Conductor derating reduces the amount of current that wires are allowed to carry. The idea behind it is to protect the wire's insulation from degradation by excessive heat. As current passes through a wire, heat is produced. As current levels rise, the amount of heat produced also rises. National Electrical Code (NEC) section 310-10 requires conductor derating in two situations: when the ambient temperature rises above 30 degrees Celsius, and when you are bundling more than three wires in a conduit or cable. You will need access to NEC tables for the following instructions.
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