The system is protected by circuit breakers and/or fuses. When there is a problem (overheating, for example), the breaker or fuse interrupts the flow of current and ceases to operate the equipment associated with that circuit. While the two devices serve the same general purpose, they have their differences.

Circuit breakers and fuses are generally located on the instrument panel in front of the pilot and/or co-pilot seats. One of the checklist items as you prepare for takeoff or landing is to check that all circuit breakers are “in.” Be sure to check all of them, including those not located with the others on the panel in front of you.

If a circuit breaker is not in, it is “popped” and recognizable as such because you will see a white ring around the breaker that is only visible when it has tripped (popped). Another way to check this in flight is to feel the breakers to ensure that none of them stick out (indicating they have popped). You should know which circuit breaker relates to which electrical system component. Your airplane’s pilot’s operating handbook (POH) or airplane flight manual describes the location of all circuit breakers and the appropriate responses to the various emergency situations that you may encounter.

Do not reset circuit breakers unless the component they protect is required for safe flight. Resetting a tripped circuit breaker can overheat wiring, ultimately leading to failure and arcing, which can cause a fire. If you need to reset a breaker to see if you are able to resume normal operations, the general rule of thumb is that if the breaker pops again it’s time to have a mechanic take a look as it may be an indication of a serious problem. Follow your aircraft’s specific guidance on whether or not to reset breakers. When in doubt, talk to a mechanic.

Fuses are generally found on older aircraft. They don’t pop out when they fail and cannot be reset. Instead, you must replace them with fuses for the proper amperage of each one. Having spares is a good idea for every flight and is required in some conditions (for example night and IFR flights) per FAR 91.205.

Review aircraft systems in your aircraft’s POH and Chapter 7 of the FAA’s Pilot’s Handbook of Aeronautical Knowledge, which is all about aircraft systems. In addition, the FAA has multiple guidance documents, including advisory circulars, concerning circuit breakers and circuit protective devices.