Nonmetallic boxes shall be used only with cabled wiring methods with entirely nonmetallic sheaths, flexible cords and nonmetallic raceways.
- Where internal bonding means are provided between all entries, nonmetallic boxes shall be permitted to be used with metal raceways and metalarmored cables.
- Where integral bonding means with a provision for attaching an equipment 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 and metal-armored cables.
All permitted wiring methods shall be secured to the boxes.
Outlet and device boxes that enclose devices or utilization equipment shall have a minimum internal depth that accommodates the rearward projection of the equipment and the size of the conductors that supply the equipment. The internal depth shall include that of any extension boxes, plaster rings, or raised covers. The internal depth shall comply with all of the applicable provisions that follow.
- Large equipment. Boxes that enclose devices or utilization equipment that projects more than 17/8 inches (48 mm) rearward from the mounting plane of the box shall have a depth that is not less than the depth of the equipment plus 1/4 inch (6.4 mm).
- Conductors larger than 4 AWG. Boxes that enclose devices or utilization equipment supplied by conductors larger than 4 AWG shall be identified for their specific function.
- Conductors 8, 6, or 4 AWG. Boxes that enclose devices or utilization equipment supplied by 8, 6, or 4 AWG conductors shall have an internal depth that is not less than 21/16 inches (52.4 mm).
- Conductors 12 or 10 AWG. Boxes that enclose devices or utilization equipment supplied by 12 or 10 AWG conductors shall have an internal depth that is not less than 13/16 inches (30.2 mm). Where the equipment projects rearward from the mounting plane of the box by more than 1 inch (25.4 mm), the box shall have a depth that is not less than that of the equipment plus 1/4 inch (6.4 mm).
- Conductors 14 AWG and smaller. Boxes that enclose devices or utilization equipment supplied by 14 AWG or smaller conductors shall have a depth that is not less than 15/16 inch (23.8 mm).
Boxes used at luminaire or lampholder outlets in a wall shall be marked on the interior of the box to indicate the maximum weight of the luminaire or lamp holder that is permitted to be supported by the box in the wall, if other than 50 pounds ( 22.7 kg).
Outlet boxes and outlet box systems used as the sole support of ceiling-suspended fans (paddle) shall be marked by their manufacturer as suitable for this purpose and shall not support ceiling-suspended fans (paddle) that weigh more than 70 pounds (31.8 kg). For outlet boxes and outlet box systems designed to support ceiling-suspended fans (paddle) that weigh more than 35 pounds (15.9 kg), the required marking shall include the maximum weight to be supported.
Where spare, separately switched, ungrounded conductors are provided to a ceiling-mounted outlet box and such box is in a location acceptable for a ceiling-suspended (paddle) fan, the outlet box or outlet box system shall be listed for sole support of a ceiling-suspended (paddle) fan.
Conduit bodies and junction, pull and outlet boxes shall be installed so that the wiring therein can be accessed without removing any part of the building or, in underground circuits, without excavating sidewalks, paving, earth or other substance used to establish the finished grade.
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 E3905.12.1.
TABLE E3905.12.1
MAXIMUM NUMBER OF CONDUCTORS IN METAL BOXESa
| BOX DIMENSIONS (inches trade size and type) | MAXIMUM CAPACITY (cubic inches) | MAXIMUM NUMBER OF CONDUCTORSa | ||||||
| 18 Awg | 16 Awg | 14 Awg | 12 Awg | 10 Awg | 8 Awg | 6 Awg | ||
| 4 × 11/4 round or octagonal | 12.5 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 4 × 11/2 round or octagonal | 15.5 | 10 | 8 | 7 | 6 | 6 | 5 | 3 |
| 4 × 21/8 round or octagonal | 21.5 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| 4 × 11/4 square | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 |
| 4 × 11/2 square | 21.0 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| 4 × 21/8 square | 30.3 | 20 | 17 | 15 | 13 | 12 | 10 | 6 |
| 411/16 × 11/4 square | 25.5 | 17 | 14 | 12 | 11 | 10 | 8 | 5 |
| 411/16 × 11/2 square | 29.5 | 19 | 16 | 14 | 13 | 11 | 9 | 5 |
| 411/16 × 21/8 square | 42.0 | 28 | 24 | 21 | 18 | 16 | 14 | 8 |
| 3 × 2 × 11/2 device | 7.5 | 5 | 4 | 3 | 3 | 3 | 2 | 1 |
| 3 × 2 × 2 device | 10.0 | 6 | 5 | 5 | 4 | 4 | 3 | 2 |
| 3 × 2 × 21/4 device | 10.5 | 7 | 6 | 5 | 4 | 4 | 3 | 2 |
| 3 × 2 × 21/2 device | 12.5 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 3 × 2 × 23/4 device | 14.0 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 3 × 2 × 31/2 device | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 |
| 4 × 21/8 × 11/2 device | 10.3 | 6 | 5 | 5 | 4 | 4 | 3 | 2 |
| 4 × 21/8 × 17/8 device | 13.0 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 4 × 21/8 × 21/8 device | 14.5 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 33/4 × 2 × 21/2 masonry box/gang | 14.0 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 33/4 × 2 × 31/2 masonry box/gang | 21.0 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
The volumes of standard boxes that are not marked with a cubic-inch capacity shall be as given in Table E3905.12.1. E3905.12.1.2 Other boxes.
Boxes 100 cubic inches (1640 cm3) or less, other than those described in Table E3905.12.1, and nonmetallic boxes shall be durably and legibly marked by the manufacturer with their cubic-inch capacity. Boxes described in Table E3905.12.1 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.