Circuit Control And Protection

Question 1

Automatic and semi-automatic switches.

Answer 1

Normally electromagnetic solenoid type.
Fitted where circumstances dictate operation:
Thermo switches
Time switches

Question 2

Cartridge fuse.

Answer 2

Fuses are the simplest protection, AC and DC.
Rated by their current carrying capacity.
PTC copper strip placed in series and melts at high current.
Ranged between 3-50A.
High current capacity fuses >350A are installed in distribution systems, can be called current limiters or isolation limiters.
Motor rated dues installed I motor circuit. Provide brief high current for start.

Question 3

Thermal circuit breaker.

Answer 3

Hot bimetallic strip releases the latch.

Question 4

Thermal-magnetic circuit breaker.

Answer 4

Sensing element is a small solenoid fitted in series.
As current increases solenoid moves towards latch until it disrupts the circuit.
Fast response time.

Question 5

Resisting circuit breaker

Answer 5

Either:
Trip free - holding the reset button whilst there’s a fault will not reconnect the circuit.
Non-trip free - holding reset button whilst there is a fault will reconnect the circuit.
Modern aircraft have trip free.

Question 6

Short circuit

Answer 6

Failure of component or cable, current increases.

Question 7

Rated current

Answer 7

Maximum it can take without blowing.