Electrical wires have a coating of an insulting material. The material, generally used is

Electrical wires have a coating of an insulting material called PVC (Polyvinylcloride). PVC is a polymer and bad conductor of electricity. It is the most common insulating material used to insulate electrical conductors from electric charge thus preventing human contact with live electricity.

Graphite is good conductor of electricity. Hence it cannot be used as insulating material.

Sulphur, although is a bad conductor of electricity, but is brittle in nature. So, cannot be used as insulating material.