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
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
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