RJ21

Female RJ21 connector

25 Pair Color Code Chart as used by 1A2 systems

RJ-21 (or RJ21) is a registered jack standard for a modular connector using 50 conductors, usually used to implement a 25-line (or less) telephone connection such as that used in the 1A2 key telephone system. It is also known as a 50-pin telco connector, or an Amphenol connector. (The latter is a genericized trademark, as Amphenol was the largest manufacturer of these at one time.)

Dual RJ-21 connectors are often used on punch blocks to make a breakout box for PBX and other key telephone systems.

RJ-21 connectors are used to connect Ethernet ports in bulk from a switch with RJ-21 ports to a CAT-5 rated patch panel, or between two patch panels. A cable with an RJ-21 connector on one end can support 12 RJ-45 connectors or Ethernet ports on a patch panel.

The same connector (with spring bail locks) is used for SCSI-1 connections. Computer printers use a shorter 36-pin version known as a Centronics connector.

See also

• Key telephone system
• Telco cable
• Micro ribbon

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