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To put it simply, the wires are twisted to protect the signal from electrical “noise.” This noise comes from two places: interference from the outside world and interference from the wires inside the cable itself. The twist is a better physical solution to both problems.
The primary reason wires are twisted is to cancel out electromagnetic interference (EMI) from external sources like power lines, motors, and fluorescent lights. The two wires in a pair carry the same data, but as opposite signals (think +1 and -1). The helical twist ensures that, on average, both wires are exposed to the same amount of external noise. The receiving equipment is designed to look only at the difference between the two wires, so it can intelligently filter out the identical noise signal that’s been induced on both, leaving the original, clean data intact.
The second, equally critical reason for the twist is to prevent the pairs from interfering with each other inside the cable. When a signal travels down one pair, it creates a small magnetic field that can bleed over and corrupt the signal in an adjacent pair—a phenomenon called crosstalk. The twisting helps solve this in two clever ways. First, because the signals in a pair are opposite, their magnetic fields are also opposite and largely cancel each other out, making the pair “quieter” to its neighbors. More importantly, if you look closely at a quality network cable, you’ll notice each colored pair has a slightly different twist rate. This is a crucial design feature that prevents the pairs from running parallel for long distances, ensuring that any crosstalk they generate is averaged out to zero over the length of the cable.
