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NEC Quiz: Article 399 Answers

by Mark Lamendola

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  1. The title of Article 399 tells us that it addresses overhead conductors over 1KV. This Article doesn't address a particular material, wire type, or installation method.

  2. That's a trick question, because there are only two. The first permitted use is also stated in the definition of "outdoor overhead conductors" [399.2]: Outdoors in free air. The second is that it can be used for service conductors, feeders, or branch circuits [399.10]. As this means all three types of power distribution circuits, this almost does not need to be stated. However, it is stated and that helps avoid confusion. While we often associate overhead conductors with services, there are other uses for such conductors. For example, maybe you want to run a feeder from a panel in one building feeder to a subpanel in another. Or maybe you have a fire pump down by the ponds 100 yards from your main building. OK, so what about branch circuits? You can go with our first example again, but run a branch circuit instead (you might do this for the lights and receptacles in a guard shack, for example; no need to run a feeder, it's just a 20A circuit).

  3. This is another trick question, because there aren't any listed. They are implied, however. Whatever is not listed under "Uses Permitted" is by default a use not permitted. There is no Section 12. There are, in fact, only four Sections (1, 2, 10, and 30).

  4. This is not specified by Article 399, but you must use materials and methods suitable to the purpose. Note that the support design must be documented by a licensed professional engineer [399.30]. The design must include consideration of the six factors enumerated in 399.30. The support structure decisions must include consideration of the ten factors enumerated in 399.30. This Section also includes requirements for the insulators.
  5. This is not specified by Article 399, but you must use materials and methods suitable to the purpose. Generally, the conductors will be run with as few splices and connections as possible; this is why, for example, you see huge spools of conductors where utility crews are running overhead conductors.