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National Electrical Code Articles and Information

NEC Quiz: Article 398 Answers

by Mark Lamendola

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  1. The wiring method in question is open wiring on insulators. That doesn't mean bare conductors on insulators; the conductors are insulated [398.2]. The "open" part means the wiring is exposed. It's cheap and it's ugly, but it works. This wiring method uses cleats, knobs, tubes, and flexible tubing to protect and support single insulated conductors run in or on buildings.

  2. The NEC lists four situations in which this wiring method may be used [398.10], but the first two don't make any sense. Those are "indoors or outdoors" and "in wet or dry locations." Maybe they should also state you can install it right side up or upside down? The two other conditions are:
    A. Where subject to corrosive vapors.
    B. For services.

    The four conditions are preceded by saying this wiring method is permitted only for industrial or agricultural establishments on systems of 600V or less.

  3. You can't use it where concealed by the building structure [398.12].

  4. Article 398 does not specify the hardware you can use, but it does specify support requirements [398.30]. Note that you can use nails to mount knobs [398.30(D)] but that's really a bad practice. It's faster to drive screws (if you have an electric screwdriver) and this will give you a far more reliable installation. So wherever possible, drive screws rather than nails.
  5. Make sure any conductor splices and taps are made and insulated by approved methods. Just because you've gone with "fast and cheap but ugly" doesn't mean you can also go with dangerous.



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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