Miswired Cable Works?
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Posted by Michael Quinlan on May 11, 2005, 7:42 am
Please log in for more thread options That's exactly the way this installation appeared. All the work area outlets were wired correctly, with the exception of one that had the brown pair wired to a separate voice jack. However, at the patch panel, the white-blue and blue-white were reversed, with the same problem appearing on EVERY pair on EVERY cable. The only explaination I can come up with is that the pair-separators on the punch down were labled with the pair colors, but not with individual conductor colors, and the installer had no idea which conductor went on which side of the separator. To clarify for anyone not following this mess, the wiremap results were: 1 - 2 2 - 1 3 - 6 4 - 5 5 - 4 6 - 3 7 - 8 8 - 7 Obviously, the original installer did no testing, with the possible exception of testing connectivity between two ethernet devices. Thanks to all for the helpful replies. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by James Knott on May 11, 2005, 12:02 pm
Please log in for more thread options Michael Quinlan wrote: One thing to remember, is that the blue pair is not used for 10 & 100 Mb ethernet. All 4 pairs are used for gigabit. So you could cut the blue pair and it shouldn't affect networking. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Robert Redelmeier on May 11, 2005, 4:00 pm
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> However, at the patch panel, the white-blue and blue-white
> were reversed, with the same problem appearing on EVERY pair > on EVERY cable. Ah, tip & ring were crossed over on every pair! Not good practice! But it works for ethernet because the signalling system looks for _changes_, not absolute levels. > The only explaination I can come up with is that the
> pair-separators on the punch down were labled with the > pair colors, but not with individual conductor colors, > and the installer had no idea which conductor went on > which side of the separator. Very typical for 110 punchdowns. -- Robert | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Mark Evans on May 11, 2005, 6:40 pm
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> > However, at the patch panel, the white-blue and blue-white
> > were reversed, with the same problem appearing on EVERY pair > > on EVERY cable. > Ah, tip & ring were crossed over on every pair!
> Not good practice! But it works for ethernet because the
> signalling system looks for _changes_, not absolute levels. But can cause all sorts of interesting problems if the link is used for for telecoms or V24. > > The only explaination I can come up with is that the
> > pair-separators on the punch down were labled with the > > pair colors, but not with individual conductor colors, > > and the installer had no idea which conductor went on > > which side of the separator. > Very typical for 110 punchdowns.
If the connectors at both ends are from the same manufacturer all that's necessary is that things are done consistently. Plenty of simple network testers will show if this has happened. -- Mark Evans St. Peter's CofE Aided School Phone: +44 1392 204764 X109 Fax: +44 1392 204763 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by James Knott on May 11, 2005, 11:59 am
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David Lesher wrote: >
> >>What do you mean by "reversed pairs", if not cross over? It doesn't
>>matter what colour the wires are, so long as proper pairing is maintained. >
> At one end, the blue-white is punched down where the white-blue > should be and vice versa. Shouldn't be a problem, as the signal is not polarity sensitive. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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> outlets were wired correctly, with the exception of one that had the
> brown pair wired to a separate voice jack. However, at the patch
> panel, the white-blue and blue-white were reversed, with the same
> problem appearing on EVERY pair on EVERY cable.