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 Question by steven lords posted 30 Mar 2004
Below is the answer to my question, but
I dont understand what is meant by:
"Digital sets for behind PBXs " what does
this mean??


The reason it works is because most analog telephones today incorporate a polarity guard within the set which is needed to get a touch-tone type dial to work. Older equipment did not include this circuitry which required then the proper polarity on the line cord.

Digital sets for behind PBXs do require, for the most part, the line to be polarized in order for the set to function. Those cords must have the pair reversal you are refering to.

Joseph Golan, RCDD
 Answer by Joseph Golan posted 09 Apr 2004
Dear steven,

Digital sets are proprietary telephones that work with PBXs (Private Branch Exchange) typically found in medium to large commercial environments and electronic key systems typically found in small to medium businesses and larger home systems.

These sets incorporate multiplexed signals that not only deliver voice but also the signals to the telephone for features (hold, conference, transfer, etc), ringing tones, indicators (lamps showing the status of the call: hold, engaged, ringing, etc.) and power to run the electronics in the telephone set.

These types of sets typically today run on one pair and the polarization of the line is important for the electronics to function. Just think of them like typically any other DC device where the positive terminal must be connected to the positive source and the negative terminal must be connected to the negative source.

To carry this illustration further in an RJ-11 jack, pin 4 of this RJ is the tip side of the line or the positive leg and pin 3 is the ring side of the line or the negative leg. In order for most digital sets to work they must be connected with the correct polarity to the line.

I hope this gives you a better idea of what was original expressed in the answer

Joseph Golan, RCDD

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