The ESS TRU 2 Tie Contractor's function is best described as:

• A. After failure of AC BUS 2 and ESS TRU 1, allows the AC ESS BUS to power ESS TRU 2
• B. It powers the DC primary bus
• C. It disconnects all TRUs
• D. It provides automatic battery charging

Answer: (A)

The ESS TRU 2 Tie Contractor is all about keeping essential power available through redundancy. It acts as a switch that ties the AC Essential Bus to the input of ESS TRU 2 so that, if AC BUS 2 and ESS TRU 1 fail, the AC Essential Bus can still feed ESS TRU 2. This preserves the essential DC power supply by using the backup TRU path, preventing loss of critical systems that rely on the ESS DC bus.

This isn’t about powering the DC primary bus directly, nor about disconnecting all TRUs, and it doesn’t provide battery charging. Its role is specifically to provide a fallback path so ESS TRU 2 can continue delivering DC power from the AC Essential Bus when the normal sources are unavailable.