A1 LT12 Flashcards
What are the two main types of cartridge fuses?
Ferrule type and knife-blade type
What was the disadvantage of the fuse that led to the search for an alternative method?
Needed to be replaced every time it opened
What happens to the breaker’s handle when it trips?
Moves midway between ON and OFF
What are the ends of cartridge fuses named after?
Shotgun cartridge
How do you reset a tripped breaker?
Move from centre to OFF, then to ON
What is the difference between ferrule and knife-blade type cartridge fuses?
Knife-blade type is used for fuses rated above 60 A
What size of circuit breaker is typically used for lights and plugs in domestic settings?
15 A
What are the types of trip elements in circuit breakers?
Thermal and magnetic
How does a fuse protect a circuit?
Melts open to break circuit
What is the other name for plug fuses?
Screw-in fuse or Edison-base fuse
What size of circuit breaker is usually used for heaters in domestic settings?
20 A
Why are fuses designed to be the weakest link in an electric circuit?
To protect the circuit from damage
What size of circuit breaker is commonly used for clothes dryers in domestic settings?
30 A
How does a fuse operate?
Higher resistance alloy with lower melting point
What size of circuit breaker is typically used for ranges in domestic settings?
40 A
What happens when the current level exceeds the fuse’s rating?
Fuse link begins to melt open.
What is the most common type of circuit breaker?
Moulded-case circuit breaker
Is a fuse guaranteed to open instantly when its rating is exceeded?
No, it may not always open instantly.
What characteristics do the identification letters on the circuit breaker frame refer to?
Voltage, current, interrupting capacity, dimensions
What triggers a circuit breaker to open?
Prolonged overload or excessive current
What is a thermal trip element made of?
Bimetal strip of two dissimilar metals
How can circuit breakers be operated?
Magnetic or thermal action
Why does a fuse open almost instantly on heavy fault current but more slowly on overload current?
Time to melt and open is inversely proportional to current magnitude.
What are the different configurations of circuit breakers?
Single-pole, double-pole, three-pole
Are circuit breakers interchangeable among different manufacturers?
No
How do amperage and voltage ratings affect the size of a fuse?
Higher ratings mean larger and longer fuse
How are standard circuit breakers rated?
In amperes
In which industries are circuit breakers with lower current ratings often used?
Auto industry and other specialized industries
Where are plug fuses commonly used?
Domestic ranges and older installations
According to Figure 5, which circuit breaker should trip first when a fault occurs?
The one closest to the fault
What is a fuse?
Overcurrent device designed to break circuit
How are the circuit breakers protecting branch circuits rated compared to upstream breakers?
Lowest current rating
How is selective protection achieved in the circuit?
By having higher ampere ratings on upstream breakers
What are time-delay fuses?
Take more time to melt and open
How are different types of moulded cases identified on the frame by manufacturers?
Manufacturer’s letters
Where are fuses used?
Homes, offices, industry, automobiles, ships, electronic equipment
What are some standard current ratings for circuit breakers?
15, 20, 30, 40, 50, 60, 70, 100 A
What should happen if a fault develops in the branch circuit?
Trip
