What is the purpose of derating wiring run above heated ceilings?

The purpose of derating wiring run above heated ceilings primarily relates to managing heat exposure. When electrical wiring runs through areas where temperatures can rise significantly, such as above heated ceilings, the heat can impact the performance of the insulation and the conductor itself. Higher temperatures typically reduce the current-carrying capacity of the wires, which could lead to overheating and potential failure if the wires are not derated accordingly.

By derating, you are effectively reducing the maximum safe load to which the wiring can be subjected while still ensuring safe operation. This helps prevent insulation breakdown and maintains the integrity of the electrical system, ensuring safety and operational efficiency in environments with elevated temperatures.