314.16 Number of Conductors in Outlet, Device, and Junction Boxes, and Conduit Bodies

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 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.

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.

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.

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.

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.