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Switches
From the flight deck, the crew can control individual circuits by means of switches which come in different forms: toggle switch, rocker switch, push switch and pull switch
Some circuits require automatic control, this can be achieved by;
Thermo switches: Temperature sensitive and will activate at a pre-determined value
Time switches: Either mechanical or electrically controlled to activate a circuit when a preset time interval has elapsed
Circuit Protection
To protect the cables and components in an electrical circuit against excessive current, one or more fuses or circuit breakers are fitted in series into that circuit.
A fuse
- Rated by its current carrying capacity (in Amps), printed on the body of the fuse
- Generally in the range of 3-50 Amps
- Used in both DC and AC circuits
- Comprises a thin white inside a glass tube which mets or 'blows' if the rated current is exceeded
- A blown fuse must be physically replaced
A circuit breaker
- Rated by its current carrying capacity (in Amps), printed on the reset button
- Used in both DC and AC circuits
- Is a mechanical switch and can be thermally or magnetically operated
- When the current rises above a rated value, it opens or "trips" the circuit breaker
Thermal circuit breakers are used to protect circuits in the event of a prolonged over-current while magnetically operated circuit breakers can be used to provide instantaneous protection for circuit components that are too sensitive to tolerate a prolonged over-current.
Resetting
A fuse cannot be reset after it blows!
A circuit breaker can be reset after it trips (with a limit on how many times)!
A trip free circuit breaker = One that prevents the current returning to the circuit if the reset button is held in should the fact still exist (safer and more common in modern aircraft)
A non trip free circuit breaker = One that does allow the button to be held in and thus power to return to the circuit, even when the fault still exists
From the flight deck, the crew can control individual circuits by means of switches which come in different forms: toggle switch, rocker switch, push switch and pull switch
Some circuits require automatic control, this can be achieved by;
Thermo switches: Temperature sensitive and will activate at a pre-determined value
Time switches: Either mechanical or electrically controlled to activate a circuit when a preset time interval has elapsed
Circuit Protection
To protect the cables and components in an electrical circuit against excessive current, one or more fuses or circuit breakers are fitted in series into that circuit.
A fuse
- Rated by its current carrying capacity (in Amps), printed on the body of the fuse
- Generally in the range of 3-50 Amps
- Used in both DC and AC circuits
- Comprises a thin white inside a glass tube which mets or 'blows' if the rated current is exceeded
- A blown fuse must be physically replaced
A circuit breaker
- Rated by its current carrying capacity (in Amps), printed on the reset button
- Used in both DC and AC circuits
- Is a mechanical switch and can be thermally or magnetically operated
- When the current rises above a rated value, it opens or "trips" the circuit breaker
Thermal circuit breakers are used to protect circuits in the event of a prolonged over-current while magnetically operated circuit breakers can be used to provide instantaneous protection for circuit components that are too sensitive to tolerate a prolonged over-current.
Resetting
A fuse cannot be reset after it blows!
A circuit breaker can be reset after it trips (with a limit on how many times)!
A trip free circuit breaker = One that prevents the current returning to the circuit if the reset button is held in should the fact still exist (safer and more common in modern aircraft)
A non trip free circuit breaker = One that does allow the button to be held in and thus power to return to the circuit, even when the fault still exists
