Which power sources energize the essential DC buses during a loss of AC power?

Which power sources energize the essential DC buses during a loss of AC power?

• A. TRUs or battery.
• B. Main AC bus.
• C. External power.
• D. No power.

Answer: (A)

Essential DC buses must stay energized even when AC power disappears, so they have a dual-source arrangement: transformer-rectifier units and a dedicated battery. When AC power is available, the transformer-rectifier units convert that AC into DC to feed the essential DC buses, keeping critical systems powered. If AC power is lost, those rectifiers no longer have AC input, and the dedicated aircraft battery automatically supplies the essential DC buses to maintain operation of the most critical systems for a limited time. External power and the main AC bus aren’t sources once AC is gone, and “no power” isn’t the reality because the battery provides the necessary DC to keep essential systems alive.

Essential DC buses must stay energized even when AC power disappears, so they have a dual-source arrangement: transformer-rectifier units and a dedicated battery. When AC power is available, the transformer-rectifier units convert that AC into DC to feed the essential DC buses, keeping critical systems powered. If AC power is lost, those rectifiers no longer have AC input, and the dedicated aircraft battery automatically supplies the essential DC buses to maintain operation of the most critical systems for a limited time. External power and the main AC bus aren’t sources once AC is gone, and “no power” isn’t the reality because the battery provides the necessary DC to keep essential systems alive.