Editing 25-pair color code

{{Short description|Form of color code used in wiring}}
[[File:Cable-singlecore-25-pair-0a.jpg|thumb|upright=1.25|Single-core 25-pair/50 conductor cable]]

The '''25-pair color code''', originally known as '''even-count color code''',<ref>AT&T, Bell System Practices, Section 461-200-101 Issue 7, ''Connector Cables—Identification'' (May 1979)</ref> is a [[color code]] used to identify individual conductors in [[twisted-pair]] [[wiring]] for [[telecommunications]].

==Color coding==
With the development of new generations of telecommunication cables with polyethylene-insulated conductors (''PIC'') by [[Bell Labs|Bell Laboratories]] for the [[Bell System]] in the 1950s, new methods were developed to mark each individual conductor in cables.<ref>F.W. Horn, ''Even-Count Cable'', Bell Laboratories Record 37(6), 208 (June 1959)</ref> Each wire is identified by the combination of two colors, one of which is the major color, and the second the minor color.  Major and minor colors are chosen from two different groups of five, resulting in 25 color combinations. The color combinations are applied to the insulation that covers each conductor. Typically, one color is a prominent background color of the insulation, and the other is a tracer, consisting of stripes, rings, or dots, applied over the background. The background color always matches the tracer color of its paired conductor, and vice versa.

The major, or primary group of colors consists of the sequence of white, red, black, yellow, and violet ([[mnemonic]]s '''W'''hy '''R'''un '''B'''ackwards, '''Y'''ou'll '''V'''omit).<ref name="Abruzzino-2000">Abruzzino, James: ''Communications Cabling (2E)'', page 187. CNC Press, 2000</ref> The minor, or secondary color is chosen from the sequence blue, orange, green, brown, and slate (mnemonics '''B'''ell '''O'''perators '''G'''ive '''B'''etter '''S'''ervice<ref name="kadiak">{{Cite web|url=http://www.kadiak.org/tel/color.htm|title = Modern Telephone Cable Color Code|website=www.kadiak.org}}</ref>).<ref name="Highhouse"/><ref name="BSPG50"/><ref>[https://archive.org/stream/MemorySuperpak_201802/131574477-memonics-pdf_djvu.txt A compilation of mnemonics for Electronics Engineering (ECE)] by Jemery Gentiles lists both the standard mnemonic pair and a not-safe-for-work alternate.</ref>

[[File:25 pair color code chart.svg|thumb|upright=1.25|25-pair color coding using twisted pairs with solid color coding only, without tracers. This method was rarely used.]]

{| class="wikitable"
|+25-pair color code
! Pair<br/>no. !!colspan="2"| Major color !!colspan="2"| Minor color
|-
|align="center"| 1 ||rowspan="5" align="right" vertical-align="middle"| White ||rowspan="5" bgcolor="white"| ||bgcolor="blue"| || Blue
|-
|align="center"| 2 ||bgcolor="orange"| || Orange
|-
|align="center"| 3 ||bgcolor="#00FF00"| || Green
|-
|align="center"| 4 ||bgcolor="brown"| || Brown
|-
|align="center"| 5 ||bgcolor="slategray"| || Slate
|-
|align="center"| 6 ||rowspan="5" align="right" vertical-align="middle"| Red ||rowspan="5" bgcolor="red"| ||bgcolor="blue"| || Blue
|-
|align="center"| 7 ||bgcolor="orange"| || Orange
|-
|align="center"| 8 ||bgcolor="#00FF00"| || Green
|-
|align="center"| 9 ||bgcolor="brown"| || Brown
|-
|align="center"| 10 ||bgcolor="slategray"| || Slate
|-
|align="center"| 11 ||rowspan="5" align="right" vertical-align="middle"| Black ||rowspan="5" bgcolor="black"| ||bgcolor="blue"| || Blue
|-
|align="center"| 12 ||bgcolor="orange"| || Orange
|-
|align="center"| 13 ||bgcolor="#00FF00"| || Green
|-
|align="center"| 14 ||bgcolor="brown"| || Brown
|-
|align="center"| 15 ||bgcolor="slategray"| || Slate
|-
|align="center"| 16 ||rowspan="5" align="right" vertical-align="middle"| Yellow ||rowspan="5" bgcolor="yellow"| ||bgcolor="blue"| || Blue
|-
|align="center"| 17 ||bgcolor="orange"| || Orange
|-
|align="center"| 18 ||bgcolor="#00FF00"| || Green
|-
|align="center"| 19 ||bgcolor="brown"| || Brown
|-
|align="center"| 20 ||bgcolor="slategray"| || Slate
|-
|align="center"| 21 ||rowspan="5" align="right" vertical-align="middle"| Violet ||rowspan="5" bgcolor="violet"| ||bgcolor="blue"| || Blue
|-
|align="center"| 22 ||bgcolor="orange"| || Orange
|-
|align="center"| 23 ||bgcolor="#00FF00"| || Green
|-
|align="center"| 24 ||bgcolor="brown"| || Brown
|-
|align="center"| 25 ||bgcolor="slategray"| || Slate
|}

The wire pairs are referenced directly by their color combination, or by the pair number. For example, ''pair 9'' is also called the ''red-brown pair''. In technical tabulations, the colors are often suitably abbreviated.

''Violet'' is the standard name in the telecommunications and [[electronics industry]], but it is sometimes referred to as ''purple''. Similarly, ''slate'' is a particular shade of gray. The names of most of the colors were taken from the conventional colors of the rainbow or optical spectrum, and in the [[electronic color code]], which uses the same ten colors, albeit in a different order.{{cn|date=July 2017}}

When used for [[plain old telephone service]] (POTS), the first wire is known as the ''tip'' or ''A''-leg (U.K.) conductor, and is usually connected to the positive side of a [[direct current]] (DC) circuit, while the second wire is known as the ''ring'' lead or ''B''-leg (U.K.), and is connected to the negative side of the circuit. Neither of these two sides of the line has a connection to the local ground. This creates a [[balanced audio]] circuit with [[common-mode rejection]], also known as a [[Differential signaling|differential pair]]. The [[tip and ring]] convention is based on the [[Phone connector (audio)|{{frac|1|4}}″ (6.5&nbsp;mm) TRS phone connector]]s, which were employed in [[telephone switchboard]]s in the 19th and 20th centuries, where the tip contact of the connector is separated from the ring contact by a spacer of insulation. The connection furthest from the cable is known as the ''tip'', the middle connection is the ''ring'', and the (largest) connection closest to the wire is the ''sleeve''.

==25-pair telco cable pinout==
A common application of the 25-pair color code is the cabling for the [[Registered Jack]] interface RJ21, which uses a female 50-pin [[miniature ribbon connector]], as shown in the following table. The geometry of the pins of the receptacle (right hand image) corresponds to the pin numbers of the table.  The left column of pins are the ring (R) conductors, while all tip (T) conductors are on the right.

{| class="wikitable"
! rowspan=2| Color<br /><small>(minor/major)</small> || (R) || || (T) || rowspan=2 | Color<br /><small>(major/minor)</small> || rowspan=2 | The corresponding<br/>pin order in the<br/>female RJ21 connector
|-
! colspan=3|Pin No.
|-
| [[File:Wire blue white stripe.svg|37px]] blue/white
| 1
|
| 26
| [[File:Wire white blue stripe.svg|37px]] white/blue
| rowspan=31 style="vertical-align: top;" | [[File:RJ21-female-connector.jpg|160px]]
|-
| [[File:Wire orange white stripe.svg|37px]] orange/white
| 2
|
| 27
| [[File:Wire white orange stripe.svg|37px]] white/orange
|-
| [[File:Wire green white stripe.svg|37px]] green/white
| 3
|
| 28
| [[File:Wire white green stripe.svg|37px]] white/green
|-
| [[File:Wire brown white stripe.svg|37px]] brown/white
| 4
|
| 29
| [[File:Wire white brown stripe.svg|37px]] white/brown
|-
| [[File:Wire gray white stripe.svg|37px]] slate/white
| 5
|
| 30
| [[File:Wire white gray stripe.svg|37px]] white/slate
|-
| colspan=5 |
|-
| [[File:Wire blue red stripe.svg|37px]] blue/red
| 6
|
| 31
| [[File:Wire red blue stripe.svg|37px]] red/blue
|-
| [[File:Wire orange red stripe.svg|37px]] orange/red
| 7
|
| 32
| [[File:Wire red orange stripe.svg|37px]] red/orange
|-
| [[File:Wire green red stripe.svg|37px]] green/red
| 8
|
| 33
| [[File:Wire red green stripe.svg|37px]] red/green
|-
| [[File:Wire brown red stripe.svg|37px]] brown/red
| 9
|
| 34
| [[File:Wire red brown stripe.svg|37px]] red/brown
|-
| [[File:Wire gray red stripe.svg|37px]] slate/red
| 10
|
| 35
| [[File:Wire red gray stripe.svg|37px]] red/slate
|-
| colspan=5 |
|-
| [[File:Wire blue black stripe.svg|37px]] blue/black
| 11
|
| 36
| [[File:Wire black blue stripe.svg|37px]] black/blue
|-
| [[File:Wire orange black stripe.svg|37px]] orange/black
| 12
|
| 37
| [[File:Wire black orange stripe.svg|37px]] black/orange
|-
| [[File:Wire green black stripe.svg|37px]] green/black
| 13
|
| 38
| [[File:Wire black green stripe.svg|37px]] black/green
|-
| [[File:Wire brown black stripe.svg|37px]] brown/black
| 14
|
| 39
| [[File:Wire black brown stripe.svg|37px]] black/brown
|-
| [[File:Wire gray black stripe.svg|37px]] slate/black
| 15
|
| 40
| [[File:Wire black gray stripe.svg|37px]] black/slate
|-
| colspan=5 |
|-
| [[File:Wire blue yellow stripe.svg|37px]] blue/yellow
| 16
|
| 41
| [[File:Wire yellow blue stripe.svg|37px]] yellow/blue
|-
| [[File:Wire orange yellow stripe.svg|37px]] orange/yellow
| 17
|
| 42
| [[File:Wire yellow orange stripe.svg|37px]] yellow/orange
|-
| [[File:Wire green yellow stripe.svg|37px]] green/yellow
| 18
|
| 43
| [[File:Wire yellow green stripe.svg|37px]] yellow/green
|-
| [[File:Wire brown yellow stripe.svg|37px]] brown/yellow
| 19
|
| 44
| [[File:Wire yellow brown stripe.svg|37px]] yellow/brown
|-
| [[File:Wire gray yellow stripe.svg|37px]] slate/yellow
| 20
|
| 45
| [[File:Wire yellow gray stripe.svg|37px]] yellow/slate
|-
| colspan=5 |
|-
| [[File:Wire blue violet stripe.svg|37px]] blue/violet
| 21
|
| 46
| [[File:Wire violet blue stripe.svg|37px]] violet/blue
|-
| [[File:Wire orange violet stripe.svg|37px]] orange/violet
| 22
|
| 47
| [[File:Wire violet orange stripe.svg|37px]] violet/orange
|-
| [[File:Wire green violet stripe.svg|37px]] green/violet
| 23
|
| 48
| [[File:Wire violet green stripe.svg|37px]] violet/green
|-
| [[File:Wire brown violet stripe.svg|37px]] brown/violet
| 24
|
| 49
| [[File:Wire violet brown stripe.svg|37px]] violet/brown
|-
| [[File:Wire gray violet stripe.svg|37px]] slate/violet
| 25
|
| 50
| [[File:Wire violet gray stripe.svg|37px]] violet/slate
|}

== Larger cables ==
For cables with more than 25 pairs, each group of 25 is called a '''binder group'''.  The binder groups are marked with mylar ribbons using the same color coding system, starting with a white/blue ribbon, then a white/orange ribbon, and so on. The 24th binder group has a violet/brown ribbon, completing a ''super binder'' of 600 pairs.<ref name="Highhouse"/><ref name="BSPG50"/>

In cables of more than 600 pairs, each of the 600-pair super binder group bundles is wrapped with a mylar binder ribbon, or string, matching the "tip" colors of the color code, starting with white. The pattern then starts over with the first 25-pair group as white/blue, and continues indefinitely, in multiples of 600 pairs or parts thereof. For example, a 900-pair cable has the first 600 pairs in 24 groups of 25 pairs in a white binder, and the remaining 300 pairs in 12 groups of 25 pairs wrapped in a red binder.<ref name="Highhouse"/><ref name="BSPG50"/>

Some cables are "mirrored" or "clocked" with a pattern that is known throughout the telephone industry.  Starting with the first binder group in the center, the technician counts the cable's groups in a spiral direction depending on the location of the central office or switch.  If looking at the cable's core and the switch is in that direction, the groups are counted counter-clockwise.  If the cable is the ''field side'', the count is clockwise. There are indicators on the mylar ribbons to know where to begin for each layer and a diagram for the different cable sizes should be readily available for reference.<ref name="Highhouse"/><ref name="BSPG50"/>

Other color schemes are sometimes used for outdoor cables, particularly outside the U.S., but this color code is common for aerial and underground cables up to several thousand pairs in North America.  In the UK, the [[Royal Mail|British Post Office]] (later BT) used this color code for what is now known loosely as CW1308 specification cables, referring to the Post Office's "Cable and Wire" specification No. 1308.

== Extra pairs and colors ==
[[File:Addl-Pairs.jpg|thumb|Colors of additional pairs in multi-pair cable as per Bell Standards]]
When working on aerial cable splicing and installation, it is common to use a [[Lineman's handset|telephone lineman's set]] or "butt set" to communicate over long distances. To facilitate this, extra pairs of wires are embedded in cables using "major" colors for both wires (instead of the major/minor color combinations used for the rest). One extra pair (red-white) may be embedded into cables that are 6 to 75 pairs; two pairs (red-white and black-white) may be encapsulated in cables of 100 to 300 pairs; and three pairs (red-white, black-white, and yellow-white) may be included in cables of 400 to 900 pairs.<ref name="BSPG50" /> These extra pairs are often referred to as "talk pairs", and are never used for subscriber service.

==Other color codings==
===Inside quad wiring===
Older Bell System wiring inside customer premises used a cable type with four conductors of solid copper wire with the insulation colors red, green, yellow, and black (legacy) or a two-color code of blue, orange, and white.
{| class="wikitable"
| [[File:Wire green.svg|37px]] green   
| [[File:Wire white blue stripe.svg|37px]] white/blue
|  Pair 1 tip
|-
| [[File:Wire red.svg|37px]] red
| [[File:Wire blue white stripe.svg|37px]] blue/white
| Pair 1 ring
|-
| [[File:Wire black.svg|37px]] black
| [[File:Wire white orange stripe.svg|37px]] white/orange
| Pair 2 tip
|-
| [[File:Wire yellow.svg|37px]] yellow
| [[File:Wire orange white stripe.svg|37px]] orange/white
| Pair 2 ring
|}

===Optical cable===
A color coding method used for [[fiber-optic cable#Multi-fiber cables|fiber-optic cable]]s, [[TIA-598-C]], starts with the same first ten colors, adding the color rose for 11, and aqua for 12.<ref name="interfacebus">{{cite web
 |url         = http://www.interfacebus.com/Fiber_Insulation_Color_Code.html
 |title       = Fiber wire color coding
 |date        = 2007-02-21
 |author      = Leroy Davis
 |access-date  = 2007-12-01
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20071212054046/http://www.interfacebus.com/Fiber_Insulation_Color_Code.html
 |archive-date = 2007-12-12
}}</ref>

== See also ==
* [[20-pair colour code (Australia)]]

== References ==
{{Reflist|refs=
* <ref name="Highhouse">{{cite book|last=Highhouse|first=John|title=A Guide for Telecommunications Cable Splicing|year=1997|publisher=Cengage Learning|isbn=9780827380660}}</ref>
* <ref name="BSPG50">{{cite web|last=American Telephone And Telegraph Company |title=Even PIC Cables |url=http://etler.com/docs/BSP/G/G50.607.3_I2.pdf |work=Bell System Practices – Outside Plant Construction and Maintenance, Section G50.607.3 Issue 2|date=February 1959}}</ref>
}}

{{Commons}}

[[Category:Color codes]]
[[Category:Telephony equipment]]
[[Category:Telecommunications equipment]]