What is the practical difference between a fuse and a circuit breaker, and when would each be preferred on an aircraft?

What is the practical difference between a fuse and a circuit breaker, and when would each be preferred on an aircraft?

• A. Fuses interrupt once and are resettable after each trip.
• B. Fuses are resettable after a trip but breakers are not.
• C. Fuses are used where simple, single-use protection is acceptable, while breakers are preferred for circuits that may require manual or automatic trips and resets.
• D. Circuit breakers have no advantage over fuses.

Answer: (C)

The practical difference lies in how protection is cleared and how the device can be reused after a fault. A fuse is a one-time protective element: when overcurrent occurs, the fuse’s thin conductor melts and opens the circuit, and it cannot be reset. You must replace the fuse before power can be restored. This makes fuses suitable where a fault should result in definite, irreversible disconnection and where downtime to replace the device is acceptable. A circuit breaker, on the other hand, is resettable. It trips when current or conditions exceed its rating and can be reset after the fault is cleared, either manually or automatically. This allows the circuit to be re-energized quickly, aids fault isolation, and reduces maintenance downtime. Breakers are preferred for circuits that may require automatic or manual trips and subsequent resets, or where rapid restoration after a fault is beneficial. In aircraft practice, circuit breakers are generally used for most circuits to enable quick restoration and easier fault diagnosis, while fuses are used where a simple, single-use protection is adequate or where a definitive, non-resettable disconnection is desired.

The practical difference lies in how protection is cleared and how the device can be reused after a fault. A fuse is a one-time protective element: when overcurrent occurs, the fuse’s thin conductor melts and opens the circuit, and it cannot be reset. You must replace the fuse before power can be restored. This makes fuses suitable where a fault should result in definite, irreversible disconnection and where downtime to replace the device is acceptable.

A circuit breaker, on the other hand, is resettable. It trips when current or conditions exceed its rating and can be reset after the fault is cleared, either manually or automatically. This allows the circuit to be re-energized quickly, aids fault isolation, and reduces maintenance downtime. Breakers are preferred for circuits that may require automatic or manual trips and subsequent resets, or where rapid restoration after a fault is beneficial.

In aircraft practice, circuit breakers are generally used for most circuits to enable quick restoration and easier fault diagnosis, while fuses are used where a simple, single-use protection is adequate or where a definitive, non-resettable disconnection is desired.