// CODE SNIPPET
314.16 Number of Conductors in Outlet, Device, and Junction Boxes, and Conduit Bodies
JUMP TO FULL CODE CHAPTER
Boxes and conduit bodies shall be of an approved size to provide free space for all enclosed conductors. In no case shall the volume of the box, as calculated in 314.16(A), be less than the fill calculation as calculated in 314.16(B). The minimum volume for conduit bodies shall be as calculated in 314.16(C).
The provisions of this section shall not apply to terminal housings supplied with motors or generators.
Informational Note: For volume requirements of motor or generator terminal housings, see 430.12.
Boxes and conduit bodies enclosing conductors 4 AWG or larger shall also comply with the provisions of 314.28. Outlet and device boxes shall also comply with 314.24.
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, and so forth, that are marked with their volume or are made from boxes the dimensions of which are listed in Table 314.16(A). Where a box is provided with one or more securely installed barriers, the volume shall be apportioned to each of the resulting spaces. Each barrier, if not marked with its volume, shall be considered to take up 8.2 cm3 (1/2 in.3) if metal, and 16.4 cm3 (1.0 in.3) if nonmetallic.
Table 314.16(A) Metal Boxes
| Box Trade Size | Minimum Volume | Maximum Number of Conductors* (arranged by AWG size) |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| mm | in. | cm3 | in.3 | 18 | 16 | 14 | 12 | 10 | 8 | 6 | |
| 100 × 32 | (4 × 11/4) | round/octagonal | 205 | 12.5 | 8 | 7 | 6 | 5 | 5 | 5 | 2 |
| 100 × 38 | (4 × 11/2) | round/octagonal | 254 | 15.5 | 10 | 8 | 7 | 6 | 6 | 5 | 3 |
| 100 × 54 | (4 × 21/8) | round/octagonal | 353 | 21.5 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| 100 × 32 | (4 × 11/4) | square | 295 | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 |
| 100 × 38 | (4 × 11/2) | square | 344 | 21.0 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| 100 × 54 | (4 × 21/8) | square | 497 | 30.3 | 20 | 17 | 15 | 13 | 12 | 10 | 6 |
| 120 × 32 | (411/16 × 11/4) | square | 418 | 25.5 | 17 | 14 | 12 | 11 | 10 | 8 | 5 |
| 120 × 38 | (411/16 × 11/2) | square | 484 | 29.5 | 19 | 16 | 14 | 13 | 11 | 9 | 5 |
| 120 × 54 | (411/16 × 21/8) | square | 689 | 42.0 | 28 | 24 | 21 | 18 | 16 | 14 | 8 |
| 75 × 50 × 38 | (3 × 2 × 11/2) | device | 123 | 7.5 | 5 | 4 | 3 | 3 | 3 | 2 | 1 |
| 75 × 50 × 50 | (3 × 2 × 2) | device | 164 | 10.0 | 6 | 5 | 5 | 4 | 4 | 3 | 2 |
| 75 × 50 × 57 | (3 × 2 × 21/4) | device | 172 | 10.5 | 7 | 6 | 5 | 4 | 4 | 3 | 2 |
| 75 × 50 × 65 | (3 × 2 × 21/2) | device | 205 | 12.5 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 75 × 50 × 70 | (3 × 2 × 23/4) | device | 230 | 14.0 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 75 × 50 × 90 | (3 × 2 × 31/2) | device | 295 | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 |
| 100 × 54 × 38 | (4 × 21/8 × 11/2) | device | 169 | 10.3 | 6 | 5 | 5 | 4 | 4 | 3 | 2 |
| 100 × 54 × 48 | (4 × 21/8 × 17/8) | device | 213 | 13.0 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 100 × 54 × 54 | (4 × 21/8 × 21/8) | device | 238 | 14.5 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 95 × 50 × 65 | (33/4 × 2 × 21/2) | masonry box/gang | 230 | 14.0 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 95 × 50 × 90 | (33/4 × 2 × 31/2) | masonry box/gang | 344 | 21.0 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| min. 44.5 depth | FS — single cover (13/4) | 221 | 13.5 | 9 | 7 | 6 | 6 | 5 | 4 | 2 | |
| min. 60.3 depth | FD — single cover (23/8) | 295 | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 | |
| min. 44.5 depth | FS — multiple cover (13/4) | 295 | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 | |
| min. 60.3 depth | FD — multiple cover (23/8) | 395 | 24.0 | 16 | 13 | 12 | 10 | 9 | 8 | 4 | |
| *Where no volume allowances are required by 314.16(B)(2) through (B)(5). | |||||||||||
The volumes of standard boxes that are not marked with their volume shall be as given in Table 314.16(A).
Boxes 1650 cm3 (100 in.3) or less, other than those described in Table 314.16(A), and nonmetallic boxes shall be durably and legibly marked by the manufacturer with their volume(s). Boxes described in Table 314.16(A) that have a volume larger than is designated in the table shall be permitted to have their volume marked as required by this section.
The volumes in paragraphs 314.16(B)(1) through (B)(5), as applicable, shall be added together. No allowance shall be required for small fittings such as locknuts and bushings. Each space within a box installed with a barrier shall be calculated separately.
Table 314.16(B) Volume Allowance Required per Conductor
| Size of Conductor (AWG) | Free Space Within Box for Each Conductor | |
|---|---|---|
| cm3 | in.3 | |
| 18 | 24.6 | 1.50 |
| 16 | 28.7 | 1.75 |
| 14 | 32.8 | 2.00 |
| 12 | 36.9 | 2.25 |
| 10 | 41.0 | 2.50 |
| 8 | 49.2 | 3.00 |
| 6 | 81.9 | 5.00 |
Each conductor that originates outside the box and terminates or is spliced within the box shall be counted once, and each conductor that passes through the box without splice or termination shall be counted once. Each loop or coil of unbroken conductor not less than twice the minimum length required for free conductors in 300.14 shall be counted twice. The conductor fill shall be calculated using Table 314.16(B). A conductor, no part of which leaves the box, shall not be counted.
Exception: An equipment grounding conductor or conductors or not over four fixture wires smaller than 14 AWG, or both, shall be permitted to be omitted from the calculations where they enter a box from a domed luminaire or similar canopy and terminate within that box.
Where one or more internal cable clamps, whether factory or field supplied, are present in the box, a single volume allowance in accordance with Table 314.16(B) shall be made based on the largest conductor present in the box. No allowance shall be required for a cable connector with its clamping mechanism outside the box.
A clamp assembly that incorporates a cable termination for the cable conductors shall be listed and marked for use with specific nonmetallic boxes. Conductors that originate within the clamp assembly shall be included in conductor fill calculations covered in 314.16(B)(1) as though they entered from outside the box. The clamp assembly shall not require a fill allowance, but the volume of the portion of the assembly that remains within the box after installation shall be excluded from the box volume as marked in 314.16(A)(2).
Where one or more luminaire studs or hickeys are present in the box, a single volume allowance in accordance with Table 314.16(B) shall be made for each type of fitting based on the largest conductor present in the box.
For each yoke or strap containing one or more devices or equipment, a double volume allowance in accordance with Table 314.16(B) shall be made for each yoke or strap based on the largest conductor connected to a device(s) or equipment supported by that yoke or strap. A device or utilization equipment wider than a single 50 mm (2 in.) device box as described in Table 314.16(A) shall have double volume allowances provided for each gang required for mounting.
Where up to four equipment grounding conductors or equipment bonding jumpers enter a box, a single volume allowance in accordance with Table 314.16(B) shall be made based on the largest equipment grounding conductor or equipment bonding jumper entering the box. A 1/4 volume allowance shall be made for each additional equipment grounding conductor or equipment bonding jumper that enters the box, based on the largest equipment grounding conductor or equipment bonding conductor.
Conduit bodies enclosing 6 AWG conductors or smaller, other than short-radius conduit bodies as described in 314.16(C)(3), shall have a cross-sectional area not less than twice the cross-sectional area of the largest conduit or tubing to which they can be attached. The maximum number of conductors permitted shall be the maximum number permitted by Table 1 of Chapter 9 for the conduit or tubing to which it is attached.
Only those conduit bodies that are durably and legibly marked by the manufacturer with their volume shall be permitted to contain splices, taps, or devices. The maximum number of conductors shall be calculated in accordance with 314.16(B). Conduit bodies shall be supported in a rigid and secure manner.
Conduit bodies such as capped elbows and service-entrance elbows that enclose conductors 6 AWG or smaller, and 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 an approved size to provide free space for all conductors enclosed in the conduit body.