What is the minimum size required for branch circuit conductors supplied from a 277/480-volt panel for a large motor?

The minimum size for branch circuit conductors supplied from a 277/480-volt panel for a large motor is determined based on the National Electrical Code (NEC) guidelines, which provide specific ampacity tables. For large motors operating at higher voltages such as 277/480 volts, proper conductor sizing is crucial to ensure that the conductors can safely carry the load without overheating or resulting in voltage drops that could affect motor performance.

The choice of 3 is correct as it typically meets or exceeds the ampacity requirements for large motors in this voltage scenario, specifically when considering various factors such as the motor's full-load current, ambient temperatures, and the installation conditions. Conductor sizing also often accounts for protection from overcurrent and short circuits, normally addressed with properly sized circuit breakers or fuses.

In this context, using a larger gauge conductor (which corresponds to a smaller number) reduces resistance and heat buildup during operation, enhancing safety and reliability. While other options represent different sizes that could potentially be used in various contexts, they do not align with the minimum requirements for safe and efficient operation concerning the specifications usually set out in electrical codes for larger motors connected to 277/480-volt systems.