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National Electrical Code Top Ten Tips: Article 394 through Article 398 -- Wiring, Miscellaneous

Based on the 2023 NEC

by Mark Lamendola

Please note, we do quote from copyrighted material. While the NFPA does allow such quotes, it does so only for the purposes of education regarding the National Electrical Code. This article is not a substitute for the NEC.

These are the 10 NEC Article 394, 395, 369, and 398 items we deem most important, based on the pervasiveness of confusion and the potential costs of same.

  1. NEC Articles 394 through 398 contain the requirements for various types of wiring, including concealed knob-and-tube wiring, messenger supported wiring, and open wiring on insulators. Remember that, and your life will be much easier. Remember also these are "in the back" of Chapter 3 for a reason. They just are not all that commonly used anymore (the notable exception is Article 395, Outdoor Overhead Conductors over 1000 Volts).
  2. Note that each of these wiring types is a subcategory of wiring in general. These are very specific wiring methods. The general wiring methods also apply--but now you have additional requirements if you use any of these three methods.
  3. Each Article in this series provides the uses permitted (Section 10) and the uses not permitted (Section 12). Section 2, which contained definitions, was eliminated with the 2023 revision. All definitions are now in Article 100. Formerly, a definition went into Article 100 only if it appeared in more than one Article. If it was a one-off, it appeared in Section 2 of that Article. What a housekeeping nightmare for the Code Making Panels, and it wasn't so great for users either.
  4. NEC Article 394 provides the requirements for concealed knob-and-tube wiring. While this method is largely disappearing, there's still an installed base of this type of wiring. You can install this kind of wiring only to extend or repair an existing installation. However, if there is open access to the wiring system (e.g., in the attic or in the basement), it may not cost that much more or take that much extra time to replace each circuit with nonmetallic sheathed cable. And you get a better-looking job.
  5. Taps on concealed knob-and-tube wiring must be soldered. Consider replacing the entire circuit with nometallic sheathed cable, so you can install a junction box and use solderless connectors.
  6. NEC Article 396 provides the requirements for messenger supported wiring. You must use one of the cable types listed in Table 396.10(A) and follow the appropriate Article for that cable type.
  7. An exception to the rule just stated applies for industrial installations [396.10(B)]. This exception does not mean you should necessarily use messenger-supported wiring. The conditions of use might dictate the use of tubing or conduit for increased protection of the cables or conductors.
  8. NEC Articles 398 provides the requirements for open wiring on insulators. You won't find open "insulators" defined in Article 100. So, what does this mean? This "open wiring on insulators" is a wiring method. It is not an approach to wiring that involves generic insulators. Nor does "open" mean "bare".
  9. If you use the open wiring on insulators method, you must use bushings to pass the open conductors through framing members [398.17]. And you cannot conceal the circuits [398.12]. This can present some interesting, if not impossible, challenges when updating an older building.
  10. Observe the clearances provided in 398.19. If doing so is impractical, then replace open wiring with something like nonmetallic sheathed cable. Generally, upgrading to an insulated cable is much easier and less expensive than trying to accomodate open wiring.