Registered Jack - Naming Confusion

Naming Confusion

The registered jack designation describes a wiring pattern and not just the physical geometry of the connectors; inspection of the connector will not necessarily show which registered jack wiring pattern is used. The same modular connector type can be used for different registered jack connections.

Strictly, registered jack refers to both the female physical connector (modular connector) and its wiring, but the term is often used loosely to refer to modular connectors regardless of wiring or gender, such as in Ethernet over twisted pair. There is much confusion over these connection standards. The six-position plug and jack commonly used for telephone line connections may be used for RJ11, RJ14 or even RJ25, all of which are names of interface standards that use this physical connector. The RJ11 standard dictates a 2-wire connection, while RJ14 uses a 4-wire configuration, and RJ25 uses all six wires. The RJ abbreviations, though, only pertain to the wiring of the jack (hence the name registered jack); it is commonplace but not strictly correct to refer to an unwired plug connector by any of these names.

Modular connectors were a development from the older telephone connectors, which were very bulky or wired directly to the wall and therefore not accommodating of modular systems. The common nomenclature for modular connectors gives the number of contact positions and the number of wires connected, for example 6P indicate a six-position modular plug or jack. A six-position modular plug with conductors in the middle two positions and the other four positions unused is called a 6P2C. RJ11 uses a 6P2C. The connectors could be supplied with more pins, but if more pins are actually wired, the interface is no longer an RJ11.