P2 5.3: Fuses.

All information was taken directly from the AQA revision guide with only the key points from P2 5.3.

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  • Created by: JSpencer
  • Created on: 08-03-16 09:24
Why does a mains appliance with a plastic case not earthrd?
As it is an insulator so cannot become live.
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What appliances need to be earthed?
Ones that have metal cases.
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Why do these need to be earthed?
If a fault develops the live wire could touch the metal case, the case would be live = shock anyone who touches it.
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What is a fuse?
A thin wire that melts and cuts off the current if too much current goes through it.
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Where is a fuse fitted?
In series with the live wire.
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What happens if a fault develops?
A large curent flows to the earth and melts the fuse, disconnecting the supply.
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What should the rating of the fuse be?
Slightly higher than the usual current.
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What happens if the rating is too high?
It will not melt quick enough.
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What happens if the rating is too low?
It will melt as soon as the appliance is turned on.
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What is a circuit breaker?
An electromagnetic switch that cuts of the current if too high.
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What is a residual current circuit breaker (RCCB)?
Cuts off the current in the live wire if different from current in neutral wire.
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What is good about a RCCB?
Works faster than a fuse or an ordinary circuit breaker.
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Other cards in this set

Card 2

Front

What appliances need to be earthed?

Back

Ones that have metal cases.

Card 3

Front

Why do these need to be earthed?

Back

Preview of the front of card 3

Card 4

Front

What is a fuse?

Back

Preview of the front of card 4

Card 5

Front

Where is a fuse fitted?

Back

Preview of the front of card 5
View more cards

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