3- pin plug

20 Jul

Three pin plug.

The three pin plug contains;

The blue neutral wire which is held at around 0 volts.
The green/yellow earth wire.
The brown live wire which alternates between +240 volts and -240 volts.
The fuse (left hand side on diagram).
The cable grip, at the bottom of the plug to hold wires in securely.


The most common fuse sizes are 3A, 5A and 13A (an electric cooker can have a 30A fuse). If the amount of current flowing through the fuse gets bigger than the fuse rating the wire inside the fuse gets hot and melts which disconnects the live wire from the appliance. Fuses are cheap but operate more slowly than circuit breakers.

Calculate Fuse Ratings

There is a formula for working out the fuse rating, voltage or wattage for each appliance

P (Power in Watts) = V (voltage) x I (current in Amps)

The fuse rating can be calculated by dividing the power used by the appliance by the voltage going into the appliance.

I (Amps) = P (Watts) ÷ V (Voltage)

To calculate the fuse rating for a 1KW (1000Watts) , 230V appliance, divide the wattage (1000) by the voltage (230).

I (Amps) = P (Watts) 1000 ÷ V (Voltage) 230
I (Amps) = 4.35

A five amp ( 5 Amps) fuse would be required.

Earth Wires

Appliances with metal cases are earthed with an earth wire. Some appliances do not require an earth wire as they are double insulated. If a fault develops and the earth wire connects to the metal case of the appliance current begins to flow down the earth wire. The extra current being drawn in through the live wire causes the fuse wire in the fuse to heat up and melt. This disconnects the live wire and makes the appliance safe.


One response to “3- pin plug

  1. mehfuza faruk

    04/08/2012 at 2:23 am

    thank you very much for your detailed diagram


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