2. 0.05 s

4. Fuses L.O.: What do we use fuses and circuit breakers for?
How to use the correct fuse
June 08, Q4, page 9

5. Fuse
Fuse

6. Fuses & Circuit Breakers
A fault in an appliance can cause the current to be too great and can lead to the wire overheating and possibly causing a fire.
A fuse is designed to melt if the current through a circuit is too high, thereby breaking the circuit
The fuse should be just higher than the normal working current
A circuit breaker can be reset rather than replaced
Fuses & Circuit Breakers

7. Fuses
Fuses

8. If an appliance has a metal case it needs to be earthed.
Earth wire
If an appliance has a metal case it needs to be earthed.
A fault could cause the live wire to touch the metal case. If the appliance is earthed a large current flows down the earth wire and melts the fuse. If the appliance was not earthed there would be a risk of electrocution.
Earth wire

9. Earth wire
Earth wire

10. An electrical fault (1)
An electrical fault (1)

11. An electrical fault (2)
An electrical fault (2)

12. Fuses in plugs are made in standard ratings.
The most common are 3A, 5A and 13A. The fuse should be rated at a slightly higher current than the device needs
if the device works at 3A, use a 5A fuse
if the device works at 10A, use a 13A fuse

13. Work faster than fuses and can be reset quicker.

14. A circuit breaker is an electromagnetic switch that opens and cuts the current off if too much current passes through it.

15. Fuses II Operating Current Fuse 2.1A 11.2A 4.7A 6.0A 4.5A 8.2A 3.0A
For the following devices choose fuses from 3A, 5A and 13A.
Operating Current
Fuse
2.1A
11.2A
4.7A
6.0A
4.5A
8.2A
3.0A
13.0A
5.0A
13.0A
5.0A
13.0A

16. Workbook page 93

17. Fuses L.O.: What do we use fuses and circuit breakers for?
How to use the correct fuse
June 08, Q4, page 9