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Wired Networks Thread, Fibre polarity on LC patch panels - do you need to flip one patch cord pair? in Technical; G'day This perhaps a stupid question, but I am unsure if our fibre installation was done right or if I'm ...
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    Fibre polarity on LC patch panels - do you need to flip one patch cord pair?

    G'day

    This perhaps a stupid question, but I am unsure if our fibre installation was done right or if I'm just thinking about it the wrong way.
    I'm looking for feedback from people who also have fibre patch panels with LC connectors - basically what most switches now come default with.
    Do you need to flip polarity on one side of your patch cords with default polarity LC duplex patch cords?

    Longer explanation:
    For years we only had the old style ST connectors on the fibre patch panels, since that's what was standard like 15y ago.
    As long as they don't break, they will stay installed and they seem to be quite trusty. :-) This kind of connector is simplex only, checking fibre polarity on them is normal procedure then.
    I'm not a fibre guy, my normal network connection in 99% of daily work is RJ45 :-)

    Now a new fibre run has been added to a building with the nowadays default-style LC connectors. These ports are duplex - I've once seen simplex LC patch cords but they seem to be rather seldom used.
    Until now I've never used LC to LC connections other than for switch to switch cabling, no passive coupling in between like a patch panel.
    With duplex LC cables I've never had to think default polarity although lots of LC patch cords allow flipping fibre pairs at the connector if you need to (but not all as I've found)

    Now with the new install I've realized that using default-polarity patch cables I've had to flip the connectors on one of the 2 ends to get correct polarity.
    Is this considered to be normal?

    Reading white papers about fibre polarity standards like this one from AMP makes me think that one should not nned to flip pairs but if connections were done right, one should not need to bother about fibre polarity ?
    http://www.ampnetconnect.com/documen...ied_090813.pdf
    Last edited by koffi2k; 9th January 2013 at 07:54 AM.

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    Koffi2K,

    We have recently had some fiber installed and we had to flip polarity as you mentioned, I did ask the installation company and they stated that the best practice was to flip polarity at the patch panel, and that most installation companies did this, it didn't seem that logical but these guys are very good so I trust there opinion, the only reason that I can think of is the difficulty is keeping track of where the cables were switched within the fiber box, it seems a lot easier to install connection 1-2 in server room A to connection 1-2 in server room B and then cross over.

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    Geoff's Avatar
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    The relevant standard you should look up is TIA/EIA-568-B.1-7-2006 (Commercial Building Telecommunications Cabling Standard). But basically there's three ways of doing this. Which you choose is entirely up to you/your installer.

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    Michael's Avatar
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    If I've understood correctly, ST > LC, you did switch it (black, red and red black) at the patch panel. As far as I'm aware LC to LC is the same. You'd know if you had wiring/connectivity problems as file transfers especially would be carp!

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    twin--turbo's Avatar
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    We have both scenarios now and in past.

    I consider it normal.

    Rob

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    Thank for all your feedbacks, that was helpful !

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    twin--turbo's Avatar
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    use you mobile phone camera to photograph the light so you can see which way it should be .

    TT



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