I need to add a circuit and the my panel is outside. The easiest way to run the cable would be to run a conduit vertically from the panel and up through the soffit. Then I would properly run the cable through the attic to. I have two questions.

My question is, what is the proper way to install the conduit? Does the conduit need to extend a certain height up into the attic?

Second, it seems that with much debate, Romex shouldn't be run through a short conduit run. Is it OK to run it since it would be just 6' down to the panel or not? If the answer is no, would I just run the Romex in the attic to a junction box. Then have THHN wires run through the conduit to the exterior of the house and down to the panel?

Thank you

  • 1
    Is running a cable down through the cavity of the exterior wall not an option for some reason? Commented Oct 15, 2018 at 4:06
  • You should run the conduit into a junction box in the attic. Then you can use THHN conductors between the panel and junction box, and any other approved wiring method through the attic. Just make sure the junction box is "accessible". And for convenience sake, I'd put it somewhere that you can work on it easily.
    – Tester101
    Commented Oct 15, 2018 at 10:51
  • You may be able to run NM cable through the conduit, if the conduit is considered a "sleeve", but I don't remember the exact requirements of a sleeve off the top of my head. I'm sure someone else will provide exact details.
    – Tester101
    Commented Oct 15, 2018 at 10:55

1 Answer 1


If you can't get the cable down the wall cavity, then use a junction box to transition to THHN in conduit and go down the wall that way from there

Normally, this run would be inside the wall cavity and then enter the panel from the back -- even if it's somewhat harder to run that way, it has the advantage that you don't have to mess with conduit. If that's not possible, though, the alternative would be to run the NM into a box in the attic, where you transition to THHN in conduit (1/2" EMT or PVC suffices for this) and then run a short length of conduit out the wall into a LB conduit body, then conduit down the wall to a point alongside the panel, where it uses a LL or LR (depends which side of the panel you're on; if you can't be sure when you're buying it, simply pick up an Arlington AnyBODY or equivalent configurable conduit body instead of the LL or LR) body to transition into a nipple into the side of the box -- do not enter the panel from the top! (NEMA 3R boxes require a hub fitting to enter from the top, and generally only have knockouts for a single hub atop the box.)

  • Thanks for the advice. We will be doing a remodel on our bathrooms/kitchen with updated circuits. The reason for not running it down the wall would be that we would eventually be running numerous new cables through the finished family room and around a window. With projects being done over the next few years, we thought the connivence of pulling wire through conduit would be the best bet. Does this make sense? Should/can we do 3/4" conduit to run more wire in one conduit? Thank you.
    – junta
    Commented Oct 16, 2018 at 3:27
  • You're going to be limited to 4 circuits in the conduit due to ampacity derates anyway, so the only sane way to go up to 3/4" is if you were running these as multi-wire branch circuits, but that requires quite a bit of care in this case in order to get the AFCI and GFCI protection right. So, I wouldn't bother upsizing unless you absolutely needed to get the most out of a single conduit.... Commented Oct 16, 2018 at 4:33
  • I finally have had a chance to get to this project. I used EMT that will bring the wires out of the house, but I am having issues finding LL conduit bodies for EMT because I only see ones that are threaded for rigid. Am I looking for the wrong thing? Also, is it appropriate to create a hole in the side of the panel if there isn't any knockouts? I only have them on the bottom of the box. Thanks.
    – junta
    Commented Jan 5, 2019 at 1:00
  • @junta -- Arlington makes an AnyBODY(tm) that will do the trick -- it's both threaded for RMC and set-screwed for EMT. Entering the box from the bottom would work, by the way, although it'd require another conduit body -- if you're familiar with a KO punch set, you should be able to make a 3/4" KO on the lower part of one of the side panels instead. Commented Jan 5, 2019 at 3:12
  • OK, that all helps. Last question I have is although the outdoor conduit bodies have the gasket where you open it up, it doesn't seem very watertight with a set-screw. Is this appropriate though? Thanks once again for all the help on this.
    – junta
    Commented Jan 5, 2019 at 3:45

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