National Electrical Code Articles and Information
Code Quiz: Article 362
Based on the 2014 NEC
Questions and answers written by Mark Lamendola, who has worked as a master electrician, electrical inspector, and design engineer. Mark is an IEEE Senior Member, and the Code article author for Codebookcity.com. Since 1996, he has been writing National Electrical Code articles for electrical trade magazines and has an extensive portfolio of hundreds of NEC articles..
The Chapter Three Articles on wiring methods run in multiple series. Article 350 was the last in the sets of series about metallic conduits. Article 352 starts a series on nonmetallic conduits and after this series, a series of tubing starts with Article 360.
Article 362 provides the requirements for Electrical Nonmetallic Tubing (ENT).
A major reason for using tubing is you can assemble it with pressure connectors instead of needing to cut threads onto the "pipe." There are three reasons (maybe more) you'd choose ENT over EMT:
Now, there's one other reason you'd use ENT and it's not along the lines of trying to do a sloppier, cheaper job than you could do with EMT. For a wide range of applications, it's just much better to use. Consider, for example, an industrial machine. Bending EMT to wire it up is much more work and will actually result in a sloppier-looking installation than if a skilled installer runs ENT along a prescribed pathway with proper supports. This is one of many examples where you're working on an oddball surface shape rather than along a straight cinder block wall. It's also great for crowded cabinets, even though their walls are straight; you can adjust the shape of the ENT without having to go nuts making all kinds of scrap attempting a set of crazy offsets for EMT.
In short, don't use ENT because you don't know how to properly bend EMT. Use it where the application makes it a time-saving option and yet permits good workmanship.
But you may be concerned about the fact ENT, being made from polyvinyl chloride (PVC) is highly toxic, especially when burned (as in a building fire) and that making PVC is very much an environmentally damaging process and that making PVC means sending even more dollars to oil-producing nations, then you'll opt for EMT every time. Remember, it's tubing rather than conduit. So while PVC conduit can provide real advantages (e.g., corrosion resistance) that metal conduit cannot, ENT isn't really in that advantage league.
Notice the distinction above, regarding tubing vs. conduit. ENT is not conduit. Many people mistakenly call it conduit, but that mistake can prove costly when trying to apply the NEC.
A final note before the quiz (below). The NEC does permit using ENT as an equipment grounding conductor [362.60], because it's an insulator not a conductor. You can't use EMT (metallic) as one either, because the connectors don't ensure a reliable low impedance path.
With tubing systems, always run a separate equipment grounding conductor inside the tubing and bond it to the tubing. The tubing, being of far greater diameter than the wire, will attenuate high frequency energy far better than the wire. But the wire gives you the ultimate in reliability. So use both, and bond them together.
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