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 Nonmetallic
Underground Conduit with Conductors (Type NUCC) [354.1, 354.2].
NUCC is a
factory assembly of conductors or cables inside a nonmetallic raceway; the
raceway itself is smooth-walled and of circular cross-section.
354 lists five permitted uses [354.10]. 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).
354 lists three prohibited uses [354.12].
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).
The third (within a building) 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.
normally use hardware with Type NUCC; that is, you're not mounting it to a wall
the way you would mount RMC. You must
install Type NUUC using approved methods [354.48, 354.50]. Article 354 also gives explicit commentary regarding
bending, bend radii, and number of
bends [354.24, 354.26].
assembling this with couplings and connectors, so that's kind of a trick
question. But where NUCC enters a box, use
bushings and/or adapters that will protect it from abrasion [354.46]. 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 [354.46].
Really, you should not be installing this wiring method until you have had
specific training in the installation methods. For example, a fairly typical
installation may involve a large spool on a trailer or motorized platform
following behind a motorized trencher. You have to know how to operate the
equipment in a manner that doesn't lead to injuring the NUCC or the people
installing it. 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.