Electrical installations are based on circuits. The electricity flows along a wire from the power source to the appliance. It then travels back to the power source again along another wire.
The flow to the appliance is the ‘Live’.
The return wire is the ‘Neutral’.
In order to be able to turn appliances on or off, we need to introduce a switch. This opens and closes a connection in the circuit. When closed, the connection is made and electricity can flow. When open, the connection is broken and electricity will not flow.
In a very simple circuit, the battery supplies the electrical current which flows along the live wire to the lightbulb. The current then continues back to the battery along the neutral wire. Whilst the switch would operate the lightbulb by being fitted in either wire, it must in fact always be in the live wire. If it were fitted in the neutral, the lightbulb could be switched off because the circuit had been broken but, because the break is after the lamp, the wires up to it and its connections would still be ‘live’. This would be exceedingly dangerous on a mains circuit since the lamp being off would give the impression that the power was off. In fact it would still be on and anyone touching the terminals at the lamp would receive an electric shock.
The wires in household electrics are colour-coded for ease of identification.
Brown (old cable colour = red) = live.
Blue (old cable colour = black) = neutral.
Green & yellow = earth.