National Electrical Code Articles and Information
National Electrical Code Top Ten Tips: Article 342 through Article 362 -- Conduits
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 320 through NEC Article 340 items we deem
most important, based on the pervasiveness of confusion and the
potential costs of same.
- NEC Article 342 through 362 contain the requirements for various
types of conduit. Remember that, and your life will be much easier. Don't confuse conduit with other types of raceway, such as EMT.
- Note that conduit is a subcategory of raceway. EMT is not a type
of conduit It's a type of raceway. People use "conduit" to mean raceway in general, only because they don't know any better.
- Each Article in this series provides the uses permitted and the
uses not permitted. At one time, "Uses Permitted" might show up as section 2 in one article, section 6 in another, and section 10 in yet another. With the 2012 NEC, this began to be standardized such that Uses Permitted" is in Section 10 and Uses Not Permitted" (if it exists in that article) is in Section 12. This pattern remains unchanged with the 2023 NEC.
- Article 350 presents requirements for Liquidtight Flexible
Metal Conduit: Type LFMC. Note that the smallest allowable trade
size is 1/2, and the largest allowable trade size is 4. There are
limits on length and bending. You don't use flexible conduit in place of nonflexible conduit for the convenience of not having to bend it. That results in an ugly installation, and it is against Code. Flexible conduits serve specific purposes that cannot be served by nonflexible conduit, the main one being vibration isolation (for example, running that last few feet to a motor). Don't use LFMC in a nonmetallic raceway system. Technically, you could separately bond it but you end up with wasted installation cost and something that looks bad. You also have two additional points of failure added to the system, plus the possibility someone will disconnect the bonding jumper inadvertently or due to not knowing why it's there.
- Article 356 provides the requirements for Liquidtight Flexible
Nonmetallic Conduit: Type LFNC. The requirements are similar to
those of Type LFMC, and they have become more harmonized with the 2023 NEC. Don't use LFNC in a metallic raceway system (for the same reasons you don't use LFMC in a nonmetallic raceway system).
- Article 352 presents the requirements for Rigid Polyvinyl Chloride Conduit: PVC. Any fittings used with the conduit must be
Listed. You cannot use plumbing pipe fittings with electrical PVC. There are
limits on where you can use this. Note, also, that you must provide
expansion fittings with PVC. If assembling with a PVC "glue", ensure you have plenty of ventilation. When assembling threaded couplings, be mindful of the torque limits.
- Article 354 presents the requirements for Nonmetallic Conduit
with Conductors: Type NUCC. You cannot use Type NUCC in exposed
locations or inside buildings. Be absolutely sure you observe the bend radius limits per Table 354.24(A). Once you exceed the minimum radius (bend tighter than that radius), discard the conduit because it is damaged.
- All types of conduit must be supported. This has a specific meaning, and you can find specific requirements in the NEC. But here are two rules of thumb. First, use only straps, clamps, and other mounting hardware designed for that specific type of raceway. Second, use these to securely fasten the raceway in place. You can find the exact minimum distance in the article for that type of raceway, but as a rule of thumb every three feet makes for a secure and aesthetic installation.
- Never use other systems for support, and never support other systems. You cannot use any conduit to support other wiring. This includes speaker wires for a PA system. Don't hang anything on electrical conduit or other raceway. Don't mechanically connect conduit to piping, either.
- Refer to 300.17 for raceway fill requirements. While you can use the NEC tables in Chapter 9 and/or go through a series of calculations, the easiest way to do this today is to use a Conduit Fill app on your phone. Summit Electric has such an app, see them at www.summit.com.