It’s everywhere. Twisted pair cable is used for every network wire in your home or office. It’s easy to understand why twisted pair cable is when you look at it — it’s one cable made up of individual smaller cables, and each pair of cables (usually one with a solid color jacket and one with a matching color jacket mixed with white) is twisted together. If there’s no braid around the cable, it’s called “unshielded twisted pair” and you may have heard that term (UTP) used to refer to network cables in the past.
But why is it there? It seems like twisting the wires is a waste of time. Sure, it makes it easier to see what cable goes with what but the colored outer jackets will do that for you. It turns out, there’s a good reason for twisted pair cable to exist.
Early in the days of telephone wiring, engineers noticed interference from one line to the other on a pole. Simpy swapping the wires as they crossed the pole actually helped with the interference quite a bit. As the cables cross, the noise they generate individually cancels out. There’s quite a bit more engineering theory there, but the point is that simply by crossing two phone lines as they cross the top of a telephone pole makes them work better.
It’s actually the same theory being used in network cables. Crossing the pairs of cables over and over again (twisting them) helps eliminate noise and therefore the cables can stay unshielded. This makes them thinner and easier to work with. Imagine if you had to work with a 1/2″ thick cable every time you plugged in a computer. In old office phone systems, which were in many ways the predecessors to today’s computer wiring, that’s what you had.
This is a typical office telephone cable of the type that was used until the end of the 20th century. Would you want to use that every time you connected a computer to the internet? Twisted pair cable is really one of those little inventions that just makes everything better.