atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring 568A vs. 568B

Chad, Everyone here has a point. As long as both ends are the same, it does not matter. However, I would look at any existing terminations, and the back of the patch panel (As these also come 568A or 568B). Also, a big consideration would be Customer preference. Since they are the end user, what do they prefer?

As far as standard, there realy isn't one, but the most popular is 568B.

Everything I have come across in Houston, TX. is 568B. We still service old 2-pair phone systems & when we move one to a new site that has been cabled by a "cabling" outfit, they pull cat-5 everywhere & terminate 568B.

Many a late night trying to use old cabling because the boss was to cheap to survey the site & I have had a mix of 568A & B jacks!

"Old 2-pair pone systems".

That's kind of funny. Seems as if 25 pair or more was perfectly acceptable for 40 years, then 4 pair pretty much happened overnight.

3-pair systems lasted a little while, but 2-pair systems still exist today, brand-new, out of the box!

568A, 568B, 568C whatever it takes!

I wanted to throw a comment in here on this too ( a comment besides the Mr. Mom 220, 221 reference.) Most everybody on here will know this but just in case someone comes across this post and doesn't know. No one has specifically spelled this out yet.

If you get in a bind on a service call and have to replace a jack. After looking at the patch panel you discover it's A and you only have B jacks on you truck, or vice versa. Just swap the orange and green pairs at the jack. I've had to do that more than once in my past technician life. I also always tried to scribble some kind of note inside the box or faceplate as to what I did. So the next tech behind me wouldn't get too bumfoozled by my creativity.

The standards state quite clearly:

ANSI/TIA/EIA-568-B.1 Section 6.2.1
"Pin/pair assignments shall be as shown in figure 61 (T568A) or, optionally, per figure 62 (T568B) if necessary to accommodate certain 8-pin cabling systems. The colors shown are associated with the horizontal distribution cable.

NOTE - US Federal Government publication NCS, FTR 1090-1997 recognizes designation T568A only."

T568B was added as an alternative to support then then installed AT&T base of 258A back in 1990.

If you ever do any residential cabling, then you need to look at ANSI/TIA/EIA-570-B which states in Section 5.2.3.1: "At outlet locations, UTP cable shall be terminated on an eight-position T568A telecommunications outlet/connector."

Now from a practical point. In nearly all RJ45 connector designs, the worst performing pair for Return Loss is 3,6. There are exceptions. Now find out which is the worst performing pair for Return Loss on the cable.

If the cable's worst pair for Return Loss is the green pair, wiring to T568B is not the best choice for optimum test results. You just put the worst performing cable pair with the worst performing connector pair.

However, if the cable's worst pair for Return Loss is the orange pair, wiring to T568A is not the best choice for optimum test results.

If the cable has equally distributed Return Loss performance across all pairs, then you will not see a performance difference.

Welcome to the forum Adrian

Thanks for the input. Feel free to help out and enjoy this great forum

Adrian, to the board.


While the 568A vs. 568B has been going on for years, a group of people started a group in Massachusetts back in the 80's that would have cured the whole thing --- and your company bought them out in the mid to late 90's. They believed that copper should be outlawed and do nothing but fiber optics to the desktop. They manufactured fiber equipment.

Have a good time, kick around the forums, and, sometime when we have nothing to do, we'll discuss the parameters on the "A vs B" per manufacturer.

KLD

Thanks, ALL, for the info, btw CCSGINC, I _am_ the end user!

Chad B., you will undoubtedly be one of the better end users for we the installers of cabling. Why? Because you were un-afraid to ask, and will obviously put this information to good use.

Set a standard that works for you, spec it when you have work done, find a comfortable fit with a vendor, and good luck to you.

KLD

Regarding the comment about pair length difference in a 4-pair cat 5. Everybody sit down and consider this: The 25th pair of a cat5 25pr feeder is twice the length of the cable if you split it out and unwind the twist. BUT IT STILL WORKS!
This is what they called Fantasy Land in the USAF when they started talking about wave guides. What is really happening is the signal is transmitted like RF and sorta floats along the twist in a straight line.
I'm sorry, I should have apologized in advance for the headaches!
John C.
ARE WE HAVING FUN YET?