What ampacity column are you allowed to use for derating using thhn wire?

When derating THHN wire, you typically refer to the ampacity column in the National Electrical Code (NEC) Table 310.16 (or its equivalent in local codes). This table provides the allowable ampacity for various wire types at different temperature ratings and installation conditions. For derating, you'll adjust the ampacity based on the number of conductors in a raceway, ambient temperature, and insulation type, ensuring compliance with NEC guidelines. Always consult the latest version of the NEC and local amendments for accurate information.