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.