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National Electrical Code Articles and Information

NEC Quiz: Article 342 Answers

by Mark Lamendola

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  1. OK, we gave that away in the prelude to the questions. IMC is Intermediate Metallic Conduit. You can thread it, which means you can use it as a bonding path and you can seal it [342.2]. You can use metallic tubing as a bonding path, but you have to jumper around the connections to ensure integrity. Obviously, you cannot use nonmetallic raceway as a bonding path.
     

  2. Article 342 lists four uses [342.10]. These four actually encompass a tremendous range of applications. But don't make the mistake of considering IMC a "light" version of RMC [344]. Each has its own "Uses Permitted," and though they can overlap it's not the case that you choose RMC over IMC just because you want more "Lift truck withstand capability" than RMC provides.

    You can use IMC in all atmospheric conditions and occupancies, corrosion environments, cinder fill, and wet locations.
     

  3. Article 342 doesn't list any prohibited uses. However, avoid introducing dissimilar metals into the IMC system [342.14].
     

  4. Use only bushings, couplings, connectors, brackets, etc., listed for use with IMC. Article 342 doesn't explicitly state this, but the listing requirement is a general requirement provided elsewhere in the Code. You can't, for example, use connectors designed for use with plumbing systems. Nor can you run a length of PVC in an IMC system (you can connect a PVC system to an IMC system, typically the case where conductors are run underground in PVC to stubs that then mate with IMC; be careful to bond the grounding/bonding wires (run inside the PVC) to the IMC so there aren't differences of potential.
     





  5. You can't use running threads on conduit for connection at couplings [342.42(B)]. Amazingly, the NEC does not define "running threads." So what does this mean?

    What you're supposed to do is thread the conduit and then screw on one fitting. Then you screw threaded conduit into the other end of the fitting. The completed assembly should not have much unused thread left over on either end of the fitting.

    What the NEC does not want you to do is stretch the threads twice; that violates the basic principle of fastening things together by tightening to the elastic limit one time and results in a mechanically compromised connection.

    With running threads, you create a long threading area on conduit piece #1. Then you run the connector up that piece until it's no longer over the end of the stick. Now you can mate piece #1 to piece #2 and spin the connector halfway onto piece #2. This overcomes the problem of trying to spin the second piece if space to do so is tight. But it results in a compromised installation that, among other things, ruins the ability of the conduit to serve as an equipment grounding conductor. And normal vibration will eventually cause that connector to move completely off of that second piece some day.

 

 

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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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