372.1 Scope. This article covers cellular concrete floor raceways, the hollow spaces in floors constructed of precast cellular concrete slabs, together with suitable metal fittings designed to provide access to the floor cells.
372.2 Definitions.
Cell. A single, enclosed tubular space in a floor made of precast cellular concrete slabs, the direction of the cell being parallel to the direction of the floor member.
Header. Transverse metal raceways for electrical conductors, providing access to predetermined cells of a precast cellular concrete floor, thereby permitting the installation of electrical conductors from a distribution center to the floor cells.
372.4 Uses Not Permitted. Conductors shall not be in stalled in precast cellular concrete floor raceways as follows:
(1) Where subject to corrosive vapor
(2) In any hazardous (classified) location, except as permitted by other articles in this Code
(3) In commercial garages, other than for supplying ceiling outlets or extensions to the area below the floor but not above
FPN: See 300.8 for installation of conductors with other systems.
372.5 Header. The header shall be installed in a straight line at right angles to the cells. The header shall be me- chanically secured to the top of the precast cellular concrete floor. The end joints shall be closed by a metal closure fitting and sealed against the entrance of concrete. The header shall be electrically continuous throughout its entire length and shall be electrically bonded to the enclosure of the distribution center.
372.6 Connection to Cabinets and Other Enclosures. Connections from headers to cabinets and other enclosures shall be made by means of listed metal raceways and listed fittings.
372.7 Junction Boxes. Junction boxes shall be leveled to the floor grade and sealed against the free entrance of water or concrete. Junction boxes shall be of metal and shall be mechanically and electrically continuous with the header.
372.8 Markers. A suitable number of markers shall be installed for the future location of cells.
372.9 Inserts. Inserts shall be leveled and sealed against the entrance of concrete. Inserts shall be of metal and shall be fitted with grounded-type receptacles. A grounding conductor shall connect the insert receptacles to a positive ground connection provided on the header. Where cutting through the cell wall for setting inserts or other purposes (such as providing access openings between header and cells), chips and other dirt shall not be allowed to remain in the raceway, and the tool used shall be designed so as to prevent the tool from entering the cell and damaging the conductors.
372.10 Size of Conductors. No conductor larger than
1/0 AWG shall be installed, except by special permission.
372.11 Maximum Number of Conductors. The com- bined cross-sectional area of all conductors or cables shall not exceed 40 percent of the cross-sectional area of the cell or header.
372.12 Splices and Taps. Splices and taps shall be made only in header access units or junction boxes.
For the purposes of this section, so-called loop wiring (continuous unbroken conductor connecting the individual outlets) shall not be considered to be a splice or tap.