What does the AC ESS XFER switchlight do when selected?

• A. Transfers the AC Essentials Bus to AC BUS 2
• B. Transfers AC BUS 1 to AC ESS
• C. Powers AC ESS BUS from DC
• D. Isolates AC ESS from AC BUS 2

Answer: (D)

AC ESS XFER is the control that manages the connection between the essential AC bus and the main AC buses. When you select this switchlight, it opens the transfer path to AC BUS 2, isolating the AC essential bus from that bus. This prevents backfeed or cross-connection from BUS 2 into the essential bus, so the essential equipment remains powered from the other available source (usually AC BUS 1). This is used to protect critical systems during a fault on bus 2 or when you need to isolate the essential bus for maintenance. It does not power the essential bus from DC, and it does not transfer the other way or alter power from BUS 1.