Resolución 2535: adopta el Código Eléctrico Nacional, versión 1993. (Sustituye el Anejo A del Reglamento 4435)

(d) Permanent Barriers. Where permanent barriers are installed in a box, each section shall be considered as a separate box. 370-29. Conduit Bodies, Junction, Pull, and Outlet Boxes to Be Accessible. Conduit bodies, junction, pull, and outlet boxes shall be so installed that the wiring contained in them can be rendered accessible without removing any part of the building or, in underground circuits, without excavating sidewalks, paving, earth, or other substance that is to be used to establish the finished grade. Exception: Listed boxes shall be permitted where covered by gravel, light aggregate, or noncohesive granulated soil if their location is effectively identified and accessible for excavation. ARTICLE 370 - BOXES AND FITTINGS 70-287 C. Construction Specifications 370-40. Metal Boxes, Conduit Bodies, and Fittings. (a) Corrosion-Resistant Metal boxes, conduit bodies, and fittings shall be corrosion-resistant or shall be well-galvanized, enameled, or otherwise properly coated inside and out to prevent corrosion. (FPN): See Section 300-6 for limitation in the use of boxes and fittings protected from corrosion solely by enamel. (b) Thickness of Metal. Sheet steel boxes not over 100 cubic inches (1640 cm³) in size shall be made from steel not less than 0.0625 inch (1.59 mm) thick. The wall of a malleable iron box or conduit body and a die-cast or permanent-mold cast aluminum, brass, bronze, or zinc box or conduit body shall not be less than 3/32 inch (2.38 mm) thick. Other cast metal boxes or conduit bodies shall have a wall thickness not less than 1/8 inch (3.17 mm). Exception No. 1: Listed boxes and conduit bodies shown to have equivalent strength and characteristics shall be permitted to be made of thinner or other metals. Exception No. 2: The walls of listed short radius conduit bodies, as covered in Section 370-5, shall be permitted to be made of thinner metal. (c) Metal Boxes Over 100 Cubic Inches. Metal boxes over 100 cubic inches (1640 cm³) in size shall be constructed so as to be of ample strength and rigidity. If of sheet steel, the metal thickness shall not be less than 0.053 inch (1.35 mm) uncoated. (d) Grounding Provisions. A means shall be provided in each metal box, designed for use with nonmetallic raceways and nonmetallic cable systems, for the connection of an equipment grounding conductor. 370-41. Covers. Metal covers shall be of the same material as the box or fitting with which they are used, or they shall be lined with firmly attached insulating material not less than 1/32 inch (0.79 mm) thick, or they shall be listed for the purpose. Metal covers shall be the same thickness as the boxes or fittings for which they are used, or they shall be listed for the purpose. Covers of porcelain or other approved insulating materials shall be permitted if of such form and thickness as to afford the required protection and strength. 370-42. Bushings. Covers of outlet boxes, conduit bodies, and outlet fittings having holes through which flexible cord pendants may pass shall be provided with approved bushings or shall have smooth, well-rounded surfaces upon which the cord may bear. Where conductors other than flexible cord may pass through a metal cover, a separate hole equipped with a bushing of suitable insulating material shall be provided for each conductor. Such separate holes shall be connected by a slot as required by Section 300-20. (FPN): For alternating-current conductors, see Section 300-20(b). 70-288 NATIONAL ELECTRICAL CODE 370-43. Nonmetallic Boxes. Provisions for supports or other mounting means for nonmetallic boxes shall be outside of the box, or the box shall be so constructed as to prevent contact between the conductors in the box and the supporting screws. 370-44. Marking. All boxes and conduit bodies, covers, extension rings, plaster rings, and the like shall be durably and legibly marked with the manufacturer's name or trademark. D. Pull and Junction Boxes for Use on Systems Over 600 Volts, Nominal 370-70. General. In addition to the generally applicable provisions of