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Telephone jack and plug

From Wikipedia, the free encyclopedia

Modular connector 6P6C plug (left) and 6P4C jack (right)
Modular connector 6P6C plug (left) and 6P4C jack (right)

A telephone jack and a telephone plug are electrical connectors for connecting a telephone set or other telecommunications apparatus to the telephone wiring inside a building, establishing a connection to a telephone network. The plug is inserted into its counterpart, the jack, which is commonly affixed to a wall or baseboard. The standards for telephone jacks and plugs vary from country to country, though the RJ11 modular connector has become by far the most common type.

A connection standard, such as RJ11, specifies not only the physical aspects of an electrical connector, but also the signal definitions for each contact, and the pinout of the device, i.e. the assignment or function of each contact.[1] Modular connectors are specified for the registered jack (RJ) series of connectors, as well as for Ethernet and other connectors, such as 4P4C (4 position, 4 contacts) modular connectors, the de facto standard on handset cords,[2] often improperly[3][4] referred to as RJ connectors.


Historically, telephones were typically owned by the telephone company, and were usually permanently wired to the telephone line. For some applications it was necessary or convenient to provide portable telephone sets that could be moved to a different location within the customer's premises. For this purpose telephone companies developed jacks and plugs in various designs with various numbers of contacts. Before c. 1930, concentric connectors with three contacts were usually sufficient, but the upgrade of telephone sets to anti-sidetone circuitry in the 1930s required at least four conductors between a desk set and the subscriber set that contained the telephone hybrid and a ringer. For this purpose, Bell System engineers developed a cube-shaped four-prong plug (type no. 283) with uneven prong spacings to avoid improper insertion into the jack.[5][6]

The cubic design was changed to a round version (No. 505A) in the mid 1960s. The four-prong jack and plug combination was the standard line connection for all portable telephone sets until the conversion to modular jacks in the 1970s, typified by the Registered Jack standards promulgated in U.S. federal law.

Many countries initially used different specifications for connectors, and some national connector types remain in service, but few are used for new installations for which modular connector types are prescribed.


The installation of a conventional wired telephone set has four connection points, each of which may be hardwired, but more often use a plug and socket:

  • telephone line to phone cord: The wall jack. This connection is the most standardized, and often regulated as the boundary between an individual's telephone and the telephone network. In many residences, though, the boundary between utility-owned and household-owned cabling is a network interface on an outside wall known as the demarcation point; all wall jacks in the home are part of the household's internal wiring.
  • telephone cord to telephone set base: This connection is generally not regulated, but instead follows de facto standards. It is often a 6P4C connector, which is often RJ11, but may be proprietary or hardwired.
  • telephone set base to handset cord: By de facto standard, this is usually a 4P4C connector.
  • handset cord to handset: The handset end of the straight-through handset cord also uses a 4P4C connector.

Some of these may be absent: Wired telephones may not have a separate base and handset. The defining characteristic of wireless telephones is that they do not have a handset cord, and the defining characteristic of mobile telephones is that they do not have a phone cord.


Typical U.S. modular phone connector
Typical U.S. modular phone connector

A standard specifies both a physical connector and how it is wired. Sometimes the same connector is used by different countries but wired in different ways.

For example, telephone cables in the UK typically have a BS 6312 (UK standard) plug at the wall end and a 6P4C or 6P2C modular connector at the telephone end: this latter may be wired as per the RJ11 standard (with pins 3 and 4), or it may be wired with pins 2 and 5, as a straight through cable from the BT plug (which uses pins 2 and 5 for the line, unlike RJ11, which uses pins 3 and 4). Thus cables are not in general compatible between different phones, as the phone base may have a socket with pins 2 and 5 (requiring a straight through cable), or have an RJ11 socket (requiring a crossover cable).

When modular connectors are used, the latch release of the connector should be on the ridge side of flat phone wire in order to maintain polarity.

Though four wires are typically used in U.S. phone cabling, only two are necessary for telecommunication. In the event that a second line is needed, the other two are used. They are also sometimes used to provide power for telephone dial lamps (6 volts AC, as in the Princess phone), or other features.

List of plugs

Modular connectors

  • 4P4C and 4P2C for handset cables (often erroneously referred to as RJ9, RJ10, and RJ22)
  • 6P2C for RJ11 single telephone line
  • 6P4C for RJ14 two telephone lines
  • 6P6C for RJ25 three telephone lines
  • 8P8C for RJ61X four telephone lines, RJ48S and RJ48C for four-wire data lines, RJ31X single telephone line with equipment disconnect, RJ38X (similar to RJ31X but with continuity circuit)

Other connectors

International standards

National standards

  • TDO-connector, Austria
  • WT-4, Polish National Standard, also adopted in Russia as ШТР-IV

The Polish WT-4 plug is adopted in Russia as ШТР-IV and has four metal pins and an additional fourth dielectric pin. The corresponding socket comes in two variants. The GTN-4 socket (РТШ-IV in Russia) provides a 4 pin connection (in most cases, the two rightmost pins are used for connecting a single line). The GTNC-4 (РТШК-IV) is a GTN-4 socket that has an additional circuit. The 5th plastic pin of the inserted plug disconnects a 1μF capacitor that otherwise closes the circuit of the telephone line when the plug is not inserted. This feature allows testing the line when the phone is not plugged in.[7] The usage of a capacitor is mostly obsolete and GTN-4 sockets produced later reuse the capacitor compartment for an additional RJ11 socket.


BTicino telephone plug and socket
BTicino telephone plug and socket

List by country or territory

This list covers only single line telephone plugs commonly used in homes and other small installations; there are 44 different variations of plugs, including an Israeli version of BS6312 with different internal wiring of the pins, plus hard wiring to a junction box with no adapter. Special telephone sets use a variety of special plugs, for example micro ribbon for key telephone systems.

Place Plug types
Albania 6P2C
Algeria F-010
Argentina 6P2C
Australia 610, 6P2C
Austria TDO
Barbados 6P2C
Belarus 6P2C, Polish national 5-pin (WT-4) [Note 1]
Belgium Tetrapolar plug, 6P2C
Bolivia 6P2C
Bosnia 6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
Botswana BS 6312
Brazil Telebrás plug, 6P2C
Brunei 6P2C
Bulgaria 6P2C, Polish national 5-pin (WT-4) [Note 1]
Canada 6P2C
Cayman Islands 6P2C
Chile 6P2C
China Mainland 6P2C
Colombia 6P2C, 2-pin national standard[8]
Costa Rica 6P2C
Croatia 6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
Cyprus BS 6312, 6P2C[Note 2]
Czech Republic 6P2C, 4-pin national plug [Note 1]
Denmark 3-prong national standard, 6P2C [Note 3]
Dominican Republic 6P2C
Ecuador 6P2C
Egypt 6P2C[Note 4]
Estonia 6P2C, Polish national 5-pin (WT-4) [Note 1]
Faroe Islands 6P2C
Finland 6P2C, Tripolar plug [Note 1]
France F-010, 8P8C [Note 5][Note 3] (since 2003)
Germany TAE, 8P8C [Note 5][Note 6]
Gibraltar BS 6312
Greece 6P2C,[Note 7] Bipolar plug in older installations
Hong Kong 6P2C[Note 3] BS 6312
Hungary 6P2C
Iceland 6P2C, SS 455 15 50 [Note 1]
India 6P2C
Indonesia 6P2C
Iran 6P2C
Ireland 6P2C, 8P8C[Note 5][Note 8]
Israel BS 6312 but wired differently from the British Standard, 6P2C
Italy Tripolar plug, 6P2C, BTicino-2021
Japan 6P2C
Korea, Republic of 6-pin modular (6P4C or 6P2C), 8-pin modular (8P8C) or 3-position weatherproof connector in accord with TIA-1096-A.[Note 9] 4-prong connector [Note 10]
Latvia 6P2C, Polish national 5-pin (WT-4) [Note 1]
Lithuania 6P2C, Polish national 5-pin (WT-4) [Note 1]
Liechtenstein Reichle-connector, 4-pin Swiss telephone plugs [Note 1]
Luxembourg 6P2C, 4-pin luxembourgish telephone plug [Note 1]
Malaysia 6P2C
Malta BS 6312, 6P2C [Note 3]
Mauritius F-010
Mexico 6P2C
Montenegro 6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
Morocco F-010, 6P2C
Netherlands 6P2C, Dutch telephone plug
Nigeria 6P2C
New Zealand BS 6312, 6P2C,[Note 3] 8P8C [Note 5][Note 3]
North Macedonia 6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
Norway 8P8C[Note 5][Note 3][Note 11] Tripolar plug[Note 1] 6-prong national standard[Note 12]
Pakistan 6P2C
Panama 6P2C
Peru 6P2C
Philippines 6P2C
Poland 6P2C, Polish national 5-pin (WT-4) coupled with 6P2C socket [Note 1]
Portugal 6P2C[Note 13]
Romania 6P2C, 3-pin triangular plug similar to the Italian Tripolar plug,[Note 14] 5-pin R.S.-79.809[Note 15][Note 1]
Russia 6P2C, Polish national 5-pin (WT-4) [Note 1]
Senegal F-010
Serbia 6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
Singapore 6P2C
Slovenia 6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
Slovakia 6P2C, 4-pin national plug [Note 1]
South Africa 6P2C, Protea, 8P8C [Note 5][Note 6]
Spain 6P2C
Sri Lanka 6P2C
Sweden SS 455 15 50, 6P2C
Switzerland Reichle-connector, 4-pin plugs [Note 1]
Taiwan 6P2C
Thailand 6P2C
Trinidad and Tobago 6P2C
Turkey 6P2C, Tripolar plug in older installations
Tunisia 6P2C, F-010 in older installations
Ukraine 6P2C, Polish national 5-pin (WT-4) [Note 1]
United Arab Emirates BS 6312
United Kingdom BS 6312, 6P2C[Note 16]
United States 6P2C and other Registered jacks, 4-pin Bell System plugs [Note 1]
Uruguay 6P2C
USSR (history) Polish national 5-pin (WT-4)
Venezuela 6P2C
Zimbabwe BS 6312, 6P2C
  1. ^ a b c d e f g h i j k l m n o p q r s t u v w x Used in older installations
  2. ^ Used for ADSL
  3. ^ a b c d e f g Used in newer installations
  4. ^ Currently the dominant plug
  5. ^ a b c d e f Often, although incorrectly referred to as "RJ45"
  6. ^ a b Used for ISDN
  7. ^ Although other types can also be found
  8. ^ Used for ISDN, Digital PBX, and office systems
  9. ^ Legal regulation
  10. ^ The old standard ruled out after 2002 but still used widely.
  11. ^ Same plug used for POTS, ISDN and LAN
  12. ^ For local battery telephones, not used since approximately 1980
  13. ^ Also known as R.I.T.A.
  14. ^ Rarely used today
  15. ^ Same as the Polish WT-4
  16. ^ Used for ADSL modem lines in British telephone sockets

See also


  1. ^ Semenov, Andrey B.; Strizhakov, Stanislav K.; Suncheley, Igor R. (October 3, 2002). "Electrical Cable Connectors". Structured cable systems (1st ed.). Springer. p. 129. ISBN 3-540-43000-8. The abbreviation for registered jack, RJ defines a particular wiring scheme of individual wires into outlet contacts. For example, a 6-position outlet may be wired to RJ-11C scheme (one pair), RJ-14C (two pairs), or RJ-25C (three pairs).
  2. ^ BICSI (October 7, 2002). "Background Information". Telecommunications Cabling Installation (2nd ed.). McGraw-Hill Professional. p. 88. ISBN 0-07-140979-3. 4-position and 4-contact connectors are used primarily for telephone handset cords.
  3. ^ Trulove, James (December 19, 2005). "User Cords and Connectors". LAN wiring (3rd ed.). McGraw-Hill Professional. p. 219. ISBN 0-07-145975-8. This 8-pin modular plug is probably the most subject to name abuse, because it resembles the specialized RJ-45 connector. However, the RJ-45 wiring pattern (which includes an interface programming resistor) is so radically different from that of T568A and B that it really should not be called by that name at all.
  4. ^ Oliviero, Andrew; Woodward, Bill (July 20, 2009). "Connectors". Cabling: The Complete Guide to Copper and Fiber-Optic Networking (4th ed.). Sybex. p. 294. ISBN 0-470-47707-5. The RJ (registered jack) prefix is one of the most widely (and incorrectly) used prefixes in the computer industry; nearly everyone, including people working for cabling companies, is guilty of referring to an eight-position modular jack (sometimes called an 8P8C) as an RJ-45.
  5. ^ Krantz H.K., Jacks and Plugs for Portable Telephones, Bell Laboratory Record 12(7), July 1934, p.343
  6. ^ AT&T, Jacks and Plugs, Bell System Practices, Section C36.201 Issue 1 (February 1, 1932)
  7. ^ "Правила техобслуживания и ремонта линейных сооружений и оконечных устройств абонентских пунктов местных сетей связи" (PDF) (in Russian). Ministry of Telecom and Mass Communications of the Russian Federation. 1996-07-10.
  8. ^ "Columbia/Venezuela phone plug". Archived from the original on April 13, 2008.

External links

This page was last edited on 7 July 2020, at 16:35
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