Modular connectors, also commonly referred to as RJ connectors, have been extremely common in telecommunications and data communications applications since their early introduction by AT&T in the 1960s. The Federal Communications Commission (FCC) further standardized this interconnect solution in the 1970s into what is today known as the Registered Jack (RJ) registration system, which standardizes the wiring patterns, signal characteristics and physical construction of the connector itself. Users today still see the naming convention of "RJ" followed by two digits to account for differences in the connector's packaging and intended use.
Basic Construction
The modular connector or RJ connector uses a molded shell that encloses stamped metal terminals separated by insulated channels to create a more “modular” and cost-effective connection system for consumer and commercial telephone systems. The contacts in the plug are mated to similar stamped metal contacts in the jack and guided into place by insulated channels while the plastic shell of the plug locks the cable in place to relieve stress. Stress is further reduced by molded features in the plug and jack, and the plug has an embedded spring that snaps into a molded recess in the jack to hold it in place. The plug is released from the jack by depressing this spring.
Modular connectors are available with two, four, six, eight or ten contact positions, although these positions are sometimes not used. For example, RJ11 telephone connectors typically have four or six connections, while Ethernet (RJ45) connectors have eight. The standard naming scheme specifies connector wiring so that 6P2C connectors have six positions and two contacts, while 4P4C connectors for telephone handset lines have four positions and four contacts. While most of the contacts are used for signaling, the RJ connector contacts can be used to provide low-voltage AC or DC power.
The benefits of modular connectors are numerous. For product manufacturers, the advantages of such connectors include
Low cost
High utilization
Solderless assembly
Easy customization
Surface mount jacks
Robust variants suitable for industrial applications
Modular connectors are well suited for field installation and maintenance tasks given the following advantages
Easy upgrade or replacement of old connectors
Easy field assembly with simple tools
Customizable cable assemblies in the field
Wide range of connector and cabling options
Field service personnel require only simple training
In both cases, the simplicity of the connector insertion/extraction action makes it easier for users to solve their problems and reduce service calls.
Common Types
There are a wide variety of application-specific modular connectors. The following are the most common types and their specifications.
RJ10 – Simple 4P4C rectangular connector for telephone handsets
RJ11 – 6P2C or 6P4C square connector for connecting a modem to a telephone line
RJ12 – Same size as RJ11, but with 6P6C
DEC MMP/MMJ – smaller version of the RJ11/12 connector for use with Digital Equipment Corporation equipment
RJ13 – 6P4C, same as RJ12 but with a behind-the-wire circuit
RJ14 – 6P4C with two lines for connecting two phones or modems
RJ21 – Modular connector with up to 50 contacts for connecting up to 25 circuits in a large telephone system
RJ22 – similar in shape to RJ11 but with 4P4C, usually used to connect cell phones
RJ25 – 6P6C, like the RJ11, but can connect three devices
RJ45 – 8P8C or 8P10C, used for Ethernet LAN Welcome to CUI Devices’ blog, The Ultimate Guide to RJ45 Connectors, for more details
RJ48 – 8P8C, like the RJ45 but for connecting shielded cables to T1 data lines
Key connector specifications and features
Additional features can be specified for modular connectors, such as
Shielding to protect longer cables from electromagnetic (EMI) or radio frequency interference (RFI). Shielded RJ45 and RJ48 connectors are used to extend the ground connection of the cable shield pigtail to its mounting panel and are extremely common.
Keyed, certified RJ45 connectors have a tab on the connector to prevent the connector from being accidentally inserted into the receptacle. Standard 8P8C connectors typically do not have this feature. Color coding can be used to indicate which cables are allowed to use a particular network connection point.
Mounting options such as panel mount, board mount, through-hole, and surface mount to PCB are typically available. Modular jacks provide vertical or horizontal orientation.
Display and indication features, such as colored LEDs to show status.
High reliability variants that can include EMI/RFI shielding, special keying, protective sleeves, and ruggedized components. All of these features increase the number of insertion/extraction operations.
Integrated magnets for improved EMI shielding performance and connection reliability in xBASE-T networks. These are wire-wound components in the jack that protect against transients and provide isolation, signal balancing, and impedance matching.
Figure : Modular connectors with integrated magnets for improved EMI shielding and connection reliability.
Other Parameters
The following parameters also need to be considered when selecting the right modular connector for a specific application.
Pin layout – the assignment of each contact within the connector
Current rating – the maximum current that the device can handle
Voltage rating – the maximum operating voltage the device can withstand
Contact size – defines the largest diameter wire that the connector can accommodate
Number of contacts – always an even number
Conclusion
Although modular connectors have been standardized for more than 40 years, they remain popular today because they are widely used, simple to use and highly utilized. While these connectors are most commonly used in telephone systems, data networks and low-speed serial connections, the development of Power over Ethernet (PoE) and its overall flexibility has further increased its use. Applications such as industrial control, motion control, smart lighting, and development boards are just a few of the designs using modular connectors today.
RJ Series modular connectors have become ubiquitous, but they are not all the same. Working with suppliers to consider the above factors helps ensure that engineers specify the correct RJ plug and jack for their application.CUI Devices’ modular connector family is available in RJ10, RJ11, RJ12, RJ13 and RJ45 jack types, offering a range of placement, contact and mounting options.
