Final answer:
The allowable ampacity of a #10TW copper conductor at an ambient temperature of 70°F is 30 amperes, following the National Electrical Code guidelines.
Step-by-step explanation:
The question regarding the allowable ampacity of a #10TW copper conductor at an ambient temperature of 70°F addresses the carrying capacity of electrical wires, which is critical for safety and efficiency in electrical systems. According to the National Electrical Code (NEC), a #10 copper wire with TW insulation has an allowable ampacity of 30 amperes at an ambient temperature of 60°C (140°F). Since 70°F is well below this threshold temperature, the ampacity does not need to be de-rated, and the answer would be 30 amperes (30A), corresponding to option (b).
Answer: b. 30