UNDERFLOOR RACEWAYS

354-1. Other Articles. Underfloor raceways shall comply with the applicable provisions of Article 300. 354-2. Use. The installation of underfloor raceways shall be permitted beneath the surface of concrete or other flooring material or in office occupancies, where laid flush with the concrete floor and covered with linoleum or equivalent floor covering. Underfloor raceways shall not be installed (1) where subject to corrosive vapors, nor (2) in any hazardous (classified) locations, except as permitted by Section 504-20 and in Class I, Division 2 locations as permitted in the exception to Section 501-4(b). Unless made of a material judged suitable for the condition or unless corrosion protection approved for the condition is provided, ferrous or nonferrous metal underfloor raceways, junction boxes, and fittings shall not be installed in concrete or in areas subject to severe corrosive influences. below. 354-3. Covering. Raceway coverings shall comply with (a) through (d) (a) Raceways Not Over 4 Inches (102 mm) Wide. Half-round and flattop raceways not over 4 inches (102 mm) in width shall have not less than 3/4 inch (19 mm) of concrete or wood above the raceway. Exception: As permitted in (c) and (d) below for flat-top raceways. (b) Raceways Over 4 Inches (102 mm) Wide but Not Over 8 Inches (203 mm) Wide. Flat-top raceways over 4 inches (102 mm) but not over 8 inches (203 mm) wide with a minimum of 1 inch (25.4 mm) spacing between raceways shall be covered with concrete to a depth of not less than 1 inch (25.4 mm). Raceways spaced less than 1 inch (25.4 mm) apart shall be covered with concrete to a depth of 1½ inches (38 mm). (c) Trench-type Raceways Flush with Concrete. Trench-type flush raceways with removable covers shall be permitted to be laid flush with the floor surface. Such approved raceways shall be so designed that the cover plates will provide adequate mechanical protection and rigidity equivalent to junction box covers. (d) Other Raceways Flush with Concrete. In office occupancies, approved metal flat-top raceways, if not over 4 inches (102 mm) in width, shall be permitted to be laid flush with the concrete floor surface, provided they are covered with substantial linoleum not less than ¹/₁₆ inch (1.59 mm) in thickness or with equivalent floor covering. Where more than one and not more than three single raceways are each installed flush with the concrete, assembly. they shall be contiguous with each other and joined to form a rigid 70-264 NATIONAL ELECTRICAL CODE 354-4. Size of Conductors. No conductor larger than that for which the raceway is designed shall be installed in underfloor raceways. 354-5. Maximum Number of Conductors in Raceway. The combined cross-sectional area of all conductors or cables shall not exceed 40 percent of the interior cross-sectional area of the raceway. (FPN): For conductor cross-sectional area, see Tables 5, 5A, 6, and 8 and the applicable Notes to Tables at the beginning of Chapter 9. 354-6. Splices and Taps. Splices and taps shall be made only in 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. Exception: Splices and taps shall be permitted in trench-type flush raceway having a removable cover that is accessible after installation. The conductors, including splices and taps, shall not fill the raceway more than 75 percent of its area at that point. 354-7. Discontinued Outlets. When an outlet is abandoned, discontinued, or removed, the sections of circuit conductors supplying the outlet shall be removed from the raceway. No splices or reinsulated conductors, such as would be the case with abandoned outlets on loop wiring, shall be allowed in raceways. 354-8. Laid in Straight Lines. Underfloor raceways shall be laid so that a straight line from the center of one junction box to the center of the next junction box will coincide with the centerline of the raceway system. Raceways shall be firmly held in place to prevent disturbing this alignment during construction. 354-9. Markers at Ends. A suitable marker shall be installed at or near each end of each straight run of raceways to locate the last insert. 354-10. Dead Ends. Dead ends of raceways shall be closed. 354-13. Junction Boxes. Junction boxes shall be leveled to the floor grade and sealed to prevent the free entrance of water or concrete. Junction boxes used with metal raceways shall be metal and shall be electrically continuous with the raceways. 354-14. Inserts. Inserts shall be leveled and sealed to prevent the entrance of concrete. Inserts used with metal raceways shall be metal and shall be electrically continuous with the raceway. Inserts set in or on fiber raceways before the floor is laid shall be mechanically secured to the raceway. Inserts set in fiber raceways after the floor is laid shall be screwed into the raceway. When cutting through the raceway wall and setting inserts, chips and other dirt shall not be allowed to remain in the raceway, and tools shall be used that are so designed as to prevent the tool from entering the raceway and damaging conductors that may be in place.