What must be built to obtain 480 volts from a 277/480 volt can?

To obtain 480 volts from a 277/480 volt system, a bank is indeed the correct choice. In electrical systems, especially in three-phase configurations, a bank often refers to a grouping of transformers that work together to manage voltage levels and phases. These transformer banks can adjust the voltage from higher levels down to the lower levels required for equipment that operates at 480 volts.

The term "bank" is commonly associated with transformer banks used in power distribution to step down voltage efficiently and maintain the three-phase balance necessary for delivering power to various loads. In this case, the 277/480 volt system typically supplies 277 volts to lighting and 480 volts to machinery and other heavy electrical equipment.

By utilizing a transformer bank set up to provide the correct phase and voltage transformation, electric utility companies and contractors can deliver power as needed without causing imbalance or loss in efficiency. The other options, while related to electrical systems, do not directly address the configuration needed to achieve the desired voltage output from a 277/480 volt system.