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NEC Quiz: Article 368 Answers

by Mark Lamendola

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  1. In the prelude to the questions, we gave away the fact this is busway. What we didn't give away is its defining characteristics. In fact, we didn't even mention any of them. A busway is always metallic (unlike conduit, tubing, or gutters, which nearly always come in nonmetallic versions). A busway enclosure is always "grounded" (bonded to the equipment "grounding" conductor, equipment bonding jumper, or the grounded conductor). The busway itself is a manufactured product that integrally contains the conductors (bare or insulated). Very commonly, these are copper aluminum bars, but may be rods or tubes [368.2].

  2. Unlike the conduit and tubing Articles, Article 368 doesn't present a list of permitted uses. Instead, it provides the requirements for using busway in three types of applications: Exposed, Behind Access Panels, and Through Walls and Floors [368.10].

  3. Article 368 does list five prohibited uses [368.12]. The first one listed [368.12(A)] contains two limitations. The first one is typical for raceway (don't install where subject to severe damage), and the second one is typical for metallic raceway (don't install where subject to corrosive vapors). You cannot install busway in hoistways, hazardous locations (unless specifically approved for the application), wet or damp locations (unless identified for such use), or less than 8 feet above the floor or working platform (unless provided with an identified cover).

  4. Oddly enough, the NEC does not explicity say what type of hardware you can use to secure the busway. But it does say to secure it at intervals of 5ft or less (unless otherwise designed or marked) [368.30].

    And since busway is sold and assembled as designed systems, common sense tells us that you use hardware that's consistent with what comes in the busway kit and/or that is appropriate for it.

    A common mistake is substituting fasteners for the factory-provided ones and then using a generic torque table to determine where to set the torque wrench; always use the exact hardware, and never re-use bolts, nuts, or lockwashers when assembling busway.

    Never set up a "tightening" program as part of "maintenence." Such a program is not maintenance. It is failure generation. Use infrared thermography to determine when busway assembly hardware needs attention, or just completely replace the hardware on some sort of schedule.
  5. For busway over 600V, you must use expansion fittings [368.244]. This requirement does not prohibit you from using expansion fittings for systems under 600V; discuss your application with the manufacturer.