Hint: Too close for comfort
If you look closely, you can see a Rigid PVC conduit installed right up against the metal-corrugated sheet roof decking and next to a couple of screws that have penetrated the metal roof decking. Installing Rigid PVC conduit this close to the metal roof decking is a violation of Sec. 300.4(E) which requires raceways, cables, and boxes to be installed with at least 1 ½ inches of space between the lowest surface of the roof decking, to the top of the raceway, cable, or box. Those screws that have penetrated the roof next to the Rigid PVC conduit are the exact reason why this 1 ½ in. spacing is required.
In this case, no wiring was damaged by those screws, but I have seen and published pictures of many other installations where roofing repairs were made, and wiring was damaged by the screws used by the contractors who were making the repairs to the roof. Section 300.4(E) Ex. 1 informs us that RMC and IMC are not required to have the 1 ½ in. spacing. Exception 2 was added to eliminate the 1 ½ in. spacing requirement where the metal roof decking is covered with a concrete slab at least 2 inches thick.
