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Mains Electricity in the UK

The UK mains supply is about 230 volts AC (it used to be stated as 240V on appliances - and in physics questions), but in 2009 was brought down by 10V to allow compatibility in the intended voltage of appliances made for both the UK and European market.

No change in voltage was required by either the Central European or the UK system, as both 220 V and 240 V fall within the lower 230 V tolerance bands (230 V ±6%). Some areas of the UK still have 250 volts for legacy reasons, but these also fall within the 10% tolerance band of 230 volts - so that is okay. In practice, this allowed countries to have supply systems at the same voltage as before (220 V or 240 V), at least until existing supply transformers are replaced.

An alternating current (a.c.) is one which is constantly changing direction.

Mains electricity is an a.c. supply.

In the UK it has a frequency of 50 cycles per second or 50 hertz (Hz) which means that it changes direction and back again 50 times each second.

It has a peak voltage of ±330V which has the same heating effect as a steady voltage of 230V - therefore the voltage is spoken about as 220V (RMS).

Cells and batteries supply a current which always flows in the same direction. This is called a direct current (d.c.).

 

for a UK Mains voltage graph.

to find out about house wiring in the UK.

to find out about safety. Mains voltage can kill if it is not used safely.

to find out about the 3-pin plug and cabling

to find out about fuses.

to find out about filament lamps

to find out about compact fluorescent lamps

 

Earthing of Metal-cased Appliances

Appliances with metal cases are usually earthed.

They have one end of a green/yellow wire fixed and connected to the metal case of the appliance, the other end of this wire is in the cable that goes to the plug. If a fault in the appliance connects the case to the live wire, and the supply is switched on, a very large current flows to earth and overloads the fuse. This 'blows' (melts and breaks the circuit) making the appliance safe to touch. for more detail on this.