Final answer:
3. 4/0. The smallest size for THW copper wire utilized in a 200 ampere commercial service entrance is 250 kcmil or 4/0 AWG.
Step-by-step explanation:
The size of the copper wire utilized for a 200 ampere commercial service entrance depends on the current-carrying capacity of the wire. To calculate the minimum wire size, we need to consider the current and the material of the wire. Copper is commonly used for its good conductivity and low resistance. According to the American Wire Gauge (AWG), which is commonly used in the United States, the smallest size for THW (Thermoplastic Heat and Water Resistant) copper wire for a 200 ampere commercial service entrance would be 250 kcmil (kilo circular mils) or 4/0 AWG.