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whats the purpose of crossing the red and green wires in a rj11 patch cable?

Started by RB, June 01, 2018, 03:03:52 PM

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RB

Title sayzit. I read about switchboards crossin wires, SOME patch cables etc...not all...
whats the point of switchin the wires if you only need 2 anyway?
am i missin something?

rdelius

one some circuits the polarity matters. Some line cords might be assebled wrong so the colors are backwards

poplar1

2-, 4-, and 6-conductor modular cords are intentionally manufactured so that the order of wires left to right are reversed on each end. The 623 jack in the base of the phone has the connectors in the opposite order as the RJ11/RJ14/RJ25 on the wall. So the 2 reversals (cord + 623) make the polarity correct so that Tip (+) goes from green of wall jack to the short  green wire going from the 623 jack to L1 on the network of a 500DM set.

The 8-conductor modular cords are usually "straight through" -- the conductors being in the same order left to right in each plug.
"C'est pas une restauration, c'est une rénovation."--François Martin.

RB

Thanks poplar1!
So the RJ11 patch cords, are supposed to be reversed, so that the jack in each phone switches it back again, So...
from the PBX to the wall socket,  is wired for straight through .
Then, the patch cable switches all 4, if line has all 4 wires.
Then, the jack in any phone switches it back again.
Is that correct?

AE_Collector

Then there are cord couplers, both straight through and rolled versions. Little hope of maintaining polarity without testing everything once set up.

Terry


poplar1

Quote from: AE_Collector on June 04, 2018, 12:09:05 PM
Then there are cord couplers, both straight through and rolled versions. Little hope of maintaining polarity without testing everything once set up.

Terry

Not to mention that the telcos here no longer guarantee that polarity is correct at the demarc.
Then there are the techs who correct the problem of can't break dial tone by reversing polarity inside one WE 2565 rather than correcting the reversed line at the input to KSU.


"C'est pas une restauration, c'est une rénovation."--François Martin.

dsk

I guess this has historical reasons, the RJ connectors came on phones and they solved this as what they found practical, and it became the standard. No trouble as long as everybody follows the same standard.

Later the RJ45 on PC-networks. (It was a real step in the right direction from a ring of coax, and when someone wanted to plug in a new unit, the entire network was disturbed.)
The PC guys (many with telecom background) saw a potential for less trouble, and LAN plugs got their pinout.

dsk

RB

Yeah, there is wisdom back in there in application.
once you understand the reason, then you can see the value in doing something in a seemingly erroneous fashion.
The problem, is that wisdom is fading away.
And once it is gone, good luck. There is only so much you can get from a book, oh, sorry... an E book... ???
A wise man surrounds himself with people who are smarter than he. ;)
Thanks for clearing the water a bit.