What is the effect of derating on circuit conductors?

Derating is a process in which the ampacity, or the maximum amount of current a conductor can carry without exceeding its temperature rating, is reduced. This typically occurs under certain conditions such as when multiple conductors are bundled together, when they are exposed to high ambient temperatures, or when they are installed in a way that restricts airflow and heat dissipation.

When multiple conductors are installed closely together, as is common in conduit and cable assemblies, the heat generated by the current flowing through them can build up. This increase in temperature can lead to overheating and potentially damage the insulation or conductors themselves. To mitigate this risk, the National Electrical Code (NEC) requires that an adjustment, or derating, be applied to the conductor's rated ampacity.

As a result of derating, the effective capacity of the conductors is reduced to a level that can safely handle the electrical load without risking overheating, ensuring both safety and longevity of the electrical system. Understanding the importance of derating helps ensure compliance with the NEC and promotes safe electrical installations.