Registered Jack-11 or RJ-11 is a type of physical connector interface frequently used for telephone wire terminals.

It is a 4- or 6-wire connector primarily used to connect telephone equipment in the United States. However, even if this connector has a total of 6 connector positions, usually only 2 or 4 connectors are actually being used.

RJ-11 is the most common type of Registered Jack. It is used to plug the handset into the telephone and the telephone into the wall.

In addition, it is used for single line POTS (Plain Old Telephone Service) telephone jacks in most homes and offices.

RJ-11 often uses a 6P4C (6-position, 4-conductor) jack which has 4 wires, 2 of which are unused, functioning to a central junction box. Two of its 6 possible contact positions are used to attach the Tip (ground or positive side) and Ring (battery or negative side) of a phone circuit.

It can also be wired with a 16P2C (6-position, 2-conductor) variety of modular jack, though this is not frequently done.

The RJ-11 connector wiring appears in 2 varieties: Unshielded Twisted Pair (UTP) cable and Untwisted or flat-satin cable.

The extra wires are utilized for various applications such as:

  • an anti-tinkle circuit to prevent a pulse-dial or loop disconnect dial telephone from ringing the bell on other extensions;
  • a ground (reference point in an electrical circuit) for selective ringers; and
  • a dial light requiring a low voltage

In the powered version of RJ-11, Pin 5 (orange) and Pin 2 (white with orange stripe) may carry either low voltage Alternating Current (AC) or Direct Current (DC) power from a central transformer plugged into a wall next to one jack. This delivers power to each of the other jacks throughout the house.

In most cases, the telephone line itself can directly supply ample power for most phone terminals. However, old phone terminals with incandescent lights require more power than the phone line can deliver. Hence, there is a need to use Pins 5 and 2.

The positive terminal in RJ-11 is Pin 3 (blue) while the negative terminal is Pin 4 (white with blue stripe).

Additional Reading on RJ11