit - the only way it works is individual THHN wires. You're not obliged to use conduit all the way - you can transition to 8/3 cable at any junction box with enough cubic inches to handle the splice. But if you do run conduit all the way, you get to run a higher ampacity: #10=35A #8=50A #6=70A.

The range needs a #10 ground (use bare to save conduit fill) and the garage circuit needs a #10 also.

The #8/#8/#10/none wiring to the range was (well, is) incorrect. It needs to be #8/#8/#8/#10. Further, if somehow it is cable, it needs to be switched to THHN wire because of the conduit fill problem.

Even if they are individual THHN wires, you need to pull them out of the conduit. You cannot modify the piping with the wire in it. Code prohibits this, and you'll nick the wire - trust me. Put the range circuit back with a #8 neutral and #10 ground. I don't care if you convert your range connection to 4-wire (removing ground jumper) today, but I hope you do it soon.

I've run the numbers and the biggest you can do is - a #8 circuit to the range and a #6 circuit to the garage - #8 circuits to both range and garage, with space left over in the pipe for up to 2 additional circuits!

A #6 cable to the garage could carry up to 70 amps if the whole run is THHN in conduit. If you switch to cable for part of it, then you're limited to only 60A. A #8 cable is similarly limited - 50A THHN-in-conduit, 40A if any cable is involved.

Or you could go with a big subpanel! You could potentially pull three #3 copper THHN wires (#8 ground) to the garage, and fit a subpanel there. The #3 copper wire would allow a 100A subpanel. That would fill the pipe, however you wouldn't have room for any more wires. You would then have to double back from the subpanel to serve the range.

* If you can't avoid a splice in a box, here are the gory details on the cubic inch math: Each #6 wire needs 5.0 cubic inches. Each #8 needs 3.0. Each #10 needs 2.5, #12 needs 2.25 cubic inches. One #10 ground can be shared among all circuits. For cubic inches, you only count the largest ground once, and all other grounds are "free".

  • Thank you Harper! I'm still a bit confused:( The range will get a 888/10, garage will get a 666/10 (this should be ok with "cable"), and you mentioned a subpanel, so what would be the line from main panel to subpanel? should the subpanel be around the range, or are you saying, the conduit can have both "888/10" and "666/10" + 2 ground (doesn't sound like it), or a even larger feed to the subpanel? – Shawn Jul 23 at 2:30
  • I'm sorry, I assumed you were putting a subpanel in the garage. If you're only feeding an EV charger, then substitute "EV charger" wherever I said "subpanel" and consult the documentation for whether you need a neutral. – Harper - Reinstate Monica Jul 23 at 2:40
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    Again, do not use cable. I understand that cable is the only thing you know. Stretch yourself and learn what "individual wires / THHN" is all about. Not super hard, quite rewarding because it is a very versatile wiring system that lets you do lots of stuff. If you're only running #8 to the garage, you have room for another circuit in there! – Harper - Reinstate Monica Jul 23 at 2:42
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    @Shawn oh no, I'm not saying to do all that (though it is certainly allowed). I'm suggesting you run the oven circuit and the to-the-garage circuit in the same conduit, even though they go to different destinations they can share the conduit for a distance. Forget the subpanel, you don't need one. I just assumed you were putting a wood shop in your garage or something. – Harper - Reinstate Monica Jul 23 at 3:03
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    Yes exactly. Also note the #10 can be bare wire, which will save cubic inches in the pipe. I've edited to remove the erroneous references to a subpanel, and I added a section that talked about the "subpanel in garage then double back to range" option. – Harper - Reinstate Monica Jul 23 at 3:20

I did something similar in my house recently, in a similar situation. The feed up from the panel on the outside of the house came up inside a soffitt, which had to come up a few inches before it even cleared the top plate. It would have been impossible to reach in there even if I did have a small child I hated enough to ask to do the job.

So what we did was: My wife stuck a coat hanger, I mean fish wire, up from the exterior, and I crawled as close as I could possibly get into the eave area, and stuck another fish wire over to meet her fish wire. Each wire had a hook, and her wire had a line taped to the wire. I was able to hook her wire, pull the string up, and use that to pull a sturdy rope afterwards. Once you have the rope in place, you can pull a cable through if one person pushes while the other pulls.

We did not feel that conduit was necessary as we were pulling 3 or 4 gauge service cable, which in my limited understanding is OK to run through attic space unprotected. If there is a code violation there, I hope someone will speak up.

I guess in your situation the difficult part would be to get a hole up inside the wall, behind the panel. You could run exterior (through properly sized conduit) into the eave/soffitt if that wasn't possible.

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    Not a code violation, but I've seen way too many gnawed Romex cables to personally feel comfortable with it. The 100% rodent-free attic is largely a myth... – Ecnerwal Jul 22 at 19:40
  • This sounds like a brilliant idea as well! I'll see if I could do something similar – Shawn Jul 23 at 18:44
  • In order to properly reproduce the experience, make sure a) your wife can't really hear you very well, and b) you shout at the top of your lungs some combination of: "Higher!" "Lower!" "Bend it left!" "No, the OTHER left!" – Puddles Jul 23 at 19:01

You want to stay away from doing anything with the conduit. I had a similar problem where I actually put in a few small sheets of plywood and crawled on my belly like a reptile and got back into that corner. If you can do that, you might just find enough space where the conduit comes through the ceiling to shove the 8/3 romex through and down to the panel. Then from the front or inside of the panel try to guide the romex into the panel.

If you have to cut the ceiling, use a hack saw because it will make a very thin cut. Cut a six inch square, do your fishing and then reattach the drywall cutout with a few furring strips and finish with joint compound.

  • Why would he want to stay away from doing anything with the conduit? If he's got the free fill space, it probably is better to run individual THHNs through to a JB in the attic at the transition point vs. trying to feed a cable through a mess of awkwardness... – ThreePhaseEel Jul 22 at 22:59
  • He probably got more than one 240v run, one for the stovetop, one for the oven. He'd have to install the JB: remove existing wires, cut section out of conduit, install JB, pull existing wires from kitchen to JB, continue pull from JB with new THHN wires into panel, splice THHN to 8/3 romex . I just figured trying to get through a mess of awkwardness was a good starting point. – JACK Jul 22 at 23:32
  • Ah...You are absolutely right on. There are two lines of 240V in there, however, only 1 of them is being used. One line is 8AWG while the other appears to be 10AWG (so there are totally 6 wires, no grounding). I turned of the "smaller" breaker of the 10AWG, it has no effect at all and my range is for sure connected to one single receptcle only. I guess it was originally for a separated stove and oven, but the previous owner might changed it to be a single source. That's probably why it's only 8AWG not 6AWG since the range requires more power.. – Shawn Jul 23 at 1:56
  • Let us know how this turns out..... Good luck... Harper definitely knows what he's talking about. – JACK Jul 23 at 14:25

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