If ESS TRU 1 and ESS TRU 2 fail, how would the DC ESS BUS remain powered?

• A. The Automatic Closure Of The ESS TIE And The CROSS TIE Allowing TRU To Power Both The DC BATT BUS And DC ESS BUS
• B. External Power Applied To ESS BUS
• C. The ESS TRU 3 Automatically Powers It
• D. It Would Not Be Powered

Answer: (A)

Redundant bus ties keep critical power accessible even when multiple power sources fail. When ESS TRU 1 and ESS TRU 2 are out, the automatic closures of the ESS TIE and the CROSS TIE connect the DC ESS BUS to the DC BATT BUS, so the remaining power source can feed both buses. This design ensures the DC essential bus stays energized for essential systems despite two TRUs failing. External power or another TRU taking over isn’t relied upon automatically in this scenario, and saying it wouldn’t be powered ignores the built-in cross-connection that preserves essential-power continuity.