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Conduit types include many different materials, each having its
own advantages and disadvantages. In general, there are metallic
and non-metallic conduits. There are several types of each metallic
and non-metallic conduit that are specifically detailed in the NEC.
NEC Articles 342 to 362 pertain to each of the accepted types of
conduit.
One common type of conduit used for the below-grade conduit
in the substation is Polyvinyl Chloride (PVC).

Figure 2.1 - Underground PVC pipe-conduit

NEC Article 352 applies to PVC conduit. PVC conduit is
corrosion resistant and therefore used for many below-grade
applications. It can be direct buried or encased in concrete.
Although PVC conduit can be used in exposed application as
well, it is restricted to areas that are not subject to physical
damage. There are other limitations to using PVC conduit that the
design engineer and installer must consider, such as the fact that it

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