[TriLUG] OT: Home Depot and Cat 5

Byarlay, Wayne A. wab at purdue.edu
Tue Oct 5 18:51:55 EDT 2004


>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 *snip*

No, the "Powers that Be" did a HORRIBLE job picking the colors for
color-coding wire. Why do I say this? I'm COLORBLIND. It's not a bad
version of colorblindness; but the "Brown" and the "Green" of cat5 look
EXACTLY the same. Same deal with Resistors: Always failed the test in my
High School Electronics class, and didn't put 2+2 together until I was
at the eye doctor's, and, Voila! I can't see the "7" in the colored
dots! :(

I never thought of myself as a "Disabled" person, but every time they
color code something without taking into consideration that percentage
of the male population (which is a significant percentage) that is
colorblind, they are in effect making it "inaccessable".

My $.02,

wab.

-----Original Message-----
From: trilug-bounces at trilug.org [mailto:trilug-bounces at trilug.org] On
Behalf Of Aaron S. Joyner
Sent: Tuesday, October 05, 2004 11:45 AM
To: Triangle Linux Users Group discussion list
Subject: Re: [TriLUG] OT: Home Depot and Cat 5

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?
>
  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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