Could anyone please inform me,
as to how a public telephone system,
actually works, I have been brought up on
the old system, with 3wire equipment,
but now we have Category 5 Enhanced,
cabling, for normal phone circuits.
Could anyone (Paul), please help.
I have heard a lot about tip and ring,
but I do not know what these terms mean.
HELP, Please.

Re. Tip and Ring:

OK...the easiest way to visualise it is this way:

Take a MONO (two conductor) earphone plug (the same kind used by telephone co. plug boards to switch between lines). The tip would be the physical tip of the plug. Next is a little plastic insulating ring. Then you have the ring (which is the second conductor) - actually a sleeve behind the insulator. So the thing looks like this:

Plug Shell=>Ring=>Insulator=>Tip

If you have a stereo (three conductor) phone plug, you wind up with tip-ring-sleeve:

Plug Shell=>Sleeve->Insulator->Ring->Insulator->Tip

Hope this helps. If anyone can post a picture of the above mentioned plugs that would definitely show things much more clearly.

--
Sven

As Sven has said, the tip & ring terms come from the 1/4-inch plugs and jacks used on manual switchboards.

Here's the standard telephone plug:
[img]http://www.members.aol.com/PBC1966EOS/ecn80.bmp[/img]

Note that the stereo audio version (as found on earphones for example)is a slightly different shape:
[img]http://www.members.aol.com/PBC1966EOS/ecn79.bmp[/img]

How does the system operate?

If you're looking at basic operating voltages on the line, in very general terms, the central office battery is a nominal 48V (U.S.) or 50V (Britain). The battery banks have the positive pole grounded.

Power is applied to the line through two coils, one on each side, so as to keep the circuit balanced. Usually, the tip side of the circuit connects to ground, and the ring side connects to -48 or -50V, each through its coil. The resistance of the coils plus that of the line to your house is why you read 48-50V on an idle (on-hook) line, but a much lower voltage when off-hook, typically 10-15V if close to the exchange, as little as 5V or less on a very long line.

I said that the polarity is as above usually. On just about all modern exchanges, it is always that way round, but on some older systems the polarity would reverse to indicate answer supervision (i.e. when the called party answered). Most telephone equipment will work fine whichever way it is connected, although some of the early TouchTone phones wouldn't work on reversed polarity. (Correct connection was also very important on party lines.)

Ringing voltage applied to the line is generally 90 to 120V AC at a frequency of about 20Hz, superimposed on the 48 or 50V DC.

Back to the plugs. The tip and ring parts of the plug would connect the two sides of the circuit through the operators board. The sleeve connection was not extended to the subscriber's line, but was just used within the exchange to control the seizure and release of switching equipment. In other words, the subscriber's loop is just two wires.

In America, the terms tip and ring are still the accepted designations for the two sides of the line. With automatic switching equipment, British GPO terminology favored calling them the "A wire" and the "B wire" respectively.



[This message has been edited by pauluk (edited 09-06-2002).]

In Austria these wires are called A and B, white and brown in phone cords, yellow and brown for fixed wiring. Typical cable for fixed work is 3 (on newer work 4) conductor solid SVT-like with the colors yellow, brown, green and blue, the latter sometimes used for 2nd line. Blue exists only on newer cables, green was used (I believe) for extra bell.
One I have seen requires a 200V DC supply. Wonder where to get that in a country with 220V AC supply?
Old color code for fixed wiring (maybe 1960ies and earlier) was white for a, red for b and green. The letters for the lines must be pretty old here, as I found them on a phone from 1949. They're used in Germany as well.

The A and B designations in the British system also go back many, many years, at least to the 1930s. I've mentioned the color code in another thread, but the flexible cords on GPO phones also used white & red for A & B respectively (and still do), although fixed wiring colors are different.

The subscriber loop to the exchange is only two wires, but many systems developed with a third line internal to the house for interconnecting the bells.

In the old U.K. hardwired system, all extension phones had their internal bell capacitors disconnected and the blue wire in the cord was used to link them all back to the capacitor in the main instrument. This insured that the bells were shunted when any phone was taken off-hook so as to prevent the bells on the other phones tapping, or tinkling during dialing.

The green wire in GPO phones was most often the bell return, and on a one-phone installation would just be linked to the white in the wall junction box. It was done that way so that an extension bell could be connected in series by just opening the box.
Some phones were fitted with only a 3-wire cord (red, white, green).

One of the old "extension plans" used a 5-way plug and jack and extra wires so that when a phone was plugged in its bell would be added in series with all the others. The jacks had shorting contacts to maintain the bell circuit through unused jacks.

The new-style wiring with modular-type jacks is wired somewhat differently as the bell capacitor is located in the jack unit rather than in the phone itself.

Many other places used similar arrangements for bell wiring, e.g. in America the yellow wire was often the bell return and would be connected to the green (or maybe to a local ground on party lines). I have an old 1962 Western Electric 500 set which has only a 3-wire cord (red, green, yellow).

Thanks Sven and Paul,
I think, Paul,that our telephone system
in New Zealand here was designed by
English Telecommunications people,who had moved over here, to get out of Britain.
The systems that you have explained, sound
very familiar.
Just a short note on the Party Line set-up,
in Temuka, a small town where I grew up,
we never had an automatic exchange until
1987, until then, we were all on party
lines, we didn't even have a Manual
exchange, with respect to the 746 GPO
telephones that we had, they did not even
need the dials that they came out with,
as we could not use them anyway.

I assume that 746 phones were shipped with a New Zealand style dial. A side note: When STD was introduced in the U.K., London was allocated the code 01 as being the shortest to dial. I always wondered why on earth the NZ phone system allocated 09 to Auckland until I learned about the "backward" dials!

Do you know how the party line system was se up for automatic operation in New Zealand? Did you use earth testing as was common in America, or did you copy the British scheme where you had to press a button to get dial tone? (The button would earth A-wire for one subscriber, B-wire for the other, and ringing would be applied between one wire and earth rather than across the pair.)

Paul,
At the time, I was only an apprentice
Electrician, but, what I do know,
was,that at the time (when the then Post
Office Telecoms), ran all new wiring
through houses, buildings, in Temuka.
But, we still had the old 746 phone,
the only difference being that we could
actually use the dial on our telephones,
to dial out directly.
Now that I live in Ashburton, here, we still have the same technology,
except we are trying to pump a certain
number of Megabytes of Data down it now.

The phone system has changed drastically in the U.K. in the last 20 years.

Now we have digital exchanges practically throughout the network, but in the early 1980s much of the system was still Step-by-Step, with just some electronic and a small number of crossbar systems (a very small percentage by American standards).

If you have a sound card, you might find this site of interest:
http://www.wideweb.com/phonetrips/index2.html

Lots of recordings of the American network of years ago.

Paul,
Is it possible, to get an Electric Shock, from the Ring Voltage, if you are working on a Telephone system, inside a customers house and somebody rings the house where you are working?.
Just interested.

Yes -- Most certainly!

The ringing voltage can give quite a tingle if you happen to be across the line when someone calls. I always try to busy out a line when working on it if I can (leave a connected phone off-hook or just jumper the loop with a clip lead).

Ringer voltage is around...90 volts or so?

It can sting you a bit....especially if your hands get sweaty while working. But it's not going to throw you across the room.

When I was adding extensions to my mom's phone I disconnected the wires at the main entry terminal block before the junction box I put in (I wired the thing up in a "star" configuration - one pair of wires to each extension box).

Well, Paul, if an Electric hazard can arise, why is there no requirement to have some form of Isolator,when working on these
circuits?, you can't simply tell the homeowner, to make sure no-one rings up, while you are working on their phone circuits.
What gives?.

Sven,
Yes, usually around 90V by the time it reaches the house, although on a lightly loaded line very close to the CO it could be higher. As you said, it's not going to throw you across the room, but the ringer voltage can pose much more of a threat to a lineman working in a water-logged telephone manhole.

Trumpy,
Subscribers (sorry, "customers" as BT calls us nowadays!) have been allowed to install their own extension wiring here since the 1980s.

The latest master jacks (i.e. the jack at which the incoming TelCo line terminates) incorporate a pull-out panel to which extension wiring can be terminated.


The lower section of this jack pulls out and disconnects the extension wiring from the line.

You can't see it in the picture, but the panel actually connects the the fixed portion using the same style jack. Thus when the panel is removed for work it's possible to leave a phone connected directly to the incoming line. (And of course, the TelCo tells people to remove the panel and plug straight into the line if they're having any problems in order to determine if the fault is on the internal extension wiring.)

I can't speak for many other countries, but many (newer) installations in the U.S. incorporate a "network interface." In many instances it's just a split duplex phone jack, line on one side, wiring to jacks on the other, linked by a short patch cord.

AFAIK in Austria any fixed wiring belongs to the phone company and is not to be touched by the customer. Earlier phone connector boxes (for our typical hardwired phones) had a sealing sticker over the cover screw. Extensions were only possible with single lines, and hence rather rare. (a vast majority of households, especially in the cities had party lines with in rural areas up to 10 subscribers on one line, in cities up to 4, thus the name "quarter lines", with a rather complex relais system preventing eavesdropping by the other subscribers).

FWIW, in Canada, the government agency overseeing the telephone industry, in early 1998 or so "Gave" all inside wiring, and the
whole responibility for, to the customer, although fo years you could buy your own extension line wiring goods for years and could do the work yourself.

Back when our phones were all under the GPO (General Post Office), internal wiring was installed by the GPO and nobody else was supposed to interfere with it in any way.

They didn't go to the lengths of putting seals on the junction box covers, though.

Today, the incoming line and the master jack (pictured above) still belong to the TelCo (BT in most areas). The subscriber can remove the plate I mentioned above to connect extension wiring, but is not supposed to open the master jack any further.


[This message has been edited by pauluk (edited 11-29-2002).]

As far as I am aware, Paul, no-one ever touched Phone wiring when it was under the control of the old P&T, but once this was sold off, the floodgates opened, every person was putting in extra telephones in their houses, using any sort of wire that they felt like(NB:This was under the old 3-wire system).
Now, people like myself over here, are trying to bring these "hook-ups", into compliance, with the new Telecom NZ requirements, are finding all sorts of wire.
We are now using a 2-wire system, which means that all of the sockets on the line are Masters, there are no Secondaries, in these systems.

Every single piece of equipment here was sealed. 1950ies and earlier even had pressed lead seals on it! In the 60ies they changed to orange stickers with the post office logo on them. They were used until about 1995, or maybe even until the privatization to Telekom Austria in 1998.

I guess I should have mentioned an exception. When the GPO monopoly on telephone service ended and BT allowed individuals to carry out their own wiring, it was under the instructions that this could only be done where BT had already installed the new-style jack. People weren't supposed to tamper with the old style 1/4-inch jacks or hard-wired units.

One good reason for this was that at that time there were still quite a lot of party lines in use. Inadvertant reversal of connections could have resulted in outgoing calls being charged to the other party!

Strange, Paul that you should say this,
as when the GPO, over here lost its "Monopoly", there were still a lot of manual exchanges, around the District.
Telecom picked up where the old GPO, left off, they still control the Majority of the Telecommunications in NZ, with ridiculous charges, etc.
They have pretty much, shut out any real competition, by hiking their access charges, beyond anything that would make them competitive.

I have had some horrible belts of phone lines, when hooking up communicators for alarm panels in pokey little cupboards all hot and sweaty. i had the misfortune to work with a utter prat for awhile who proceeded to strip of the incoming pair for line grabbing to the alarm then put them in his mouth while sorting out a return pair, you guessed it the line went live. I still laugh about it 8 years after.....hahahahaha.
FYI the highest ring voltage i have seen here is 45 volts AC, someone told me when i was a tech for the Post Office, way back when. Ours is a BT3 system, terminals 5,2,3 still ring a bell.
CW

45 volts sounds rather low for the "highest" ring voltage. I'd normally only expect to see ring voltage that low on a heavily loaded long line.

Do I take it that NZ is now using the BT connectors as standard then, following the same pattern as the U.K. with a master jack (incorporating blocking capacitor, spark gap, etc.) and then secondaries for extensions?

Trumpy said

“as when the GPO, over here lost its "Monopoly", there were still a lot of manual exchanges, around the District.”

Manual exchanges certainly had certain advantages. Once trying to reach a certain person in Babanango, Kwa Zulu Natal in the mid 80’s ...

Ring – ring …

“Hello, Babanango exchange”

“Hello, could I have number 15 please”

“Are you after Mr B****?”

“Yes I am”

“Well he’s not there right now”

“Oh”

“No, he’s over at Oom K****’s place having a braai [barbeque] ”

“Oh – OK”

“I’ll put you through to Oom K**** if you like”

“Yes please, Thank-you”

Ring-ring …

Eat your heart out Mr. Gates!

May well have been higher i have never spent any real time looking, sure feels higher when i get a tickle
CW

Appy,
Don't forget that the AC ring voltage is superimposed on 48 or 50V DC battery as well. I'm not sure how the frequency affects the "feel" of the tingle either -- AC ringing is generally around 15 to 25Hz rather than 50/60Hz powerline frequencies.

Hutch,
I guess the "all-knowing" operator could be a mixed blessing. Ever seen the Little House episodes where Harriett Olson is running the switchboard? Probably a Mrs. Olson existed at many rural boards!

SvenNYC:

A Verizon tech told me that the 90VAC was raised (this was about a year ago) to over 100VAC. He also told me that they were going to be removing a whole lot of fiber (fibre?) optics because so many people can't get DSL. (I must be right on the border...just down the street a neighbor was told his line could not qualify...)

Another voltage number to throw at you is for the coin phones. (Here, I refer to the good old-fashioned "telephone company" phones, not the private ones that pop up on every corner. The collection method may have changed with the more modern switching equipment--I am not certain.) They were set up so that the coin(s) were held until the disposition of the call was determined. If the call was completed, there were 70VDC sent across the line via a 3rd wire. If the call was not completed, again, 70VDC came over the 3rd wire. Depending on the polarity, the coin would drop into the collection box or down the "coin return" chute.

The privately-owned coin phones are not set up this way. (Thus the muted mouthpiece until the call connects...)

ThinkGood has raised a good point about the old coin phone lines.

I've never heard of the 3rd-wire 70V system (phone companies would normally try to minimize wiring where possible), but it may well have been used by one of the former independent companies now in the Verizon area.

Many coin phones used a local ground connection -- They were often ground-start, meaning that to get dial tone the phone grounded one side of the line when you inserted your nickel or dime (or dimes/quarter after inflation!).

I know that for many years the Bell System coin phones used a coin collect/return system based on a + or - 120V DC pulse on one side of the line. I forget which polarity was for which function. I don't know if any of these systems are still in use in some remote part of the country.

In the U.K. our old coin phones were less sophisticated, and callers were instructed to press one of two buttons. Button A was coin collect and through a mechanical linkage dropped the coin(s) into the box and removed a short from the transmitter so that the caller could talk. Button B returned the coins (after getting a busy signal for example) and engaged a timer which opened the line for a few seconds to drop the call.

Ma Bell was the more sophisticated!

Hi, Paul.

Actually, the installer I had spoken with was working on a real "Ma Bell" coin phone (this was, oh, almost 15 years ago).

Cheers ;-)

One more thing.

I once bought a reconditioned test set from a company over 10 years ago. Still works just fine. The website is http://www.southerninstruments.com/

The same guy (George) is still there ;-)

They are great about answering questions, so if there's something that can't be answered here, maybe they can help.

One more is http://www.becophones.com/

They have a lot of the older equipment that is POTS-oriented.

(Standard disclaimer...I have nothing to do with the companies other than I bought some stuff from them years ago...good, old-fashioned phones/testers that survive the ladder-drop test--ouch!)

[This message has been edited by ThinkGood (edited 12-15-2002).]

I'll post a message about the 3rd-wire 70V coin collect/return system on one of the Telecoms newsgroups to which I subscribe. I'm sure that somebody there will have some details on how widely this might have been used.

Let you know what I get back....