From the outside in, a cable is made up of three components: the sheath or outer jacket, the filler (optional), and one or more wires that each consist of an insulator and a conductor. Each of these components serves a particular purpose and each may vary in material depending on the cable’s intended use. Let’s start by exploring each of the components of a cable, starting from the outside in.
The Sheath/Outer Jacket.
When viewing a piece of cable this is the first thing you will see. The sheath can be made up of many materials including: metal, PVC, rubber, nylon, etc. Each outer jacket/sheath is chosen based on the conditions the wiring will be exposed to: moisture, temperature, chemicals, etc. Cables that need to take a beating, in say industrial locations, may have a rigid metal outer jacket. Cables that need to be buried underground will have a waterproof plastic sheath. Much of the wiring that runs through your house is cable with a flexible plastic outer jacket that allows for bending around tight corners. The outer jacket is the conductor’s first line of defense.
This is an optional feature that is not found in every cable. Filler is often used for maintaining structure and strength. Ever notice how your garden hose can sometimes kink and cut off your water? Well you wouldn’t want this happening with electricity. Filler can prevent this by occupying the empty space between the wire(s) and outer jacket. Filler can also be used to enhance the properties of a cable like heat or moisture resistance. Filler materials include: paper, plastic, foam, and cotton.
Moving on to individual wires, the insulator is the conductor’s last line of defense. Insulators protect conductors from each other and other current-carrying objects, like you! Insulators are most often made up of paper or some kind temperature or moisture resistant plastic. Some wire types even have multiple layers of insulators for extra protection in harsh or hazardous environments. Wires without an insulator are called bare.
This is the single most important component; it is what holds and distributes the electricity. Conductors are often made up of metals like copper, aluminum and even gold, as these metals conduct electricity the best. Other materials like plastic provide too much resistance to the flow of electricity which is exactly why they are used as insulators and jackets. When choosing what metal to use, factors like resistance, cost, melting point, etc. are considered. Another key consideration is whether to use a stranded or solid conductor. If you cut open a thin piece of stranded wire, you would see that it is made up of many hair-like thin strands. The benefit of stranded is that it increases the flexibility of the wire. The larger the stranded wire, the bigger the individual strands will be. A solid conductor, while less flexible, offers easier connecting to receptacles, switches and breakers.
In your house, behind your walls, the majority of the wiring you will see is Romex™ (non-metallic sheathed cable). A Romex™ cable consists of multiple wires (each with a conductor and insulator), wrapped in paper and surrounded by a flexible jacket which allows it to be bent around all the hard right angles in your home. This is not the only wiring necessary to supply your electricity; think about the power lines, the cable coming into your breaker panel, the cord on your coffee pot. Even though the materials used in each of these may be different, they are all still made up of the same key components. Without these wires and cables there would be no way to distribute the electricity throughout your house. Simply put, without wires and cables, electricity wouldn’t be able to power our world.