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Twisted Pair

Introduction
There are two types of twisted pair cables. There is UTP (Unshielded Twisted Pair) and there is STP (Shielded Twisted Pair). Lately we hear more about FTP (Foil-shielded Twisted Pair). In this document we will treat FTP as a member of the STP group, since Shielded doesn't say anything about the shield. It can be foil, it can be braided.

General
A twisted pair cable has its wires twisted. This means that the wires do not run next to eachother, but are twisted with eachother.

The consequence is that the actual cable run is shorter then the copper length. Dependend on the tightness of the twists and the amount of twistes the difference could be up to 20% of the actual copper length.

Twisted pair cable is mostly used in environments where the signals are balanced. Due to the fact that one twisted pair is used for the A and B lead an induced signal will not cause much trouble. The induction will be similar on both wires, so the differential voltage will not change.

There are different qualities of twisting, and all serve a different puspose.

The EIA/TIA Technical System Bulletins (TSB) 36 and 40 define the 568 standard. This is a standard for customer premisis cabling and defines the different UTP cable types into categories. This standard defines also a pinning for UTP cabling.

Electrical Specification
Category	Frequency	Min. NEXT per 1000 ft/ 304 m	Max. Attenuation per 1000 ft/ 304 m	Resistance per 1000 ft/ 304 m	Capacitance	Impedance
3	1 MHz	41 dB	7,3 dB	28,6 ohms	18 pF/ft	100 ± 15 ohms
	4 MHz	32 dB	16 dB	28,6 ohms	18 pF/ft	100 ± 15 ohms
	10 MHz	26 dB	27 dB	28,6 ohms	18 pF/ft	100 ± 15 ohms
	16 MHz	23 dB	36 dB	28,6 ohms	18 pF/ft	100 ± 15 ohms
4	1 MHz	56 dB	6 dB	28,6 ohms	15 pF/ft	100 ± 15 ohms
	4 MHz	47 dB	12 dB	28,6 ohms	15 pF/ft	100 ± 15 ohms
	10 MHz	41 dB	20 dB	28,6 ohms	15 pF/ft	100 ± 15 ohms
	16 MHz	38 dB	25 dB	28,6 ohms	15 pF/ft	100 ± 15 ohms
	20 MHz	36 dB	31 dB	28,6 ohms	15 pF/ft	100 ± 15 ohms
5	4 MHz	53 dB	13 dB	28,6 ohms	14 pF/ft	100 ± 15 ohms
	10 MHz	47 dB	20 dB	28,6 ohms	14 pF/ft	100 ± 15 ohms
	20 MHz	42 dB	28 dB	28,6 ohms	14 pF/ft	100 ± 15 ohms
	100 MHz	32 dB	67 dB	28,6 ohms	14 pF/ft	100 ± 15 ohms

An UTP cable can be 1 to 25 twisted pairs. Below you will find a brief description of each category.

Category 1
There are no performance criteria for this cable. Functional it is equivalent to UL level 1. The cable usage is for basic communications and power-limited circuits.

Category 2
Usage up to 2 MHz, not EIA/TIA specified for data use. Functional equivalent to UL level 2 or IBM Type 3. The usage is voice and low-speed data.

Category 3
Usage up to 16 MHz, EIA/TIA 568 Commercial Building Telecommunications Wiring Standard for Horizontal UTP Cable (TSB PN-2841) for both UTP and STP. Functional equivalent to UL level 3. Usage e.g. 4 Mbps Tokenring 10 Mbps ethernet.
1.25"-2.50"/twist
4.8"-9.6"/foot

Category 4
Usage up to 20 MHz, EIA/TIA 568 TSB PN-2841 for both UTP and STP. Functional equivalent to UL level 4. Usage e.g. 16 Mbps Tokenring 10 Mbps ethernet.
0.60"-1.00"/twist
12"-20"/foot

Category 5
Usage up to 100 MHz, EIA/TIA 568 TSB PN-2841 for both UTP, STP and SCTP. Functional equivalent to UL level 5. Usage e.g. 100 Mbps ethernet.
0.50"-0.80"/twist
15"-24"/foot

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