In the prelude to the questions, we gave away the fact this is cellular metal
floor raceway. What we didn't give away is the detail that tells you its
defining characteristics. Basically, each cell is a tubular space in an array of cells (called a cellular metal floor member). It's a system, and you use metal fittings to connect the cells.
Also, that row created by the arrangement of cells is parallel to the direction
of the floor member. Wires also must run vertically (to get into the raceway),
and for that purpose you use a header [374.1, 374.2].
The NEC does not provide a list of "Uses Permitted" for this wiring method.
Article 374 is arranged differently from the wiring method Articles that precede
Article 372 (which also lacks this list) in chapter order. There's no subsection 10 (Uses Permitted) and what normally
appears in subsection 12 is instead in subsection 3.
- You can't use it in hazardous locations or where subject to corrosion. In
commercial garages, you can use the concrete version (Article 372) but those places are off limits to this metallic version. [374.3].
- There's no 374.30, either. That's because the raceway support is inherent.
For the same reason, you don't provide supports for the 2x4 wall studs in a
stick frame building when you use them to form the raceway; they are the
- You must use "suitable fittings" [374.2]. Notice here that the NEC does not say "suitable metal fittings" as it does with the concrete version of Article 372. Probably, that omission is because adding "metal" is redundant. Connections to cabinets and other enclosures and/or to extensions from other cells must be made with listed metal raceways and listed fittings [374.11].