How much current can twelve 1 AWG THWN copper conductors carry installed in a three-inch EMT at 101°F?

To determine the current-carrying capacity, or ampacity, of twelve 1 AWG THWN copper conductors installed in a three-inch EMT at 101°F, it's essential to reference the National Electrical Code (NEC) and applicable ampacity charts.

The ampacity values for conductors are influenced by various factors, including the type of insulation, the number of conductors in a conduit, and the ambient temperature. For THWN copper conductors, the base ampacity is typically provided in tables within the NEC. For 1 AWG copper wire, the ampacity is usually around 130 A under standard conditions for a single conductor in free air or in an ideal temperature setting, but must be adjusted for the installation conditions.

Since there are twelve conductors, a derating factor must be applied according to NEC Table 310.15(B)(3)(a), which indicates derating for conductors when installed in a raceway. When more than three conductors are present, the ampacity must be adjusted down to account for heat buildup due to multiple conductors carrying current within the same conduit.

When the ampacity of 1 AWG is derated for 12 conductors from its original value, the adjusted capacity results