What is the minimum distance that must be measured from the lowest surface of the roof decking to the top of the cable when installed under metal-corrugated sheet roof decking?

The correct minimum distance of 1.5 inches from the lowest surface of the roof decking to the top of the cable when installed under metal-corrugated sheet roof decking is essential for several reasons. This clearance is intended to ensure safety and compliance with electrical codes, preventing potential hazards such as overheating or damage to the cable insulation.

Maintaining this specific distance allows for proper airflow around the cable, reducing the risk of heat buildup, which can lead to insulation failure and potentially cause electrical fires. It also accounts for physical protection against any potential water ingress or condensation that might occur above the roof decking, which is particularly relevant with metal roofing materials that can conduct heat and moisture.

Furthermore, adhering to this established clearance aligns with the National Electrical Code (NEC) requirements, which are designed to promote safe electrical installations and minimize risks related to cable installations under various roofing types.