Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!

Did you know?

We also have Bitesize study guides covering many subjects at National 4 and National 5 on our Knowledge & Learning BETA website.

Home > Physics > Using electricity > Behind the wall

Physics

Behind the wall

  • Page
  • 1
  • 2
Back

This bite deals with fuses and circuit breakers and the mains supply.

Fuses and circuit breakers

Fuses are used in 3-pin plugs and in the fixed wiring in a house.

Fuses

  • Fuses in plugs protect the flex of the appliance, and in doing so, the appliance itself.
  • Fuses in the fixed wiring of a house protect the mains wiring.
  • If a fault develops and the current in the wire becomes dangerously large, the fuse melts and breaks the circuit.
  • Plug fuses come in different values. Although other values are available, the following rule is used to decide on the correct value of fuse to use:
    • for an appliance with a power rating of up to 700 watts, use a 3 ampere fuse
    • for an appliance with a power rating of 700 watts or greater, use a 13 ampere fuse

Circuit breakers

  • Circuit breakers are automatic switches in the mains supply which do the same job as fuses. They break the live wire if a fault causes the current to become too large.
  • (Credit) You should be able to say why fuses are in the live lead of an appliance. This is so that when a fuse blows it cuts off the live wire which is at a high voltage. The neutral wire is never at a high voltage.
  • (Credit) You should be able to give a reason why a circuit breaker is better than a fuse. Some reasons are:
    • they operate more quickly
    • they only need to be reset, not replaced
    • they cannot be replaced with the wrong size of wire

 

Video: How fuses and RCDs help protect us from electrocution

In order to see this content you need to have both Javascript enabled and Flash installed.

 

  • Page
  • 1
  • 2
Back

Play

A picture of Mia Cadaver

Tombstone Timeout

Test out your knowledge of physics with Mia Cadaver's physics game - it's serious fun!

BBC navigation

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.