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I have bulk Cat 5e Ethernet cable with "TIA/EIA-568B.2" stamped on the jacket. I'm assuming this means I should use the T568B color scheme. If I were to crimp both ends using the T568A color scheme instead, would it affect signal quality?

I suspect it might, as the arrangement of the four pairs in the jacket might be different than if the cable was T568A, and maybe that makes a difference in signal quality. But I'm not sure—maybe it's just a matter of color preference/convention and it doesn't affect the signal quality at all.

Related question: Suppose I had T568A jacks wired to a T568A patch panel with cable labeled T568A. Would it matter if I used T568B patch cables (T568B stamped on the jacket and heads crimped to the T568B color scheme) instead of T568A cables? I would expect not, but again I'm not sure.

(Citations to the relevant sections in standards documents, if available online, would be appreciated.)

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I think that this here is just misinterpretation of the marking on the cable. The TIA/EIA-568B.2 is the actual name and version of the TIA/EIA-568 standard covering balanced twisted pair cabling and I believe that the cable was marked with the standard to which it was made. The main point of that document isn't just the pinout. It has numerous other technical characteristics to which the cable must conform. Some of them are the DC resistance, capacitance between the pairs, bending radius of the cable at different temperatures.

In fact the named standard does NOT specify that the "B" version of the pinout should be used. Instead it says: Pin/pair assignments shall be as shown in figure 1 or, optionally, per figure 2 if necessary to accommodate certain 8 -pin cabling systems., with figure one showing T568A and figure two showing T568B cable.

The TIA/EIA-568C is relatively new standard and it is possible that the cable manufacturer hasn't switched to it yet. I also haven't seen the actual document, so I don't know if it has any major or important changes. Also the B version of the standard only covers the cable categories 3 and 5e and since your cable is of 5e category, it could be that there are no changes for that category in TIA/EIA-568C.

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  • Thanks for your answer. I think this makes it clear that either option is acceptable and that there is no electrical difference. I've had the bulk cable for many years, so it is probably older than 568C. – Richard Hansen Mar 17 '14 at 1:31
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No, it doesn't matter, as long as you're consistent at both ends of the cable (assuming you're not deliberately creating a crossover cable).

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  • Thank you for answering. If it doesn't matter, then I'm guessing the relevant standards documents are silent on how the four pairs are arranged inside the jacket. Do you know if that's the case? – Richard Hansen Mar 16 '14 at 22:37
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    That's right, there's no difference in the electrical characteristics of the wire pairs within the cable, and therefore, no reason from that point of view that any specific pair of wires should be attached to a given pair of pins. – Dave Tweed Mar 16 '14 at 22:49

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