What is the role of protection devices in an interconnected aircraft power system?

• A. They isolate sources or prevent backfeed during faults.
• B. They continuously connect all sources to all loads.
• C. They store energy for standby power.
• D. They provide visual indicators only.

Answer: (A)

Protection devices in an interconnected aircraft power system are there to isolate sources or prevent backfeed during faults. When a fault happens on one generator or feeder, protective relays and breakers trip to disconnect that source from the common bus. This stops fault current from energizing other sources or feeding into a fault path, protecting generators, wiring, and equipment and helping the remaining system continue to power critical loads. In practice, these devices also work with bus-tie switches to reconfigure the network so essential systems stay powered while the faulty section is isolated.

That’s why this option is the best: it describes the core protective role—breaking the connection to a source to prevent backfeed and limit fault impact. The other choices describe functions that aren’t the primary role of protection devices in this context: continuous connection of all sources to all loads would risk backfeed and widespread faults; storing energy for standby power is an energy-storage function, not protection; and being only visual indicators ignores the active protective action these devices perform.