When used as a networking medium, unshielded twisted-pair (UTP) cabling consists of four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath. Network UTP cable has four pairs of either 22- or 24-gauge copper wire. A UTP cable has an external diameter of approximately 0.43 cm (0.17 inches), and its small size can be advantageous during installation.
UTP cable does not use shielding to counter the effects of EMI and RFI. Instead, cable designers have discovered that they can limit the negative effect of crosstalk by:
- Cancellation: Designers now pair wires in a circuit. When two wires in an electrical circuit are placed close together, their magnetic fields are the exact opposite of each other. Therefore, the two magnetic fields cancel each other out and also cancel out any outside EMI and RFI signals.
- Varying the number of twists per wire pair: To further enhance the cancellation effect of paired circuit wires designers vary the number of twists of each wire pair in a cable. UTP cable must follow precise specifications governing how many twists or braids are permitted per meter (3.28 feet) of cable. Notice in the figure that the orange/orange white pairs are twisted less than the blue/white blue pair. Each colored pair is twisted a different number of times.
UTP cable relies solely on the cancellation effect produced by the twisted wire pairs to limit signal degradation and effectively provide self-shielding for wire pairs within the network media.