RJ11 (short for Registered Jack-11) is a telephone jack with six possible connections. It is widely used in America, although it is also used in other countries. Statistics suggest that virtually all single line (POTS) telephone jacks in most homes and offices in North America use this jack. The nearest competitors for this Jack would include RJ14 (designed for a 2-line telephone jack), RJ25 (suitable for a 3-line jack), and RJ61 (meant for a 4-line telephone jack), but a common thread among them is that they utilize 6-position modular connectors. The telephone jacks in the United States are required to be registered with the Federal Communication Commission (FCC). The nomenclature was derived from AT&T’s Universal Service Order Codes (USOC) and the FCC adopted the code as part of its regulations (to be precise, Part 68, Subpart F. Section 68.502).
The term jack is sometimes used to denote both the plug and the receptacle and sometimes used to refer only the receptacle. RJ11 has six conductors, although only four of them are generally used. RJ11 is mostly used for home and offices phones which are plugged into them from the “untwisted wire” as the gray wire is known to many. The jack, in turn, connects to the “outside “wires that connect to the telephone company or to a private branch exchange (PBX). The four wires that are implemented are usually the Green and Red pair, and Black and white pair. Usually, the green and red pair carries voice and data, while the black and white are used for low voltage phone requirements such as lights. If the PBX system is the one in use, the black and white pair may also be used for other kinds of signaling. PCs that use a dial-up modem for connectivity also use the RJ11 jack.
The extra two wires are mostly unused, although they could be used as a ground for selective ringers or as an “anti-tinkle” circuit to stop a pulse dialing phone from ringing the bell on the rest of the extensions. There is also a powered version of RJ11 whereby, pins 2 and 5 (the black and yellow ones) may carry some low voltage power. In most cases, the phone carries enough power for most of its terminals, but the older terminal with incandescent lights (which includes the Western Electric Princess and Trimline telephones) may require more power than would be available. Trimline and Western Electric Princess dial lights are about 6.3 volts and the transformer has around 5 volts. The power from the two aforementioned pins may come from the transformer plugged into a wall near one jack which then supplies power to all the jacks in the house.
There is a new color coding based on the Cat-5 cable. Green is swapped for black and yellow is swapped for red even though the phone will work perfectly if you followed the older color coding, but that is not considered to be the standard. The negative and positive terminals are:
* (Pin 3) the negative terminal is Red for the old color code and blue for the new color code.
* (Pin 4) the positive terminal is green for the old color code. It is white with blue stripes in the new color code.
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