Fixing telephone polarity

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Old 06-03-20, 08:32 AM
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Fixing telephone polarity

I have a radioshack telephone line tester that has little LEDs that light up to show if a line is connected correctly or with reversed polarity. All of the outlets in my house check out except one, which shows as reversed. I switched the wires in the basement (only two are connected), but bizarrely, it still shows as reversed...

All of the lines are in a star topology, but the line in question has at least two splices to extend the cable through its run.

I still have a dial tone and I realize that with modern equipment polarity doesn't make much of a difference, but I'd still love to fix it if possible. Any ideas on what could be causing this, or how to fix it?
 
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Old 06-03-20, 08:07 PM
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You may have to reverse the wires right at the jack.
It can be almost impossible to figure out how the cabling was run and connected.
 
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Old 06-06-20, 07:41 AM
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Are you sure you did not reverce one of the other jacks?
Shold be OK to reverce the 2 wires to that jack at any point as long as you do it on the right pair.
I aggree in that modern phones are not sensitive on polarity, but the oldest touch tone phones are if you find one and want to use it.

:-)

dsk
 
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Old 06-09-20, 08:06 AM
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This is the strange thing - I'm sure it was the right wires in the basement. Reversing them in basement didn't seem to change the polarity indication on the wire. So I wonder if there's some other wiring weirdness going on... Will continue to debug this...
 
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Old 06-09-20, 07:18 PM
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There are so many different ways of wiring that there is no standard that we can give you.

Ma Bell originally wired a house by taking a multipair cable and running it from location to location. Then each jack tapped off a pair depending on which line was needed at that jack.

When we run phone wiring and jacks now...... each location is taken to a common point called a demarc location.

I install alarm system that require the use of a phone line and have spent quite a bit of time tracing wiring. So many people do their own wiring that it can be a challenge to locate. Typically I'll go thru, cut all the splices open, identify each cable and then re-do the splices.
 
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Old 06-10-20, 08:59 AM
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The only time polarity mattered on residential lines was with the first generation Central Office-powered lighted phones (like a Princess). Ground start residential lines were as rare as hen's teeth. In the last 40 years polarity seems to have been largely ignored by the TELCOs, so I wouldn't worry about it.
 
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Old 06-10-20, 11:37 AM
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I would also be extremely interested in finding out why, even when it doesn't matter, just the way I am :-)
dsk
 
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Old 06-13-20, 07:30 AM
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I understand, but don't have an answer. I just know from experience that even the telcos aren't as particular on loop start polarity as they used to be. The telcos would reverse polarity for some signaling, but that was on inter-office trunks, not residential lines.
 
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Old 06-29-20, 10:08 AM
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As d_s_k stated very old touch tone phones were polarity sensitive. We used to reverse tip and ring on key system CO lines as a very basic method of dial restriction, while the polarity of the intercom was normal. The same could be done on a rotary dial by installing a diode. On a key system, the diode was reversed biased on the intercom line, so it would not conduct and operate as normal. On an outside line it was forward biased - always conducting, so there was no break-make when dialing.

As PJMax said the easiest thing to do would be reverse the one jack that's not correct. I wonder now when houses are built, will the telco still even run Cat3 cable (if it's even still available) for phones and install RJ11 jacks? My house isn't normal as I'm still using a modified version of a 1A2 key system with 25 and other multi pair cables to and MDF in the basement. I have a 25 pair cable with a 66 block behind the living room couch.
 
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