Twisted Pair

Twisted pair cabling is a form of wiring in which two conductors are wound together for the purposes of canceling out electromagnetic interference (EMI) from external sources, electromagnetic radiation  from the UTP cable, and  crosstalk between neighboring pairs. Twisting wires decreases interference because the loop area between the wires (which determines the magnetic coupling into the signal) is reduced. In balanced pair operation, the two wires typically carry equal and opposite signals (differential mode) which are combined by addition at the destination. The common-mode noise from the two wires (mostly) cancel each other in this addition because the two wires have similar amounts of EMI that are 180 degrees out of phase. This results in the same effect as subtraction.  Differential mode also reduces electromagnetic radiation from the cable, along with the attenuation that it causes.
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<hardware> A type of cable in which pairs of conductors are twisted together to randomise possible cross-talk from nearby wiring. Inadequate twisting is detectable using modern cable testing instruments.
(1995-02-23)