rj12 keystone jack

Cabling-Design.com FREE cabling and networking Helpdesk
 Question by Tony C posted 05 Feb 2004
 rj12 keystone jack
I have a rj-12 keystone telephone jack. There are no instructions on the wire order (red, black, yellow, green) to put into the jacks knife leads. Looking at the back of the jack, what order do the wires go? And why are there 6 knife leads when most telephone lines only have 4 wires (for two lines)? Thanks
 Answer by Joseph Golan posted 05 Feb 2004
Dear Tony,

An RJ-12 is typically used to connect single line set with ancillary control (like the old key systems) If this is for a two line operation it is then called an RJ-14. In either case the red/green pair goes to the center 2 pins (pins 3 & 4) and the 2nd pair goes on the next set on pins counting outward on both sides of pair 1 (pins 2 & 5). The connector has a total of 6 pins because both the RJ-12 and the RJ-14 are built into a 6 conductor jack. This was set up in the old Bell days and has continued through the FCC regulation on the RJs. Pins 1 & 6 if used could accomidate a 3rd pair and if all were being used for telephone lines it would then be called an RJ-25.

While a three line telephone is rare, it was more popular years ago.

Please see the following links for diagrams of these pinning configurations:


Joseph Golan, RCDD

Click here to see the expert's profile
Back to the current page of questions | Back to all the questions
Back to Cabling-Design.com HELPDESK | Ask your question
Residential Cabling Guide

Home Cabling Guide

Finally, an instantly downloadable book that saves you thousands in home improvement dollars! Enjoy living in 21st century technology-advanced home while increasing its selling value and competitive advantage on the real estate market. Whether your cabling is for home office or high-tech leisure, you can wire your home yourself or learn "wirish" to speak with your cabling contractors in their language!

Learn more ...