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.