FAA Aviation Mechanic Airframe (AMA)Airframe Electrical and InstrumentsEasy
A technician is comparing circuit protection devices for a new installation and must explain why fuses are still used in some older aircraft circuits instead of circuit breakers. Which statement correctly describes an advantage of a fuse over a circuit breaker?
- AA fuse automatically resets once it cools down
- BA fuse is trip-free and cannot be held closed against a fault
- CA fuse responds more quickly and precisely to an overcurrent because it melts directly, without mechanical linkage delay
- DA fuse can be reset multiple times without replacement
Show answer & explanationAnswer & explanation
Correct answer: C. A fuse responds more quickly and precisely to an overcurrent because it melts directly, without mechanical linkage delay
A fuse element melts directly in response to excess current, giving a fast, precise, and consistent interrupting response since there are no mechanical parts to overcome. Its drawback is that it is a one-time device and must be replaced after opening.
Why the other options are wrong
- A. Fuses do not self-reset; that describes some thermal circuit breakers.
- B. Trip-free is a circuit breaker characteristic, not a fuse characteristic.
- D. Fuses are one-time use only, not resettable.
Fuse vs Circuit Breaker
A fuse is a one-time overcurrent device that melts to open a circuit, offering fast and precise protection, while a circuit breaker is a resettable mechanical device.
- Fuse melts and must be replaced after opening
- Fuses respond quickly since no mechanical linkage is involved
- Circuit breakers are resettable but slightly slower due to mechanical action
Memory trick: Fuse = one-shot flame, Breaker = reset button