Yes, according to the National Electrical Code (NEC), a main breaker is required for any service entrance, including those with a generator and automatic transfer switch.

NEC Article 230.90 states that:> "Each service disconnecting means shall be provided with a readily accessible means within or adjacent to the building or structure served of manually disconnecting all ungrounded service conductors from the premises wiring."In this case, the main breaker serves as the service disconnecting means required by the NEC. It provides a convenient and accessible way to disconnect all ungrounded service conductors from the premises wiring in the event of an emergency or for maintenance purposes.

Additional Considerations: The main breaker rating should be sized appropriately for the size of the generator and the existing service. The main breaker should be installed in a location that is readily accessible for emergency disconnecting.* The main breaker should be labeled to indicate its function and location. Flag for review