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National Electrical Code Articles and Information

NEC Quiz: Article 390 Answers

by Mark Lamendola

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  1. This wiring method is the counterpart to the surface raceway covered in Articles 386 and 388. The diference is it goes under the floor, instead of on the surface. The NEC does not specify whether it is metallic or nonmetallic. Typically, it is metallic (as far as this author knows, it always is metallic). It's designed to be under (or flush with) the surface of a floor.

  2. There are only two permitted uses. It can be used beneath the surface of concrete (or other flooring material). A second use is in office occupancies where laid flush with the concrete floor and covered with linoleum or equivalent floor covering [390.3(A)]. Notice, that the "Uses Permitted" is in Subsection 3, not in Subsection 10 as is normal for Chapter 3.

  3. The "Uses Not Permitted" is also is in Subsection 3, not in Subsection 10 as is normal for Chapter 3. And there are two such uses. First, these cannot be used where subject to corrosive vapors [390.3(B)]. Second, you can't use them in any hazardous location except as specifically permitted in 504.20 and 501.10(B)(3).

  4. Use the mounting hardware that comes with it, or use equivalent hardware. This raceway is manufactured as a system, and is defined as such [390.2]. Install it as such, also.
  5. You must use couplings and connectors designed for use with the system you are installing. Also: Before you secure it, make sure you lay it out in straight lines 390.9], put markers at the ends [390.10], and level the junction boxes [390.13]. Secure the raceway per the manufacturer's installation instructions.



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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