Can someone tell me why the green white/3 and the green/6 are on either side of blue/4 and blue white/5? I have connected them in colored order and it does not work. Why???

Tom

 

<p>Hi,

<p>Following text explains pin & pair assigments in CAT 5 cable:

<p>There are two wiring standards for these cables, called T-568A and T-568B. They differ only in pin assignments, not in uses of the various colors. With the T-568B specification the orange and green pairs are located on pins 1, 2 and 3, 6 respectively. The T-568A specification reverses the orange and green connections, so that the blue and orange pairs are on the center 4 pins, which makes it more compatible with the telco voice connections.

<p>T-568A is supposed to be the standard for new installations, and T-568B is the alternative. However, most off-the-shelf data equipment and cables seem to be wired to T568B.
<pre>
T-568B

Pin Color Pair Description

1 white/orange 2 TxData +
2 orange 2 TxData -
3 white/green 3 RecvData +
4 blue 1 Unused
5 white/blue 1 Unused
6 green 3 RecvData -
7 white/brown 4 Unused
8 brown 4 Unused
</pre>

 

Because the cores using the green colour are designated as the RX pair and pin 3 is RX+ and pin 6 is RX-

 

There are three different configurations for CAT 5 wiring. They are: straight, cross, roll over.

Straight connection is "1 to 1". meaning same order on both ends, and is used commonly to connect a PC to a hub

Cross cable is almost the same as straight but 4 cables interchanged. This is used to connect PC to PC directly without a hub.

Roll over cables are used to configure routers.

Hope this helps.

ANA

 

Cat 5 has Rx+ on 3/White/Green and Rx- on 6/Green.

But Tx+ is on 1/White/orange and Tx- is on 2/orange, which you haven't wired in.

Blue, white/blue isn't "normally" used.

 

Geoff and Vedran's answers are tautalogical: The pairs are seperated because the standard says seperate them. I (and presumably Tom) want to know why does the standard seperate them, not why do I have to conform to the standard.

In other words, why would a human being with an IQ higher than 12 choose to deliberately split up the pairs like that. I'm a complete moron, and if I designed a connector with four pairs it would go Pair 1, Pair 2, Pair 3, Pair 4. Instead, someone presumably way smarter than me decided to go Pair 1, Part of Pair 2, Pair 3, The Other Part of Pair 2, Pair 4. Huh?

So to reiterate Tom's question: Why are the pairs on CAT5 cable split up?

-James Ingraham
Sage Automation, Inc.

 

You cannot assume that the wires are located in a rational order. See this website to get the correct wiring information for the RJ45 plug/socket that is used with CAT5, CAT5e, CAT6, and CAT7 cabling.

http://yoda.uvi.edu/InfoTech/rj45.htm

Dick Caro
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Richard H. Caro, CEO
CMC Associates
2 Beth Circle, Acton, MA 01720
Tel: +1.978.635.9449 Mobile: +.978.764.4728
Fax: +1.978.246.1270
E-mail: [email protected]
Web: http://www.CMC.us
===========================================

 

To supplement some of the previous answers, if you do wire them up sequentially, Pair 1, Pair 2, Pair 3 and Pair 4, the cables can work for short runs or low transfer speeds, but as soon as you start to increase either the distance or the speed, cross talk and other factors start to become a problem as the wires being used are no longer in a twisted pair, but a single wire in Pair 2, and another single wire of Pair 3.

I second Mr. Ingraham's question of "Why this seemingly bizarre standard exists in the first place?". I know it has led to a lot of confusion around here until the standard is firmly implanted in everyones brain. I am willing to bet the logic that goes with this one is at least 20-30 years old if not more!

 

Because a human being with an IQ higher than 11 found out that the pairs of wire have "chatter" (crosstalk) between them gecuase of their locations (next to each other) in the wire and by seperating them, they could get more reliable communications...

As with most things (not all) there are reasons for such things and I applaud your question...

Dave

 

Here is paragraph from Wikipedia (http://en.wikipedia.org/wiki/RJ-45)
which explains reasons for today pin assigment in RJ-45:

The original concept (RJ-11, RJ-14, RJ-25, RJ-48, RJ-61) was that the central two pins would be one pair, the next two out the second pair, and so on until the outer pins of an eight-pin connector would be the fourth twisted pair. Additionally, signal shielding was optimised by alternating the "live" and "earthy" pins of each pair. This pattern for the eight-pin connector results in a pinout where the outermost pair are then too far apart to meet the electrical requirements of high-speed LAN protocols. Two commonly used standard pinouts known as TIA-568A and TIA-568B overcome this by using adjacent pairs on the outer four pins.

 

Pins 4 & 5 are not used for Ethernet because at the time this spec was created a large percentage of existing "structured wiring systems" in office buildings used pins 4 & 5 of an RJ45 for the analog desk phone. So this is a legacy/retrofit trade-off - it allowed adding Ethernet UTP over existing wires in large office buildings.

Now, why didn't they just use pin 1&2 and 7&8 then? Allow some other function use the split pins 3&6? Who knows, but i imagine this caused megabytes (if not gigabytes) of debate during spec development.

best regards
- LynnL, www.digi.com