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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 main types of fusesA replaceable wire fuse Cartridge fuseA length of wire is The wire enclosed in aattached to the terminals cylindrical tube made ofThe wire can be an insulating materialreplaced when breaksdue to excessive current
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
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
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
Example : Determine the suitable rating ofthe 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 ATherefore, the suitable fuse rating is 10A
EARTH WIRE1. 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.
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.