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The RJ11 Jack and What It's Used For



faceplate with RJ11 jackThe RJ11 jack is the receiving area on your wall where you plug in the clear plastic terminal on the end of a telephone cable, known as a modular plug.  RJ11 jacks, or modular plugs, are six position, because both the modular plug and the jack can utilize up to six wires (3 pairs). The pair is a term used in telecommunications to represent the twisting of two copper wires together, called a copper pair.

telephone cable

RJ11 formats are designed to carry voice or analog signals and have been popular in home and business environments even before the 1980’s, when many business telephone systems would use up all three copper pairs. The first pair would be used on two way talk, the second for incoming data (time display, speaker phone, line appearance, etc…), and the third pair would be used for bringing power to run the phone. When an older phone system lacked a built-in intuitive device (usually known as a "key service unit" or "pbx") for separating incoming phone lines, it would typically use each pair of wire for a separate line. Example: pair one would be line one, pair two would be line two, and pair three would be line three. Aside from business phone systems, the RJ11 format is typically found in household phones, fax machines, and modems.

People are sometimes confused by the difference between RJ11 and RJ45 due to their close similarities. One difference is that RJ45’s have 8 wire positions whereas the RJ11’s have 6 wire positions. Certification is another way to broaden the gap between RJ11 and RJ45’s; for example, RJ11 has no certifications, but RJ45 is classified in many levels: CAT3, CAT5e, CAT6, etc…Even though RJ45’s have been the standard for many years on computer networks, Apple started off using RJ11’s for the “Apple Talks Network” to connect several Apple computer and printers together, using one pair for voice, and the second for data. It fell out of favor when using ethernet wires, such as 10baseT, came into play around the early 90’s.

patch cables

AT&T is the company responsible for the RJ formats and many others, and has signified the modular jack application. The RJ11 has typically been the standard for telephone systems, but as far back as the 1970’s, AT&T was the first company to actually use RJ45’s for their phone systems. AT&T’s method still holds true today for some installers who prefer to use a RJ45 jack. If the patch panel is properly terminated and pinned out by the installer, it can be used for either an Ethernet cable for a computer network or a digital, analog phone system. Unless you are a trained installer, it’s always best to stay on the safe side and use RJ11 modular and jacks for voice or analog applications, except when dealing with VOIP (Voice over IP), because they are never used in this situation.


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