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A modular connector is a type of
electrical connector Components of an electrical circuit are electrically connected if an electric current can run between them through an electrical conductor. An electrical connector is an electromechanical device used to create an electrical connection between ...
for cords and cables of electronic devices and appliances, such as in
computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
ing, telecommunication equipment, and audio headsets. Modular connectors were originally developed for use on specific
Bell System The Bell System was a system of telecommunication companies, led by the Bell Telephone Company and later by the American Telephone and Telegraph Company (AT&T), that dominated the telephone services industry in North America for over one hundr ...
telephone sets in the 1960s, and similar types found use for simple interconnection of customer-provided telephone subscriber premises equipment to the telephone network. The
Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...
(FCC) mandated in 1976 an interface registration system, in which they became known as
registered jack A registered jack (RJ) is a standardized telecommunication network interface for connecting voice and data equipment to a service provided by a local exchange carrier or long distance carrier. Registration interfaces were first defined in the ...
s. The convenience of prior existence for designers and ease of use led to a proliferation of modular connectors for many other applications. Many applications that originally used bulkier, more expensive connectors have converted to modular connectors. Probably the best-known applications of modular connectors are for
telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...
and
Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
. Accordingly, various electronic interface specifications exist for applications using modular connectors, which prescribe physical characteristics and assign electrical signals to their contacts.


Nomenclature

Modular connectors are often referred to as ''modular phone jack and plug'', ''RJ connector'', and ''Western jack and plug''. The term ''modular connector'' arose from its original use in modular wiring components of telephone equipment by the
Western Electric Company The Western Electric Company was an American electrical engineering and manufacturing company officially founded in 1869. A wholly owned subsidiary of American Telephone & Telegraph for most of its lifespan, it served as the primary equipment ma ...
in the 1960s. This includes the
6P2C A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...
used for telephone line connections and
4P4C A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...
used for
handset A handset is a component of a telephone that a user holds to the ear and mouth to receive audio through the receiver and speak to the remote party using the built-in transmitter. In earlier telephones, the transmitter was mounted directly on ...
connectors.
Registered jack A registered jack (RJ) is a standardized telecommunication network interface for connecting voice and data equipment to a service provided by a local exchange carrier or long distance carrier. Registration interfaces were first defined in the ...
designations describe the signals and wiring used for voice and data communication at customer-facing interfaces of the
public switched telephone network The public switched telephone network (PSTN) provides Communications infrastructure, infrastructure and services for public Telecommunications, telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that ...
. It is common to use a registered jack number to refer to the physical connector itself; for instance, the 8P8C modular connector type is often labeled RJ45 because the registered jack standard of that name specified 8P8C modular connectors. Similarly, various six-position modular connectors may be called ''RJ11''. Likewise, the 4P4C connector is sometimes called ''RJ9'' or ''RJ22'' though no such official designations exist.


History

The first types of small modular telephone connectors were created by AT&T in the mid-1960s for the plug-in handset and line cords of the
Trimline The Trimline telephone is a series of telephones that was produced by Western Electric, the manufacturing unit of the Bell System. These telephones were first introduced in 1965 and are formally referred to as the ''No. 220 Hand Telepho ...
telephone.Krumreich C.L., Mosing L.W., ''The Evolution of a Telephone'', Bell Laboratories Record 44(1) p.14 (January 1966) Driven by demand for multiple sets in residences with various lengths of cords, the Bell System introduced customer-connectable part kits and telephones, sold through ''PhoneCenter'' stores in the early 1970s. For this purpose, Illinois Bell started installing modular telephone sets on a limited scale in June 1972. The patents by Edwin C. Hardesty and coworkers, (1972) and (1975), followed by other improvements, were the basis for the modular molded-plastic connectors that became commonplace for telephone cords by the 1980s. In 1976, these connectors were standardized nationally in the United States by the Registration Interface program of the
Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...
(FCC), which designated a series of Registered Jack (RJ) specifications for interconnection of customer-premises equipment to the
public switched telephone network The public switched telephone network (PSTN) provides Communications infrastructure, infrastructure and services for public Telecommunications, telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that ...
(PSTN).FCC 47 CFR Part 68 ''Connection of Terminal Equipment to the Telephone Network''
Section 68.502 superseded by T1.TR5-1999


Gender

Modular connectors have
gender Gender is the range of characteristics pertaining to femininity and masculinity and differentiating between them. Depending on the context, this may include sex-based social structures (i.e. gender roles) and gender identity. Most cultures u ...
: ''plugs'' are considered to be ''male'', while ''jacks'' or ''sockets'' are considered to be ''female''. Plugs are used to terminate cables and cords, while jacks are used for fixed locations on surfaces of walls, panels, and equipment. Other than telephone extension cables, cables with a modular plug on one end and a jack on the other are rare. Instead, cables are usually connected using a female-to-female coupler, having two jacks wired back-to-back.


Latching tab and orientation

Most modular connectors are designed with a latching mechanism that secures the physical connection. As a plug is inserted into a jack, a plastic tab on the plug locks against a ridge in the socket so that the plug cannot be removed without disengaging the tab by pressing it against the plug body. The standard orientation for installing a jack in a vertical surface is with the tab down. The modular plug is often installed with a ''boot'', a plastic covering over the tab and body, to prevent the latching tab to hook into other cords or edges, which may cause excessive bending or breaking of the tab. Such cords, are usually constructed by installing the protective boot before the modular plug is crimped.


Size and contacts

Modular connectors are designated using two numbers that represent the maximum number of contact positions and the number of installed contacts, with each number followed by ''P'' and ''C'', respectively. For example, ''6P2C'' is a connector having six positions and two installed contacts. Alternate designations omit the letters while separating the position and contact quantities with either an ''x'' (''6x2'') or a slash (''6/2''). When not installed, contacts are usually omitted from the outer positions inward, such that the number of contacts is almost always even. The connector body positions with omitted or unconnected contacts are unused for the electrical connection but ensure that the plug fits correctly. For instance,
RJ11 A registered jack (RJ) is a standardized telecommunication network interface for connecting voice and data equipment to a service provided by a local exchange carrier or long distance carrier. Registration interfaces were first defined in the ...
cables often have connectors with six positions and four contacts, to which are attached just two wires. The contact positions are numbered sequentially starting from 1. When viewed head-on with the retention mechanism on the bottom, jacks will have contact position number 1 on the left and plugs will have it on the right. Contacts are numbered by the contact position. For example, on a six-position, two-contact plug, where the outermost four positions do not have contacts, the innermost two contacts are numbered 3 and 4. Modular connectors are manufactured in four sizes, with 4-, 6-, 8-, and 10-positions. The insulating plastic bodies of 4P and 6P connectors have different widths, whereas 8P or 10P connectors share an even larger body width.


Insulation displacement contact types

Rj-45 male compare.jpg, 8P8C plug with contacts for solid wire (left) and stranded wire (right) Rj-45 male compare 2.jpg, Contacts for solid wire (top left) and stranded wire (bottom right) Internally, the contacts on the plugs have sharp prongs that, when crimped, pierce the wire insulation and connect with the conductor, a mechanism known as insulation displacement. Ethernet cables, in particular, may have solid or stranded (
tinsel wire Tinsel wire is a type of electrical wire used for applications that require high mechanical flexibility but low current-carrying capacity. Tinsel wire is commonly used in cords of telephones, handsets, headphones, and small electrical appliances. ...
) conductors and the sharp prongs are different in the 8P8C connectors made for each type of wire. A modular plug for solid (single-strand) wire often has three slightly splayed prongs on each contact to securely surround and grip the conductor. Modular plugs for stranded have prongs that are designed to connect to multiple wire strands. Connector plugs are designed for either solid or stranded wire and a mismatch between plug and wire type may result in an unreliable connection.


Interchangeability

Some modular connectors are ''indexed'', meaning their dimensions are intentionally non-standard, preventing connections with connectors of standard dimensions. The means of indexing may be non-standard cross-sectional dimensions or shapes, retention mechanism dimensions or configuration. For example, a
Modified Modular Jack The Modified Modular Jack (MMJ) is a small form-factor serial port connector developed by Digital Equipment Corporation (DEC). It uses a modified version of the 6P6C modular connector with the latch displaced off-center so standard modular conne ...
using an offset latching tab was developed by
Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unt ...
to prevent accidental interchange of data and telephone cables. The dimensions of modular connectors are such that a narrower plug can be inserted into a wider jack that has more positions than the plug, leaving the jack's outermost contacts unconnected. The height of the plug's insertion area is 0.260 inches (6.60 mm) and the contacts are 0.040 inches (1.02 mm) apart (contact pitch), so the width is dependent on the number of pin positions. However, not all plugs from all manufacturers have this capability, and some jack manufacturers warn that their jacks are not designed to accept smaller plugs without damage. If an inserted plug lacks slots to accommodate the jack's contacts at the outermost extremes, it may permanently deform those outermost contacts of an incompatible jack. Excessive resistance may be encountered when inserting an incompatible plug, as the outermost contacts in the jack are forcibly deformed. Special modular plugs have been manufactured (for example, the
Siemon Siemon is both a surname and a masculine given name, a variant of Simon. People with the name include: Surname: *Gustav Siemon (1918–2011), German politician *Jeff Siemon (1950), former professional American football player *Uwe Siemon-Netto (193 ...
UP-2468) which have extra slots beyond their standard contacts, to accommodate the wider jack's outermost contacts without damage. These special plug connectors can be visually identified by carefully looking for the extra slots molded into the plug. The molded plastic bodies of the special plugs may also be colored with a light blueish tinge, to aid in quick recognition. The special plugs are preferred for test equipment and adapters, which may be rapidly connected to a large number of corresponding connectors in quick succession for testing purposes. The use of the special plugs avoids inadvertent damage to the equipment under test, even when a narrower plug is inserted into a nominally incompatible wider jack.


Termination

Termination of cables with modular connectors is similar across the various number of positions and contacts in the plug. The crimping tool contains a die which is often exchangeable and is closely matched to the shape and pin count of the modular plug. A crimping die-set looks similar to an 8P8C jack, except for the eight teeth lining the top portion of the die. When the tool is operated, the die compresses around the 8P8C plug. As the die compresses, these teeth force the plug contacts into the conductors of the cable being terminated. The crimper may also permanently deform part of the plastic plug body in such a way that it grips the outer sheath of the cable for secure fastening and
strain relief Cable management refers to management of electrical or optical cable in a cabinet or an installation. The term is used for products, workmanship or planning. Cables can easily become tangled, making them difficult to work with, sometimes re ...
. These actions permanently attach the plug to the cable.


Pinout

The contact assignments (
pinout In electronics, a pinout (sometimes written "pin-out") is a cross-reference between the contacts, or ''pins'', of an electrical connector or electronic component, and their functions. "Pinout" now supersedes the term "basing diagram" that was the s ...
) of modular connectors vary by application. Telephone network connections are standardized by registered jack designations, and
Ethernet over twisted pair Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers. Early Ethernet used various grades of coaxial cable, but in 1984, Sta ...
is specified by the
ANSI/TIA-568 ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...
standard. For other applications, standardization may be lacking; for example, multiple conventions exist for the use of 8P8C connectors in
RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such a ...
applications. For this reason,
D-sub The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems. Description, no ...
-to-modular adapters are typically shipped with the D-sub contacts (pins or sockets) terminated but not inserted into the connector body, so that the D-sub-to-modular contact pairing can be assigned as needed.


4P4C

The four-position four-conductor (4P4C) connector is the standard modular connector used on both ends of telephone
handset A handset is a component of a telephone that a user holds to the ear and mouth to receive audio through the receiver and speak to the remote party using the built-in transmitter. In earlier telephones, the transmitter was mounted directly on ...
cords, and is therefore often called a ''handset connector''. This handset connector is not a registered jack, because it was not intended to connect directly to telephone lines. However it is often referred to as ''RJ9'', ''RJ10'', or ''RJ22''.


Handset wiring

Handsets and often
headsets Headset may refer to: * Headset (audio), audio headphone(s), particularly with an attached microphone * Head Set (band), an American alternative rock band * Headset (bicycle part), a bicycle part that connects the fork to the frame * Head-mounted ...
for use with telephones commonly use a 4P4C connector. The two center pins are commonly used for the receiver, and the outer pins connect the transmitter so that a reversal of conductors between the ends of a cord does not affect the signal routing. This may differ for other equipment, including hands-free headsets.


Data port

The
Macintosh 128K The Apple Macintosh—later rebranded as the Macintosh 128K—is the original Apple Inc., Apple Macintosh personal computer. It played a pivotal role in establishing desktop publishing as a general office function. The motherboard, a CRT monit ...
,
Macintosh 512K The Macintosh 512K is a personal computer that was designed, manufactured and sold by Apple Computer from September 1984 to April 1986. It is the first update to the original Macintosh 128K. It was virtually identical to the previous Macintos ...
and
Macintosh Plus The Macintosh Plus computer is the third model in the Macintosh line, introduced on January 16, 1986, two years after the original Macintosh and a little more than a year after the Macintosh 512K, with a price tag of US$2,599. As an evolutiona ...
from
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
as well as the
Amiga 1000 The Commodore Amiga 1000, also known as the A1000, is the first personal computer released by Commodore International in the Amiga line. It combines the 16/32-bit Motorola 68000 CPU which was powerful by 1985 standards with one of the most adv ...
from
Commodore Commodore may refer to: Ranks * Commodore (rank), a naval rank ** Commodore (Royal Navy), in the United Kingdom ** Commodore (United States) ** Commodore (Canada) ** Commodore (Finland) ** Commodore (Germany) or ''Kommodore'' * Air commodore, a ...
used 4P4C connectors to connect the keyboard to the main computer housing. The connector provided power to the keyboard on the outer two contacts and received data signals on the inner pair. The cable between the computer and the keyboard was a coiled cord with an appearance very similar to a telephone handset cable. The connector on the
Amiga 1000 The Commodore Amiga 1000, also known as the A1000, is the first personal computer released by Commodore International in the Amiga line. It combines the 16/32-bit Motorola 68000 CPU which was powerful by 1985 standards with one of the most adv ...
used crossover wiring, similar to a telephone handset. The connector wiring on the Apple computers, however, required a polarized straight through pinout. Using a telephone handset cable instead of the supplied cable could short out the +5 volt DC supply and damage the Apple computer or the keyboard. Modular connectors are often used for data links, such as serial line connections, because of their compact dimensions. For example, some
DirecTV DirecTV (trademarked as DIRECTV) is an American multichannel video programming distributor based in El Segundo, California. Originally launched on June 17, 1994, its primary service is a digital satellite service serving the United States. It ...
set top boxes include a 4P4C data port connector with an adapter cord to a computer serial port so that remote control is possible from the computer.


6P6C

Modular plugs are described by the maximum number of physical
contact Contact may refer to: Interaction Physical interaction * Contact (geology), a common geological feature * Contact lens or contact, a lens placed on the eye * Contact sport, a sport in which players make contact with other players or objects * ...
positions and the actual number of contacts installed in these positions. The 6P2C, 6P4C, and 6P6C modular connectors are probably best known for their use as
RJ11 A registered jack (RJ) is a standardized telecommunication network interface for connecting voice and data equipment to a service provided by a local exchange carrier or long distance carrier. Registration interfaces were first defined in the ...
,
RJ14 A registered jack (RJ) is a standardized telecommunication network interface for connecting voice and data equipment to a service provided by a local exchange carrier or long distance carrier. Registration interfaces were first defined in the ...
, and
RJ25 A registered jack (RJ) is a standardized telecommunication network interface for connecting voice and data equipment to a service provided by a local exchange carrier or long distance carrier. Registration interfaces were first defined in the ...
registered jacks, respectively. These interfaces use the same six-position modular connector body, but have different numbers of pins installed. RJ11 is a physical interface often used for terminating single telephone lines. RJ14 is similar, but for two lines, and RJ25 is for three lines.
RJ61 A registered jack (RJ) is a standardized telecommunication network interface for connecting voice and data equipment to a service provided by a local exchange carrier or long distance carrier. Registration interfaces were first defined in the ...
is a similar registered jack for four lines, but uses an 8P8C connector.


RJ11 wiring

Cables sold as RJ11 often actually use 6P4C connectors (six positions, four contacts) and RJ14 wiringfour wires running to a central
junction box An electrical junction box (also known as a "jbox") is an enclosure housing electrical connections. Junction boxes protect the electrical connections from the weather, as well as protecting people from accidental electric shocks. Construction ...
. Two of its six possible contact positions connect
tip and ring Tip and ring are the two conductors or sides of a telephone line. Their names are derived from the telephone plugs used for connecting telephone calls in manual switchboards. One side of the line is connected to the metal ''tip'' of the plug, and ...
, and the other two contact positions may be unused or provide low-voltage power for night-light or other features on the telephone set. In some installations an extra contact was also required for the
ground Ground may refer to: Geology * Land, the surface of the Earth not covered by water * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth Electricity * Ground (electricity), the reference point in an electrical c ...
connection for selective ringers.


Pinout

The pins of the 6P6C connector are numbered 1 to 6, counting left to right when holding the connector tab side down with the opening for the cable facing the viewer. However, with German domestic telephone equipment, and that in some neighboring countries,
6P4C A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...
plugs and sockets are typically only used to connect the telephone cord to the phone base unit, whereas the mechanically different
TAE connector TAE (''Telekommunikations-Anschluss-Einheit'' or telecommunications connection unit) is the German standard for telephone plugs and sockets. The standard covers two TAE types: F  ("Fernsprechgerät": for telephones) and N  ("Nebengerà ...
is used at the other end to connect to a service provider interface. Older base units may accommodate the additional connectors of TAE (E, W, a2, b2) and may feature non-RJ standard sockets that can be connected directly to TAE plugs. Further, flat DIN 47100 cables typically place the wires in ascending order. When used directly with 6P4C plugs, the color coding may be undetermined.


Powered version of RJ11

In the powered version of the RJ11 interface, pins 2 and 5 (black and yellow) may carry low voltage AC or DC power. While the telephone line on pins 3 and 4 (red and green) supplies enough power for most telephone terminals, old telephone terminals with incandescent lights, such as the Western Electric
Princess Princess is a regal rank and the feminine equivalent of prince (from Latin ''princeps'', meaning principal citizen). Most often, the term has been used for the consort of a prince, or for the daughter of a king or prince. Princess as a subst ...
and
Trimline telephone The Trimline telephone is a series of telephones that was produced by Western Electric, the manufacturing unit of the Bell System. These telephones were first introduced in 1965 and are formally referred to as the ''No. 220 Hand Telephone ...
s, need more power than the phone line can supply. Typically, the power on pins 2 and 5 is supplied by an
AC adapter An AC adapter or AC/DC adapter is a type of external power supply, often enclosed in a case similar to an AC plug. Other common names include wall wart, power brick, wall charger, and power adapter. Adapters for battery-powered equipment may ...
plugged into a nearby power outlet which potentially even supplies power to all of the jacks in the house.


Compatibility with structured cabling

Structured cabling In telecommunications, structured cabling is building or campus cabling infrastructure that consists of a number of standardized smaller elements (hence structured) called subsystems. Structured cabling components include twisted pair and opti ...
networks adhering to
ANSI/TIA-568 ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...
,
ISO/IEC 11801 International standard ISO/IEC 11801 ''Information technology — Generic cabling for customer premises'' specifies general-purpose telecommunication cabling systems (structured cabling) that are suitable for a wide range of applications (analog an ...
(or ISO/IEC 15018 for home networks) are widely used for both computer networking and analog telephony. These standards specify the T568A or T568B wiring arrangements compatible with
Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
. The 8P8C jack used by structured cabling physically accepts the 6-position connector used by RJ11, RJ14 and RJ25. Only RJ11 and RJ14 have full electrical compatibility because Ethernet-compatible pin-outs split the third pair of RJ25 across two separate cable pairs, rendering that pair unusable by an analog phone. Both the third and fourth pairs of RJ61 are similarly split. The incompatible T568A and T568B layouts were necessary to preserve the electrical properties of the third and fourth pairs for Ethernet, which operates at much higher frequencies than analog telephony. Because of these incompatibilities, and because RJ25 and RJ61 were never very common, the T568A and T568B conventions have largely displaced RJ25 and RJ61 for telephones with more than two lines.


8P8C

The 8 position 8 contact (8P8C) connector is a modular connector commonly used to terminate
twisted pair Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted ba ...
and multi-conductor
flat cable A ribbon cable (also known as multi-wire planar cable) is a cable with many conducting wires running parallel to each other on the same flat plane. As a result, the cable is wide and flat. Its name comes from its resemblance to a piece of rib ...
. These connectors are commonly used for
Ethernet over twisted pair Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers. Early Ethernet used various grades of coaxial cable, but in 1984, Sta ...
, registered jacks and other telephone applications,
RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such a ...
serial communication using the
ANSI/TIA-568 ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...
(formerly TIA/EIA-568) and Yost standards, and other applications involving
unshielded twisted pair Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted bal ...
,
shielded twisted pair Twisted pair cabling is a type of wiring used for communications in which two conductors of a single Electronic circuit, circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a Single-ended signa ...
, and multi-conductor flat cable. An 8P8C modular connection consists of a male plug and a female jack, each with eight equally spaced contacts. On the plug, the contacts are flat metal bars positioned parallel to the connector body. Inside the jack, the contacts are metal spring wires angled away from the insertion interface. When the plug is mated with the jack, the contacts meet and create an electrical connection. The spring tension of the jack contacts ensures a good interface. Although commonly referred to as RJ45 in the context of Ethernet and
category 5 cable Category 5 cable (Cat 5) is a twisted pair cable for computer networks. Since 2001, the variant commonly in use is the Category 5e specification (Cat 5e). The cable standard provides performance of up to 100 MHz and is ...
s, ''RJ45'' originally referred to a specific wiring configuration of an 8P8C connector. The original telephone-system-standard RJ45 plug has a key which excludes insertion in an un-keyed 8P8C socket. The original RJ45S was intended for high-speed modems, and is obsolete. The RJ45S jack mates with a keyed 8P2C modular plug, and has pins 4 and 5 (the middle positions) wired for the ring and tip conductors of a single telephone line and pins 7 and 8 shorting a programming resistor. This is a different mechanical interface and wiring scheme than
ANSI/TIA-568 ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...
T568A and T568B schemes with the 8P8C connector in Ethernet and telephone applications. Generic 8P8C modular connectors are similar to those used for the RJ45S variant, although the RJ45S plug is keyed and not compatible with non-keyed 8P8C modular jacks. Telephone installers who wired RJ45S modem jacks or RJ61X telephone jacks were familiar with the pin assignments of the standard. However, the standard un-keyed modular connectors became ubiquitous for computer networking and informally inherited the name ''RJ45''.


Standardization

The shape and dimensions of an 8P8C modular connector are specified for US telephone applications by the Administrative Council for Terminal Attachment (ACTA) in national standard
ANSI The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...
/TIA-1096-A and international standard ISO-8877. This standard does not use the short term 8P8C and covers more than just 8P8C modular connectors, but the 8P8C modular connector type is the eight position connector type described therein, with eight contacts installed. For data communication applications ( LAN,
structured cabling In telecommunications, structured cabling is building or campus cabling infrastructure that consists of a number of standardized smaller elements (hence structured) called subsystems. Structured cabling components include twisted pair and opti ...
), International Standard IEC 60603 specifies in parts 7-1, 7-2, 7-4, 7-5, and 7-7 not only the same physical dimensions but also high-frequency performance requirements for shielded and unshielded versions of this connector for carrying frequencies up to 100, 250 and 600 
MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
.


Pinout

8P8C connectors are frequently terminated using the T568A or T568B assignments that are defined in
ANSI/TIA-568 ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...
. The drawings to the right show that the copper connections and pairing are the same, the only difference is that the orange and green pairs (colors) are swapped. A cable wired as T568A at one end and wired as T568B at the other end (Tx and Rx pairs reversed) is an
Ethernet crossover cable An Ethernet crossover cable is a crossover cable for Ethernet used to connect computing devices together directly. It is most often used to connect two devices of the same type, e.g. two computers (via their network interface controllers) or two ...
. Before the widespread acceptance of
auto MDI-X A medium dependent interface (MDI) describes the interface (both physical and electrical/optical) in a computer network from a physical layer implementation to the physical medium used to carry the transmission. Ethernet over twisted pair also d ...
capabilities, a crossover cable was needed to interconnect similar network equipment (such as
Ethernet hub An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/out ...
s to Ethernet hubs). Crossover cables are sometimes still used to connect two computers together without a switch or hub, however most network interface cards (NIC) in use today implement auto MDI-X to automatically configure themselves based on the type of cable plugged into them. A cable wired the same at both ends is called a ''patch'' or ''straight-through'' cable, because no pin/pair assignments are swapped. If a ''patch'' or ''straight'' cable is used to connect two computers with auto MDI-X capable NICs, one NIC will configure itself to swap the functions of its Tx and Rx wire pairs.


Types and compatibility

Two types of 8P8C plugs and crimping tools for installing the plug onto a cable are commonly available: Western Electric/Stewart Stamping (WE/SS) and Tyco/AMP. While the two types are similar, the tooling and plug types cannot be interchanged. WE/SS compatible plugs are available from a large number of manufacturers, whereas Tyco/AMP plugs are produced exclusively by
Tyco Electronics TE Connectivity is an American Swiss-domiciled technology company that designs and manufactures connectors and sensors for several industries, such as automotive, industrial equipment, data communication systems, aerospace, defense, medical, o ...
. Both types of modular plugs can be mated with a standard 8P8C modular jack. Both types of 8P8C plugs are available in shielded and unshielded varieties for different
attenuation In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable att ...
tolerances as needed. Shielded plugs are more expensive and require shielded cable, but have a lower attenuation, and may reduce
electromagnetic interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electros ...
. Although a narrower 4-pin and 6-pin plug fits into the wider 8-pin jack and makes a connection with the available contacts on the plug, because the body of the smaller connector may stress the remaining contacts, the smaller connector can potentially damage the springs of the larger jack.


Applications

8P8C connectors are commonly used in computer networking applications, where interconnecting cables are terminated at each end with an 8P8C modular plug wired according to TIA/EIA standards. Most wired Ethernet communications are carried over Category 5e or Category 6 cable terminated with 8P8C modular plugs. The connector is also used in other telecommunications connections, including ISDN and T1. Where building network and telephone wiring is pre-installed, the center (blue) pair is often used to carry
telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...
signals. While this allows an RJ11 plug to connect, it may damage the modular jack; an approved converter prevents damage. In landline telephony, an 8P8C jack is used at the point a line enters the building to allow the line to be broken to insert automatic dialing equipment, including intrusion alarm panels. The
EIA Eia or EIA may refer to: Medicine * Enzyme immunoassay * Equine infectious anemia * Exercise-induced anaphylaxis * Exercise-induced asthma * External iliac artery Transport * Edmonton International Airport, in Alberta, Canada * Erbil Internation ...
/TIA-561 standard describes the use of 8P8C connectors for RS-232 serial interfaces. This application is common as a console interface for
network equipment Networking hardware, also known as network equipment or computer networking devices, are electronic devices which are required for communication and interaction between devices on a computer network. Specifically, they mediate data transmission in ...
, such as
switches In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
, routers, and
headless computer A headless computer is a computer system or device that has been configured to operate without a monitor (the missing "head"), keyboard, and mouse. A headless system is typically controlled over a network connection, although some headless system ...
s. 8P8C modular connectors are also commonly used as a microphone connector for PMR, LMR, and
amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communic ...
transceivers. Frequently the pinout is different, usually mirrored (i.e. what would be pins 1 to 8 in the ANSI/TIA-568 standard might be pins 8 to 1 in the radio and its manual). In analog mobile telephony, the 8P8C connector was used to connect an AMPS cellular handset to its (separate) base unit; this usage is now obsolete. The physical connector is standardized as the IEC 60603-7 8P8C modular connector with different ''categories'' of performance. The physical dimensions of the male and female connectors are specified in ANSI/TIA-1096-A and ISO-8877 standards and normally wired to the T568A and T568B pinouts specified in the
ANSI/TIA-568 ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...
standard to be compatible with both telephone and Ethernet. A similar standard jack once used for modem and data connections, the RJ45S, used a ''keyed'' variety of the 8P8C body with an extra tab that prevents it mating with other connectors; the visual difference compared to the more common 8P8C is subtle, but it is a different connector. The original RJ45S keyed 8P2C modular connector, obsolete today, had pins 5 and 4 wired for tip and ring of a single telephone line and pins 7 and 8 shorting a programming resistor. Electronics catalogs commonly advertise 8P8C modular connectors as ''RJ45''. An installer can wire the jack to any pin-out or use it as part of a generic
structured cabling In telecommunications, structured cabling is building or campus cabling infrastructure that consists of a number of standardized smaller elements (hence structured) called subsystems. Structured cabling components include twisted pair and opti ...
system such as ISO/IEC 15018 or
ISO/IEC 11801 International standard ISO/IEC 11801 ''Information technology — Generic cabling for customer premises'' specifies general-purpose telecommunication cabling systems (structured cabling) that are suitable for a wide range of applications (analog an ...
using 8P8C patch panels for both phone and data.


Crossover cables

A router to router
crossover cable A crossover cable connects two devices of the same type, for example DTE-DTE or DCE-DCE, usually connected asymmetrically (DTE-DCE), by a modified cable called a crosslink. Such a distinction between devices was introduced by IBM. The cross ...
uses two 8-position connectors and a
unshielded twisted pair Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted bal ...
(UTP) cable with differently wired connectors at each end.


10P10C

The 10P10C connector is commonly referred to as an RJ50 connector, although this was never a standard registered jack. The 10P10C has 10 contact positions and 10 contacts. The most common uses of the 10P10C connector are in proprietary data transfer systems, such as the Digiboard. and Equinox Super-Serial multi-port
TIA-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such a ...
adapters. 10P10C connectors are also used to implement
RS-485 RS-485, also known as TIA-485(-A) or EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and multipoint systems are supported. The st ...
interfaces, and for data link connections in
uninterruptible power supplies An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system ...
. This connector is also used by some vendors, for example,
Cyclades The Cyclades (; el, Κυκλάδες, ) are an island group in the Aegean Sea, southeast of mainland Greece and a former administrative prefecture of Greece. They are one of the island groups which constitute the Aegean archipelago. The nam ...
(later absorbed by Equinox) used pin 1 as an ''RI'' (ring indicator) signal, which is seldom used, allowing an 8P8C plug to be inserted to their 10P10C socket for most applications. The
Cisco Systems Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational corporation, multinational digital communications technology conglomerate (company), conglomerate corporation headquartered in San Jose, California. Cisco develo ...
STS-10X terminal server features this connector. FordNet, a five-pair communications networking medium, also used the 10P10C between terminals.
Motorola Motorola, Inc. () was an American Multinational corporation, multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent p ...
uses the 10-pin connector as a microphone connector in several of their mobile radio product lines.
Polycom Poly, formerly Polycom, a part of HP Inc., is an American multinational corporation that develops video, voice and content collaboration and communication technology. Polycom was co-founded in 1990 by Brian L Hinman and Jeffrey Rodman. In 2018 P ...
utilizes this connector on their Conference Link bus to connect their HDX and Group Series codecs and microphones to their SoundStructure audio mixers, although pins 1 and 10 are not used. The 10-pin connector is also used by
Demag Cranes AG Konecranes Oyj (KCI Konecranes prior to 16 March 2007) is a Finland, Finnish company, headquartered in Hyvinkää, which specialises in the manufacture and service of crane (machine), cranes and lifting equipment as well as the service of machine ...
in some pendant connections.
National Instruments National Instruments Corporation, doing business as NI, is an American multinational company with international operation. Headquartered in Austin, Texas, it is a producer of automated test equipment and virtual instrumentation software. Comm ...
is also using the 10p10c connector for their NI 9237..
MTS Systems Corporation MTS Systems Corporation (MTS) is a global supplier of test systems and industrial position sensors. The company provides test and measurement products to determine the performance and reliability of vehicles, aircraft, civil structures, biomedica ...
is using the 10p10c connector for their MTS FlexTest Controller Family.


Standards

* ANSI/TIA-968-A: * ANSI/TIA-1096-A: Telecommunications telephone terminal equipment connector requirements for connection of terminal equipment to the telephone network * IEC 60603-7-1: Connectors for electronic equipment: Part 7-1: Detail specification for 8-way, shielded free and fixed connectors with common mating features, with assessed quality * IEC 60603-7-2: Connectors for electronic equipment: Part 7-2: Detail specification for 8-way, unshielded, free and fixed connectors, for data transmissions with frequencies up to 100 MHz * IEC 60603-7-4: Connectors for electronic equipment: Part 7-4: Detail specification for 8-way, unshielded, free and fixed connectors, for data transmissions with frequencies up to 250 MHz * IEC 60603-7-5: Connectors for electronic equipment: Part 7-5: Detail specification for 8-way, shielded, free and fixed connectors, for data transmissions with frequencies up to 250 MHz * IEC 60603-7-7: Connectors for electronic equipment: Part 7-7: Detail specification for 8-way, shielded, free and fixed connectors, for data transmissions with frequencies up to 600 MHz * ISO/IEC 8877, EN 28877: Information Technology—Telecommunications and Information Exchange between Systems—Interface Connector and Contact Assignments for ISDN Basic Access Interface Located at Reference Points S and T * US government documents define registered jack applications of modular connectors for telecommunications. See


See also

*
BS 6312 BS, B.S., Bs or bs may refer to: Arts and entertainment *BS-, a prefix for all games broadcast for the Satellaview modem via the Japanese Broadcasting Satellite system * "B.S." (song), a song by Jhené Aiko from the album ''Chilombo'' *Team BS, ...
– British equivalent to RJ25 *
EtherCON The EtherCON is a ruggedized and lockable connector for Ethernet over twisted pair wiring. It is manufactured by Neutrik and is designed for professional audio and stage lighting network applications. Design The design is modeled after the XLR c ...
– ruggedized 8P8C Ethernet connector *
GG45 GG45 (GigaGate 45) and ARJ45 (Augmented RJ45) are two related connectors for Category 7, Category 7A, and Category 8 telecommunication cabling. The GG45 interface and related implementations are developed and sold by Nexans S.A., while the A ...
*
TERA TERA is a shielded twisted pair connector for use with Category 7 twisted-pair data cables, developed by The Siemon Company and standardised in 2003 by the International Electrotechnical Commission (IEC) with the reference IEC 61076-3-104. The ...


Notes


References


Bibliography

* .


External links

*
John R. Carlsen: On wiring modular telephone connectorsModular wiring reference
showing differences between 8P8C, true RJ45 8-position keyed connector, 6P6C, and 6-position modified offset tab
Common outlet configurations
graphical representation of twisted pair pinouts * Catalog page showing the difference between solid and stranded contacts * {{DEFAULTSORT:Modular Connector Computer connectors Ethernet Connector Networking hardware Telephone connectors