National Electrical Code Articles and Information
National Electrical Code Top Ten Tips: Article 366 through Article 392 -- Raceways, Miscellaneous
Based on the 2020 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 366 through NEC Article 392 items we deem
most important, based on the pervasiveness of confusion and the
potential costs of same. It could be the case that something not mentioned here is important to your particular application.
- NEC Articles 366 through 392 contain the requirements for various
types of raceway, including auxiliary gutters, busway, and cable tray. Remember that, and your life will be much easier.
- Note that of these raceways is a subcategory of raceway in general.
Do not call any of these "conduit." For example, EMT is not conduit. It is tubing (that's what the T stands for). A type of conduit will have the word "conduit" in its name. I looked very hard in Electrical Metallic Tubing and did not find the word "conduit". I even tried rearraning the letters, changing each letter to the one that comes next in the alphabet, and then holding the page sideways and then upside down. After hours of effort, I collapsed into a sweaty heap and gave up. If you can find the word "conduit" in Electrical Metallic Tubing, I bow before you.
- Each Article in this series provides the uses permitted and the
uses not permitted. Years ago, the various code-making panels started standardizing the subsection functions across articles. So a .1 is nearly always the Scope, .2 has definitions, and so on. Uses Permitted is .10 and Unses Not Permitted is .12. So whether you are in 366.10 or 380.10, you are looking at Uses Permitted.
- NEC Article 366 provides the requirements for auxiliary gutters.
The main thing to remember about these is they are just what they
say they are--auxiliary. That means you cannot use them for a main
wiring raceway method. The
equipment you can use them with is limited to meter centers, distribution centers,
switchboards, and the like [366.2].
- NEC Article 368 provides the requirements for busway. In addition
to following these requirement, you must follow the manufacturer's
instructions. For example, if you overtorque Belleville washers, you
violate their UL listing. Busway must, except for the exceptions
noted in 368.10, be installed such that it's visible and in the open
[368.10]. So, don't install busway in a place where you will conceal
it behind a wall or in a warehouse behind stacks of boxes. Note that if it's installed were boxes *could* be stacked, that is likely to be the only location in the facility where boxes will be stacked. Those box-stacking no-gooders always find a way to crowd the busway. In one facility I visited, they had jammed boxes under the busway so tightly, the tops of the boxes were crunched! Talk about a fire waiting to happen.... They brought me there because they had "electrical problems." Yah, I would never have guessed. I joked with a buddy that the heat built up in the busway was being vented through all the unclosed holes in enclosures (I stopped counting at 30).
- NEC Articles 370, 372, and 374 provide the requirements for
cablebus, cellular concrete floor raceways, and cellular metal floor
raceways, respectively. These are normally modular or pre-assembled
constructions. Do note the application limitations before
- Article 376 provides the requirements for metal wireways. These
are sheet metal troughs with hinged or removable covers. Note that
their fill ratio is only 20 percent [376.22]. If you are using
nonmetallic wireways, follow the requirements provided in Article
- Article 380 provides the requirements for multioutlet assemblies.
These are becoming increasingly common. Note the application
- Surface metal and surface nonmetallic raceways (Article 386 and
Article 388, respectively) are becoming increasingly common. They
are especially useful in retrofit situations, where they provide
aesthetic and economic solutions to otherwise ugly and expensive
installation problems. Note their uses and limitations in 386.10 / 12 and
388.10 / 12, respectively. Follow the manufacturer's instructions.
"Field engineering" these systems violates their UL rating
and opens you to civil--and possibly criminal--liability. Follow the
instructions, and you will have a safe installation. If you need a
modification, simply contact the manufacturer for assistance and get
the mod instructions in writing.
- Cable trays, covered by Article 392, have been a mainstay of
construction for decades. You may notice that of all the Articles in
this series, this one is by far the longest. Read it carefully
before working with cable tray. One requirement many people fail to
follow is that of bonding all cable tray sections [392.60]. To
avoid power quality problems and personnel hazards, follow this