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National Electrical Code Articles and Information

NEC Quiz: Article 358 Answers

by Mark Lamendola

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  1. In the prelude to the questions, we gave away the fact this is a metallic tubing. We also gave away that it's EMT. What we didn't give away is its defining characteristics (though we did mention some of them).

    EMT [358.1, 358.2] is an unthreaded, thinwall raceway of circular cross section. It may be ferrous (made of steel) or nonferrous (made of aluminum). Many people mistakenly think that because it's metallic, it can be used as a "grounding" (bonding) path. But because there's so little electrical contact at the connectors and because those connectors can work loose, that is not the case. Run your bonding jumper inside the EMT.  
     

  2. Article 358 lists three permitted uses [358.10]. That would seem rather limiting, but the number of installations that qualify is significant. Partly, that's because 358.10 is quite vague. You really cannot tell from it where you can use EMT. You get your answer by looking at 358.12 and seeing where you cannot use EMT. 
     

  3. Article 358 lists six prohibited uses [358.12]. Let's look at three of those:

    One of those is in hazardous locations; that's because EMT is an "open" raceway (at the connectors).

    Obviously, you can't use it where the location would subject it to severe damage. For example, on a loading dock you're probably better off with rigid than EMT.

    You can't use it to support luminaires or other equipment. The sole exception is a conduit body no larger than the size of the tubing. No, it is not permissible to then support a luminaire from that conduit body. This support limitation is a "high rate" code violation. Very common. The reason for this limitation is the connectors are not threaded and thus the linear force of supported weight can pull the tubing apart.
     

  4. You must install EMT using approved methods. Article 358 gives explicit commentary regarding bending, bend radii, number of bends, trimming, supporting, securing, and other facets of installation [358.24 - 358.42]. And don't thread it! You can use factory-threaded integral couplings [358.100]. You just can't thread EMT yourself. If you do residential work, be on the lookout for DIY installations using pipe fittings to the EMT; you cannot reassemble these but must instead replace them.
     

  5. You can use only fittings that are listed for use with EMT [358.42]. Make them tight. On a connector, for example, turn your screwdriver hard enough to slightly dent the EMT where the screw contacts it. If you use an electric screwdriver with a torque collar, set it so that it stops turning at the point the screw dimples the EMT.

 

 

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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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