National Electrical Code Articles and Information
National Electrical Code Top Ten Tips:
Article 312 and Article 314 -- Enclosures and boxes
Based on the 2017 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.
- 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.
- 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
- 314.4 requires all metal boxes to be grounded
- 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.
- 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.
How the NEC is arranged
- The first four Chapters of the NEC apply to all installations.
- Article 90 precedes Chapter One, and establishes the authority of the NEC.
- Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
- Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
- Chapter 8 provides the requirements for communications systems.
- Chapter 9 provides tables.
- The appendices provide mostly reference information.
- Appendix D contains examples that every NEC user should study.
Try your NEC moxy:
- Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
- Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
- When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
- Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
- Take our Code Quizzes.
Remember other applicable codes, rules, standards, and references:
- OSHA's electrical worker safety rules.
- IEEE standards.
- NETA standards.
- NFPA standards.
- International Codes (if applicable to the installation).
- State Codes (if the state has them).
- Local ordinances and permit requirements.
- Local fire codes.
- Manufacturer requirements or guidelines.
- Customer security requirements.
- Industry standards.
- Your company's own internal standards, practices, and procedures.
- Engineering drawing notes.
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