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568A is a recoginized standard , not quite the same as making ones own code up . a dozen 568A and a dozen 568b will work the same to the end user . only issue would be someone re-terminating a connector b stanard to a aApatch panel (or vice versa )

This is really a cable topic so I'll butt in.
The Bicsi people (read overseas telecom manufacturers)want 568A (computer wiring) so the wiring comes out standard for the two pair sets. Prior to this, the WECO 568B was used for Merlins, etc., as WECO/AT&T/Bell System found "B" had better data transmission qualities. I know this shocks a lot of CGs but telecom was doing what is now considered "data" long before the internet/networked information sharing ever was even thought of. It was called telephones, inter-office, switch to switch signalling or for the general public, long distance direct dial.

Class dismissed, Mr. Baudit.

KLD

Ironically, I am pretty sure that AT&T accidentally created the 568A jack wiring standard, although they didn't call it that. They had their own terminology, if any was ever given. At that time in the early 1970's, the general public wasn't really involved in the phone business; the phone company took care of that. If a customer wanted a plug and jack, all they did was pay an additional monthly fee as opposed to a hard-wired phone.

You see, the early modular connectors were four-conductor line cords for basic phones, nothing fancy. The standard was developed to reduce labor costs in cord failure replacements, not to create BICSI and TIA/EIA.

Problem is, it was too simple: The line was on the center two pins, and anything else, like A leads or dial light power appeared on the outer pins. That's all that it was meant to be. Then came a need for more pairs and common sense said just keep the pairs working outward from the center, hence the accidental birth of the 568A (and later "RJ") wiring pattern.

This modular jack concept worked well with the Bell companies (and most independent telcos followed), so when AT&T developed electronic key sets or other applications requiring more than four conductors, the 6- and 8-pin modular cords and jacks were introduced. The problem was that the earlier 4-conductor or even the 6-conductor plugs could fit the 8-conductor jacks.

That's not a problem by today's standards, but then, since many four-conductor telephone line cords were connected to sets with A leads that effectively short out the W/O pair when the phone is off-hook, there was a risk of a customer plugging into the wrong jack and shorting out whatever was on the second pair. Back in those days, a short on a data pair could fry a card. A short on a power pair could cause a fire. They had to make sure that customer error on that second pair in a business environment wouldn't create a liability.

I think that they intentionally vacated the "W/O" pair under the original "568A-type" design (pins 3 and 6) because their power or data may have been on this pair. They moved the W/O pair to a place where a 4-conductor cord couldn't reach, pins 1 & 2 of an 8/C jack. While they were at it, they created another unreachable pair on pins 7/8. Goof-proof.

Hence, the birth of 568B, or frequently referred to as "258A or WECO". This is a misnomer since it's just the part number or company's name acronym for an adapter. The 258A adapter derived six "568B" jacks from a 25 pair cable. They just became so commonplace that people adapted that part number as the name for the wiring pattern that AT&T adopted as their standard.

TIA/EIA actually came up with the nomenclature for the wiring of jacks that AT&T and it's Bell companies had been doing for years. Kind of like the chicken watching the fox coop. Get it? Some newcomers establishing "standards" that had already been "established" for years!

Any of you guys out there familiar with Dimension or Horizon systems might finally understand why the W/G pair wasn't used under "WECO" or "568B". That was that controversial "second pair". I am probably boring you guys with this post.

There's the answer to the question as to why network cables use pins 1,2,3 and 6. This keeps the data hardware away from the potentially hot center pair.

OK, this ends yet another of my sermons on jacks and I hope I have not worn this subject out. I feel like Uncle Remus and you are all sitting on my knee as I read you a story. Feel free to comment, good or bad.

Could I get that on cd Ed, so I can leson to it as I drive down the road?

:toothy: :toothy:

Thanks for the lesson Ed, I was just getting into telecom about that time and aways wondered why they did it that way.

EV60797
My memory is not what it used to be. But it seems to me the AT&T 8 pin wiring problems came out when they introduced the Horizon phones . 8 pins non USOC . I think .

I can't say for sure about what happened and when. I do know that the Dimension PBX came out first and it used MET (Modular Electronic Telephone) sets, just like the Horizon system. The ECTS cabinets had to be provided to power the phones on the Dimension though. The first exposure I had to the Dimension was in 1976, but I was still in diapers at the time.

Horizon didn't really hit the streets until about 1982 around here. Regardless, their 8-conductor jack configuration had been around for quite a while and wiring was identical for Horizon or Dimension.

USOC was something that the FCC took on by themselves. They just created a standard that "just happened to be similar to" what AT&T and Western Electric had been working on for years. I suppose with AT&T being so big, the FCC respected their experience and research enough to trust their findings and start their regulations for the USOC program. Maybe the FCC worked with them in the development. I don't have a definitive answer on that one.

I have kept on top of a lot of this stuff through research, experience in the business, and some outright speculation. That being said, most of what I have stated here is my interpretation of things and it's VERY possible that I may be wrong.

I did a very poor job of making my point . As it seemed to me that with the advent of the Horizon sytems 8pin jacks . That pins 3456 changed forever . Was it a Bell 258A ,568A, 568B, RJ48c ,RJ48S, RJ48X , Token Ring 8x4 or 8 pin USOC or an MMJ configuration . Sorry EV I do not have the Hemingway gift that you have .

OBTW:

The point you just made is a perfect answer. The simple 8-conductor jack started off on the wrong track and really never reached any standard. Even to this day, it has no fewer than twenty "names". Nobody is actually right anymore when it comes to these jacks.

I think that when dial light power (6.8 VAC) ended up on the second pair in residences, they had to take a serious second look at jack wiring. Someone could steal a 2500 set from work and plug it in at home. The phone is equipped with A leads and after a 30-minute phone call, the dial light transformer burned a hole in the wall.

Again, most of my knowledge on this stuff is just from exposure to it. Honestly, you had me checking my Horizon manuals at first because I wasn't sure!

There's nothing wrong with double-checking ourselves and Lord knows I need to do it.

Thanks EV607797
Don't know about burning holes in walls . I do remember princess phones with lighted dials when the hansdet was lifted . I still have a dtmf one. It iluminated the room .