P2 - Fuses And Earthing Flashcards
What does the live wire touching the metal case cause?
A surge in current which melts the fuse, cuts off the live supply and breaks the circuit.
What does the melted fuse after a current surge prevent? [2].
Electric shocks & fires.
How should fuses be rated?
Slightly higher than the normal operating current.
The larger the current, the _____ the cable, the _____ the fuse rating.
The larger the current, the thicker the cable, the higher the fuse rating.
What is a double insulated appliance?
One with plastic casing & no metal showing.
What cables do double insulated appliances have?
Two-core cables, without an earth wire.
What do circuit breakers do?
Protect the circuit from damage if too much current flows.
How do circuit breakers work?
When they detect a surge in current the break the circuit by opening a switch.
What are the pros and cons of circuit breakers over fuses? [3].
+ more convenient: don’t need replacing.
+ faster.
- more expensive.
Name a type of circuit breaker.
Residual Current Circuit Breaker (RCCB).
Why are RCCBs more effective at protecting against electrocution?
They detect small current changes which could be fatal.
What happens when the live wire somehow touches the metal case?
Too great a current flows through the live wire, case and earth wire.
