Modular Connector Guides

What are modular connectors?

​​​​​​​Modular connectors are commonly used for telephone systems, data networks, and low-speed serial connections. These connectors are inexpensive, relatively simple to terminate, and easy to plug and unplug. A modular connector typically has a clear, plastic body, with a tab that locks the plug and jack into place when connected. In the vernacular used by the technology industry, they are called "RJ" connectors. This is technically inaccurate, but the naming convention is widely used. RJ is an acronym for Registered Jack, which is part of a coding system developed in the 1970s by AT&T to classify telephone services and equipment. The system, called the Universal Service Order Code (USOC), used designations that began with the letters RJ to denote the capabilities of jacks in a building, and how they should be wired in order to connect to the public phone network. RJ plug connections are typically terminated by using a special tool to crimp the connector onto the conductors of a cable. These connections are often made in the field for convenience; however, a factory-assembled RJ cable typically offers the best performance.