The AC ESS Bus is normally powered by___________.

The AC ESS Bus is normally powered by___________.

• A. AC Bus 2
• B. AC Bus 1
• C. External Power
• D. APU

Answer: (B)

AC ESS bus powers vital systems that must stay energized even if other power sources fail. It’s connected to the main AC buses through an automatic transfer arrangement, and in normal operation it is fed from AC Bus 1. If AC Bus 1 loses power but AC Bus 2 remains powered, the ESS bus will automatically be supplied from Bus 2. External power or the APU can supply power to the aircraft when connected or during start, but they are not the normal source for the ESS bus when both main buses are available. So, the AC ESS bus is normally powered by AC Bus 1.

AC ESS bus powers vital systems that must stay energized even if other power sources fail. It’s connected to the main AC buses through an automatic transfer arrangement, and in normal operation it is fed from AC Bus 1. If AC Bus 1 loses power but AC Bus 2 remains powered, the ESS bus will automatically be supplied from Bus 2. External power or the APU can supply power to the aircraft when connected or during start, but they are not the normal source for the ESS bus when both main buses are available. So, the AC ESS bus is normally powered by AC Bus 1.