RJ11, RJ14, RJ25

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Two views of an RJ25 6P6C crimp-on style connector

RJ11 is a physical interface often used for terminating telephone wires. It is probably the most familiar of the registered jacks, being used for single line POTS telephone jacks in most homes and offices in North America and many other countries.

RJ14 is similar, but for a two line telephone jack, and RJ25 is for a three line jack. RJ61 is a similar registered jack for four lines.

RJ11, RJ14, and RJ25 all use six-position modular connectors.

An RJ11 jack uses two of the six positions, so could be wired with a 6P2C (six position, two conductor) variety of modular jack, but such jacks are quite rare. An RJ11 jack is nearly always a 6P4C jack, with four wires running to a central junction box, two of them unused. The extra wires are used for various things such as a ground for selective ringers, low voltage for a dial light, or as an 'anti-tinkle' circuit to prevent a pulse-dialing phone from ringing the bell on other extensions. With tone dialing this isn't required so the connectors are used to provide flexibility so the jack can be rewired later as RJ14 or to supply additional power for special uses. Similarly, the cables used to plug telephone terminals into RJ11 jacks frequently are four-wire cables with 6P4C plugs.

In the powered variation, Pins 2 and 5 (black and yellow) may carry low voltage AC or DC power. While the phone line itself supplies enough power for most telephone terminals, old telephone terminals with incandescent lights in them (such as the classic Western Electric Princess and Trimline telephones) need more power than the phone line can supply. Typically, the power on Pins 2 and 5 comes from a transformer plugged into a wall near one jack, supplying power to all of the jacks in the house. Trimline and Princess phone dial lights are rated at 6.3 volts and the transformer output is typically around 5 volts for long life.

[edit] Pinouts

pin	RJ25	RJ14	RJ11	Pair	T/R	±	Color	Old
1	X			3	T	+	white/green	orange
2	X	X		2	T	+	white/orange	black
3	X	X	X	1	R	-	blue	red
4	X	X	X	1	T	+	white/blue	green
5	X	X		2	R	-	orange	yellow
6	X			3	R	-	green	blue

Note that while the old solid color code was well established for pairs 1 and 2, there are several conflicting conventions for pair 3. The colors shown above were taken from a vendor of "silver satin" flat 8-conductor phone cable that claims to be standard. At least one other vendor of flat 8-conductor cable uses the sequence blue, orange, black, red, green, yellow, brown and white/slate.

In the RJ11 pictured above you would read the pinouts 1 through 6 from right to left

[edit] See also

BS 6312 - British equivalent to RJ25
RJ45 - Eight position connector used with Ethernet
Telephone plug - Includes a table of the countries where RJ-11 and other telephone connectors are used