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NEC Quiz: Article 353 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 High Density Polyethylene Conduit (HDPE) [353.1, 353.2].

    Polyethylene is a type of plastic made from petroleum. It's inexpensive (if you discount the costs of the oil wars, environmental damage, etc.) and is widely used. It is also highly toxic, both in normal condition (you can smell its toxic fumes wafting off of products made from it) and egregiously so when burned. Try to avoid using it anywhere that humans are likely to spend much time.

  2. Article 353 lists six permitted uses [353.10]. Even though these are permitted, you should avoid using HDPE when another (nonplastic) type of material is suitable for the conditions and application.

  3. Article 353 lists five prohibited uses [353.12]. One of those is in hazardous locations; that's because plastic and static electricity tend to be ready playmates. Two of the other prohibited uses are for the protection of the conduit itself (where subject to temperatures above 122 DegrF and where exposed). But the other one, within a building, is a small consolation to the fact this highly toxic material 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.

  4. Though Article 353 doesn't explicitly say so, you have to install HDPE as a complete system, using the appropriate listed hangers, clamps, fittings, and so forth. Pay close attention to the MDS and product labels. Article 353 does give explicit commentary regarding bend radii and number of bends [353.24].

  5. Use only bushings, couplings, connectors, brackets, etc., listed for use with HDPE (not stated in subsection 353.42 because there isn't one; see 353.28, 353.30, and 353.48.

    Really, you should not be installing this wiring method until you have had specific training in the installation methods and safety features. If you are the project engineer, factor that training into your budget so your project doesn't incur rework costs and health liability baggage.