Final answer:
To determine the maximum size of a copper conductor for an air-conditioning unit, one must consult the NEC code ampacity charts and apply correction factors for higher ambient temperatures.
Step-by-step explanation:
The question regarding the maximum size of copper conductor permitted for a 3-ton air-conditioning unit requires consulting the National Electrical Code (NEC) and considering factors such as current load, temperature rating of the conductor insulation, and ambient temperature. According to NEC tables, for a load of 25 amps, one must look at the ampacity charts and consider correction factors due to higher ambient temperatures (like 122°F) to determine the appropriate conductor size. However, the actual NEC code and tables are not provided in the examples, so determining the exact size would typically involve checking these resources.