What electrical component allows isolation of the generator and battery buses?

The bus tie switch is the correct answer because it serves the essential function of isolating the generator and battery buses within an aircraft's electrical system. By opening or closing the connections between these buses, the bus tie switch can either link the power sources together so they can share electrical loads or isolate them to prevent potential backfeed or malfunction of one system affecting the other. This capability is crucial for ensuring that both the generator and battery can operate independently when necessary, maintaining electrical reliability and safety in the aircraft.

The other options perform different functions within the electrical system. The voltage regulator primarily manages the output voltage of the generator to ensure it remains within acceptable limits. The circuit breaker serves as a protective device that interrupts the flow of electricity in the event of an overload or short circuit, preventing damage to the electrical components. The generator control unit acts as a monitor and controller for the generator, managing its operation but not specifically designed for bus isolation. Each of these components plays a vital role in the aircraft's electrical system, but only the bus tie switch is responsible for the isolation function.