john@jetson.UPMA.MD.US (12/22/88)
Hello! I need some help from TELECOM readers. There's a suggestion for modifying our project's wiring scheme which would result in tip and ring being reversed for some number of outlets within a house (residential, single-pair, POTS usage). What kind of problems will this polarity reversal cause? I've heard that a standard, old electromechanical phone won't have any trouble, but what about answering machines, modems, and other devices? My intuition is that it will be a problem, but I'm just a software person - what do I know? :-) Thanks for any help! -- John Owens john@jetson.UPMA.MD.US uunet!jetson!john +1 301 249 6000 john%jetson.uucp@uunet.uu.net
pozar@toad.com (Tim Pozar) (12/25/88)
In article <telecom-v08i0207m02@vector.UUCP> john@jetson.UPMA.MD.US writes: >X-Administrivia-To: telecom-request@vector.uucp >X-TELECOM-Digest: volume 8, issue 207, message 2 > >I need some help from TELECOM readers. There's a suggestion for >modifying our project's wiring scheme which would result in tip and ring >being reversed for some number of outlets within a house (residential, >single-pair, POTS usage). What kind of problems will this polarity >reversal cause? Shouldn't cause any hardware dammage. You may notice that some answering machines will not reconize the battery reversal so it may not hangup as soon as the caller disconnects. Also the DTMF pad may not work. On newer phones this shouldn't be a problem. Tim -- ...sun!hoptoad!\ Tim Pozar >fidogate!pozar Fido: 1:125/406 ...lll-winken!/ PaBell: (415) 788-3904 USNail: KKSF / 77 Maiden Lane / San Francisco CA 94108
jbn@glacier.stanford.edu (John B. Nagle) (12/26/88)
A "classical" Touch-Tone phone (WE 2500) won't work with tip and ring
reversed. Talk and ring work, but the keypad is dead. Newer phones have
diode bridges so that polarity is irrelevant.
Older coin telephones use polarity reversals to control the coin
mechanism, incidentally.
John Nagledave@rutgers.edu (Dave Levenson) (12/26/88)
In article <telecom-v08i0207m02@vector.UUCP>, john@jetson.UPMA.MD.US writes: > ...wiring scheme which would result in tip and ring > being reversed for some number of outlets within a house... > ... What kind of problems will this polarity reversal cause?... Older 2500 sets (single-line touch-tone) will not generate touch tones when tip and ring are reversed. Some 2500 and 500 (dial-pulse) sets will not ring when the loop is reversed. The newer sets are largely insensitive to polarity. It has been my experience (from several years of selling and installing business telephone systems) that about half of the loops in the country are reversed an odd number of times between the central office and the subscriber's equipment. When installing ground-start or DID equipment (where loop polarity is important) we usually had to swap leads on about half of the trunks serving a typical PBX installation to make things work right. For recent-manufacture single-line sets, however, it will probably make no difference. -- Dave Levenson Westmark, Inc. The Man in the Mooney Warren, NJ USA {rutgers | att}!westmark!dave
mhw@wittsend.LBP.HARRIS.COM (Michael H. Warfield (Mike)) (12/27/88)
In article <telecom-v08i0207m02@vector.UUCP> john@jetson.UPMA.MD.US writes: > >Hello! I need some help from TELECOM readers. There's a suggestion for >modifying our project's wiring scheme which would result in tip and ring >being reversed for some number of outlets within a house (residential, >single-pair, POTS usage). What kind of problems will this polarity >reversal cause? I've heard that a standard, old electromechanical phone >won't have any trouble, but what about answering machines, modems, and >other devices? Old style "dial" phones won't be affected, however most (if not all) modern electronic phones which derive power for their "dialing" circuits will not be able to call out. Most will be able to answer an incoming call. Phones, attachments, and accessories which use an external power supply or battery (modems, answering machines, speaker phones, memory phones, auto dialers, etc.) should work just fine since they are not "line powered" devices. This is also a word to the wise - if your touch tone phone won't dial the phone but will answer a call then tip and ring may have been reversed on you. Check for someone working on the phone systems. Over the last 10 or 15 years this has happened to me a couple of times. One time the phone man was still on the pole when I discovered the problem. He quickly fixed it and was nice enough to explain to a "technical type like me" what happened. Generally, when they're not caught in the act, your phone will magically start working again but "nobody did anything". --- Michael H. Warfield (The Mad Wizard) | gatech.edu!galbp!wittsend!mhw (404) 270-2123 / 270-2098 | mhw@wittsend.LBP.HARRIS.COM An optimist believes we live in the best of all possible worlds. A pessimist is sure of it!
john@jetson.UPMA.MD.US (John Owens) (12/28/88)
Thanks to all the replies to my question, both in TELECOM and in private mail. The wire people here talked to some telephone people, and were convinced not to swap polarity. Interestingly, while most of the responses contained the same basic information, that Touch-Tone phones without a full-wave bridge won't be able to generate touch tones, about half the responses said "this is a terrible problem - don't do it", while the other half said "but this shouldn't be a problem"! :-) Since we need to be compatible with existing customer equipment, we're keeping polarity correct. Thanks again, -John Owens