Circuit Protection Flashcards
(13 cards)
What is the purpose of fuses or circuit breakers?
They are fitted in series into the circuit to protect cables and components in an electrical circuit against excessive current.
When does a short circuit occur?
When part of a wire carrying current touches another wire or part of the circuit and gives the electricity a path of less resistance.
What is a dipole system?
Two wire system
What is unipole?
1 wire
In what sort of circuits are fuses and circuit breakers used?
Both AC and DC.
What does a fuse comprise?
Thin piece of wire inside a glass tube.
What happens to the wire if its rated current is exceeded?
Melt or blow.
This interrupts the current flow and opens the circuit to safeguard the components in the circuit and the circuit itself.
What range is a fuse in?
3-50 amps
What is a current limiter or isolation limiter?
Large capacity fuses in the range of 100 to 350 amps.
Fitted to protect against short circuit faults in the distribution system.
Cannot be changed in flight.
Allow short-term overload before rupturing.
Found in series with busbars.
What is a circuit breaker?
A type of mechanical switch used to provide automatic circuit protection.
In what two ways can circuit breakers operate?
Thermally - Invar and brass. Used to protect circuits in the event of a prolonged over-current.
Magnetically - solenoid switch. Used to provide instantaneous protection for circuit components that are too sensitive to tolerate prolonged over current.
Difference between fuse and circuit breaker.
Circuit breaker is resettable, provided it is within reach and can be reset only once during the flight but cannot be replaced.
Fuse has to be replaced. Can be replaced once with one of the same rating or less.
Difference between trip free and non trip free circuit breakers
Non trip free - dangerous of the fault still exists
Trip free - safer and more common in modern aircraft
