Electrical – Can Romex (NM-B) be run in conduit for more than 10 ft when starting from the breaker panel


The answers to this question indicate that NM can be run in conduit: Can Romex (NM-B) be run through conduit?

I was hoping to enclose 12-2 NM-B in EMT for about 20 feet from the breaker box up my garage wall and into my attic to protect it from physical damage as needed when running perpendicular to the joists in my accessible attic. Then, the NM cable would just run the rest of the way unenclosed and parallel to a joist to a non-metallic box with integral cable clamps to feed my garage door motor:
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However, it looks like I may not be able to do so because of section 312.5(C).

Section 312.5(C) lists some additional restrictions which seem to indicate that cable cannot be fully enclosed in raceways (such as EMT) for a length greater than 10 ft if the raceway starts at a cabinet, cutout box, or meter socket enclosure — I understand these definitions to include things known as service panels, breaker boxes, or load centers in language of the typical homeowner. I know there are other options to achieve what I want that do not raise this question (e.g. use something other than EMT for protection, run THHN inside the EMT and then use a junction box to transition to NM), but I would like to know if I'm correctly interpreting section 312.5 in this situation. I have quoted section 312.5(C) from the 2014 NEC below:

312.5 Cabinets, Cutout Boxes, and Meter Socket Enclosures. Conductors entering enclosures within the scope of this article shall be
protected from abrasion and shall comply with 312.5(A) through (C).

(C) Cables. Where cable is used, each cable shall be secured to the
cabinet, cutout box, or meter socket enclosure. Exception: Cables with
entirely nonmetallic sheaths shall be permitted to enter the top of a
surface-mounted enclosure through one or more nonflexible raceways not
less than 450 mm (18 in.) and not more than 3.0 m (10 ft) in length,
provided all of the following conditions are met:

(a) Each cable is fastened within 300 mm (12 in.), measured along the
sheath, of the outer end of the raceway

(b) The raceway extends directly above the enclosure and does not
penetrate a structural ceiling.

(c) A fitting is provided on each end of the raceway to protect the
cable(s) from abrasion and the fittings remain accessible after

(d) The raceway is sealed or plugged at the outer end using approved
means so as to prevent access to the enclosure through the raceway.

(e) The cable sheath is continuous through the raceway and extends
into the enclosure beyond the fitting not less than 6 mm (1⁄4 in.).

(f) The raceway is fastened at its outer end and at other points in
accordance with the applicable article.

(g) Where installed as conduit or tubing, the cable fill does not
exceed the amount that would be permitted for complete conduit or
tubing systems by Table 1 of Chapter 9 of this Code and all applicable
notes thereto. Informational Note: See Table 1 in Chapter 9, including
Note 9, for allowable cable fill in circular raceways. See
310.15(B)(3)(a) for required ampacity reductions for multiple cables installed in a common raceway.

Best Answer

After some reading, the interpretation in the question is correct.

In every edition of the NEC since 2002 when the clause was introduced, you cannot run NM-B in conduit for more than 10ft if the conduit run starts at a cabinet, cutout box, or meter socket enclosure -- this includes "breaker panels".