When installing under metal-corrugated sheet roof decking, cables should be supported at least _____ inches from the lowest roofing surface.

The correct choice indicates that when installing cables under metal-corrugated sheet roof decking, they should be supported at least 1 1/2 inches from the lowest roofing surface. This requirement is in place to ensure that cables are adequately protected from potential damage caused by moisture, condensation, or other environmental factors that may accumulate on the roofing surface.

Maintaining this distance helps to minimize the risk of water infiltration, which can lead to insulation breakdown or other issues affecting the integrity and safety of the electrical system. Furthermore, adequate spacing allows for air circulation, helping to prevent overheating of the cables due to excessive heat buildup. Adhering to this requirement is essential not only for safety but also for the longevity and reliability of the electrical installation.