What Is Unshielded-Twisted-Pair (UTP) Cable

January 10, 2011
By Colin Yao

:: What is UTP Cable?

UTP cable picture

UTP stands for Unshielded Twisted Pair cable. UTP cable is a 100 ohm copper cable that consists of 2 to 1800 unshielded twisted pairs surrounded by an outer jacket. They have no metallic shield. This makes the cable small in diameter but unprotected against electrical interference. The twist helps to improve its immunity to electrical noise and EMI.

(You can get Cat 5e and Cat 6 UTP Patch Cable from us)

For horizontal cables, the number of pairs is typically 4 pair as shown below.

UTP Cable Picture

For backbone cables, the number of pairs will typically be some increment of 25, because multi-pair UTP cables are constructed in 25-pair binder group. A sample backbone UTP cable is shown below.

Backbone UTP cable

:: UTP Copper Cable Conductor Size

The copper conductor of both horizontal and backbone UTP cables are either 22 AWG or 24 AWG. 24 AWG is the most common size, but higher-performance cables like Category 6 UTP employ the larger 23 AWG copper wires.

:: Solid Conductor UTP Cable and Stranded Conductor UTP Cable

1) Solid Conductor UTP Cable

solid conductor UTP cable

Solid Conductor UTP Cable Picture

As its name implies, solid conductor UTP cables have a single, solid conducting copper wire as the conductor. In addition to being physically stronger and easier to work with, these larger wires have superior electrical characteristics that remain stable over a wider range of frequencies.

Solid conductor cables have a lower DC resistance and a lower susceptibility to high-frequency effects based on their larger diameters alone. These properties allow solid conductor cables to support longer transmission runs and higher data rates than their stranded cable counterparts.

UTP cables used for both horizontal and backbone applications are typically solid conductor cables.

2) Stranded Conductor UTP Cable

stranded conductor UTP cable

Stranded Conductor UTP Cable Picture

Stranded-conductor UTP cables are typically used as patch cables in either work areas or telecommunication rooms. They are the most common Category-type cables we often directly work with.

Inside the twisted pairs of a stranded cable, each individual conductor is made up of a bundle of smaller-gauge wire strands. These are arranged so that several wires (commonly 6 or 18) surround a single wire at the bundle’s center. The outer wires are wrapped helically around the central wire through a process called stranding. The stranded wires together form a single conductor with an overall diameter about the same as that of a conductor in a solid cable, but with a much smaller conducting area (based on the smaller diameters of the conducting wire strands).

The stranding of the wire conductors serves to protect them, and gives stranded cables their flexibility.

:: UTP Cable Applications

UTP cables are mostly used for LAN networks. They can be used for voice, low-speed data, high-speed data, audio and paging systems, and building automation and control systems. UTP cable can be used in both the horizontal and backbone cabling subsystems.

:: UTP Cable Categories and Performance Specifications

UTP cables were invented for voice applications. Voice UTP cables only needed to carry analog signals which are very robust and not easily corrupted by electrical noise or EMI. However, as UTP cables were used for different systems, higher quality UTP cables were required to support data systems that used digital signaling.

As the applications evolved, different categories or grades of UTP cables were created  along these years. Higher category UTP cables are referred to as data grade UTP cables, and low category UTP cables are referred to as voice grade UTP cables.

The following table shows different Category UTP cables, their business applications and corresponding performance specification.

Note:

TIA/EIA-568 only recognized cables of Category 3 ratings or above. Category 1 cable (Cat 1) and Category 2 (Cat 2) voice-grade coppers are a misnomer, probably adopted by those who assumed that TIA set up “Categories” for all types of cables originally defined by Anixter International, the distributor, under the grades called “Levels.”

Cat 1 cable is used in earlier times. It is used for typically voice networks that carries only voice traffic example telephones.

Anixter Level 2 (Cat 2) was a grade of UTP cable capable of transmitting data at up to 4 Mbit/s. It is the first cable which can transmit voice and data up to 4mbps. Anixter Level 2 cable was frequently used on ARCnet and 4 Mbit/s token ring networks, it is also used in telephone networks but it is no longer commonly used.

Category Grade Business Application Frequency Range
Category 1 voice grade voice-grade telephone networks only; not for data transmissions 750 kHz
Category 2 voice grade voice-grade telephone networks, as well as IBM dumb-terminal connections to mainframe computers 1 MHz
Category 3 data grade voice-grade telephone networks, 10Mbps Ethernet, 4Mbps Token Ring, 100BaseT4 Fast Ethernet, and 100VG Any LAN 16 MHz
Category 4 data grade 16Mbps Token Ring networks 20 MHz
Category 5 data grade 100BastTX Fast Ethernet, SONET, and OC-3 ATM networks 100 MHz
Category 5e data grade Gigabit (1000Mbps) Ethernet 100 MHz
Category 6 data grade Gigabit (1000Mbps) Ethernet 250 MHz
Category 6A data grade Gigabit (1000Mbps) and 10 Gigabit Ethernet 500 MHz

:: UTP Cable Color Codes

1) UTP Horizontal Cable Color Code

Horizontal UTP cable is four-pair construction by industry cabling standard. Each pair has two conductors. One wire of the pair is assigned the pair color with a white stripe and the other wire is assigned the color white with the pair color stripe. The table below lists the pair and color code for a four-pair horizontal UTP cable.

Wire Number Pair Number Color
1 1 60px-Wire_white_blue_stripe.svg white/blue
2 1 60px-Wire_blue.svg blue
3 2 60px-Wire_white_orange_stripe.svg white/orange
4 2 60px-Wire_orange.svg orange
5 3 60px-Wire_white_green_stripe.svg white/green
6 3 60px-Wire_green.svg green
7 4 60px-Wire_white_brown_stripe.svg white/brown
8 4 60px-Wire_brown.svg brown

2) UTP Backbone Cable Color Code

UTP backbone cables are large, multi-pair cables. These cables are constructed of 25-pair binder groups. Each binder group is individually color coded and each pair within a 25-pair binder group is individually color coded.

(a) 25-pair Binder Group Color Code

The 25-pair binder group is organized into five groups and there are five pairs in each group. The five color groups in a 25-pair binder are

  • White – pairs 1 to 5
  • Red – pairs 6 to 10
  • Black – pairs 11 to 15
  • Yellow – pairs 16 to 20
  • Violet – pairs 21 to 25

Within each color group, the five pairs are designated with the group color code and the pair color code. The pair color code for each of the five pairs with a color coded group are

  • Blue – 1st pair of the color code group
  • Orange – 2nd pair of the color code group
  • Green – 3rd pair of the color code group
  • Brown – 4th pair of the color code group
  • Slate – 5th pair of the color code group

The color code for a 25-pair binder group is shown in the following table.

Wire Number Pair Number Group Color Code Pair Color Code Color
1 1 white blue white/blue stripe
2 1 blue/white stripe
3 2 orange white/orange stripe
4 2 orange/white stripe
5 3 green white/green stripe
6 3 green/white stripe
7 4 brown white/brown stripe
8 4 brown/white stripe
9 5 slate white/slate stripe
10 5 slate/white stripe
11 6 red blue red/blue stripe
12 6 blue/red stripe
13 7 orange red/orange stripe
14 7 orange/red stripe
15 8 green red/green stripe
16 8 green/red stripe
17 9 brown red/brown stripe
18 9 brown/red stripe
19 10 slate red/slate stripe
20 10 slate/red stripe
21 11 black blue black/blue stripe
22 11 blue/black stripe
23 12 orange black/orange stripe
24 12 orange/black stripe
25 13 green black/green stripe
26 13 green/black stripe
27 14 brown black/brown stripe
28 14 brown/black stripe
29 15 slate black/slate stripe
30 15 slate/black stripe
31 16 yellow blue yellow/blue stripe
32 16 blue/yellow stripe
33 17 orange yellow/orange stripe
34 17 orange/yellow stripe
35 18 green yellow/green stripe
36 18 green/yellow stripe
37 19 brown yellow/brown stripe
38 19 brown/yellow stripe
39 20 slate yellow/slate stripe
40 20 slate/yellow stripe
41 21 violet blue violet/blue stripe
42 21 blue/violet stripe
43 22 orange violet/orange stripe
44 22 orange/violet stripe
45 23 green violet/green stripe
46 23 green/violet stripe
47 24 brown violet/brown stripe
48 24 brown/violet stripe
49 25 slate violet/slate stripe
50 25 slate/violet stripe

This is shown clearly in the following picture.

25 pair UTP backbone cable color coding

(b) More than 25-pair binder groups

Multi-pair UTP cables that have more than 25 pairs organize the 25-pair binder groups in color-coded groups using the same color-coding sequence. This is shown in the following table.

Pair Count Binder Group Color
1—25 White—blue
26—50 White—orange
51—75 White—green
76—100 White—brown
101—125 White—slate
126—150 Red–blue
151—175 Red—orange
176—200 Red—green
201—225 Red—brown
226—250 Red—Slate
251—275 Black—blue
276—300 Black—orange
301—325 Black—green
326—350 Black—brown
351—375 Black—slate
376—400 Yellow-blue

Mor than 25 pair Multipair UTP backbone cable

:: UTP Cable Connectors

1) RJ45 Jack and Plug

Four-pair UTP horizontal cables are terminated with an 8-position modular connector in the work area as shown below. The RJ45 jack is an 8-conductor, compact, modular jack used to terminate UTP data cable. RJ45 jacks are engineered to maintain specific Category 5, 5e, 6, or 6A performance, and therefore must match the category of the cable they are terminating.

UTP-connector

UTP cable connector

:: 568A and 568B Wiring Standards

When we refer to a jack or patch panel’s wiring connection, we refer to either the 568A or 568B wiring scheme. 568A and 568B wiring scheme define the pin-pair assignments for terminating UTP cable. These assignments define the pinout, or order of connections, for wires in 8P8C eight-pin modular connector plugs and sockets.

In UTP cable, each pair is represented by a specific color. Pair 1 is Blue, Pair 2 is Orange, Pair 3 is Green, and Pair 4 is Brown. In each pair, one wire is a solid color, and the other is predominantly white with a color stripe. When terminating UTP cable, each pair corresponds to a specific pin on the IDC contacts of the jack or patch panel.

The following charts illustrate the difference between 568A and 568B wiring scheme.

Notice that the only difference between 568A and 568B is that pairs 2 and 3 (orange and green) are swapped. Both configurations wire the pins “straight through”, i.e., pins 1 through 8 on one end are connected to pins 1 through 8 on the other end.

One can use cables wired according to either configuration in the same installation without significant problem. The primary thing one has to be careful is not to accidentally wire the ends of the same cable according to different configurations.

UTP 68A and 568B Wiring Scheme

Pin T568A Pair T568B Pair Wire T568A Color T568B Color Pins on plug face (socket is reversed)
1 3 2 tip 60px-Wire_white_green_stripe.svg
white/green stripe
60px-Wire_white_orange_stripe.svg
white/orange stripe
RJ45 Plug 8P8C
2 3 2 ring 60px-Wire_green.svg
green solid
60px-Wire_orange.svg
orange solid
3 2 3 tip 60px-Wire_white_orange_stripe.svg
white/orange stripe
60px-Wire_white_green_stripe.svg
white/green stripe
4 1 1 ring 60px-Wire_blue.svg
blue solid
60px-Wire_blue.svg
blue solid
5 1 1 tip 60px-Wire_white_blue_stripe.svg
white/blue stripe
60px-Wire_white_blue_stripe.svg
white/blue stripe
6 2 3 ring 60px-Wire_orange.svg
orange solid
60px-Wire_green.svg
green solid
7 4 4 tip 60px-Wire_white_brown_stripe.svg
white/brown stripe
60px-Wire_white_brown_stripe.svg
white/brown stripe
8 4 4 ring 60px-Wire_brown.svg
brown solid
60px-Wire_brown.svg
brown solid