What is the primary purpose of a fuse or circuit breaker in an aircraft circuit?

• A. To rectify the current from AC to DC.
• B. To protect wiring by interrupting current during overcurrent conditions.
• C. To store energy for peak demand.
• D. To monitor voltage across a load.

Answer: (B)

Fuses and circuit breakers exist to protect wiring by interrupting current when it becomes too high. When everything is normal, they let current flow; if a fault causes an overcurrent, they open the circuit to stop the flow, preventing overheating, insulation damage, or fire in aircraft wiring. A fuse melts its metal link and sacrifices itself to break the circuit, while a circuit breaker trips and can be reset after the fault is cleared. This protective interruption is what keeps the wiring safe. The other functions—rectifying AC to DC, storing energy, or monitoring voltage—don’t describe how fuses or breakers protect the circuit.