Circuit breakers and fuses
Breaker or fuse protects one circuit: opens before overload overheats wiring (RIC-21 App C).
Fuse: one-time device (PHAK ch.7; RIC-21 Appendix C).
- Melts on overload. Cannot be reset. Replace with same amperage rating.
- Carry spares of right amperage.
- Higher-amperage fuse defeats protection, creates fire hazard.
- Correct underlying fault before replacing fuse.
Circuit breaker types:
| Type | Trips on overload | Pilot can open by hand | Reset |
|---|---|---|---|
| Push-to-reset | Yes (pops open) | No | Push button in |
| Pull-off, push-to-reset | Yes | Yes, isolates circuit deliberately | Push in to restore power |
| Auto-reset | Yes | - | Self-resets, no pilot action |
(PHAK ch.7, fig. 7-34)
After a breaker pops (TC AIM AIR 4.11): can signal a potential problem in that circuit.
- One reset only, and only if equipment is essential to continued safety of flight.
- Reset can be worse than leaving circuit open, depending on breaker amperage and place in circuit.
- Electrical fire: popped breaker or blown fuse likely linked to fire. Consult AFM before resetting or replacing (TP 1102).
- Never pull breaker just to silence alerting or warning device (gear-warning horn, overspeed, GPWS, smoke detector): may be valid warning.
- Only exception: obvious, continuously false warning. Still log pull as defect in journey log.
Trap: popped breaker is not a habit-reset; reflex reset can turn nuisance trip into something worse.
References
- TC AIM AIR 4.11
- FAA-H-8083-25 PHAK ch.7
- RIC-21 Appendix C
- TP 1102 (Flight Training Manual), Emergency Procedures: Electrical Fire