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

OK, folks. It's slow in here today and I have been thinking about this issue for a very long time. In the telecommunications business, we have our practices frequently dictated by architects and IT personnel who have absoultely NO concept of what the term "RJ" actually means.

Now I will get upon my soap box. RJ was a national standard that was created so that a customer with a piece of FCC registered equipment could contact any local telephone company, anywhere in the US, give them the RJ requirement (Registered Jack) indicated on the device and the installer would know exactly how the jack needed to be wired. It had absolutely nothing to do with the size, brand or model of the jack itself; it was how the pins were wired when connecting to the public network (PSTN).

Today, you frequently hear "RJ45" as the description of an 8-wire (4-pair) jack. RJ45 was a single telephone line appearing on pins 4 and 5 of an 8-position jack. Pins 7 and 8 were shorted with a resistor that was sized to "tell" the modem connected to the jack the level of line loss that was determined by the installer. Computer room guys back in the '70's and '80's picked up on the buzz word RJ45 because it made them sound as if they actually knew something about this subject. I mean, the plug and jack look different, Bell installed an RJ45, so the 8-pin plug must simply be and RJ45. The rest is history.

What really kills me is the variations of 4 pin, 6 position plugs and jacks. I am sure we all know the basic RJ11, where the telco line was connected to pins 3 and 4 of a standard 6 position jack. All other pins were simply not used. Then there came the RJ12, where the RJ11 was wired to accommodate a pair of 1A2 "A" leads on pins 2 and 5. RJ13 was a variation of this, RJ14 was an RJ11 with a second telco line connected to pins 2 and 5. RJ17, etc. never were big items, but still the RJ25 existed for a while. This was a three line jack; an RJ14 plus a third line on pins 1 and 6.

Then lastly, the ever-popular RJ21X. A 66 block with a female 25 pair Amphenol connector on the lower right side of the block. It was a mass demarcation point where the telelphone company provided up to 25 one-pair lines. There were other RJ variations usinig this same type of block, but the pros out there know what I am talking about.

Today, look in any datacom catalog (not one from a reputable telecom supplier) and look at their product descriptions:

2 pair modular plugs = RJ11
3 pair modular plugs = RJ12
4 pair modular plugs = RJ45

And the ever-popular:

25 pair cables, regardless of length, type or connector gender = RJ21X

Nowhere in my days have I ever seen an industry's standardization so grossly butchered by outsiders. I try to correct IT guys all the time that what they really want is a cable run and jack conforming to the EIA/TIA 568A/B wiring standard, not an RJ45. I have even gotten sadistic and given them a real RJ45 wired connection! I then refer them to the wiring pinout diagrams in any Suttle, Siemon or Leviton catalog. It shuts them up, but do you really think they listen or better yet, comprehend?

OK. I will come down from my soap box now. I thank you for your time and input!

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Ed
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How come there's always enough time to go back and fix it a second time?

I'm sure that is with any business, people call things that they are not. You yourself called a 25 pair connector an "Amphenol connector" when in fact Amphenol is a manufacturer of electrical and electronic equipment. 3M, Amp, TRW, and several other companies make the 25 pair connectors.
Another example would be inline skates, people often refer to them as rollerblades, rollerblades is a company that makes inline skates.

Brilliant observation!!!! As I reviewed my post (and even went back and edited it), I thought about that terminology since it was a name-brand. That pretty-much countered half of what I stated! I just figured that that was the most easily-recognized name for a 25 pair connector. Yikes! I am falling into the IT trap! Thanks for keeping an eye on us old-timers.

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Ed
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How come there's always enough time to go back and fix it a second time?

Ed, BRAVO! Fifteen years ago I had this same discussion with a rocket scientist at NASA at Edwards AFB. They wanted an RJ45 on the end of a "computer" wire. It seems after only 6 years of college education in the technology of computers HE STILL DIDN'T know that he didn't know.
After involving the chief of engineering the issue was resolved --- the IT types would tell us what they wanted to accomplish and we "Wire Monkies" would install the proper hardware. The brain boys always had a hard time even telling us what they wanted. They could tell you all you wanted to know about the thermal dynamics of rentry but couldn't dial a phone.

OOOPS, I'd better get off your soap box. Tanx for the chance.
KLD

That's one reason I switched from IT to phones. Too many idiots that say they need more memory when they really need a bigger hard drive, calling a 3.5" floppy disk a hard disk, putting CD's into 5.25" floppy drives, ...

Oops, someone please kick me off the soap box.

Back in the old MA Bell monopoly days it was all Universal Service Order Code (USOC). Then Carterphone said "Let My People Connect". All the USOC jacks with detailed sketches were added to the FCC regs. Today they are gone from the FCC regs and administered by a privet telco assocation.

Wow. Awesome post! It's so hard to get this info in the field, because I get the feeling that no one around here really knows what they're talking about.

Here's a question for you. When I'm shopping modular plugs, they're labeled "6 position RJ-11". Since there's obviously no wire yet connected to the plug, is it acceptable terminology to refer to them as RJ-11, or is there a more suitable name?

Well, as you can tell by my original post, I tend to put way too much thought into a dying part of our industry's orginial standard.

Just for the record, there are generally only two types of modular plugs and jacks. The six position, commonly referred to as RJ11, and the eight position, commonly referred to as RJ45.

The six position can be wired with two wires on pins 3/4, therefore an RJ11. This same plug can be wired with four wires on pins 3/4 and 2/5, thus becoming an RJ12, 13 or 14. Finally, this same plug can be wired with three pairs on pins 3/4, 2/5 and 1/6 to become an RJ25 wiring configruation. So, as you can see, it's not the actual plug that determines the "RJ" number, it's how that same plug is wired for the different configurations.
So, to answer your original question, yes, it's OK to refer to a 6 position plug or jack as an RJ11 because it's how you wire it that determines the true RJ configuration. Play it safe and buy 6-position plugs and jacks and you can't go wrong.

This program was originally developed as "USOC" (Universal Service Order Code) by the FCC so that all telephone companies in the United States were on the same page when a customer called requiring a jack installation. Whether it was GTE or Michigan Bell, an RJ11, RJ14, etc. was the same to all operating companies.

By all means, the most common RJ configurations you will see today is the RJ11 (one line on a 6-position jack) and RJ14 (two lines on a 6-position jack).

You won't see an RJ45 being installed anymore since it dealt largely with telephone company-owned modems or very high end ones provided by the customer. It was an 8-position jack wired with a single phone line wired to pins 4/5. A resistor was connected across pins 7/8 by the telephone company installer who measured the line's loss and this resistor told the modem to adjust it's transmit/receive levels accordingly.

Today's RJ45 is just a misnomer for an 8-position jack/plug used for data network wiring. Today, usually all 8 positions are wired with four pairs of wire, regardless of category 5,5e or 6. It's a far cry from the original RJ45, but since the jack remains pretty much the same with regard to physical shape and appearance, it got it's name that way.

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Ed
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How come there's always enough time to go back and fix it a second time?

[This message has been edited by ev607797 (edited May 02, 2005).]

[This message has been edited by ev607797 (edited May 02, 2005).]

Nice. I will from this point onward be referring to my network jacks by 568A or 568B

Wasn't the USOC code for a mod plug "266"?
That was for the line cords --- but ---fuzzy memory ---- 264 for the handset cord?

But I don't smoke cigars. GS.

No, USOC codes were prefaced with "RJ", even adapters had RJ codes, such as RJ2AX, which I believe was a two-way duplex splitter.

The numbers you indicated sound like Suttle part numbers, but I am not positive.

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Ed
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How come there's always enough time to go back and fix it a second time?

Yeah, it probably was a Suttle number as they produced the majority of connectors and blocks for the Bell System. (Or the other way around?) 425 blocks were an item. A 4625 was a modular block. When I ordered items from stock at SWB we had to use the part identifier.

Does anyone remember the old phone connector that had four long pins about one inch appart in a box formation?

"4-prong plug and jack"?

Remember them? We still have them in stock! Up until about a year ago, we were still using them but not for phones. We had a retail customer that used them for their cash register network connection.

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Ed
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How come there's always enough time to go back and fix it a second time?

So where does a 4P4C come into history?
4P4C is commonly used for termination of coiled handsets.

I thought RJ9 was a handset cord termination?
Anyway what do you call a "Band-Aid"? Product brand recognition will never change because of memory association. Its still fun to give a customer(IdioT) exactly what they ask for when you know its wrong and go back and charge them twice to change it and educate them. It really makes you feel like you enlightened them.

I don't remember an RJ designation for handset cords, but it makes sense that there would be a uniform standard for them as well. Still, I know that the same cord and jacks work with thousands of different handsets (ie: Trimline, keysets, disposable phones, etc.) and I would think that electrically, the wiring is never the same. True, the transmit is on one pair and the receive is on the other, but what about with say for example, Trimline phones? It's just tip and ring on the handset cord for the newer models.

Man, you hit it right on the head when you mentioned "Band Aid". You'd never say "I just cut my finger, get me an adhesive strip"! That's like Chlorox, Coke, or Jell-o.

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Ed
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How come there's always enough time to go back and fix it a second time?

KUDOS EV607797!!!

Thank you! Thank you!! Thank you!!!

Glad to know I'm not the only one who is regularly irritated by this uneducated simplification of terminology. I can't tell you how many times I've had customers ask for "RJ45" data jacks.

Therein starts the whole education process. 8P8C, 6P6C, 6P4C, 6P2C and 4P4C describes the connector and plug whereas USOC RJ##x or EIA/TIA T568A, T568B, etc., etc. is the wiring topology ("scheme"). The few times a customer was adament about using RJ45's, they soon started second guessing themselves when I told them we required a signed, written specification and that rewiring when it doesn't work would COST $$$!

By the way, I believe a handset 4P4C may be a USOC RJ22.

Thanks "ev", for your post!

To: BRADYLAND & DTU

Re: Clarification of modular jack and plug "hardware"

8P8C = 8 Position 8 Conductor
(Specify Category 3 or 5)

6P6C = 6 Position 6 Conductor

6P4C = 6 Position 4 Conductor

4P4C = 4 Position 4 Conductor

The word "Position" refers to the jack size (width) and number of slots in the plug. "Conductor" is self explanatory, referring to how many copper "terminals" are included in the connecting hardware.

In today's world, Category 5 8P8C's are used for data connections and wired either as EIA/TIA T568A or T568B. Cateory 3 8P8C's can be wired with 8 conductors and used for the rare occurance of 4-line KSU-less feature-phones. If I am remembering correctly (and it is 01:38 in the morning so who know's what I'm writing here) this is a USOC RJ48. There are also some older 8P8C wiring topologies ("schemes").

6P6C and 6P4C hardware are generally used for voice connections, wired with either 6 (USOC RJ25), 4 (USOC RJ14) or 2 (USOC RJ11) conductors based on the application.

The 4P4C is generally used for handset connections as mentioned in previous posts. However, in the last few years I have seen one manufacturer using the 4P4C's (with a flat not coiled cord) for a system programming interface cable.

Hope that helps!

Doctor:

You are close! The four-line phone configuration (4 lines on a single 8P8C) is RJ61X.

The RJ48 is a demarcation for a T1 circuit and has shorting bars to keep the transmit and receive pairs shorted when nothing is plugged in so as to keep the circuit "alive". These create a loopback condition.

Thanks for the kudos!

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Ed
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How come there's always enough time to go back and fix it a second time?

Yeah thanks was already fully aware of what the P and C stood for. I am a qualified installer was just wondering if they were common in other parts of the world.
What sort of system would use a 4P4C interface cable for programming, a Keysytem? Surely not a PABX.

[This message has been edited by dtu (edited May 31, 2005).]

Same thing with T568A and T568B. The "T" is IMPORTANT! 568B is a written EIA/TIA standard.

OK, Does anyone know what a
10p10 plug and jack is called?
And where can I get one?

REALLY, it's for real.


Corwyn

I know exactly what you are talking about; I have seen them used a lot with cash registers and sometimes with computers. I think your best bet would be from one of those computer hardware catalogs we all get in the mail.

PI Manufacturing in Walnut, CA that has that kind of stuff. Their number is 909-598-3718. It is on page 27 of their spring catalog.

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Ed
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How come there's always enough time to go back and fix it a second time?

I have used the 5 pair jacks your talking about on some Fordstar installs. Jacks and cable were always provided.

This is making my eyes hurt -- let me get a
Kleenex and go to the Frigidaire for a Coke.
If anybody wants, I'll Xerox them a copy of this.

Speaking (or in this case, writing) of mis-designated connectors.. May I introduce the D-sub connector.

This connector is frequently (and incorrectly) called a DB connector.

The correct designations are D[A/B/C/D/E][# pins], where A-E designate the shell size.

Standard sizes include the DA-15, DB-25, DC-37, DD-50, and DE-9, as well as some more specialized versions such as the DB-13W3 (13 pins, 3 coax. used for Sun monitors)

There are many variations to choose from, and the final reference is the ITT/Cannon catalog. (I have a hardcopy from 1970, which agrees with the PDF currently available on the website.)

Thanks tantivy. Some times they only sorce of imformation I can find is catalogs. Every little bit helps.

Tantivy:

You have just enlightened me on a misnomer I have been using for years! I guess the term "DB-9" makes your skin crawl, too!

I never knew that, but now that you have enlightened me, I will sound that much more intelligent when conversing with 24 year old computer "engineers". I am guilty of using the wrong terminology forever when it comes to D-Sub connectors. I shudder to think of the number of people who heard me using the incorrect termiology and just "kept quiet" and talked about me later in private in a chat around the network server. For all I know, they may have had a laugh about me on their own bulletin board/chat room.

I am telling you, these guys have not only developed their own terminology for our industry and theirs, they are forcing it upon us. It's like an X-Files episode.

Guilty as charged here. Line me up against the server room wall and shoot me with RJ12's.


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Ed
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How come there's always enough time to go back and fix it a second time?

[This message has been edited by ev607797 (edited August 29, 2005).]

I was looking at a list of RJ designations the other day, and I realised that RJ-45 actually calls for a KEYED 8p8c (as do most of the other RJ-4x's),
as opposed to the UNKEYED 8p8c used for ethernet, RJ31, 37, 61, etc..

So the RJ-45 == Ethernet is even more incorrect than we thought.. it's not only the wrong term for the connector, it's not even the right connector..

I knew I could find someone to be my deputy here on this subject!

I just ran into this thread, when I started in this industry I was being taught by both computer techs and older telecom guys. I got pretty confused trying to sort out what each one was talking about, same name/numbers but different uses. I use Newton's Telecom Dictionary now to try to figure out what is right.

Perhaps there is hope, though. One of our guys is getting ready to take the practical portion of the low-voltage electrician licensing exam for CT (or was it Rhode Island?) and they sent a list of supplies he'll need to bring to the exam.

That list includes a bag of "8P8C Modular Plugs". Not a mention of RJ-45 anywhere!

I'm currently taking a couple of networking courses at the local community college, one of the courses is the Cisco CCNA-1 course.
Since I already know most of this stuff, and am simply taking the courses for the certification, I'm having a grand time correcting errors in the texts..

Both of the texts refer to 8p8c modular plugs as "RJ-45", and the cisco text refers to 9 pin D-sub connectors as "DB-9".

What is this world coming to, when the certification courses can't even get the terminology correct?

I am impressed with the following I have gained in my quest, albeit a seemingly losing battle.

I guess RJ45 versus 8P8C has become:

"Chlorox" to bleach
"Coke" to cola soda
"Ty-Rap" to cable tie
"Sheetrock" to gypsum board (yes, it's a brand name)
"Vaseline" to petroleum jelly
"Crisco" to shortening
"Xerox" to copier
"Velcro" to hook & loop fastener
"FedEx" to overnight letter/shipping
"Reynolds Wrap" to aluminum foil

I could go on forever.

You get my drift here. The popular name with the general public for an item prevails and it's never going to change!

Yea Ed!
Pass me an orange coke would ya! :rofl:

I have absolutely no useful technical knowledge to add here, just wanted to say thanks for this amazing thread. The amount of wisdom in this one thread is incredible. All of you deserve HUGE kudos for this and again, THANK YOU!!!!!!
John
P.S. As far as I'm concerned you guys should never get off your so-called soap boxes

Thanks, TRONIC1, but I am finding that I am wasting my time on this subject. I appreciate your support and positive comments, though. Even distributors and manufacturers have drifted toward "whatever terminology the general public uses". They don't want to risk losing sales to newcomers who have been trained using the improper terminolgy.

La-Z-Boy from rocker-recliner

what he said doubled.

I don't know if they have an RJ designation but I have used them and have referred to them as a 10 position modular plug.

https://www.accesscomms.com.au/Products/P2170.htm

I had to use them on digi-port scsi modem adaptor. 10 lines in.

I also believe they are generally used on cellular mobile transceivers and small multi-line telephone systems.

OK, folks. I was hoping to not drag this topic back out, and hence another of my sermons. I can't resist, so here's a short one:

RJ means Registered Jack. RJ is a uniform wiring standard for any telephone company in the United States to follow; it's a wiring pattern, not a piece of hardware. This standard was developed by the FCC in the late 1960's/early 1970's so that customers could have the same jack installed anywhere in the country without conflict. The RJ number was understood by ANY telephone company nationwide. All phone equipment had the "RJ" requirement included on a label attached to it. It seemed to be a relatively foolproof strategy until CAT5 cabling for data came along. Then it went to hell in a handbasket, literally.

I can name at least ten RJ configurations that can be wired on the same 8-wire jack. Yes, an 8 position jack can be wired as an RJ11. Imagine that!

There was never a 10 position RJ in North America, period.

10 position plugs/connectors were designed for proprietary use with computers and cell phones. There was never a 10 conductor connector used for voice equipment connected to the public network.

To reiterate: RJ is a wiring diagram, A.K.A: schematic that can be applied to many different pieces of hardware.

I think it's reached the point that there's no solution here. I give up....this issue has become a lost cause....the computer geeks win.

Just let me up, I've had enough in trying to correct the world's error on this subject and I have bigger fish to fry. Hal, am I wasting my fingertips here?

Sorry Ed I think you are :rolleyes:

But on a better note its always good reading when you post. :toast:

Actually Ed, I'll disagree with you..

The RJ designation is two parts, one is the connector type, the other is the wiring pattern.
Combined, they create an RJ designation.

It is certainly possible to deliver a single POTS line on a 8p8c modular connector, but it dosen't have an RJ11 designation when delivered in this manner. It would probably be a RJ61 instead.

I guess you might be correct, a four-line RJ61 can technically be ordered with only one line wired. I don't know how anyone could convey this to a telephone company business office person, but that's another issue. Maybe the customer simply has a four-line set but only need one line connected initially.

On the same note, though, a 6P4C jack can be wired with one line (RJ11) or two lines (RJ14). If you were to call the phone company and ask for an RJ14 with only one line on it, wouldn't that create information overload for them? I mean, let's face it, it's the same thing as the single-line RJ61X when you think about it.

I'll give you the hardware part though!

Ed,

In response to your 01/03/2006 & 01/12/2006 follow up posts (and just 'cause I couldn't believe this thread was stillllllllll alive):

I feel your pain!

Everytime a prospective prewiring customer asks for "RJ45 Jacks" for their (usually EIA/TIA T568B, occassionally T568A) data wiring I have to step up onto the Tide Box and educate them... again and again and again and again!

I really wish the manufacturers of NICs, hubs, routers, switches, etc. would stop listing "RJ45 Connectors" on their boxes.

Oh well... Meanwhile, I think I need some "Q-Tips" or "Scotch Tape" to clean up the toner overflow in my "XEROX Copier".

You forot

Car > Automobile > Horseless carriage

Hand me that "sawzall" and we'll fix this once and for all.

Scott.

Rexel carries a box of 100. Box is labeled RJ45 but it is full of 8 pin mods. And the same goes on everywhere. Nowdays when I'm getting instructions from the know-it-alls I hardly even listen. My ex-wife said I did that with her too.

Isnt brand recognition wonderful?
Im 40 now and learned telephony on an AT&T Dimension 2000 but shortly before we upgraded I had an MDM-100 which was a Stromberg Carlson XY switch system.

I know some of you are saying what the heck is that. Just forget it...You'll be bald like me before your time.

I have always been a stickler for correct designations as Ed is.
Just like Ed, I tend to use the "new" names just so others know what I am talking about as well as out of habit.

I do call them AMP tails, and DB-9.

In 1993 installing the Georgia Lottery no one could ever put the proper termination spec on paper for the job. Someone knew because it was spec'ed in the project.
I identified it as TP-PMD.

Nowadays, Proper designation of wiring is considered courteous instead of mandatory.

Think if we used the "Cane" on a few people for getting it wrong we could turn the industry around?

I thought it was an AMPHENOL TAIL?

what do I know...I just the village idiot.

Ed, Did that worthless loser ever pay you the money he owed you for them phone jacks? Let me know if he didnt and I will drive to his town and pound on his noggin for a few minutes giving him whatever message you want me to deliver.
No charge.

Actually he was quite a gentleman and took care of things promptly. A lot more professionally than many people are.

I agree about some of those terminologies and brands that just can't go away. We wouldn't know what to call them, except those "things". I guess male or female tail, when used in the proper context, is about the best thing to call one. Still can't drop Band-Aid or Chlorox though!

Now that caning idea might just be a possible solution. Hmmm. We should think about that the next time the IT "manager" tells us he wants an RJ45 installed. One quick whack across the back will set him straight for good. Good thinking!

I admit it! I'm one of those non-tecchies who have been using the "RJxx" terminology wrong all this time. I stumbled onto this forum via a Google search because I was looking for a cable with a 4p4c (I used to think it was called an "RJ9") at one end and a 2.5mm headset jack at the other.

...and I'm still trying to source the sucker! Can anyone suggest a vendor - preferably one in Canada as I'm up in the "Great White North".

Irv
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Can I get a recap on RJ45-X AND RJ45-S. What are some of the readings that I can readily detect that can alert me as a technician, sitting at an office computer terminal, that should alert me that it is not the customer's problem or the lec's problem but AT&T's problem.

Thank you,

Elsevier Lippincott

https://img.alibaba.com/photo/50545650/Telephone_Coiled_Cord_with_2_5mm_Plug.jpg

I know this is old..but on another one of my forums someone asked about mod plugs...so I gave them the info. They didnt know if cat5 and cat6 plugs were the same size... :shrug:

Jeff ---

Tell'em the CAT 5 is a right hand connector and the CAT 6 is a left hand connector. :rofl:

Otherwise they are a 8p8c connector,m size-wise. :toothy:

KLD

what's funny is that i give a definitive answer to these questions on other boards...and nobody asks another question...they must think I know something..
Jeff

they must think I know something..

More likely they couldn't figure out what you were telling them.

-Hal

yeah, that too...

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

That's it, Jeff in PA (there are two Jeffs in this thread). Yes, these were six-conductor modular plugs/jacks where the plug's finger clip was at the right side instead of the center of the plug/jack. It was impossible to plug these cords into an NON-DEC jack or vice-versa.

I only did one installation that involved this system. It was very, very short-lived.

I am not sure, but I think the S mean Shielded and the X means it has a shorting bar...

so an RJ48S would use STP cable (shielded twisted pair) instead of UTP (un-shielded TP) cable.

and an RJ48X would have a shorting bar so that when the plug is removed the shorting bars creat a loop-back condition (commonly used in T1 pigtails).

an RJ31X is used by alarm systems so that when the alarm system is unplugged from the jack, the line still has dial tone.

---

but don't quote me on any of this, It's almost four in the morning and I'm on NyQuil (Vicks Nite Time cold actually, but I couldn't resist )

Ed

I would have uploaded a graphic of the MMJ but either can't or don't know how. :scratch:

Anyhow, since I'm not a true 'phoneguy' I always refered to the MMJ as an offset type connector.

Jeff (in PA)

The MMJ's came and went so quickly that I don't know if they picked up too many nicknames.

I only saw them in use once. At a BJ's Wholesale Club I noticed them on the back of the computer terminals.

ed. what is an RJ25?