Can I put 12/2 romex in 15" of 1/2" conduit running from inside wall to the outside?
I am installing an outside light. I can run a 12/2 from the inside and then into 15" of conduit to a box where the exterior light mounts.

 

Yes, in fact you must use protective conduit if the cable is running through a masonry wall (brick, stucco, etc). The conduit should be sealed with caulk or duct sealant once wire is pulled through. Jurisdictions which are very strict on the code may want you to use UF-B or another type of waterproof wiring method in place of that segment of NM-B which is "dry use" only.

 

Thanks. I thought romex, whether NM-B or UF-B in conduit is not permitted due to heat considerations but the short distance might be allowed. I was thinking I might have to run individual conductors.

 

NM in a conduit sleeve inside is fine. NM used outside, even in conduit, is not.

 

Romex® is a federally registered trademark owned by Southwire. It refers to their brand of Type NM cable. It is (too) commonly used as a nickname for any and all Type NM cable, but does not refer to any other type of wiring assembly.

That said, you are right. Type NM cable cannot be installed in conduit and be in compliance with the NEC. Pcboss is also right. Running type NM cable through a conduit sleeve for protection is not only fine, it's required.

Confused? Here's the distinction: Type NM cable cannot be installed in place of individual conductors in a closed conduit system. The potential for damage from excessive heat is a primary reason for that prohibition.

"Sleeving" type NM cable involves running it through a (usually) short piece of conduit which is open on both ends, to protect it from physical damage while allowing the heat to escape. I only put a sealant around a sleeve, not in it.

If what you're planning to do is have one end of the conduit attach to the box that the light will be mounted on, then you aren't planning to use a sleeve. That would be an extension of the enclosed mounting box. In that case, the conduit needs to run to a second, interior, closed box. The Type NM should be spliced to individual conductors in the first box, and those should be run to the outside box.

 

No cable assembly can be installed in a complete and closed conduit system in my area, but I am not aware of the NEC actually prohibiting NM cable from being run in conduit.