The fuse protects electric circuits from excessive current by containing a wire that melts when overheated. There are two main types: replaceable wire fuses and cartridge fuses. The fuse rating indicates the maximum current it can withstand without melting. Fuses should be rated slightly higher than the appliance's normal current to prevent tripping during regular use. Earth wires connect appliances to ground and provide a path for current in case of a loose live wire, preventing electric shocks.

1. 8.6 The functions of fuse and
earth wire
What is a fuse?
A fuse is a device used to protect an electric
circuit against excessive current
It consists of a wire that will melt at a certain
temperature.
The wire is usually made of an alloy of tin and
lead

2. 2 main types of fuses
A replaceable wire fuse Cartridge fuse
A length of wire is The wire enclosed in a
attached to the terminals cylindrical tube made of
The wire can be an insulating material
replaced when breaks
due to excessive current

3. The rating of a fuse amount?
• It is a maximum amount of current that
can flow through the fuse without the wire
of the fuse melting
• Always indicated on the fuse
• Common fuse rating are 1A,2A,3A,5A,10A
and 13A

4. What is the function of a fuse?
• To prevent short circuit that can cause fire
and damage to electrical appliances
• A short circuit occurs when there is a low
resistance and a large amount of current
flowing in the circuit

5. How to determine the suitable
rating of a fuse for an electrical
appliance?
• Fuses to be used in an electrical
appliances should have rating of just slight
more than the current which the electrical
appliances will use under the normal
condition
• Example, a fuse of 3A may be used for an
electrical appliances that operates on
current of 2.5A

6. Example : Determine the suitable rating of
the fuses that should be used in an electric
iron marked 240V,2000W.
Solution : Current = Power
Voltage
Current flowing through the iron = 2000W
240V
= 8.33 A
Therefore, the suitable fuse rating is 10A

7. EARTH WIRE
1. The earth wire in a 3-pin plug
connects an electrical appliance to
the earth.
2. In normal operation:
- electric current flows from the
mains through the live wire to the
appliance and back to the mains
through the neutral wire.

8. 3. When a loose live wire touches the metal
part of an appliance, the electric current
will flow to the ground through the earth
wire.
4. This prevents a person who touches the
metal part of the appliance from getting
an electric shock.