Cut Sheet

Commercial Products
Switch and Outlet BOxeS and cOverS
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© February 2015
1406
Capacity of Steel Boxes and Covers
314.16 Number of Conductors in Outlet, Device, and Junction
Boxes, and Conduit Bodies. Boxes and conduit bodies shall be of
sufficient 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.
FPN: For volume requirements of motor terminal housings, see
430.12.
Boxes and conduit bodies enclosing conductors 4 AWG or larger
shall also comply with the provisions of 314.28.
(A) Box Volume Calculations. 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).
(1) Standard Boxes. The volumes of standard boxes that are not
marked with their volume shall be as given in Table 314.16(A).
(2) Other Boxes. 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.
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.
(B) Box Fill Calculations. 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.
(1) Conductor Fill. 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. A looped, 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 (fixture) or similar canopy and
terminate within that box.
(2) Clamp Fill. 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.
(3) Support Fittings Fill. Where one or more luminaire (fixture) 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.
Table 314.16(B) Volume Allowance Required per Conductor
Size of Conductor (AWG)
Free Space Within Box for Each Conductor
cm
3
(in
3
)
18 24.6 (1.50)
16 28.7 (1.75)
14 32.8 (2.00)
12 36.9 (2.25)
10 41 (2.50)
8 49.2 (3.00)
6 81.9 (5.00)
(4) Device or Equipment Fill. 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.
(5) Equipment Grounding Conductor Fill. Where one or more
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 present in the box. Where
an additional set of equipment grounding conductors, as permitted
by 250.146(D), is present in the box, an additional volume allowance
shall be made based on the largest equipment grounding conductor
in the additional set.
406.8 Receptacles in Damp or Wet Locations.
(B) Wet Locations.
(1) 15- and 20-Ampere Receptacles in a Wet Location. 15- and
20-Ampere, 125- and 250-Volt receptacles installed in a wet
location shall have an enclosure that is weatherproof whether or not
the attachment plug cap is inserted.
(2) Other Receptacles. All other receptacles installed in a wet
location shall comply with (B)(2)(a) or (B)(2)(b).
(a) A receptacle installed in a wet location, where the product
intended to be plugged into it is not attended while in use, shall
have an enclosure that is weatherproof with the attachment plug
cap inserted or removed.
(b) A receptacle installed in a wet location where the product
intended to be plugged into it will be attended while in use (e.g.,
portable tools) shall have an enclosure that is weatherproof when
the attachment plug is removed.
Table 314.16(A) Metal Boxes
Box Trade Size
mm (in)
Minimum
Volume
cm
3
(in.
3
)
Maximum Number of
Conductors 
18 16 14 12 10 8 6
100x32 (4x1¼)
round/
octagon
205 (12.5) 8 7 6 5 5 5 2
100x38 (4x1½)
round/
octagon
254 (15.5) 10 8 7 6 6 5 3
100x54 (4x2)
round/
octagon
353 (21.5) 14 12 10 9 8 7 4
100x32 (4x1¼) square 295 (18) 12 10 9 8 7 6 3
100x38 (4x1½) square 344 (21) 14 12 10 9 8 7 4
100x54 (4x2) square 497 (30.3) 20 17 15 13 12 10 6
120x32 (4x1¼) square 418 (25.5) 17 14 12 11 10 8 5
120x38 (4x1½) square 484 (29.5) 19 16 14 13 11 9 5
120x54 (4x2) square 689 (42) 28 24 21 18 16 14 8
75x50x38 (3x2x1½) device 123 (7.5) 5 4 3 3 3 2 1
75x50x50 (3x2x2) device 164 (10) 6 5 5 4 4 3 2
75x50x57 (3x2x2¼) device 172 (10.5) 7 6 5 4 4 3 2
75x50x65 (3x2x2½) device 205 (12.5) 8 7 6 5 5 4 2
75x50x70 (3x2x2¾) device 230 (14) 9 8 7 6 5 4 2
75x50x90 (3x2x3½) device 295 (18) 12 10 9 8 7 6 3
100x54x38 (4x2x1½) device 169 (10.3) 6 5 5 4 4 3 2
100x54x48 (4x2x1) device 213 (13) 8 7 6 5 5 4 2
100x54x54 (4x2x2) device 238 (14.5) 9 8 7 6 5 4 2
95x50x65 (3¾x2x2½)
masonry
box/gang
230 (14) 9 8 7 6 5 4 2
95x50x90 (3¾x2x3½)
masonry
box/gang
344 (21) 14 12 10 9 8 7 4
min. 44.5
depth
FS - single cover/
gang (1¾)
221 (13.5) 9 7 6 6 5 4 2
min. 60.3
depth
FD - single cover/
gang (2)
295 (18) 12 10 9 8 7 6 3
min. 44.5
depth
FS - multi. cover/
gang (1¾)
295 (18) 12 10 9 8 7 6 3
min. 60.3
depth
FD - multi. cover/
gang (2)
395 (24) 16 13 12 10 9 8 4
 Where no volume allowances are required by 314.16(B)(2) through (B)(5).
Reproduced with permission NFPA. – All National Electrical Code references
are from the 2008 edition.