I need to run electrical from the right side of my home where the panel is located on the inside wall of my garage to the total opposite left side of the home where I have a 115v mini split to wire up using 12/2 romex. The easiest way would be for me to come off the panel on the exterior right side of the house and run conduit strait up and pop in the attic then across to the opposite side of the house and pop out again coming down with conduit to a disconnect for the unit. Can I do that whole run from the panel with romex going through the conduit on exterior but when I enter through the attic can I keep going with romex wire without using conduit until I come out on the opposite left side of the house then continue down to the disconnect with conduit? Conduit run on each side would be about 15ft.

  • metal conduit on the outside and in the walls, no conduit on the attic
    – Traveler
    Commented Oct 21, 2022 at 20:14
  • PVC sch 40 ok to use on exterior? Commented Oct 21, 2022 at 20:18

1 Answer 1


No, because NM-B is not allowed outdoors.

The outdoor conduit counts as an outdoor location.

Other issues you'll run into

NM being inside conduit is not a problem, however it takes a great deal of cross-section so you need to use fairly large conduit.

NM exiting conduit in a protected location and continuing onward is not a problem (presuming of course that NM is legal at all in your community; it's not in Chicagoland for instance).

If the conduit is longer than 2 feet, there are thermal derates which limit you to four circuits of 15-20A per conduit. Does not apply to <2’ long conduits. Larger circuits are limited more severely.

Thus the idea of "1 fat conduit coming into the top fitting with all my Romex in it" does not work.

Outdoor panels are a less desirable choice anyway, since it puts your costly and sensitive AFCI and GFCI breakers outdoors.

  • My panel is not on the exterior of the house. It is inside my garage. What is the best & proper way to run from the panel to the opposite side of the house coming out from the garage wall then up the siding to the attic. 1” pvc pipe instead of 3/4 with cabled THHN once in the attic do a junction box an run romex across the attic to the opposite side then another junction switching back to cabled THHN coming out of the attic back into 1” PVC pipe to the disconnect? Commented Oct 22, 2022 at 12:51
  • 1
    @envie nobody says you have to use NM-B cable (Romex). That's just habit. You could use UF-B cable which is basically outdoor NM. (just watch your conduit fill, that stuff takes a lot of fill!) Or if you want to do THHN in the conduit and change to NM in junction boxes accessible from inside the attic, that is fine too. THHN is very favorable for conduit fill, so 1/2" pipe might suffice. Commented Oct 22, 2022 at 20:45
  • Is it ok to hide conduit that is on exterior of the house with a gutter? Visually a gutter run would look better than seeing the grey conduit but I’m not sure if that is ok. Commented Oct 27, 2022 at 21:31
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    @Envieddesigns Sure, as long as you're not covering up the lid of a conduit body or junction box. Just remember conduit needs to have an ability to shed heat, so don't bury it too much. Alternately, feel free to paint the stuff. With PVC, give it a light scuff-sand with a Scotchbrite pad e.g. the green kind used in the kitchen, so the primer has a rough surface to bite into. With metal conduit, give the galvanizing a year to age, same effect. Note that gray PVC is gonna turn white from UV exposure from the sun. It's not that UV resistant. Commented Oct 27, 2022 at 21:47

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