RJ-11
(Registered Jack-11) A telephone interface that uses a cable of twisted wire pairs and a modular jack with two, four or six contacts. RJ-11 is the common connector for plugging a telephone into the wall and the handset into the telephone. See modular connector.
RJ-11, 14, 25 - One, Two and Three Lines
RJ-11 cables can hold six wires for up to three telephone lines, and their nomenclature is technically RJ-11, RJ-14 or RJ-25 depending on the number of lines (see chart below).
RJ-21X, RJ-26X and RJ-27X
For PBX and other telecom connections, RJ-21X, 26X and 27X cables use a 50-pin Centronics-style "Miniature Ribbon" connector to handle 25 telephone lines in one cable.
C and W
The C refers to a desk phone jack, such as RJ-11C, while RJ-11W means a wall-mounted jack. See modular connector.
RJ-11 Connectors
Four-wire RJ-11 connectors (6P4C) are commonly used for telephone handsets and wall outlets. The six-wire variation (6P6C) is used for three telephone lines (see below).
Jack
Positions (P)
RJ U.S. and
Type Wire Pair Colors Contacts (C)
RJ-11 Line 1 - red-green 6P2C
RJ-14 Line 1 - red-green 6P4C
Line 2 - yellow-black
RJ-25 Line 1 - red-green 6P6C
Line 2 - yellow-black
Line 3 - blue-white
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