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NEC Quiz: Article 355 Answers

by Mark Lamendola

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  1. In the prelude to the questions, we gave away the fact this is a nonmetallic conduit. What we didn't give away is the particular type. This is Reinforced Thermosetting Resin Conduit (Type RTRC) [355.1, 355.2].

    RTRC is a rigid nonmetallic conduit of circular cross section. It has integral couplings, similar to those in the PVC used for plumbing.
     

  2. Article 355 lists seven permitted uses [355.10]. Basically, you're going to use it where you would otherwise use a metallic raceway but corrosion is a limiting factor. That's why, for example, you'd use it in a cinder fill. It is suitable for direct burial, if you follow the minimum cover requirements for Rigid Nonmetallic Conduit (see Tables 300.5 and 300.500).
     

  3. Article 355 lists five prohibited uses [355.12].

    One of those is in hazardous locations; that's because plastic and static electricity tend to be ready playmates.

    A second is for the protection of the conduit itself (where exposed).

    A third (in theaters and similar locations) is a small consolation to the fact the highly toxic material the raceway is made of is, well, highly toxic.

    On the Wireville site, Frank Bisbee has covered the fact that the European Union far more widely limits the use of highly toxic materials in electrical installations. And not just in conduit but also as an electrical conductor insulating material. The Europeans have really objected to the use of Teflon, another outrageously toxic material that you should avoid using unless you have absolutely no other choice. And it's likely you will always have another choice.

    You can't use it to support luminaires, and you can't use it where the temperature may exceed 122 DegrF (unless it's listed for a higher temperature.
     

  4. You must install Type RTRC using approved methods. Article 355 gives explicit commentary regarding bending, bend radii, number of bends, and other facets of installation [355.24 - 355.48].
     

  5. Couplings and connectors are integral to the conduit (though you can also attach couplings and connectors to cut conduit). Where RTRC enters a box, use bushings and/or adapters that will protect the wires from abrasion [355.46]. If the box, fitting, or enclosure provides the equivalent protection of a bushing and/or adapter, then you don't have to add more bushings and/or adapters [355.46].

    Really, you should not be installing this wiring method until you have had specific training in the installation methods. If you are the project engineer, factor the necessary training into your budget so your project doesn't incur rework costs and lost time accidents.

 

 

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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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