Most electrical appliances are connected to the mains by a three-core cable. Each wire has insulation that is colour coded so it can be identified easily. The live wire is brown, the neutral wire is blue and the earth wire has green and yellow stripes.
The live wire carries the alternating potential difference from the supply. The neutral wire completes the circuit. The earth wire is a safety wire, which stops the appliance becoming live. It only carries a current if there is a fault.
The potential difference between the live wire and earth (0 V) is about 230 V. The neutral wire is at, or close to, earth potential (0 V), so there is almost no potential difference between the neutral wire and earth.
A switch in the mains circuit should be in the live wire. If it is, opening the switch cuts off the 230 V. If it is not, the live wire stays connected to the appliance even when the switch is open, so the live wire can be dangerous even when a switch is open. Touching a live wire is dangerous because a current can flow through your body to earth. Any connection between the live wire and earth is dangerous too, because it allows a large current to flow, which can cause electric shock or fire.
