You may have noticed the over-head power lines outside your homes. You might also have witnessed the sight of birds perched on these cables. These wires are actually high tension lines that could be having a voltage of more than 20000 Kilovolts. Also they are not insulted. You may see two wires – one of which is the phase wire and other neutral. So how do they sit over the bare wires without getting electrocuted?
Electricity is the flow of electrons which needs a motivation. This motivation is nothing but the difference in electric potential. When there is a potential difference across a circuit, current starts to flow through the circuit. Also electricity always tries to find the easiest path to the ground. So when a bird perches on a single wire, they get charged for a moment. Both its feet are at the same potential. Hence because of lack of any potential difference, current does not flow through the bird. Now the bird is safe.
But if the bird by any chance touches the other wire (say by flapping its wings), it forms a circuit. There being a potential difference between both the wires, current flows through the bird and bird dies. Also when the bird sits on the poles which are in contact with the ground and touch a wire, they get electrocuted as current happily finds its way to the ground.
That’s why line men always switch off the power supply to these wires before they work on them. Also if they work on a live wire, they use insulating things like thick rubber gloves, rubber slippers for their safety. One must be very careful while climbing trees or climbing on a ladder around the house.