Electrical Exam Term
Derating
The reduction of a conductor's ampacity due to factors such as high ambient temperature, conduit fill with multiple conductors, or continuous loading.
Detailed Explanation
Derating ensures conductors don't overheat under adverse conditions. NEC 310.15(C)(1) requires derating when more than 3 current-carrying conductors are in a raceway: 4-6 conductors = 80%, 7-9 = 70%, 10-20 = 50%. Temperature correction factors from Table 310.15(B)(1) are applied for ambient temperatures above 30°C. Continuous loads (operating 3+ hours) must also be calculated at 125% per NEC 210.20(A).
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