ELECTRICAL METALLIC TUBING

348-1. Use. The use of electrical metallic tubing shall be permitted for both exposed and concealed work. Electrical metallic tubing shall not be used (1) where, during installation or afterward, it will be subject to severe physical damage; (2) where protected from corrosion solely by enamel; (3) in cinder concrete or cinder fill where subject to permanent moisture unless protected on all sides by a layer of noncinder concrete at least 2 inches (50.8 mm) thick or unless the tubing is at least 18 inches (457 mm) under the fill; (4) in any hazardous (classified) location except as permitted by Sections 502-4, 503-3, and 504-20; or (5) for the support of fixtures or other equipment. I Where practicable, dissimilar metals in contact anywhere in the system shall be avoided to eliminate the possibility of galvanic action. Exception: Aluminum fittings and enclosures shall be permitted to be used with steel electrical metallic tubing. Ferrous or nonferrous electrical metallic tubing, elbows, couplings, and fittings shall be permitted to be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition. (FPN): See Section 300-6 for protection against corrosion. 348-2. Other Articles. Installations of electrical metallic tubing shall comply with the applicable provisions of Article 300. A. Installation 348-4. Wet Locations. All supports, bolts, straps, screws, etc., shall be of corrosion-resistant materials or protected against corrosion by corrosion-resistant materials. (FPN): See Section 300-6 for protection against corrosion. 348-5. Size. (a) Minimum. Tubing smaller than 1/2-inch electrical trade size shall not be used. Exception: For enclosing the leads of motors as permitted in Section 430-145(b). (b) Maximum. The maximum size of tubing shall be the 4-inch electrical trade size. 348-6. Number of Conductors in Tubing. The number of conductors permitted in a single tubing shall not exceed the percentage fill specified in Table 1, Chapter 9. (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. 348-7. Threads. Electrical metallic tubing shall not be threaded. Where integral couplings are utilized, such couplings shall be permitted to be factory threaded. 70-252 NATIONAL ELECTRICAL CODE 348-8. Couplings and Connectors. Couplings and connectors used with tubing shall be made up tight. Where buried in masonry or concrete, they shall be concrete-tight type. Where installed in wet locations, they shall be of the raintight type. 348-9. Bends - How Made. Bends in the tubing shall be so made that the tubing will not be damaged and the internal diameter of the tubing will not be effectively reduced. The radius of the curve of the inner edge of any field bend shall not be less than shown in Table 346-10. Exception: For field bends made with a bending machine designed for the purpose, the minimum radius shall not be less than indicated in Table 346-10, Exception. 348-10. Bends - Number in One Run. There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points, e.g., conduit bodies and boxes. 348-11. Reaming. All cut ends of electrical metallic tubing shall be reamed or otherwise finished to remove rough edges. 348-12. Supports. Electrical metallic tubing shall be installed as a complete system as provided in Article 300 and shall be securely fastened in place at least every 10 feet (3.05 m) and within 3 feet (914 mm) of each outlet box, junction box, device box, cabinet, conduit body, or other tubing terminations. Exception: Fastening of unbroken lengths shall be permitted to be increased to a distance of 5 feet (1.52 m) where structural members do not readily permit fastening within 3 feet (914 mm). 348-13. Boxes and Fittings. Boxes and fittings shall comply with the applicable provisions of Article 370. 348-14. Splices and Taps. Splices and taps shall be made only in junction boxes, outlet boxes, device boxes, or conduit bodies. See Article 370. B. Construction Specifications 348-15. General. Electrical metallic tubing shall comply with (a) through (d) below. (a) Cross Section. The tubing, and elbows and bends for use with the tubing, shall have a circular cross section. (b) Finish. Tubing shall have such a finish or treatment of outer surfaces as will provide an approved durable means of readily distinguishing it, after installation, from rigid metal conduit. (c) Connectors. Where the tubing is coupled together by threads, the connector shall be so designed as to prevent bending of the tubing at any part of the thread. (d) Marking. Electrical metallic tubing shall be clearly and durably marked at least every 10 feet (3.05 m) as required in the first sentence of