Plugs and Fuses



In a plug the wires must be firmly and fully screwed in by each pin to make sure no bare wires are be shown.

There are three different coloured wires in a plug:

1) There is the LIVE wire this wire is BROWN. This plug carries the Voltage and alternates between a high positive and a high negative voltage of around 230V.

2) There is the NEUTRAL wire which is BLUE. This wire completes the circuit. Electricity normally flows IN through the LIVE wire and OUT through the NEUTRAL. This wire is always at 0 volts.

3) The last wire is the EARTH wire which has a GREEN AND YELLOW  casing on it. This wire works with the Fuse (circuit breaker - mentioned later). They work together to make appliances safe. The wire is also there to stop any outer casing of metal becoming live

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Fuses and Circuit Breakers

Fuses and miniture circuit breakers (MCB) are in place for if there is a fault in the circuit. The main diffence between a fuse and a circuit breaker is that a circuit breaker can be reset after it has 'tripped' but a fuse has to be replaced after it 'blows'.

The reason this would happen is if this scenario occured:

A FAULT causes the LIVE wire to touch the metal case of a toaster. A big current now flows out through the EARTH wire. The big current then surges to earth, the big surge of current blows the fuse (breaks it) which then isolates the appliance from the live. This then makes the appliance safe.

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Electrical Power and Fuse Ratings

The formula for electrical power is:


Written as the symbols:                P = V x I

This equation can be used to work out the fuse that should be used in an appliance. However first you need to work out the current the item will use.

The fuse should be rated* just a little higher that the current.

Fuses come with fixed ratings e.g. 3A, 5A and 13A. You should choose the first one that is just higher than the current.

* Electrical devices come with POWER RATINGS. This is the maximum power a device can use without being damaged or dangerous. This is why it is extremely imporatant that you have the correct size of fuse or MCB because otherwise the fault current would not trip the MCB or blow the fuse. This would either mean that the metal casing would stay live or the cable its self would melt and possibly set on fire.

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