BOXES AND FITTINGS

70-279 duit bodies, and fittings referred to in Section 300-15 used as outlet, junction, or pull boxes, depending on their use. Cast, sheet metal, nonmetallic, and other boxes such as FS, FD, and larger boxes are not classified as conduit bodies. (FPN): For systems over 600 volts, nominal, see Part D of this article. 370-2. Round Boxes. Round boxes shall not be used where conduits or connectors requiring the use of locknuts or bushings are to be connected to the side of the box. 370-3. Nonmetallic Boxes. Nonmetallic boxes shall be permitted only with open wiring on insulators, concealed knob-and-tube wiring, nonmetallic-sheathed cable, and nonmetallic raceways. Exception No. 1: Where internal bonding means are provided between all entries, nonmetallic boxes shall be permitted to be used with metal raceways or metal-jacketed cables. Exception No. 2: Where integral bonding means with a provision for attaching a grounding jumper inside the box are provided between all threaded entries in nonmetallic boxes listed for the purpose, nonmetallic boxes shall be permitted to be used with metal raceways or metal-jacketed cables. 370-4. Metal Boxes. All metal boxes shall be grounded in accordance with the provisions of Article 250. 370-5. Short Radius Conduit Bodies. Conduit bodies such as capped elbows and service-entrance elbows enclosing conductors No. 6 or smaller, and that are only intended to enable the installation of the raceway and the contained conductors, shall not contain splices, taps, or devices and shall be of sufficient size to provide free space for all conductors enclosed in the fitting. B. Installation 370-15. Damp, Wet, or Hazardous (Classified) Locations. (a) Damp or Wet Locations. In damp or wet locations, boxes, conduit bodies, and fittings shall be so placed or equipped as to prevent moisture from entering or accumulating within the box, conduit body, or fitting. Boxes, conduit bodies, and fittings installed in wet locations shall be listed for use in wet locations. (b) Hazardous (Classified) Locations. Installations in hazardous (classified) locations shall conform to Articles 500 through 517. (FPN No. 1): For boxes in floors, see Section 370-27(b). (FPN No. 2): For protection against corrosion, see Section 300-6. 370-16. Number of Conductors in Outlet, Device, and Junction Boxes, and Conduit Bodies. Boxes shall be of sufficient size to provide free space for all conductors enclosed in the box. 70-280 NATIONAL ELECTRICAL CODE The provisions of this section shall not apply to terminal housings supplied with motors. See Section 430-12. Boxes and conduit bodies containing conductors, size No. 4 or larger, shall also comply with the provisions of Section 370-28. (a) Standard Boxes. The maximum number of conductors permitted in standard boxes shall be as is listed in Table 370-16(a). See Section 370-28 where boxes or conduit bodies are used as junction or pull boxes. (1) Table 370-16(a) shall apply where no fittings or devices, such as fixture studs, cable clamps, hickeys, switches, or receptacles, are contained in the box and where no equipment grounding conductors are part of the wiring within the box. Where one or more of these types of fittings, such as fixture studs, cable clamps, or hickeys are contained in the box, the number of conductors shown in the table shall be reduced by one for each type of fitting; an additional deduction of two conductors shall be made for each mounting yoke or strap containing one or more devices or equipment; and a further deduction of one conductor shall be made for one or more equipment grounding conductors entering the box. Where a second set of equipment grounding conductors, as permitted by Section 250- 74, Exception No. 4, is present in the box, then an additional deduction of one conductor shall be made. A conductor running through the box shall be counted as one conductor, and each conductor originating outside of the box and terminating inside the box is counted as one conductor. Conductors, no part of which leaves the box, shall not be counted. The volume of a wiring enclosure (box) shall be the total volume of the assembled sections, and, where used, the space provided by plaster rings, domed covers, extension rings, etc., that are marked with their volume in cubic inches, or are made from boxes the dimensions of which are listed in Table 370-16(a). Exception: Where an equipment grounding conductor or not over four fixture wires smaller than No. 14, or both, enter a box from a fixture canopy and terminate within that box, it shall be permitted to omit these conductors from the calculations. Where branch-circuit conductors enter a fixture canopy from a box and terminate within that canopy, it shall be permitted to count these conductors as not leaving the box. (2) For combinations of conductor sizes shown in Table 370-16(a), the maximum number of conductors permitted shall be computed using the volume per conductor listed in Table 370-16(b), with the deductions provided for in Section 370-16(a)(1). For fixture studs, cable clamps, or hickeys, these deductions shall be based on the largest conductor entering the box; for each yoke or strap containing one or more devices or equipment, the deduction shall be based on the largest conductor connected to device(s) or equipment supported by that yoke or strap; and for equipment grounding conductors, the deductions shall be based on the largest equipment grounding conductor entering the box. The maximum number and size of conductors listed in Table 370-16(a) shall not be exceeded. (b) Other Boxes. Boxes 100 cubic inches (1640 cm³) or less other than those described in Table 370-16(a) and nonmetallic boxes shall be durably and legibly marked by the manufacturer with their cubic inch capacity. The maximum number of conductors permitted shall be computed using the volume per conductor listed in Table 370-16(b), with the deductions pro- ARTICLE 370 - BOXES AND FITTINGS 70-281 vided for in Section 370-16(a)(1). For fixture studs, cable clamps, or hickeys, these deductions shall be based on the largest conductor entering the box; for each yoke or strap containing one or more devices or equipment, the deduction shall be based on the largest conductor connected to device(s) or equipment supported by that yoke or strap; and for equipment grounding conductors, the deductions shall be based on the largest equipment grounding conductor entering the box. Boxes described in Table 370- 16(a) that have a larger cubic inch capacity than is designated in the table shall be permitted to have their cubic inch capacity marked as required by this section, and the maximum number of conductors permitted shall be computed using the volume per conductor listed in Table 370-16(b). Table 370-16(a). Metal Boxes Maximum Number of Conductors Min. Box Dimension, Inches Cu. In. Trade Size or Type Cap. No. 18 No. 16 No. 14 No. 12 No. 10 No. 8 No. 6 4 X 1½ Round or Octagonal 12.5 8 7 6 5 5 4 2 4 X 1½ Round or Octagonal 15.5 10 8 7 6 6 5 3 4 X 2½ Round or Octagonal 21.5 14 12 10 9 8 7 4 4 X 1½ Square 18.0 12 10 9 8 7 6 3 4 X 1½ Square 21.0 14 12 10 9 8 7 4 4 X 2½ Square 30.3 20 17 15 13 12 10 6 411/16 x 1½ Square 25.5 17 14 12 11 10 8 5 411/16 X 1½ Square 29.5 19 16 14 13 11 9 5 4¹¹/₁₆ x 2½ Square 42.0 28 24 21 18 16 14 8 3 x 2 X 1½ Device 7.5 5 4 3 3 3 2 1 3 X 2 X 2 Device 10.0 6 5 5 4 4 3 2 3 X 2 X 2½ Device 10.5 7 6 5 4 4 3 2 3 X 2 X 2½ Device 12.5 8 7 6 5 5 4 2 3 X 2 X 23/4 Device 14.0 9 8 7 6 5 4 2 3 x 2 X 3½ Device 18.0 12 10 9 8 7 6 3 4 X 2½ X 1½ Device 10.3 6 5 5 4 4 3 2 4 X 2½ X 17/8 Device 13.0 8 7 6 5 5 4 2 4 X 2½ X 2 1/8 Device 14.5 9 8 7 6 5 4 2 33/4 X 2 X 2½ Masonry Box/Gang 14.0 9 8 7 6 5 4 2 33/4 X 2 X 3½ Masonry Box/Gang 21.0 14 12 10 9 8 7 4 FS-Minimum Internal Depth 13/4 Single Cover/Gang 13.5 9 7 6 6 5 4 2 FD-Minimum Internal Depth 23/8 Single Cover/Gang 18.0 12 10 9 8 7 6 3 FS-Minimum Internal Depth 13/4 Multiple Cover/Gang 18.0 12 10 9 8 7 6 3 FD-Minimum Internal Depth 23/8 Multiple Cover/Gang 24.0 16 13 12 10 9 8 4 For SI units: one cubic inch = 16.4 cm.³ 70-282 NATIONAL ELECTRICAL CODE Table 370-16(b). Volume Required per Conductor Size of Free Space within Box Conductor for Each Conductor No. 18 1.5 cubic inches No. 16 1.75 cubic inches No. 14 2. cubic inches No. 12 2.25 cubic inches No. 10 2.5 cubic inches No. 8 3. cubic inches No. 6 5. cubic inches For SI units: one cubic inch = 16.4 cm.³ (c) Conduit Bodies. Conduit bodies enclosing No. 6 conductors or smaller other than short radius conduit bodies as described in Section 370-5 shall have a cross-sectional area not less than twice the cross-sectional area of the largest conduit or tubing to which it is attached. The maximum number of conductors permitted shall be the maximum number permitted by Table 1 of Chapter 9 for the conduit to which it is attached. Conduit bodies shall not contain splices, taps, or devices unless they are durably and legibly marked by the manufacturer with their cubic inch capacity. The maximum number of conductors permitted shall be computed using the provisions of Section 370-16(b) for other than standard boxes. Conduit bodies shall be supported in a rigid and secure manner. 370-17. Conductors Entering Boxes, Conduit Bodies, or Fittings. Conductors entering boxes, conduit bodies, or fittings shall be protected from abrasion and shall comply with (a) through (d) below. (a) Openings to Be Closed. Openings through which conductors enter shall be adequately closed. (b) Metal Boxes, Conduit Bodies, and Fittings. Where metal outlet boxes, conduit bodies, or fittings are installed with open wiring or concealed knob-and-tube wiring, conductors shall enter through insulating bushings or, in dry locations, through flexible tubing extending from the last insulating support and firmly secured to the box, conduit body, or fitting. Where raceway or cable is installed with metal outlet boxes, conduit bodies, or fittings, the raceway or cable shall be secured to such boxes, conduit bodies, and fittings. (c) Nonmetallic Boxes. Nonmetallic boxes shall be suitable for the lowest temperature rated conductor entering the box. Where nonmetallic boxes are used with open wiring or concealed knob-and-tube wiring, the conductors shall enter the box through individual holes. Where flexible tubing is used to encase the conductors, the tubing shall extend from the last insulating support to no less than ¼ inch (6.35 mm) inside the box. Where nonmetallic-sheathed cable is used, the cable assembly, including the sheath, shall extend into the box no less than ¼ inch (6.35 mm) through a nonmetallic-sheathed cable knockout opening. In all instances, all permitted wiring methods shall be secured to the boxes. ARTICLE 370 - BOXES AND FITTINGS 70-283 Exception: Where nonmetallic-sheathed cable is used with boxes no larger than a nominal size 2½ inch by 4 inch mounted in walls and where the cable is fastened within 8 inches (203 mm) of the box measured along the sheath and where the sheath extends into the box no less than ¹/₄ inch (6.35 mm), securing the cable to the box shall not be required. Multiple cable entries shall be permitted in a single knockout opening. (d) Conductors No. 4 or Larger. Installation shall comply with Section 373-6(c). 370-18. Unused Openings. Unused openings in boxes, conduit bodies, and fittings shall be effectively closed to afford protection substantially equivalent to that of the wall of the box, conduit body, or fitting. Metal plugs or plates used with nonmetallic boxes, conduit bodies, or fittings shall be recessed at least ¼ inch (6.35 mm) from the outer surface. 370-19. Boxes Enclosing Flush Devices. Boxes used to enclose flush devices shall be of such design that the devices will be completely enclosed on back and sides, and that substantial support for the devices will be provided. Screws for supporting the box shall not be used in attachment of the device contained therein. 370-20. In Wall or Ceiling. In walls or ceilings of concrete, tile, or other noncombustible material, boxes and fittings shall be so installed that the front edge of the box or fitting will not set back of the finished surface more than ¼ inch (6.35 mm). In walls and ceilings constructed of wood or other combustible material, outlet boxes and fittings shall be flush with the finished surface or project therefrom. 370-21. Repairing Plaster and Dry Wall or Plasterboard. Plaster, dry wall, or plasterboard surfaces that are broken or incomplete shall be repaired so there will be no gaps or open spaces greater than ¹/₈ inch (3.18 mm) at the edge of the box or fitting. 370-22. Exposed Surface Extensions. Surface extensions from an outlet box of a concealed wiring system shall be made by mounting and mechanically securing a box or extension ring over the concealed box. Where required, equipment grounding shall be in accordance with Article 250. Exception: A surface extension shall be permitted to be made from the cover of a concealed box where the cover is designed so that it cannot fall off, or be removed if its security means becomes loose, and if the wiring method is flexible and so arranged that any required grounding continuity is independent of the connection between the box and cover. 370-23. Supports. Enclosures within the scope of Article 370 shall be below. rigidly and securely fastened in place in accordance with (a) through (g) (a) Surface Mounting. They shall be fastened to the surface upon which they are mounted unless such surface does not provide adequate support, in which case they shall be supported in accordance with (b). 70-284 NATIONAL ELECTRICAL CODE (b) Structural Mounting. They shall be rigidly supported from a structural member of the building either directly or by using a metal or wood brace. Support wires that do not provide rigid support shall not be permitted as the sole support. (1) Nails, where used as a fastening means, shall be permitted to pass through the interior of the enclosure if located within ¼ inch (6.35 mm) of the back or ends of the enclosure. (2) Metal braces shall be protected against corrosion and formed from metal not less than .020 inch (508 micrometers) thick uncoated. Wood braces shall have a cross section not less than nominal 1 inch (25.4 mm) by 2 inches (50.8 mm). (c) Nonstructural Mounting. It shall be permissible to make a flush installation in existing covered surfaces where adequate support is provided by clamps, anchors, or fittings. Framing members of suspended ceiling systems shall be permitted as the support if the framing members are adequately supported and securely fastened to each other and to the building structure. Enclosures so supported shall be fastened to the framing member by mechanical means such as bolts, screws, or rivets. Clips identified for use with the type of ceiling framing member(s) and enclosure(s) shall also be permitted. (d) Raceway Supported Enclosure(s), Without Devices or Fixtures. Enclosures that are not over 100 cubic inches (1640 cm³) in size and that have threaded entries or have hubs identified for the purpose, and that do not contain devices or support fixtures, shall be considered to be adequately supported where two or more conduits are threaded wrenchtight into the enclosure or hubs, and where each conduit is supported within 3 feet (914 mm) of the enclosure on two or more sides so as to provide the rigid and secure installation intended by this section of the Code. Exception: Conduit or electrical metallic tubing shall be permitted to support conduit bodies provided the conduit bodies are not larger than the largest trade size of the conduit or electrical metallic tubing. Such enclosures shall also be considered to be adequately supported if they comply with subsection (e) following. (e) Raceway Supported Enclosures, With Devices or Fixtures. Enclosures that are not over 100 cubic inches (1640 cm³) in size and that have threaded entries or have hubs identified for the purpose, and that support fixtures or contain devices, or both, shall be considered adequately supported where two or more conduits are threaded wrenchtight into the enclosure or hubs and where each conduit is supported within 18 inches (457 mm) of the enclosure so as to provide the rigid and secure installation intended by this section of the Code. Exception: Conduit shall be permitted to support conduit bodies provided the conduit bodies are not larger than the largest trade size of the conduit. (f) Enclosure(s) in Concrete or Masonry. Enclosure(s) shall be permitted to be supported by being embedded. ARTICLE 370 - BOXES AND FITTINGS 70-285 (g) Pendant Boxes. Boxes shall be supported from a multiconductor cord or cable in an approved manner that protects the conductors against strain, such as a strain relief connector threaded into a box with a hub. 370-24. Depth of Outlet Boxes. No box shall have an internal depth of less than ½ inch (12.7 mm). Boxes intended to enclose flush devices shall I have an internal depth of not less than ¹⁵/₁₆ inch (23.8 mm). 370-25. Covers and Canopies. In completed installations, each outlet box shall have a cover, faceplate, or fixture canopy. (a) Nonmetallic or Metal Covers and Plates. Nonmetallic or metal covers and plates shall be permitted with nonmetallic outlet boxes. Where metal covers or plates are used, they shall comply with the grounding requirements of Section 250-42. (FPN): See Sections 410-18(a) and 410-56(c) for metal faceplates. (b) Exposed Combustible Wall or Ceiling Finish. Where a fixture canopy or pan is used, any combustible wall or ceiling finish exposed between the edge of the canopy or pan and the outlet box shall be covered with noncombustible material. (c) Flexible Cord Pendants. Covers of outlet boxes and conduit bodies having holes through which flexible cord pendants pass shall be provided with bushings designed for the purpose or shall have smooth, well-rounded surfaces on which the cords may bear. So-called hard-rubber or composition bushings shall not be used. 370-27. Outlet Boxes. (a) Boxes at Lighting Fixture Outlets. Boxes used at lighting fixture outlets shall be designed for the purpose. At every outlet used exclusively for lighting, the box shall be so designed or installed that a lighting fixture may be attached. (b) Floor Boxes. Boxes listed specifically for this application shall be used for receptacles located in the floor. Exception: Boxes located in elevated floors of show windows and similar locations where the authority having jurisdiction judges them to be free from physical damage, moisture, and dirt. (c) Boxes at Fan Outlets. Outlet boxes shall not be used as the sole support for ceiling (paddle) fans. Exception: Boxes listed for the application shall be permitted as the sole means of support. 370-28. Pull and Junction Boxes. Boxes and conduit bodies used as pull or junction boxes shall comply with (a) through (d) of this section. (a) Minimum Size. For raceways containing conductors of No. 4 or larger, and for cables containing conductors of No. 4 or larger, the minimum dimensions of pull or junction boxes installed in a raceway or cable run shall comply with the following: 70-286 NATIONAL ELECTRICAL CODE (1) Straight Pulls. In straight pulls, the length of the box shall not be less than eight times the trade diameter of the largest raceway. (2) Angle or U Pulls. Where angle or U pulls are made, the distance between each raceway entry inside the box and the opposite wall of the box shall not be less than six times the trade diameter of the largest raceway in a row. This distance shall be increased for additional entries by the amount of the sum of the diameters of all other raceway entries in the same row on the same wall of the box. Each row shall be calculated individually, and the single row that provides the maximum distance shall be used. Exception: Where a raceway or cable entry is in the wall of a box or conduit body opposite to a removable cover and where the distance from that wall to the cover is in conformance with the column for one wire per terminal in Table 373-6(a). The distance between raceway entries enclosing the same conductor shall not be less than six times the trade diameter of the larger raceway. When transposing cable size into raceway size in (a)(1) and (a)(2) above, the minimum trade size raceway required for the number and size of conductors in the cable shall be used. (3) Boxes or conduit bodies of dimensions less than those required in (a)(1) and (a)(2) above shall be permitted for installations of combinations of conductors that are less than the maximum conduit or tubing fill (of conduits or tubing being used) permitted by Table 1 of Chapter 9, provided the box or conduit body has been approved for and is permanently marked with the maximum number and maximum size of conductors permitted. Exception: Terminal housings supplied with motors, which shall comply with the provisions of Section 430-12. (b) Conductors in Pull or Junction Boxes. In pull boxes or junction boxes having any dimension over 6 feet (1.83 m), all conductors shall be cabled or racked up in an approved manner. (FPN): See Section 373-6(c) for insulation of conductors at bushings. (c) Covers. All pull boxes, junction boxes, conduit bodies, and fittings shall be provided with covers compatible with the box, conduit body, or fitting construction and suitable for the conditions of use. Where metal covers are used, they shall comply with the grounding requirements of