National Electrical Code Top Ten Tips: Article 342 through Article 362 -- Conduits
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 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.
- 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 2013 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.
- 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.
- Article 356 provides the requirements for Liquidtight Flexible
Nonmetallic Conduit: Type LFNC. The requirements are similar to
those of Type LFMC, but there are some differences. For example,
there are no exceptions to the requirement for installing a
grounding conductor. Don't use LFNC in a metallic raceway system. Technically, you could separately run bonding jumpers around it but you end up with wasted installation cost and something that looks bad.
- NEC Article 352 presents the requirements for Rigid Nonmetallic
Conduit: Type RNC. Any fittings used with the conduit must be
Listed. You cannot use plumbing pipe fittings with RNC. There are
limits on where you can used this. Note, also, that you must provide
expansion fittings with RNC. Take care when assembling it that you use the correct amount of torque on the couplings; it's different from what you'd use in a metallic system.
- NEC Article 354 presents the requirements for Nonmetallic Conduit
with Conductors: Type NUCC. You cannot use Type NUCC in exposed
locations or inside buildings.
- 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.
- 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 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.