Which method can determine the actual operating voltage of a power line?

Asking an authorized company representative is the most reliable method for determining the actual operating voltage of a power line. Company representatives are trained professionals who have direct access to the necessary information and tools to accurately assess and report the voltage levels. They can provide detailed insights based on their expertise and the data available to them, ensuring that the information is both accurate and up-to-date.

Other methods, while helpful in certain contexts, do not offer the same level of certainty. For instance, examining transformer functionality may give some clues about the voltage, but it doesn't provide direct measurement. Similarly, checking circuit breaker settings can indicate the maximum rating but may not reflect the actual operating conditions. Testing the ground fault interrupter is primarily focused on safety and protection from electrical faults, rather than measuring the voltage itself. Therefore, the most straightforward and reliable way to ascertain the operating voltage is by consulting an authorized company representative.