Twisted pair

Twisted pair cabling is a common form of wiring in which two conductors are wound around each other for the purposes of canceling out electromagnetic interference which can cause crosstalk. The twist rate (usually defined in twists per meter) makes up part of the specification for a given type of cable. The greater the number of twists, the more crosstalk is reduced. Twisting wires decreases interference because:

The loop area between the wires (which determines the magnetic coupling into the signal) is reduced as much as physically possible.
The direction of current generated by a uniform coupled magnetic field is reversed by every twist, so that the currents in successive twists cancel each other.

Cable Shielding

Main article please see Electromagnetic shielding.

Twisted pair cables are often shielded to prevent electromagnetic interference. Because the shielding is made of metal, it also serves as a ground. This shielding can be applied to individual pairs, or to the collection of pairs. When shielding is applied to the collection of pairs, this is referred to as screening.

Unshielded Twisted Pair (UTP)

UTP cables are not shielded. This lack of shielding results in a high degree of flexibility as well as rugged durability. UTP cables are found in many ethernet networks and telephone systems.

Shielded Twisted Pair (STP)

STP cabling includes metal shielding over each individual pair of copper wires. This type of shielding prevents cable from external EMI (electromagnetic interferences).

Screened Shielded Twisted Pair (S/STP)

S/STP cabling is STP cabling with metal shielding also covering the group of shielded copper pairs. This type of cabling offers still improved protection from interference from external sources.

Screened Unshielded Twisted Pair (S/UTP)

S/UTP, also known as Fully-shielded (or Foiled) Twisted Pair (FTP) and Screened Fully-shielded Twisted Pair (S/FTP), is a screened UTP cable.

Cable Categories

Unshielded Twisted Pair (UTP) cabling is categorized by its performance capability and adherence to standards.

Category 5

Main article please see Category 5 cable.

Category 5 is a cable standard based on the ANSI/TIA/EIA-568-A standard.

Category 6

Main article please see Category 6 cable.

Category 6 is a cable standard based on the ANSI/TIA/EIA-568-B.2-1 specification. Apart from being backwards compatible with Category 3, 5, and 5e cabling, it provides bandwidth performance of up to 250 MHz.

Category 7

Main article please see Category 7 cable.

Category 7 is a cable standard based on the ISO-IEC 61156-5 specification. Apart from being backwards compatible with Category 3, 5, 5e and 6 cabling, it provides bandwidth performance of up to 600 MHz.

Uses

Data Networks

Twisted pair cabling is often used in data networks for short and medium length connections because of its relatively lower costs compared to fiber and coaxial cabling.

Telephone Networks

In telephone applications, UTP is often grouped into sets of 25 pairs according to a standard 25-pair color code originally developed by AT&T. A typical subset of these colors (white/blue, blue/white, white/orange, orange/white) shows up in most UTP cables.

External links

Signal cables | Telephony

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