Which statement about circuit breakers is accurate in aircraft systems?

• A. They are designed to open before an overload or circuit fault
• B. They are designed to trip only if commanded manually
• C. They must be replaced after every trip
• D. They do not protect against inductive faults

Answer: (A)

Circuit breakers protect aircraft electrical circuits by interrupting current whenever a fault or overload is detected, preventing damage to wiring and components. They are typically thermal-magnetic devices: the thermal element responds to sustained overcurrent, while the magnetic element provides an instantaneous trip for a short circuit. Once tripped, they are resettable—crew or maintenance can reset after the fault is cleared—so nothing must be replaced after every trip. They operate automatically rather than only on manual command, though manual trip/test actions exist. They do protect against faults caused by inductive loads, since a surge or fault current from inductive equipment can trigger the trip.