Definition
Protective devices installed in an aircraft's electrical system that automatically interrupt the flow of current to a circuit when the current exceeds a safe level. A circuit breaker opens the circuit by tripping a switch-like mechanism and can be reset after the fault is addressed. A fuse opens the circuit by melting a thin metal element inside it and must be physically replaced once it has blown.
Plain English
Safety devices that cut off electrical power to a part of the aircraft if too much current flows through it. A circuit breaker can be reset by pushing it back in. A fuse is a one-time device that has to be swapped out for a new one after it blows.
Context Anchor
Seen on cockpit electrical panels, in aircraft equipment lists, and during electrical-system troubleshooting.
Derivation
Circuit' comes from the Latin circuitus, meaning 'a going around' — an electrical circuit is a closed loop the current travels around. 'Breaker' is simply something that breaks the loop. 'Fuse' comes from the Latin fundere, 'to pour or melt' — which is exactly how a fuse works: a small metal strip melts to break the circuit.
Why Pilots Care
Pilots must locate and understand these devices to diagnose electrical failures quickly and avoid creating additional hazards such as smoke or fire.
Analogy
They function like the breakers in a home electrical panel that trip when too many appliances are used at once.
Grounding Statement
If too much electricity tries to flow through a wire, a circuit breaker or fuse opens the path before the wire overheats.
Intuition Check
A circuit breaker is not just an ordinary on/off switch, even if it can look like one. A fuse is not an explosive fuse; in this context, it is a small protective part that melts to stop unsafe electrical flow.
Example Sentence 1
After the landing light stopped working, the pilot checked the panel and found the circuit breaker had popped out.
Example Sentence 2
Older aircraft may use replaceable fuses instead of resettable circuit breakers for certain circuits.