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NEC Quiz: Article 352 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 Rigid Polyvinyl Chloride Conduit [352.1, 352.2].

    Polyvinyl Chloride 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 the third most-produced type of plastic. 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 352 lists nine permitted uses [352.10]. Even though these are permitted, you should avoid using PVC when another (nonplastic) type of material is suitable for the conditions and application.

    It's worth noting that PVC-coated rigid is often used in corrosive environments. Now, think about this. Adding PVC fumes to an environment that already is too dangerous for steel is (in most cases) about like shooting a corpse. No real problem, there.

    And installing PVC underground, though it slightly contaminates the soil over time, usually isn't going to pose an immediate health risk to humans.

  3. Article 352 lists five prohibited uses [352.12]. One of those is in hazardous locations; that's because plastic and static electricity tend to be ready playmates. Three of the other prohibited uses are for the protection of the conduit itself. But the fifth one, in theaters and similar locations, 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. You have to install it as a complete system [352.30]. The NEC doesn't provide detail on what exactly this means for PVC, but it does provide a fair amount of detail on how you should fasten and support it (including Table 352.30).

    A common method of joining PVC is to use a highly toxic glue. While traditionally workers use this glue without paying the slightest attention to ventilation and PPE requirements, you should ensure you read and follow those requirements as laid out in the MDS (formerly know as MSDS before harmonization with the European standard).

  5. Use only bushings, couplings, connectors, brackets, etc., listed for use with PVC (not stated in subsection 352.42 because there isn't one; see 352.30 "install as a system" requirement). Make sure you use the expansion fittings [352.44] and bushings [352.46] as required, and when making joints [352.48] use an approved method.

    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.