Why Do We Use Plastic Coated Wiring in Our Homes?

Shorts

• When a "hot" wire and a wire leading to ground come in contact, current takes the path of least resistance and flows from the hot wire straight to ground. The result is a massive increase in the current called a short. Shorts can melt wires and start fires. Insulation prevents the current-carrying metal in two wires from coming in contact with each other. It also protects you by ensuring that you don't come in contact with the wire and give yourself a shock.

Plastic

• Metals like copper are conductors; they present a fairly low level of resistance to an electric current. Some of the electrons are shared between many different copper atoms and thus fairly free to move when an electric field is applied. Plastic, by contrast, is an insulator that has very high resistance. The electrons in the plastic are bound tightly by individual molecules; it would take much more energy to dislodge them.

Insulators

• Humans have discovered many other insulators besides plastics, of course. Materials such as glass, wood, rubber and mica can also serve as insulators. Plastic's unique properties, however, make it superior to some of these other materials for many applications. If your wires were insulated in glass, for example, they would be more difficult to cut or repair. And while the mineral mica is suitable for certain applications in industry, it's much more rigid than plastic and thus less suitable for insulating wires around your home.

Considerations

• Many plastics have excellent corrosion resistance, which makes them all the more effective for applications where the wire may come in contact with corrosive fumes -- in your car, for example. Some plastics also have fire-retardant properties. PVC, for example, contains chlorine atoms attached to a carbon backbone. At the very high temperatures in a fire, some of the chlorine atoms become detached. These "chlorine radicals" interfere with the combustion reaction and hence slow the progress of the fire.