National Electrical Code Top Ten Tips: Article 366 through Article 392 -- Raceways, 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 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.

1. 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.
    
2. Note that "miscellaneous raceways" is a subcategory of raceway in general, not a subcategory of "conduit".. 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.
    
3. 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. Prior to the 2023 revision, .2 had definitions, but with the 2023 revision all definitions have been moved to Article 100. 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.
    
4. 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 (not centimeters, don't confuse the two), distribution centers, switchboards, and the like [366.2].
    
5. NEC Article 368 provides the requirements for busway. In addition to following these requirements, 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).
    
6. NEC Articles 370, 371, 372, and 374 provide the requirements for cablebus, flexible bus systems, cellular concrete floor raceways, and cellular metal floor raceways, respectively. These are normally modular or pre-assembled constructions. Flexible bus systems are relatively new, they are engineered systems. For all of these, note the application limitations before purchasing.
    
7. 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 378.
    
8. Article 380 provides the requirements for multioutlet assemblies. These are becoming increasingly common. Note the application limitations [380.12]. Nonmetallic extensions are relatively new, and they are covered in Article 382.
    
9. Strut-type channel raceway is covered by Article 384 and underfloor raceway by Article 390.. 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.
    
10. 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 requirement diligently.