Final answer:
The smallest copper wire size for a 600-volt, 60 ft overhead wire cannot be determined without additional information. Wire gauge selection is based on NEC codes and requires knowledge of current, environmental factors, and safety codes. Professional consultation is needed for a definitive answer.
Step-by-step explanation:
The smallest size copper wire allowed for an overhead wire operating at 600 volts and with a span length of 60 ft is determined based on the National Electrical Code (NEC) and factors such as current carrying capacity, voltage drop, and mechanical strength for support. Considering that this question doesn't provide enough information regarding current and other mechanical considerations, the answer cannot be determined purely from the question provided. It is essential to consult the NEC code together with additional parameters such as the expected current, weather conditions, and safety measures to calculate the correct wire gauge.
Under standard circumstances, wire sizes are chosen to minimize power losses and ensure mechanical robustness. As for the provided options (42, 6, 8, 10), these seem to reflect wire gauge numbers rather than sizes. The standard wire gauge numbers in ascending order of diameter are 14, 12, 10, 8, 6, 4, 2, 1, 0 (0-gauge is thicker than 10-gauge). A qualified electrician or electrical engineer would be able to give a conclusive answer regarding the minimum required wire gauge considering all safety codes and application requirements.