6.) The improper supporting of Rigid Non-Metallic (PVC) raceways.
Section 347-8 requires that runs of Rigid Non-Metallic Conduit be supported in accordance with Table 347-8 and in addition must be securely fastened within 3' of junction boxes, conduit bodies, etc. Section 347-8 also requires that the fastening method must be designed to allow for expansion and contraction of the raceway system. This means that a fitting that is designed for use with Rigid Non-Metallic Conduit should be used.
Example: Table 347-8 requires that a run of 1/2" PVC be supported at intervals not exceeding 3' and a run of 2" be supported at intervals not exceeding 5'. The distance between supports varies depending upon the size of the conduit. The issue of the clips used to support the raceway always raises some questions. There are but only a few clips, available at the supply houses, that are actually designed to secure PVC conduits and still allow for the expansion and contraction of the raceway. Two commonly used methods are the "two hole" and the "snap-in" type plastic clips. Two hole metallic clips, hangers and strut type clips that are designed to be used with Rigid Metallic Conduit may not be suitable for use with PVC raceways that are subject to thermal expansion and contraction. They may not allow for the expansion and contraction of the raceway.