4.) The non-use of expansion fittings in Rigid Non-Metallic (PVC) conduits that are subject to thermal expansion and contraction.
Sections 300-7 (b) and 347-9 require the use of an expansion fitting in exposed straight runs between securely mounted items such as boxes, conduit bodies and elbows of non-metallic raceways that are subject to large temperature variations. The expansion fitting is required when the length change, in accordance with Table 347-9, is 0.25" or greater.
Example: in a 100' run of Rigid Non-Metallic Conduit, that is exposed to a 100 degree difference in temperature, the computed expansion is 4.1". With a 100 degree difference in temperature the length change in a 10' section of Non-Metallic conduit will be more than 0.25".