Which aircraft electrical circuit does not normally contain a fuse or circuit breaker?

Which aircraft electrical circuit does not normally contain a fuse or circuit breaker?

• A. The starter motor circuit
• B. The standby radio circuit
• C. The instrument power circuit
• D. The flight lighting circuit

Answer: (A)

Starting circuits are designed to deliver a very large, short-duration current to crank the engine, so placing a fuse or circuit breaker in that path would often cause nuisance trips and prevent engine start. To avoid that, the starter motor feed is arranged to be essentially direct from the battery through the starter solenoid/contactor, with protection provided by fusible links in the power lead near the battery rather than a standard in-line fuse or breaker. Those fusible links act as a one-time protection in the wiring harness, not a removable protective device like a circuit breaker. Because of this, the starter motor circuit normally does not contain a fuse or circuit breaker in the same way the other systems do. The standby radio, instrument power, and flight lighting circuits are all typically protected by fuses or circuit breakers to guard wiring and prevent faults from propagating.

Starting circuits are designed to deliver a very large, short-duration current to crank the engine, so placing a fuse or circuit breaker in that path would often cause nuisance trips and prevent engine start. To avoid that, the starter motor feed is arranged to be essentially direct from the battery through the starter solenoid/contactor, with protection provided by fusible links in the power lead near the battery rather than a standard in-line fuse or breaker. Those fusible links act as a one-time protection in the wiring harness, not a removable protective device like a circuit breaker. Because of this, the starter motor circuit normally does not contain a fuse or circuit breaker in the same way the other systems do. The standby radio, instrument power, and flight lighting circuits are all typically protected by fuses or circuit breakers to guard wiring and prevent faults from propagating.