[TriLUG] OT: Home Depot and Cat 5

[Aaron S. Joyner]

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