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NEC Quiz: Article 355 Answers

by Mark Lamendola

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  1. In the prelude to the questions, we gave away the fact this is a nonmetallic conduit. What we didn't give away is the particular type. This is Reinforced Thermosetting Resin Conduit (Type RTRC) [355.1, 355.2].

    RTRC is a rigid nonmetallic conduit of circular cross section. It has integral couplings, similar to those in the PVC used for plumbing.

  2. Article 355 lists seven permitted uses [355.10]. Basically, you're going to use it where you would otherwise use a metallic raceway but corrosion is a limiting factor. That's why, for example, you'd use it in a cinder fill. It is suitable for direct burial, if you follow the minimum cover requirements for Rigid Nonmetallic Conduit (see Tables 300.5 and 300.500).

  3. Article 355 lists five prohibited uses [355.12].

    One of those is in hazardous locations; that's because plastic and static electricity tend to be ready playmates.

    A second is for the protection of the conduit itself (where exposed).

    A third (in theaters and similar locations) is a small consolation to the fact the highly toxic material the raceway is made of is, well, highly toxic.

    On the Wireville site, Frank Bisbee has covered the fact that the European Union far more widely limits the use of highly toxic materials in electrical installations. And not just in conduit but also as an electrical conductor insulating material. The Europeans have really objected to the use of Teflon, another outrageously toxic material that you should avoid using unless you have absolutely no other choice. And it's likely you will always have another choice.

    You can't use it to support luminaires, and you can't use it where the temperature may exceed 122 DegrF (unless it's listed for a higher temperature.

  4. You must install Type RTRC using approved methods. Article 355 gives explicit commentary regarding bending, bend radii, number of bends, and other facets of installation [355.24 - 355.48].

  5. Couplings and connectors are integral to the conduit (though you can also attach couplings and connectors to cut conduit). Where RTRC enters a box, use bushings and/or adapters that will protect the wires from abrasion [355.46]. If the box, fitting, or enclosure provides the equivalent protection of a bushing and/or adapter, then you don't have to add more bushings and/or adapters [355.46].

    Really, you should not be installing this wiring method until you have had specific training in the installation methods. If you are the project engineer, factor the necessary training into your budget so your project doesn't incur rework costs and lost time accidents.