Questions about polarity issues

[AE_Collector]

Polarity had to be correct back in the day of party lines with selective ringing (as opposed to party lines where all phones on the line rang when there was a call).

Polarity still matters for some phones such as digital sets on Nortel SL1/M1 PABX's and Nortel DMS Digital Centrex sets only work if the polarity is correct. The Centrex sets ARE CO based lines, not internal PABX sets.

Modular cords and jacks can add a lot of confusion. If the plugs are both put on a cord facing the same way as opposed to one being rolled over, the cord reverses the polarity. Modular jacks in phones are (or were?) supposed to be wired backwards (colors intentionally in the wrong place in the jack assembly) in order to use modular set cords that had a reversal built into them. Now take an item like a CID box, answering machine or FAX machine that usually has 2 jacks..should one be straight and the other rolled? Does it matter which one goes to the wall jack and which one goes to a telephone set.....

Terry

[Jim Stettler]

The overall simplist way to fix this is to home run all you jacks to your d-marc.
At the D-marc install a DPDT switch. Have the down position as "normal", and the up "on" position for when you need to reverse the polarity.

The way you want to wire the switch is with the house side off of the center terminals. On one side of the switch connect the line,  Reverse the line and jumper it over to the otherside of the switch.

I beleive in mounting the DPDT Reversing switch in a surface jack and mounting it inside where the wire comes into the house.
JMO,
Jim