National Electrical Code Top Ten Tips:
Article 312 and Article 314 -- Enclosures and boxes
Based on the 2020 NEC
by Mark Lamendola
Please note, we do quote from copyrighted material. While the NFPA
does allow such quotes, it does so only for the purposes of education
regarding the National Electrical Code. This article is not a substitute
for the NEC.
These are the ten Article 312 and Article 314 items we deem
most important, based on the pervasiveness of confusion and the
potential costs of same.
- 312.4 requires that you repair any non-combustible surfaces that are broken or incomplete so there's a maximum 1/4 inch gap at the edge of a cabinet or cutout box employing a flush-type cover.
- 312.5 requires the use of proper fittings at enclosure
openings, to protect and secure the cables and wiring. This rule is commonly violated, so be looking for it when reviewing or inspecting an installation.
- Table 312.6(A) provides the minimum bending space at terminals
and the minimum width of wiring gutters, based on wire size and the
number of wires per terminal. Note that this applies to power cables. Signal cables may require much more room, so check the specs on each type of signal cable you are using.
- Table 312.6(B) provides the minimum wire-bending space at
terminals, based on wire size and the number of wires per terminal.
- 312.8 provides various clearances within an
enclosure or cabinet.
- 314.2 forbids the use of round boxes where conduits or
connectors requiring locknuts or bushings are to be connected to the
side of the box.
- 314.3 places certain restrictions on nonmetallic
boxes. Generally, you go all non-metallic or all metallic with raceways and boxes.
- 314.4 requires all metal boxes to be "grounded
and bonded", but it means they should be bonded if on the load side.
- 314.16 provides the details of box volume
calculations, box fill, conductor fill, clamp fill, support fittings
fill, device fill, equipment fill, equipment grounding conductor
fill, and other factors. It includes NEC Table 314.6(A), which the
minimum volume of that qualifies an enclosure to be a certain box
trade size. It also shows the maximum number of conductors a given
box trade size can legally hold. Some guy named Phil came up with these rules. Just kidding.
- 314.21 provides the same requirment as 312.4: You must repair any non-combustible surfaces that are broken or incomplete so there's a maximum 1/4 inch gap at the edge of a cabinet or cutout box employing a flush-type cover.
The other NEC Articles from this point forward to the end of NEC
Chapter 3 are short, and each is specific to a type of cable or wireway.