[TriLUG] OT: Home Depot and Cat 5

[Rick DeNatale]

Well, I'll see your sticklering and raise you a pedantry.

While most of what you say is true, and I wouldn't argue with you
about the merits of the color code.  The electrons really are color
blind. They could care less what color the insulation is. But what is
important is the proper pairing.

The thing which gives UTP good noise rejection is the combination of
twisted pairs with differential inputs and outputs. The twisted pair
means that noise is pretty much equal in amplitude and polarity on
both wires in the pair, this means that it will cancel out in a
differential input. As someone else pointed out having different twist
ratios between the different pairs in the cable helps with cross talk.

The big advantages of the color code are you don't need to think about
it, and 2 you can get a straight through cable by using either 568B or
568A on both ends, and a cross-over by using A on one side and B on
t'other.


On Tue, 05 Oct 2004 12:44:35 -0400, Aaron S. Joyner <aaron at joyner.ws> wrote:
> Steve Litt wrote:
> 
> >On Tuesday 05 October 2004 09:21 am, Aaron S. Joyner wrote:
> >
> >
> >
> >>If anyone else has any insights or disagreements, I'd be quite
> >>interested to hear.  I am not an authoritative source on cabling by any
> >>means, I've just observed the common industry practices for the better
> >>part of a decade and am kind of a stickler when it comes to proper cabling.
> >>
> >>Aaron S. Joyner
> >>
> >>
> >
> >I have an additional question. I have a 150' cat5 cable hand made by my
> >vendor. It doesn't work. A friend told me that with long runs there's a
> >special wiring method than with short runs, in order to limit capacitance or
> >inductance or some such.
> >
> >Anyone know about that?
> >
> >One thing I can tell you is that the non-working cable has only 4 conductors
> >crimped. For long cables, should all 8 be crimped?
> >
> Okay, here's where my stickler-side comes out.  There is sound
> engineering behind the 568B color code for data wiring, and it's usually
> labeled right there on every jack, patch panel, etc that you're likely
> to use (not RJ-45 ends of course, but if you're making those you should
> know what it is :p ).  In short, it's very important to follow the color
> code.  The simple reasoning is that (for 10/100 Ethernet) data is
> carried on pins 1 and 2, and 3 and 6.  Pins 1 and 2 are one circuit,
> pins 3 and 6 are the other.  One is used for Transmit, the other for
> Receive - which one is which of course depends on your perspective, and
> if you're talking as an end point or a mid point (think device vs
> switch).  The 568B color code ensures that the orange pair (orange, and
> white with an orange stripe) is used for pins 1 and 2, and the blue pair
> (blue, and white with a blue stripe) is used for pins 3 and 6.  Why is
> this important, you ask?  Well basic electrical engineering will point
> out that two wires, twisted together, will produce less inductance in
> other near-by conductors.  In other words, you don't get "cross talk"
> between the wires, and the signal is more clean.  That's the reason the
> wires are twisted so tightly in Cat-V cable, it's to help ensure there's
> no interference between the two very sensitive "BIG ANTENNAS" you've
> essentially attached to your Ethernet devices.  If you have a look at
> older Cat-III (Category 3) cable, it's a much looser twist.  Take a look
> at older telephone cable, it's even less twisted, the point of basically
> not being twisted at all.  Which is why cross talk between two lines in
> the same phone jack used to be really common in the telephone world.  :)
> 
> So please, follow the color code.  If you don't understand the
> engineering behind something, trust that the "code" was designed so that
> you don't have to, so long as you follow it.  Also, note that this is a
> dramatic over-simplification of the electrical workings of Cat-V cable,
> if you'd like a more thorough explanation consult google or your local
> physics / EE professor.
> 
> Aaron S. Joyner
> 
> 
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