When Battery Master is OFF, which busses are powered?

When Battery Master is OFF, which busses are powered?

• A. APU Battery Direct Bus; Main Battery Direct Bus; DC Emergency Bus
• B. APU Battery Direct Bus only
• C. Main Battery Direct Bus and DC Essential Bus
• D. DC Emergency Bus only

Answer: (A)

When Battery Master is OFF, some power paths stay active because they’re designed to operate independently of that switch. The APU Battery Direct Bus is a direct connection to the APU battery, so it remains energized even when Battery Master is off. The Main Battery Direct Bus is similarly tied straight to the main battery, providing a separate, always-ready feed to that bus. The DC Emergency Bus has its own dedicated emergency power source, meant to stay powered to essential systems in case normal power is lost. So those three buses can remain powered, while other buses tied to the normal power system would not be energized without Battery Master or generator support.

When Battery Master is OFF, some power paths stay active because they’re designed to operate independently of that switch. The APU Battery Direct Bus is a direct connection to the APU battery, so it remains energized even when Battery Master is off. The Main Battery Direct Bus is similarly tied straight to the main battery, providing a separate, always-ready feed to that bus. The DC Emergency Bus has its own dedicated emergency power source, meant to stay powered to essential systems in case normal power is lost. So those three buses can remain powered, while other buses tied to the normal power system would not be energized without Battery Master or generator support.