Final answer:
The ampacity of #10 THWN-2 copper wire in a conduit with three conductors at 70ºF ambient temperature is typically 30 amperes, according to NEC guidelines, without needing temperature derating adjustments.
Step-by-step explanation:
The ampacity of copper #10 THWN-2 is determined by referring to the National Electrical Code (NEC) tables, which provide the current ratings for wires based on their gauge, insulation type, and the number of conductors in a conduit. At an ambient temperature of 70ºF, which is close to the NEC's assumed ambient temperature of 30ºC, the ampacity of a #10 THWN-2 conductor is not impacted by temperature derating.
Ampacity of Copper #10 THWN-2
Considering that there are three conductors in the conduit, we must take into account the adjustment factor for more than three current-carrying conductors in a single conduit. According to the NEC, this adjustment factor can reduce the ampacity of the wire. For #10 THWN-2, the base ampacity is 30 amperes when used in a raceway or cable with not more than three current-carrying conductors and without any ambient temperature adjustments.