When it comes to electricity, there are two types of materials: conductors and insulators. Conductors are materials that are known for their low opposition to electrical flow. Insulators are known for their great capability to stop the flow of current. For successful wiring and usage of electricity, both materials have to work together to get clean and safe energy where it is needed.
Perhaps the most important reason why electrical wires are covered in plastic is to protect people from electrical shock. Electricity is a dangerous form of energy and it can kill. Covering electrical wires in plastic guarantees that the electrons flowing through the wires will not flow through your body when the wire is touched. Studies show that only 0.05 amp of electric current can cause heart attack and skin damage and high probability of death. The service coming to an ideal house in the U.S. is rated at 200 amps.
Electrons flowing through a conductor or wire tend to generate heat from their high speed motion and the energy they need to move electrons from their valance shell to new atoms, creating current flow. The heat can build up and if surrounded by flammable materials such as wood, paper and sheet rock, it can ignite and cause fire. Plastic helps dissipate the heat as well as prevent the wire from getting too hot and causing fire.
Plastic does a great job of insulating the conductor used in electrical systems. Without plastic, hot and neutral wires cannot be run in the same conductor or same wire. another means would have to be developed to convey electricity safely to electrical devices. This would cause a great deal of hardship as well as consume a lot of finances to do it safely. Plastic does a great job of keeping the cost down, preventing electrical shock and preventing fire by helping dissipate heat properly.
Why can't electrical wires be covered with other materials known for their resistance to electrical current, such as wood or glass? The main reason plastic is used is because of its flexibility and ability to easily bend around corners and enter electrical boxes safely. It also has the great capability to dissipate heat, and is slow burning as well.