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Flashcards in P2 - Fuses And Earthing Deck (12)
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1
Q

What does the live wire touching the metal case cause?

A

A surge in current which melts the fuse, cuts off the live supply and breaks the circuit.

2
Q

What does the melted fuse after a current surge prevent? [2].

A

Electric shocks & fires.

3
Q

How should fuses be rated?

A

Slightly higher than the normal operating current.

4
Q

The larger the current, the _____ the cable, the _____ the fuse rating.

A

The larger the current, the thicker the cable, the higher the fuse rating.

5
Q

What is a double insulated appliance?

A

One with plastic casing & no metal showing.

6
Q

What cables do double insulated appliances have?

A

Two-core cables, without an earth wire.

7
Q

What do circuit breakers do?

A

Protect the circuit from damage if too much current flows.

8
Q

How do circuit breakers work?

A

When they detect a surge in current the break the circuit by opening a switch.

9
Q

What are the pros and cons of circuit breakers over fuses? [3].

A

+ more convenient: don’t need replacing.
+ faster.

  • more expensive.
10
Q

Name a type of circuit breaker.

A

Residual Current Circuit Breaker (RCCB).

11
Q

Why are RCCBs more effective at protecting against electrocution?

A

They detect small current changes which could be fatal.

12
Q

What happens when the live wire somehow touches the metal case?

A

Too great a current flows through the live wire, case and earth wire.