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NEC Quiz: Article 378 Answers

by Mark Lamendola

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  1. In the prelude to the questions, we gave away the fact this is nonmetallic wireway. Well, actually, the title gives that away. What we didn't give away is the detail that tells you its defining characteristics. Nonmetallic wireways are flame-retardant troughs made of some material other than metal. Like the metal versions, they have covers that are either hinged or removable. It is this feature that makes them so efficient for installation purposes. You don't need to fish cables through them, as you do with (for example) metallic tubing. Instead, you lay the wires in the trough. Once you've run them all, you close or attach the cover. [378.1, 378.2].

  2. The NEC provides a list of four "Uses Permitted" for this wiring method [378.10]. You can use it for exposed work, in corrosive environments, in wet locations (if it's listed for that use), and in concealed spaces. This last use has three conditions for it to be permissible: the wireway must be an extension that passes transversely through a wall, the length passing through the wall must be unbroken, and the conductors must be accessible on both sides of the wall. These permitted uses are almost identical to those for the metal version; the exception is you can use metal in hazardous locations but not corrosive environments, while you can use nonmetallic in corrosive environments but not hazardous locations.

  3. There are five. You can't use it in hazardous locations (except as permitted by other Articles), where subject to physical damage (standard prohibition for all wireway and raceway), where exposed to sunlight unless listed and marked suitable for the purpose, where subject to temperatures other than those it's rated for, and for conductors whose insulation temperature limitations exceed those of the wireway [378.12].

  4. Typically, this question is answered in section 30 of an Article. But 378.30 does not specify the hardware. That's because the exact hardware isn't an electrical safety issue. Use something suitable, such as the mouting hardware that (usually) comes with the wireway or use screws of the appropriate size. What the NEC does say in 378.30 is you must provide support at minimum horizontal and vertical distances (which it specifies). Same thing with the metal version.
  5. This is kind of a trick question, as couplings and connectors generally aren't needed. You don't assemble lengths of this the way you do, say, Intermediate Rigid Conduit (IRC). In a typical application, you usually cut it to the lengths you need and screw those lengths onto a surface. That could be something like a building wall or the interior of a control panel. But make sure you use expansion fittings [378.44], else this wireway is prone to separation that exposes the conductors or causes some other problem. You must close all dead ends with listed fittings, too [378.58].