What is the purpose of the ESS TRU 2 Tie Contractor?

• A. After failure of AC BUS 2 and ESS TRU 1, allows the AC ESS BUS to power ESS TRU 2. It will also do this if on ADG power and ESS TRU 1 fails
• B. It isolates ESS TRU 2
• C. It connects DC BATT to DC ESS
• D. It powers the cabin lights

Answer: (A)

The ESS TRU 2 Tie Contractor is a switching path that automatically connects ESS TRU 2 to the essential DC bus when the primary feed to TRU 1 is lost. If AC Bus 2 and ESS TRU 1 fail, the tie closes so the AC essential bus can energize ESS TRU 2, keeping the essential DC bus powered. It also engages if the airplane is on ADG power and ESS TRU 1 fails, providing power to the essential bus through TRU 2 from the ADG path. This setup maintains power to critical systems even in multiple-failure situations. It isn’t about isolating TRU 2, feeding the battery directly to the essential bus, or powering cabin lights.