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RJ11, RJ12, RJ45 Defined

Jacks are called by various names RJ11, RJ45 etc. These terms are incorrect (though widely used by all of us -OK, OK we use them as well), they should be called Modular Connectors according to the following table:

Common Name Correct Name No of connectors Notes
RJ11 4 Position Modular Connector 4 mostly used in analog (telephone) wiring
RJ11 or RJ12 6 Position Modular Connector 6 more commonly used these days in analog (telephone) wiring.
RJ45 8 Position Modular Connector 8 Used in telephone wiring (ISDN and T1), LAN (10baseT and 100BaseT) and RS232 (RS232D) wiring

NOTE: Male Modular connectors are numbered LEFT to RIGHT when viewed from the TOP (TOP is when the plastic lever is on the bottom). Female connectors are numbered from LEFT to RIGHT when viewed from the FRONT. An RJ45 (or 8 Position Modular Connector) example for both Male and Female connectors is shown below (the same principle applies to all modular connectors)

Male Connector Numbering

Female Connector Numbering

Telephone Wiring

Telephone Wiring is defined by USOC (Universal Service Order Code) which is now maintained by the TIA and uses the following conventions for cable pairing.

Analog Line Pair Numbering

The following diagrams show the various ways that single line pairs may be taken from a range of jacks.

NOTE: All numbering is viewed from the TOP (TOP on a Modular connector is when viewed with the lever/tab on the bottom). The diagrams show all possible types that will satisfy the Wiring Code.

USOC Code No of Pairs Diagram
USOC RJ11 or RJ11C

1
USOC RJ14C or RJ14

2
USOC RJ25 or RJ25C

3
USOC RJ48 or RJ48C

4

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LAN Wiring

LAN Wiring is defined by EIA/TIA and uses the following two conventions for RJ45 (8 Position Modular Connector) pairing on UTP cable. See our LAN wiring page.

EIA/TIA wiring Code Diagram Notes
568A (colour diagram)
568B (colour diagram)

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Last modified: November 7, 2011

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