Which protective devices are commonly used in aircraft DC electrical systems to interrupt fault current?

Which protective devices are commonly used in aircraft DC electrical systems to interrupt fault current?

• A. Diodes and inductors.
• B. Fuses and circuit breakers.
• C. Capacitors and resistors.
• D. Transformers and relays.

Answer: (B)

In aircraft DC electrical systems, protecting wiring and equipment from overcurrent is achieved by devices that sense excessive current and physically open the circuit. Fuses and circuit breakers are designed for this role. A fuse contains a metal link that melts when current exceeds its rating, opening the circuit quickly and providing simple, one-time protection. A circuit breaker uses a trip mechanism—thermal or magnetic—to separate the contacts when an overcurrent is detected, and it can be reset after the fault is cleared. In aviation, these DC-rated devices are essential because they reliably interrupt fault currents to prevent damage or fire, even under vibration and environmental stress. Diodes and inductors aren’t intended to interrupt fault current; diodes block reverse current and can fail under fault conditions, while inductors limit how fast current can rise but don’t guarantee disconnection. Capacitors and resistors store or dissipate energy but don’t provide automatic interruption of a fault. Transformers and relays by themselves don’t interrupt current—the transformer changes voltage levels, and relays may sense faults or actuate protection, but the actual interruption is performed by fuses or circuit breakers.

In aircraft DC electrical systems, protecting wiring and equipment from overcurrent is achieved by devices that sense excessive current and physically open the circuit. Fuses and circuit breakers are designed for this role. A fuse contains a metal link that melts when current exceeds its rating, opening the circuit quickly and providing simple, one-time protection. A circuit breaker uses a trip mechanism—thermal or magnetic—to separate the contacts when an overcurrent is detected, and it can be reset after the fault is cleared. In aviation, these DC-rated devices are essential because they reliably interrupt fault currents to prevent damage or fire, even under vibration and environmental stress.

Diodes and inductors aren’t intended to interrupt fault current; diodes block reverse current and can fail under fault conditions, while inductors limit how fast current can rise but don’t guarantee disconnection. Capacitors and resistors store or dissipate energy but don’t provide automatic interruption of a fault. Transformers and relays by themselves don’t interrupt current—the transformer changes voltage levels, and relays may sense faults or actuate protection, but the actual interruption is performed by fuses or circuit breakers.