Communications Cables Revised: 04.08.00
RJ Type Plug Designations & Pin-Outs Reason for Revision: New page

Prior to the break up of the Bell system in 1984, the telephone system had a unified and consistent system of identification for modular jacks and plugs used in communications systems. The term "registered jack" origninated then, along with the Universal Service Ordering Code (USOC). An RJ designation and the appropriate USOC served the dual purpose of telling technicians how to wire the system and of telling the payables department what the billing rate should be.

Since divestiture, the FCC incorporated some of the designations into FCC Part 68, Subpart F, Section 68.502, where the jack configurations are detailed. The term "RJ" isn't really accurate anymore, but the designation still is used.

Modular plugs (which go into modular jacks) come in 4, 6, and 8 position variations. The number of positions both establishes the width of the plug and also represents the maximum number of contacts (or wires) that can be terminated in the plug. However, to save costs, manufacturers will only put in as many metal contacts as necessary for the intended application. Know what you need and make sure you get plugs that have the proper number of contacts. Jacks are usually fully populated with contacts, but this is not always the case. Check before buying.

The table below details several common plug and jack configurations.

Designation RJ 11 RJ 14 RJ 22 RJ 25 RJ 45 RJ 48 RJ 61
Number of positions 6 6 4 6 8 8 8
Number of contacts 2 4 2 or 4 6 8 4 8
Application single line voice 1 or 2 line voice handset cords 1, 2, or 3 line voice LAN data transmission 1.54 Mbps T1 or 10Base2 1, 2, 3, or 4 line voice
Pinout Scheme USOC USOC USOC USOC TIA 568A or 568B system dependent USOC

 

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