atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring "RJ" designations?

Irv, are you trying to connect a plantronics CS50 to a Panasonic 76XX headset jack? We finally gave up, ordered a dozen M-M 2.5mm 6 feet long and started making our own. Whack it in 1/2, arrange the wires right, stuff 'em in a modular handset plug, squeeze firmly ,"and awaaay we go".
John

This is a very informative thread. We all use "incorrect" shorthand in most phases of life, but its often good to know (a) the formally correct usage and (b) key conflicts between formally correct and common usage.

If Ed or his deputies have any energy left, they might consider submitting some of the clarifying information to the wikipedia at https://en.wikipedia.org/.

That generally excellent site has a decent discussion of RJ related stuff, but sure doesn't get into the big disconnect between common usage of RJ45 vs formally correct usage. That would be a great extended footnote section.

See:

• https://en.wikipedia.org/wiki/Registered_jack
• https://en.wikipedia.org/wiki/RJ11
• https://en.wikipedia.org/wiki/RJ45

, Charlie B.

Please complete your profile so we know who we are talking with.

You are very correct on correct usage and terminology.

Use the search feature --- Ed has a full seminar on the RJ facts.

What most people don't understand is that the RJ designations do NOT signify a piece of hardware --- it is a wiring methodology.

KLD

Q-tip instead of cotton swab.

As an IT guy (programmer no less), I've been learning telcom and wiring in my efforts to support my various employers a bit better. To that end, I've made the effort to learn proper terminology.

I sometimes still slip and call a T568A or B connection an RJ45 but I do so a lot less than I used to.

Keep up the effort, Ed and the rest of you that care. It really benefits the rest of us that also care and are trying to shed our ignorance.

Thanks for the pat on the back. I know that I am way too passionate about this subject. It's a losing battle since even suppliers of hardware don't understand what we are talking about, so we are being forced into just going with the flow.

I forgot about Q-Tips. That's a good one!

Welcome to the forum

I have to forewarn you though, IT guys get beat up pretty badly around here! Hopefully, you have thick skin and a good sense of humor. Hope to see you around.

Hi, Thanks to all for sharing the knowledge. I too feel that precision is important. However, in the case of the misuse of the term "RJ45" as piece of plastic that has 1 to 8 wires coming out of one end and plugs into a square hole on the other end, I have to point out that, in this case, the nomenclature itself is more to blame than the lazy thought habits of the average person. I say that for one simple reason: the meaning of the letters "RJ". They stand for Registered Jack. Jack is the key word here. If they would have called it a WS45 (for Wiring Scheme), and given the piece of plastic another name, that would have been one thing, but they didn't. They called it a registered JACK 45. Well, then, while not correct, it seems perfectly commonsense and reasonable to call the piece of plastic that FITS into the RJ45 Jack an RJ45. After all the piece of plastic is the same, is it not, whether you wire to the telephone scheme or the data scheme. That's all that people mean, and with all due respect, I really don't think that it is so unreasonable of them to do so in light of that J in RJ.
That said, could someone enlighten me as to the normal standard wiring of a "RJ9" handset jack. I see a red, green, black and yellow wire. But which is which? In other words which is the speaker positive and negative and which is the mic. p. and n.? I know, I know, there is no such thing as an RJ9. It was never part of the standard so was not "Registered". Still, I am pretty sure that most phones follow the same scheme.
Does anyone know where to buy one of these: https://img.alibaba.com/photo/50545650/Telephone_Coiled_Cord_with_2_5mm_Plug.jpg ? The link just point to a picture on one of those Chinese marketing websites. I don't want to buy a thousand of them - more like one.
Thanks,

Randy:

Welcome aboard! Your input is valuable and you will find tons of information on other subjects related to telecommunications as well. I somewhat agree with you on the "RJ" vs: "J" statement you made. Maybe there should have been an "RJ" designation for the jack itself and an "RP" designation for the plug.

It's a good thing that these misnomers and assumptions don't exist with electrical wiring or we would be in trouble. Fortunately, there is a uniform standard with electrical wiring (NEMA), but not so with telephone/data wiring. It's basically a crap shoot. You guess if that 8P8C jack in the wall is wired for what you need for the phone you have.

It's just not possible for 4P4C (handset) cord jacks to have a uniform standard since all manufacturers have different ways of doing things. You can't plug a Nortel handset into the base of an AT&T Trimline and get it to work, despite the fact that the plugs on the handset cord fit the jacks. My computer keyboard uses a 4P4C (handset) cord jack. I don't think that I will get a dial tone if I plug my phone's handset into the keyboard jack.

That's just it. An 8P8C PLUG is just that, 8 positions and 8 conductors. It's not a registered jack, but the piece of plastic fits into the square hole. Agreed, but it's a plug, not a jack.

Isn't the 'keyed' RJ 45 really (or the same as ) an MMJ :shrug: Which was used on DEC equipment? I installed hundreds of these when setting up a computer network in a glass plant.

No the MMC is an offset jack.

Jeff you made me google a MMJ

DEC MMJ
MMJ=Modified Modular Jack
Invented by Digital Equipment Corporation (DEC) (now: Compaq)

(at the devices)
(at the cables)

MMJ FEMALE CONNECTOR at the devices.
MMJ MALE CONNECTOR at the cables.

Pin Name Description
1 DTR Data Terminal Ready
2 TXD+ Transmit Data +
3 TXD- Transmit Data -
4 RXD+ Receive Data +
5 RXD- Receive Data -
6 DSR Data Set Ready

Jeff