ELECTRICAL NONMETALLIC TUBING

70-221 (2) Ten times the external diameter of the metallic sheath for cable greater than 3/4 inch (19 mm) but not more than 1 inch (25.4 mm) in external diameter. 330-14. Fittings. Fittings used for connecting Type MI cable to boxes, cabinets, or other equipment shall be identified for such use. Where singleconductor cables enter ferrous metal boxes or cabinets, the installation shall comply with Section 300-20 to prevent inductive heating. 330-15. Terminal Seals. Where Type MI cable terminates, an approved seal shall be provided immediately after stripping to prevent the entrance of moisture into the insulation. The conductors extending beyond the sheath shall be individually provided with an approved insulating material. 330-16. Single Conductors. Where single-conductor cables are used, all phase conductors and, where used, the neutral conductor shall be grouped together to minimize induced voltage on the sheath. Where singleconductor cables enter ferrous enclosures, the installation shall comply with Section 300-20 to prevent heating from induction. C. Construction Specifications 330-20. Conductors. Type MI cable conductors shall be of solid copper or nickel-clad copper with a resistance corresponding to standard AWG sizes. 330-21. Insulation. The conductor insulation in Type MI cable shall be a highly compressed refractory mineral that provides proper spacing for all I conductors. 330-22. Outer Sheath. The outer sheath shall be of a continuous construction to provide mechanical protection and moisture seal. Where made of copper, it shall provide an adequate path for equipment grounding purposes. Where made of steel, an equipment grounding conductor in accordance with Article 250 shall be provided. ARTICLE 331 - ELECTRICAL NONMETALLIC TUBING A. General 331-1. Definition. Electrical nonmetallic tubing is a pliable corrugated raceway of circular cross-section with integral or associated couplings, connectors and fittings listed for the installation of electric conductors. It is composed of a material that is resistant to moisture, chemical atmospheres, and is flame-retardant. A pliable raceway is a raceway that can be bent by hand with a reasonable force, but without other assistance. 70-222 NATIONAL ELECTRICAL CODE (FPN): It is intended that the material used has ignitibility, flammability, smoke generation, and toxicity characteristics that do not exceed those of rigid (nonplasticized) polyvinyl chloride. 331-2. Other Articles. Installations for electrical nonmetallic tubing shall comply with the provisions of the applicable sections of Article 300. Where equipment grounding is required by Article 250, a separate equipment grounding conductor shall be installed in the raceway. 331-3. Uses Permitted. The use of electrical nonmetallic tubing and fittings shall be permitted: (1) In any building not exceeding three floors above grade. a. For exposed work, where not subject to physical damage. b. Concealed within walls, floors, and ceilings. (FPN): See Section 336-4(a) for definition of first floor. (2) In any building exceeding three floors above grade, electrical nonmetallic tubing shall be concealed within walls, floors, and ceilings where the walls, floors, and ceilings provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies. (3) In locations subject to severe corrosive influences as covered in Section 300-6 and where subject to chemicals for which the materials are specifically approved. (4) In concealed, dry, and damp locations not prohibited by Section 331-4. (5) Above suspended ceilings where the suspended ceilings provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies, except as permitted in Section 331-3(1)a. (6) Embedded in poured concrete, provided fittings identified for this purpose are used for connections. (7) For wet locations indoors or in a concrete slab on or below grade, with fittings listed for the purpose. (FPN): Extreme cold may cause some types of nonmetallic conduits to become brittle and, therefore, more susceptible to damage from physical contact. 331-4. Uses Not Permitted. Electrical nonmetallic tubing shall not be used: (1) In hazardous (classified) locations. Exception: Except as permitted by Section 504-20. (2) For the support of fixtures and other equipment. (3) Where subject to ambient temperatures exceeding those for which the tubing is listed. (4) For conductors whose insulation temperature limitations would exceed those for which the tubing is listed. (5) For direct earth burial. ARTICLE 331 - ELECTRICAL NONMETALLIC TUBING 70-223 (6) Where the voltage is over 600 volts. (7) In exposed locations, except as permitted by Sections 331-3(1), 331- 3(5), and 331-3(7). (8) In theaters and similar locations, except as provided in Articles 518 and 520. B. Installation 331-5. Size. (a) Minimum. Tubing smaller than ½-inch electrical trade size shall not be used. (b) Maximum. Tubing larger than 2-inch electrical trade size shall not be I used. 331-6. Number of Conductors in Tubing. The number of conductors in a single tubing shall not exceed that permitted by the percentage fill in Table 1, Chapter 9. 331-7. Trimming. All cut ends of tubing shall be trimmed inside and outside to remove rough edges. 331-8. Joints. All joints between lengths of tubing and between tubing and couplings, fittings and boxes shall be by an approved method. 331-9. Bends - How Made. Bends of electrical nonmetallic tubing shall be so made that the tubing will not be damaged and that the internal diameter of the tubing will not be effectively reduced. Bends shall be permitted to be made manually without auxiliary equipment, and the radius of the curve of the inner edge of such bends shall not be less than shown in Table 346-10. 331-10. 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. 331-11. Supports. Electrical nonmetallic tubing shall be installed as a complete system as provided in Article 300 and shall be securely fastened in place within 3 feet (914 mm) of each outlet box, device box, junction box, cabinet, or fitting. Tubing shall be secured at least every 3 feet (914 mm). Exception No. 1: Where support is being provided at least every 3 feet (914 mm) by openings through framing members. Exception No. 2: Lengths not exceeding a distance of 6 feet (1.83 m) from a fixture terminal connection for tap connections to lighting fixtures. 331-12. Boxes and Fittings. Boxes and fittings shall comply with the applicable provisions of Article 370. 331-13. Splices and Taps. Splices and taps shall be made only in junction boxes, outlet boxes, device boxes, or conduit bodies. See Article 370. I 70-224 NATIONAL ELECTRICAL CODE 331-14. Bushings. Where a tubing enters a box, fitting, or other enclosure, a bushing or adapter shall be provided to protect the wire from abrasion unless the box, fitting, or enclosure design provides equivalent protection. (FPN): See Section 373-6(c) for the protection of conductors size No. 4 or larger. C. Construction Specifications 331-15. General. Electrical nonmetallic tubing shall be clearly and durably marked at least every 10 feet (3.05 m) as required in the first sentence of Section 110-21. The type of material shall also be included in the marking. Tubing that has limited-smoke-producing characteristics shall be permitted to be identified with the suffix LS.