why electric wire coated with PVC ?
PVC is short form of Poly vinyl Chloride. It is a polymer which is an insulator which means it does not allow electricity to pass through it. It is wrapped around electric wires so that two wires can be crossed around one another like in many cases you must have seen in your houses where two or more wires runs together.
Also, by any chance a person touches the wire while the switch on, he will not get electric shock as PVC acts as a barrier.