This wiring method is the counterpart to the surface raceway covered in Articles 386 and 388. The diference is it goes under the floor, instead of on the surface. The NEC does not specify whether it is metallic or nonmetallic. Typically, it is metallic (as far as this author knows, it always is metallic). It's designed to be under (or flush with) the surface of a floor.
There are only two permitted uses. It can be used beneath the surface of concrete (or other flooring material). A second use is in office occupancies where laid flush with the concrete floor and covered with linoleum or equivalent floor covering [390.3(A)]. Notice, that the "Uses Permitted" is in Subsection 3, not in Subsection 10 as is normal for Chapter 3.
- The "Uses Not Permitted" is also is in Subsection 3, not in Subsection 10 as is normal for Chapter 3. And there are two such uses. First, these cannot be used where subject to corrosive vapors [390.3(B)]. Second, you can't use them in any hazardous location except as specifically permitted in 504.20 and 501.10(B)(3).
- Use the mounting hardware that comes with it, or use equivalent hardware. This raceway is manufactured as a system, and is defined as such [390.2]. Install it as such, also.
- You must use couplings and connectors designed for use with the system you are installing. Also: Before you secure it, make sure you lay it out in straight lines 390.9], put markers at the ends [390.10], and level the junction boxes [390.13]. Secure the raceway per the manufacturer's installation instructions.