What is RJ11?

RJ11 interface and RJ45 interface are very similar, but only 4 pins (RJ45 for 8 pins). In the computer system, RJ11 is mainly used to connect the modem.

RJ11 usually refers to a 6-position (6-pin) modular jack or plug. There is no international standard for this type of connector and it is mentioned in the Common Integrated Wiring Standard. Also, the name is often used for 4-pin versions of modular connectors, which causes confusion.

In the general integrated cabling standard, there is no separate mention of ‘RJ11’ in the discourse, and all connecting devices must be 8-pin. Therefore the synergy and compatibility of RJ11 and RJ45 are not yet written.

The name RJ stands for Registered Jack and is derived from the Bell System’s USOC (Universal Service Ordering Codes) code. USOC is a series of registered jacks and their wiring methods that were developed by the Bell System to connect a user’s device to the public network. FCC regulations control the application of this purpose.

RJ11 is the common name of the connector developed by Western Electric, abbreviated as rj11 connector. The form factor is defined as a 6-pin connection device. The original name is WExW, where the x stands for ‘active’, contact, or wire punch pin. For example, WE6W has all 6 contacts, numbered 1 to 6, WE4W interface uses only the outermost two contacts (1 and 6) of the 4-pin without, WE2W uses only the middle two pins. For RJ11, the source of information is contradictory, it can be a 2 or 4 pole 6-pin connector. To add to the confusion, RJ11 is not only used to represent a 6-pin connector, it also refers to the 4-pin version.

RJ11 and RJ14, RJ25 for the same series

RJ11 and RJ14, RJ25 for the same series, the same size, are 9.5mm wide, only the number of contacts is different. RJ11 only the middle pair of contacts, can connect a pair of wires, said 6P2C (six posiTIon, two-conductor); RJ14 use the middle four contacts, can connect two pairs of wires, said 6P4C; RJ25 use all six contacts can connect three pairs of wires, said 6P6C. RJ25 uses all 6 contacts, can connect 3 pairs of wires, said 6P6C.

RJ11 and RJ14, RJ25 series of wire sequence and color table

RJ11 will also be used as an interface for RS-232 or 485, the following are 3 examples

Interface for RS-232 or 485

RJ11 is the U.S. standard telephone connector, while the United Kingdom for BS 6312, France for F-010, Germany for TAE connector, basically similar, while Austria is TDO-connector, Poland for WT-4, the difference is very big.

Currently more commonly used RJ connector is RJ45, for ethernet connection, 8P8C, you can connect four pairs of twisted pairs, 12mm wide, wider than the RJ11 series. RJ45 is sometimes used for telephone or RS232 connections, but also some people use it to pass VGA video signals.

There is also an 8P8C connector called RJ61, used to connect twisted pairs, the line sequence is as follows.

8P8C connector called RJ61 wire sequence

Because this line sequence in the 3rd and 4th pair of twisted pairs in the two lines are far apart, it will cause greater crosstalk, not suitable for Ethernet such high-frequency signal transmission.

There is also an RJ48 connector, also 8P8C can be used to connect four pairs of T1 data links, each pair of lines can transmit time-division multiplexing of 23 voice circuits.

Other less common RJ series connectors

  • RJ2MB: 50-pin miniature ribbon connector
  • RJ12C/RJ12W: 6P6C, for one telephone line ahead of the key system
  • RJ13C/RJ13W: 6P4C, for one telephone line behind the key system
  • RJ15C: 3-pin weatherproof, for one telephone line
  • RJ18C/RJ18W: 6P6C, for one telephone line with a make-busy arrangement
  • RJ21X: 50-pin miniature ribbon connector, for up to 25 lines
  • RJ26X: 50-pin miniature ribbon connector, for mulTIple data, lines
  • RJ27X: 50-pin miniature ribbon connector, for mulTIple data lines
  • RJ31X: 8P8C (usually only 4C are used), single line with alarm – center pins #4 & #5 connect to phone line; outside pins #1 & #8 connect to another phone jack allowing the alarm dialer or medical alert system to dial the monitoring company when triggered.
  • RJ38X: 8P8C, similar to RJ31 but a connecTIon between pin #2 & #7 indicates that a plug is inserted.
  • RJ41S: 8P8C keyed, for one data line, universal
  • RJ45S: 8P2C + keyed, for one data line with a programming resistor
  • RJ49C: 8P8C, for ISDN BRI via NT1
  • RJ50: 10P10C, the same size as RJ45 but with ten contacts Business phone
  • RJ71C: 12 line series connection using 50 pin connector