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Article 312

Cabinets, Cutout Boxes, and Meter Socket Enclosures

Part I. Scope and Installation

  1. Scope. This article covers the installation and construc‐ tion specifications of cabinets, cutout boxes, and meter socket enclosures. It does not apply to equipment operating at over 1000 volts, except as specifically referenced elsewhere in the Code.
  2. Damp and Wet Locations. In damp or wet locations, surface-type enclosures within the scope of this article shall be placed or equipped so as to prevent moisture or water from entering and accumulating within the cabinet or cutout box, and shall be mounted so there is at least 6-mm (1∕4-in.) airspace between the enclosure and the wall or other supporting surface. Enclosures installed in wet locations shall be weather‐ proof. For enclosures in wet locations, raceways or cables enter‐ ing above the level of uninsulated live parts shall use fittings listed for wet locations.Exception: Nonmetallic enclosures shall be permitted to be installed without the airspace on a concrete, masonry, tile, or similar surface.Informational Note: For protection against corrosion, see 300.6.
  3. Position in Wall. In walls of concrete, tile, or other noncombustible material, cabinets shall be installed so that the front edge of the cabinet is not set back of the finished surface more than 6 mm (1∕4 in.). In walls constructed of wood or other combustible material, cabinets shall be flush with the finished surface or project therefrom.
  4. Repairing Noncombustible Surfaces. Noncombustible surfaces that are broken or incomplete shall be repaired so there will be no gaps or open spaces greater than 3 mm (1∕8 in.) at the edge of the cabinet or cutout box employing a flush-type cover.
  5. Cabinets, Cutout Boxes, and Meter Socket Enclosures. Conductors entering enclosures within the scope of this article shall be protected from abrasion and shall comply with 312.5(A) through (C).
  1. Openings to Be Closed. Openings through which conductors enter shall be closed in an approved manner.
  2. Metal Cabinets, Cutout Boxes, and Meter Socket Enclo‐ sures. Where metal enclosures within the scope of this article are installed with messenger-supported wiring, open wiring on insulators, 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 enclosure.
  3. Cables. Where cable is used, each cable shall be secured to the cabinet, cutout box, or meter socket enclosure.

Exception: Cables with entirely nonmetallic sheaths shall be permitted to enter the top of a surface-mounted enclosure through one or more nonflexible raceways not less than 450 mm (18 in.) and not more than

3.0 m (10 ft) in length, provided all of the following conditions are met:

  1. Each cable is fastened within 300 mm (12 in.), measured along the sheath, of the outer end of the raceway.
  2. The raceway extends directly above the enclosure and does not penetrate a structural ceiling.
  3. A fitting is provided on each end of the raceway to protect the cable(s) from abrasion and the fittings remain accessible after installation.
  4. The raceway is sealed or plugged at the outer end using approved means so as to prevent access to the enclosure through the race‐ way.
  5. The cable sheath is continuous through the raceway and extends into the enclosure beyond the fitting not less than 6 mm (1∕4 in.).
  6. The raceway is fastened at its outer end and at other points in accordance with the applicable article.
  7. Where installed as conduit or tubing, the cable fill does not exceed the amount that would be permitted for complete conduit or tubing systems by Table 1 of Chapter 9 of this Code and all appli‐ cable notes thereto. Note 2 to the tables in Chapter 9 does not apply to this condition.

Informational Note: See Table 1 in Chapter 9, including Note 9, for allowable cable fill in circular raceways. See 310.15(B)(3)(a) for required ampacity reductions for multiple cables installed in a common raceway.

  1. Deflection of Conductors. Conductors at terminals or conductors entering or leaving cabinets or cutout boxes and the like shall comply with 312.6(A) through (C).Exception: Wire-bending space in enclosures for motor controllers with provisions for one or two wires per terminal shall comply with 430.10(B).
    1. Width of Wiring Gutters. Conductors shall not be deflec‐ ted within a cabinet or cutout box unless a gutter having a width in accordance with Table 312.6(A) is provided. Conduc‐ tors in parallel in accordance with 310.10(H) shall be judged on the basis of the number of conductors in parallel.
    2. Wire-Bending Space at Terminals. Wire-bending space at each terminal shall be provided in accordance with 312.6(B)(1) or (B)(2).
      1. Conductors Not Entering or Leaving Opposite Wall. Table 312.6(A) shall apply where the conductor does not enter or leave the enclosure through the wall opposite its terminal.
      2. Conductors Entering or Leaving Opposite Wall. Table 312.6(B) shall apply where the conductor does enter or leave the enclosure through the wall opposite its terminal.Exception No. 1: Where the distance between the wall and its terminal is in accordance with Table 312.6(A), a conductor shall be permitted to enter or leave an enclosure through the wall opposite its terminal, provi‐ ded the conductor enters or leaves the enclosure where the gutter joins an adjacent gutter that has a width that conforms to Table 312.6(B) for the conductor.Exception No. 2: A conductor not larger than 350 kcmil shall be permitted to enter or leave an enclosure containing only a meter socket(s) through the wall opposite its terminal, provided the distance between the terminal and the opposite wall is not less than that specified in Table 312.6(A) and the terminal is a lay-in type, where the terminal is either of the following:
        1. Directed toward the opening in the enclosure and within a 45 degree angle of directly facing the enclosure wall
        2. Directly facing the enclosure wall and offset not greater than 50 percent of the bending space specified in Table 312.6(A)Informational Note: Offset is the distance measured along the enclosure wall from the axis of the centerline of the terminal to a line passing through the center of the opening in the enclo‐ sure.
    3. Conductors 4 AWG or Larger. Installation shall comply with 300.4(G).
  2. Space in Enclosures. Cabinets and cutout boxes shall have approved space to accommodate all conductors installed in them without crowding.
  3. Switch and Overcurrent Device Enclosures. The wiring space within enclosures for switches and overcurrent devices shall be permitted for other wiring and equipment subject to limitations for specific equipment as provided in (A) and (B).
    1. Splices, Taps, and Feed-Through Conductors. The wiring space of enclosures for switches or overcurrent devices shall be permitted for conductors feeding through, spliced, or tapping off to other enclosures, switches, or overcurrent devices where all of the following conditions are met:
      1. The total of all conductors installed at any cross section of the wiring space does not exceed 40 percent of the cross- sectional area of that space.
      2. The total area of all conductors, splices, and taps installed at any cross section of the wiring space does not exceed 75 percent of the cross-sectional area of that space.
      3. A warning label complying with 110.21(B) is applied to the enclosure that identifies the closest disconnecting means for any feed-through conductors.
      imageN
    2. Power Monitoring Equipment. The wiring space of enclo‐ sures for switches or overcurrent devices shall be permitted to contain power monitoring equipment where all of the follow‐ ing conditions are met:
    1. The power monitoring equipment is identified as a field installable accessory as part of the listed equipment, or is
      a listed kit evaluated for field installation in switch or overcurrent device enclosures.
    2. The total area of all conductors, splices, taps, and equip‐ ment at any cross section of the wiring space does not exceed 75 percent of the cross-sectional area of that space.
  4. Side or Back Wiring Spaces or Gutters. Cabinets and cutout boxes shall be provided with back-wiring spaces, gutters, or wiring compartments as required by 312.11(C) and (D).
    Part II. Construction Specifications
  5. Material. Cabinets, cutout boxes, and meter socket enclosures shall comply with 312.10(A) through (C).
    1. Metal Cabinets and Cutout Boxes. Metal enclosures within the scope of this article shall be protected both inside and outside against corrosion.
    2. Strength. The design and construction of enclosures within the scope of this article shall be such as to secure ample strength and rigidity. If constructed of sheet steel, the metal thickness shall not be less than 1.35 mm (0.053 in.) uncoated.
    3. Nonmetallic Cabinets. Nonmetallic cabinets shall be listed, or they shall be submitted for approval prior to installa‐ tion.
  6. Spacing. The spacing within cabinets and cutout boxes shall comply with 312.11(A) through (D).
  1. General. Spacing within cabinets and cutout boxes shall provide approved spacing for the distribution of wires and cables placed in them and for a separation between metal partsof devices and apparatus mounted within them in accordance with 312.11(A)(1), (A)(2), and (A)(3).
    1. Base. Other than at points of support, there shall be an airspace of at least 1.59 mm (0.0625 in.) between the base of the device and the wall of any metal cabinet or cutout box in which the device is mounted.
    2. Doors. There shall be an airspace of at least 25.4 mm (1.00 in.) between any live metal part, including live metal parts of enclosed fuses, and the door.Exception: Where the door is lined with an approved insulating mate‐ rial or is of a thickness of metal not less than 2.36 mm (0.093 in.) uncoated, the airspace shall not be less than 12.7 mm (0.500 in.).
    3. Live Parts. There shall be an airspace of at least 12.7 mm (0.500 in.) between the walls, back, gutter partition, if of metal, or door of any cabinet or cutout box and the nearest exposed current-carrying part of devices mounted within the cabinet where the voltage does not exceed 250. This spacing shall be increased to at least 25.4 mm (1.00 in.) for voltages of 251 to 1000, nominal.
    Exception: Where the conditions in 312.11(A)(2), Exception, are met, the airspace for nominal voltages from 251 to 600 shall be permitted to be not less than 12.7 mm (0.500 in.).
  2. Switch Clearance. Cabinets and cutout boxes shall be deep enough to allow the closing of the doors when 30-ampere branch-circuit panelboard switches are in any position, when combination cutout switches are in any position, or when other single-throw switches are opened as far as their construction permits.
    Table 312.6(A) Minimum Wire-Bending Space at Terminals and Minimum Width of Wiring Gutters
    imageimageimageimageimageimageWire Size (AWG or kcmil) Wires per TerminalCompact Stranded AA-8000 Aluminum Alloy ConductorsAll Other Conductors (see Note 2)
    mm1
    in.
    mm2
    in.
    mm3
    in.
    mm4
    in.
    mm5
    in.14–1012–8Not specified————————8–66–438.111∕2————— — — —4–32–150.82————— — — —21/063.521∕2————— — — —12/076.23————— — — —1/0–2/03/0–4/088.931∕212751787— — — —3/0–4/0250–300102415262038————25035011441∕21526203825410——300–350400–500127520382541030512——400–500600–75015262038254103051235614600–700800–1000203825410305123561440616750–900—2038305123561440616457181000–1250—25410————————1500–2000—30512————————Notes:
    1. Bending space at terminals shall be measured in a straight line from the end of the lug or wire connector (in the direction that the wire leaves the terminal) to the wall, barrier, or obstruction.
    2. This column shall be permitted to be used to determine the minimum wire-bending space for compact stranded aluminum conductors in sizes up to 1000 kcmil and manufactured using AA-8000 series electrical grade aluminum alloy conductor material in accordance with 310.106(B). The minimum width of the wire gutter space shall be determined using the all other conductors value in this table.
      Table 312.6(B) Minimum Wire-Bending Space at Terminals

      Wire Size (AWG or kcmil)Wires per Terminal1234 or More
      All Other ConductorsCompact Stranded AA-8000 Aluminum Alloy Conductors (See Note 3.)
      mm
      in.
      mm
      in.
      mm
      in.
      mm

      in.14–1012–8Not specified————
      —8638.1 11∕2————
      —6450.8 2————
      —4276.2 3————
      —3176.2 3————
      —21/088.9 31∕2————
      —12/0114 41∕2————
      —1/03/014051∕214051∕2178
      7—
      —2/04/015261526190
      71∕2—
      —3/0250165a61∕2 a165a61∕2 a203
      8—
      —4/0300178b7b190c71∕2 c216a
      81∕2 a—
      —250350216d81∕2 d229d81∕2 d254b
      9b25410
      300400254e10e254d10d279b
      11b30512
      350500305e12e305e12e330e
      13e356d14d
      400600330e13e330e13e356e
      14e381e15e
      500700–750356e14e356e14e381e
      15e406e16e
      600800–900381e15e406e16e457e
      18e483e19e
      7001000406e16e457e18e508e
      20e559e22e
      750—432e17e483e19e559e
      22e610e24e
      800—4571850820559
      2261024
      900—4831955922610
      2461024
      1000—50820——
      —
      —

      1250—55922——
      —
      —

      1500—61024——
      —
      —

      1750—61024——
      —
      —

      2000—61024——
      —
      —

      Notes:
      1. Bending space at terminals shall be measured in a straight line from the end of the lug or wire connector in a direction perpendicular to the enclosure wall.
      2. For removable and lay-in wire terminals intended for only one wire, bending space shall be permitted to be reduced by the following number of millimeters (inches):a12.7 mm (1∕2 in.) b25.4 mm (1 in.) c38.1 mm (11∕2 in.) d50.8 mm (2 in.)e76.2 mm (3 in.)
      3. This column shall be permitted to determine the required wire-bending space for compact stranded aluminum conductors in sizes up to 1000 kcmil and manufactured using AA-8000 series electrical grade aluminum alloy conductor material in accordance with 310.106(B).
  3. Wiring Space. Cabinets and cutout boxes that contain devices or apparatus connected within the cabinet or box to more than eight conductors, including those of branch circuits, meter loops, feeder circuits, power circuits, and similar circuits, but not including the supply circuit or a continuation thereof, shall have back-wiring spaces or one or more side-wiring spaces, side gutters, or wiring compartments.
  4. Wiring Space — Enclosure. Side-wiring spaces, side gutters, or side-wiring compartments of cabinets and cutout boxes shall be made tight enclosures by means of covers, barri‐ ers, or partitions extending from the bases of the devices contained in the cabinet, to the door, frame, or sides of the cabinet.

Exception: Side-wiring spaces, side gutters, and side-wiring compart‐ ments of cabinets shall not be required to be made tight enclosures where those side spaces contain only conductors that enter the cabinet directly opposite to the devices where they terminate.

Partially enclosed back-wiring spaces shall be provided with covers to complete the enclosure. Wiring spaces that are required by 312.11(C) and are exposed when doors are open shall be provided with covers to complete the enclosure. Where space is provided for feed-through conductors and for splices as required in 312.8, additional barriers shall not be required.

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