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National Electrical Code Articles and Information

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.

  1. 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.
  2. 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.
  3. 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.
  4. Table 312.6(B) provides the minimum wire-bending space at terminals, based on wire size and the number of wires per terminal.
  5. 312.8 provides various clearances within an enclosure or cabinet.
  6. 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.
  7. 314.3 places certain restrictions on nonmetallic boxes. Generally, you go all non-metallic or all metallic with raceways and boxes.
  8. 314.4 requires all metal boxes to be "grounded and bonded", but it means they should be bonded if on the load side.
  9. 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.
  10. 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

  1. The first four Chapters of the NEC apply to all installations.
  2. Article 90 precedes Chapter One, and establishes the authority of the NEC.
  3. Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
  4. Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
  5. Chapter 8 provides the requirements for communications systems.
  6. Chapter 9 provides tables.
  7. The appendices provide mostly reference information.
  8. 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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