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Ethernet Cabling Standards, T-568A or T-568B?

Whats the difference between the A and B versions of the Ethernet Cabling standard and which one should I use?


The short answer is “USE B” its the newer standard.

However I did say that was the short answer. As in most things related to technology, there is a much longer answer…Smile  So sit back, relax, and get an education!

If you are making a straight through Ethernet cable (often referred to simply as a “patch cable”) to connect your computer to your wall Ethernet jack, then wiring your RJ-45 Jack per the “B” version of the Ethernet wiring standard will do just fine. Just for reference, the B version of the standard is diagrammed below:

TIA/EIA 568-B (T568B)Ethernet Cabling Standard T568B

Pin 1 – white / orange stripe
Pin 2 – orange
Pin 3 – white / green stripe
Pin 4 – blue
Pin 5 – white / blue stripe
Pin 6 – green
Pin 7 – white / brown stripe
Pin 8 – brown


So Why is there an ‘A’ version of the Ethernet Wiring Standard at all?

Well time for a little history now or this won’t really make sense.  You see in 1985, the Computer Communications Industry Association requested that the Electronic Industries Alliance (EIA) develop standards for the cable used in telecom applications.

The first revision of this standard was released in 1991, but was later updated again in 1995 due to the massive development of networking technology and new faster high-speed ethernet cables and networking components. This was also replaced later with the current TIA/EIA 568-B standard.

Although many aspects of networking structure and performance are addressed in these standards, the most visible and often misunderstood component is the definition of the wiring assignments in the RJ45 plug. A colored wire must be placed in a specific pin location in the plug in order for the cable to meet the standard. It is these wiring assignments that differ between the T568A and T568B standard.

The pins on the RJ45 plug are numbered 1 to 8. If you are holding a CAT 5 patch cable in your hand, as if inserting into a jack, with the contacts facing in the up position, pin 1 will be on the far left. Pin 8 will be the pin on the far right. This is the orientation you should use when trying to figure out the wiring assignments in the RJ45 plug which can give even the most experienced technicians, an Excedrin moment.

So What is the ‘A’ Version of the standard used for at all anymore?

Well golly, that’s a logical question isn’t it?  The fact is that in almost any patch cable type application, either version of the standard will work just fine because the wires are connected to the same pins on each end, only the colors change.  But the A version of the standard still comes into play when you make something called a “crossover cable”.  This is mostly used by technical folks like myself for testing things and the end consumer will rarely if ever have a need for this.

But if you ever did, simply wire one end of the Crossover Cable to the ‘A’ standard and the other end to the ‘B’ standard and Voila!  You have a bonafide Ethernet Crossover Cable.  And so for the sake of completeness, I include the T-568A standard wiring below.

TIA/EIA 568-A (T568A)Ehternet Cabling Standard T-568A

Pin 1 – white / green stripe
Pin 2 – green
Pin 3 – white / orange stripe
Pin 4 – blue
Pin 5 – white / blue stripe
pin 6 – orange
pin 7 – white / brown stripe
pin 8 – brown

If you’ve made it this far, I applaud you!  Maybe you’ll go a little further and realize that rather than breaking your back and straining your eyeballs to do all this technical work, you can just hire us to do it. We’re fast, friendly, and our prices won’t put you in the poor house.

Call us at (973) 335-4000 and we can give you an estimate right over the phone.

All the best,

John Haldy,

President HALCOM LLC

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