FLEXIBLE METALLIC TUBING

A. General 349-1. Scope. The provisions of this article apply to a raceway for electric conductors that is circular in cross section, flexible, metallic, and liquidtight without a nonmetallic jacket. 349-2. Other Articles. Installations of flexible metallic tubing shall comply with the provisions of the applicable sections of Article 300 and Section 110-21. 349-3. Uses Permitted. Flexible metallic tubing shall be permitted to be used (1) in dry locations; (2) in accessible locations where protected from physical damage or concealed, such as above suspended ceilings; (3) for 1000 volts maximum; and (4) in branch circuits. 349-4. Uses Not Permitted. Flexible metallic tubing shall not be used (1) in hoistways; (2) in storage battery rooms; (3) in hazardous (classified) locations unless otherwise permitted under other articles in this Code; (4) underground for direct earth burial, or embedded in poured concrete or aggregate; (5) where subject to physical damage; and (6) in lengths over 6 feet (1.83 m). B. Construction and Installation 349-10. Size. (a) Minimum. Flexible metallic tubing smaller than 1/2-inch electrical trade size shall not be used. Exception No. 1: ³/₈-inch trade size shall be permitted to be installed in accordance with Sections 300-22(b) and (c). Exception No. 2: ³/₈-inch trade size shall be permitted in lengths not in excess of 6 feet (1.83 m) as part of an approved assembly or for lighting fixtures. See Section 410-67(c). (b) Maximum. The maximum size of flexible metallic tubing shall be the ³/₄-inch trade size. 349-12. Number of Conductors. (a) 1/2-Inch and 3/4-Inch Flexible Metallic Tubing. The number of conductors permitted in 1/2-inch and ³/₄-inch trade sizes of flexible metallic tubing shall not exceed the percentage of fill specified in Table 1, Chapter 9. (b) 3/8-Inch Flexible Metallic Tubing. The number of conductors permitted in ³/₈-inch trade size flexible metallic tubing shall not exceed that permitted in Table 350-3. (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. 70-254 NATIONAL ELECTRICAL CODE 349-16. Grounding. See Section 250-91(b), Exception No. 1. 349-17. Splices and Taps. Splices and taps shall be made only in junction boxes, outlet boxes, device boxes, or conduit bodies. See Article 370. 349-18. Fittings. Flexible metallic tubing shall be used only with approved terminal fittings. Fittings shall effectively close any openings in the connection. (FPN): See Sections 300-22(b) and (c) for use in ducts, plenums, and other spaces used for environmental air. 349-20. Bends. (a) Infrequent Flexing Use. Where the flexible metallic tubing shall be infrequently flexed in service after installation, the radii of bends measured to the inside of the bend shall not be less than specified in Table 349-20(a). Table 349-20(a). Minimum Radii for Flexing Use Trade Size Minimum Radii 3/8 inch 10 inches ½ inch 12½ inches 3/4 inch 17½ inches For SI units: (Radii) one inch = 25.4 millimeters. (b) Fixed Bends. Where the flexible metallic tubing is bent for installation purposes and is not flexed or bent as required by use after installation, the radii of bends measured to the inside of the bend shall not be less than specified in Table 349-20(b). Table 349-20(b). Minimum Radii for Fixed Bends Trade Size Minimum Radii 3/8 inch 3½ inches ½ inch 4 inches 3/4 inch 5 inches For SI units: (Radii) one inch = 25.4 millimeters.