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Mains electricity is the electricity generated by power stations and transported around the country through the National Grid
Everyone connects to the mains when plugging in an appliance such as a phone charger or kettle
Mains electricity is an alternating current (a.c.) supply
In the UK, the domestic electricity supply has a frequency of 50 Hz and a potential difference of about 230 V
A frequency of 50 Hz means the direction of the current changes back and forth 50 times every second
Mains electricity, being an alternating current, does not have positive and negative sides to the power source
The equivalent to positive and negative are called live and neutral and these form either end of the electrical circuit
plug-socket, IGCSE & GCSE Physics revision notes
The live and neutral wires deliver the electricity to the device. The Earth wire is purely for safety
Exam Tip
You will be expected to remember the values of frequency and potential difference for mains electricity in the UK, so make sure you memorise these numbers!
Three Core Cables
All electrical appliances are connected to the mains using at least a live wire and a neutral wire
In the UK, most electrical appliances are connected to the mains using a three-core cable consisting of
A live wire
A neutral wire
An Earth wire
The insulation covering each wire is colour coded for easy identification:
Live wire – brown
Neutral wire – blue
Earth wire – green and yellow stripes
A diagram showing the three wires going to a mains powered appliance: Live, Neutral and Earth
Every country has a slightly different configuration, with many using two-pin plugs and plug sockets such as in the USA and mainland Europe
The earth wire is still present in the two-pin plugs, just more hidden
Exam Tip
One way to remember which colours is which wire on the diagram, try looking at the second letter of each colour which corresponds to its position:
Blue = Left (Neutral)
Brown = Right (Live)
Striped = Top (Earth)
Live, Neutral and Earth Wires
The three wires have distinct purposes
The Live Wire
The live wire:
Carries the alternating potential difference from the supply to a circuit
It is the most dangerous of the three wires
If it touches the appliance without the Earth wire, it can cause electrocution
The Neutral Wire
The neutral wire:
Forms the opposite end of the circuit to the live wire to complete the circuit
Because of its lower voltage, it is much less dangerous than the live wire
The Earth Wire
The earth wire:
Acts as a safety wire to stop the appliance from becoming live
This prevents electric shocks from occurring if the appliance malfunctions or the live wire breaks off and touches the case of the plug
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