How do you re-energize the essential DC bus after a TRU failure?

How do you re-energize the essential DC bus after a TRU failure?

• A. Replace both TRUs immediately.
• B. Use the remaining TRU or battery to supply the essential DC bus; ensure the essential AC bus is energized and verify DC voltages.
• C. Disconnect all loads, reset CBs.
• D. Use external power only.

Answer: (B)

Essential DC power comes from transformer-rectifier units that convert AC on the essential AC bus into the DC needed by critical systems. If a TRU fails, you can still restore power to the essential DC bus by using the remaining TRU, as long as the essential AC bus feeding that TRU is energized. On the ground or in flight, this typically means the generators or APU (or external power on the ground) are supplying the essential AC bus so the remaining TRU can deliver DC to the essential bus. If needed, the battery can also back up the essential DC bus to provide a temporary source of power while you verify and monitor voltages. After re-energizing, check the DC voltages to confirm they’re within the normal range and that critical systems have the power they require.

Essential DC power comes from transformer-rectifier units that convert AC on the essential AC bus into the DC needed by critical systems. If a TRU fails, you can still restore power to the essential DC bus by using the remaining TRU, as long as the essential AC bus feeding that TRU is energized. On the ground or in flight, this typically means the generators or APU (or external power on the ground) are supplying the essential AC bus so the remaining TRU can deliver DC to the essential bus. If needed, the battery can also back up the essential DC bus to provide a temporary source of power while you verify and monitor voltages. After re-energizing, check the DC voltages to confirm they’re within the normal range and that critical systems have the power they require.