Telephone jack and plug

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 6P2C style modular plug has become by far the most common type.

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

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.

History

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.

Connections

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.

Wiring

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 and Eastern Bloc national standard, also adopted in Russia as ШТР-IV (SHTR-IV)

The Polish WT-4 plug is also adopted in the Eastern Bloc and Russia as ШТР-IV (SHTR-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 (RTSH-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, RTSHK-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.

Legacy

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
Albania6P2C
AlgeriaF-010
Argentina6P2C
Australia610, 6P2C
AustriaTDO
Barbados6P2C
Belarus6P2C, Polish national 5-pin (WT-4) [Note 1]
BelgiumTetrapolar plug, 6P2C
Bolivia6P2C
Bosnia6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
BotswanaBS 6312
BrazilTelebrás plug, 6P2C
Brunei6P2C
Bulgaria6P2C, Polish national 5-pin (WT-4) [Note 1]
Canada6P2C
Cayman Islands6P2C
Chile6P2C
China Mainland6P2C
Colombia6P2C, 2-pin national standard[8]
Costa Rica6P2C
Croatia6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
CyprusBS 6312, 6P2C[Note 2]
Czech Republic6P2C, 4-pin national plug [Note 1]
Denmark3-prong national standard, 6P2C [Note 3]
Dominican Republic6P2C
Ecuador6P2C
Egypt6P2C[Note 4]
Estonia6P2C, Polish national 5-pin (WT-4) [Note 1]
Faroe Islands6P2C
Finland6P2C, Tripolar plug [Note 1]
FranceF-010, 8P8C [Note 5][Note 3] (since 2003)
GermanyTAE, 8P8C [Note 5][Note 6]
GibraltarBS 6312
Greece6P2C,[Note 7] Bipolar plug in older installations
Hong Kong6P2C, [Note 3] BS 6312
Hungary6P2C, legacy 3 and 5-prong national standard[9] [10]
Iceland6P2C, SS 455 15 50 [Note 1]
India6P2C
Indonesia6P2C
Iran6P2C
Ireland6P2C, 8P8C, [Note 5][Note 8]
IsraelBS 6312 but wired differently from the British Standard, 6P2C
ItalyTripolar plug, 6P2C, BTicino-2021
Japan6P2C
Korea, Republic of6-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]
Latvia6P2C, Polish national 5-pin (WT-4) [Note 1]
Lithuania6P2C, Polish national 5-pin (WT-4) [Note 1]
LiechtensteinReichle-connector, 4-pin Swiss telephone plugs [Note 1]
Luxembourg6P2C, 4-pin Luxembourgish telephone plug [Note 1]
Malaysia6P2C
MaltaBS 6312, 6P2C [Note 3]
MauritiusF-010
Mexico6P2C
Montenegro6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
MoroccoF-010, 6P2C
MyanmarBS 6312
Netherlands6P2C, 4-pin Dutch telephone plug
Nigeria6P2C
New ZealandBS 6312, 6P2C,[Note 3] 8P8C [Note 5][Note 3]
North Macedonia6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
Norway8P8C, [Note 5][Note 3][Note 11] Tripolar plug, [Note 1] 6-prong national standard[Note 12]
Pakistan6P2C
Panama6P2C
Peru6P2C
Philippines6P2C
Poland6P2C, Polish national 5-pin (WT-4) coupled with 6P2C socket [Note 1]
Portugal6P2C[Note 13]
Romania6P2C, 3-pin triangular plug similar to the Italian Tripolar plug,[Note 14] 5-pin R.S.-79.809[Note 15][Note 1]
Russia6P2C, Polish national 5-pin (WT-4) [Note 1]
SenegalF-010
Serbia6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
Singapore6P2C
Slovenia6P2C, 3-pin plug used in countries of former Yugoslavia [Note 1]
Slovakia6P2C, 4-pin national plug [Note 1]
South Africa6P2C, Protea, 8P8C [Note 5][Note 6]
Spain6P2C
Sri Lanka6P2C
SwedenSS 455 15 50, 6P2C
SwitzerlandReichle-connector, 4-pin plugs [Note 1]
Taiwan6P2C
Thailand6P2C
Trinidad and Tobago6P2C
Turkey6P2C, Tripolar plug in older installations
Tunisia6P2C, F-010 in older installations
Ukraine6P2C, Polish national 5-pin (WT-4) [Note 1]
United Arab EmiratesBS 6312
United KingdomBS 6312, 6P2C[Note 16]
United States6P2C and other Registered jacks, 4-pin Bell System plugs [Note 1]
Uruguay6P2C
USSR (history)Polish national 5-pin (WT-4)
Venezuela6P2C
ZimbabweBS 6312, 6P2C
  1. Used in older installations
  2. Used for ADSL
  3. Used in newer installations
  4. Currently the dominant plug
  5. Often, although incorrectly referred to as "RJ45"
  6. 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

References

  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 978-0-470-47707-6. 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. (July 1934). "Jacks and Plugs for Portable Telephones" (PDF). Bell Laboratories Record. 12 (7): 343–346. Retrieved October 13, 2022.
  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.
  9. "Régiféle telefonkonnektor" [Old-school telephone connectors] (in Hungarian).
  10. "CB35 fali aljzat" [CB35 wall connector] (in Hungarian).
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