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National Electrical Code Articles and Information

National Electrical Code Top Ten Tips: Article 320 through Article 340 -- Cables

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 10 NEC Article 320 through NEC Article 340 items we deem most important, based on the pervasiveness of confusion and the potential costs of same.

  1. NEC Article 320 through 340 contain the requirements for various types of cable. Remember that, and your life will be much easier.
  2. Each Article in this series provides the uses permitted and the uses not permitted. At one time, you had to hunt for where each article listed these. Now you will find them in subsection 10 and 12, respectively.
  3. Article 320 presents requirements for type AC: Armored Cable. This kind of cable has a metallic jacket. While many people assume it's the most durable of all cables and can be used anywhere, this is not true.
  4. Article 322 and Article 324 address two types of flat cable assembly. Only one of them is designed for use under carpet squares.
  5. Article 326: You cannot use Integrated Gas Spacer Cable (Type IGS) inside buildings. This makes sense when you think about it. What happens if it leaks?
  6. Article 328 provides the requirements for Medium Voltage Cable (Type MV).  You cannot use it on systems above 35 kV (35,000 volts).
  7. Article 330 provides the requirements for Metal-Clad Cable (Type MC). Note, this differs from armored cable. Article 332 provides the requirements for Mineral Insulated, Metal-Sheathed Cable, Type MI.
  8. Article 334 provides the requirements for various kinds of Non-Metallic Sheathed Cable (Types NM, NMC, and NMS). Article 336 provides the requirements for Power and Control Tray Cable, Type TC.
  9. Article 337 covers Type P Cable. Article 338 provides the requirements for Service Entrance Cable ((Type SE and Type USE).
  10. Article 340 provides the requirements for Underground Feeder and Branch-Circuit Cable (Type UF).

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 raceway.


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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