NEC Quiz: Article 350 Answers

by Mark Lamendola

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  1. In the prelude to the questions, we gave away the fact this is a flexible conduit. What we didn't give away is the particular type. This is Liquidtight Flexible Metal Conduit (LFMC), whereas in Article 348 the wiring method was Flexible Metal Conduit. Many people confuse the two, because they are both flexible and have a metal spiral as part of their construction. But they do not look alike. LFMC has a nonmetallic outer covering that gives it the characteristic of being liquidtight.
     

  2. Article 350 lists three permitted uses (in contrast to only one listed for Article 348) [350.10]. It can be used where conditions require flexibility, as permitted by the Hazardous Location Articles (501.10, 502.10, 503.10, 504.20), and for direct burial where listed and marked for the purpose.





    From an engineering standpoint, you want to avoid using LFMC except where you need the flexibility. It's necessarily weaker than RMC or IMC and is more easily broached due to its continuous joints. Don't use it for the reason of trying to get around raceway support issues. It still must be supported, and it's going to be more difficult to install than RMC or IMC simply because it is flexible.

     

  3. Whereas Article 348 lists seven prohibited uses, Article 350 lists only two [350.12]. There are big advantages to that outer coating!

    The first prohibition listed is the standard, "use your brain" one that is more a disclaimer than an actual requirement. Don't use it where subject to physical damage. On the surface, this is nonsense because the main reason for using conduit is to protect the enclosed wires from physical damage. What is meant here is that you should use common sense in how you install this conduit knowing full well it's not invincible.

    The second one addresses an issue people might not be inclined to consider. Don't use it where the ambient temperature is too high for the rating of the conduit. That outer coating is not as temperature-resilient as the steel underneath it.
     

  4. You must use an approved means [350.30]. The NEC doesn't provide detail on what exactly this means for LFMC, but using "approved" anything is a general principle throughout the Code. Also, see 110.2.
     

  5. Use only bushings, couplings, connectors, brackets, etc., listed for use with LFMC [350.42].