Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!wuarchive!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: julian@bongo.uucp (Julian Macassey) Newsgroups: comp.dcom.telecom Subject: Re: Basic Questions About Telephones Message-ID: <10881@accuvax.nwu.edu> Date: 12 Aug 90 16:59:42 GMT Sender: news@accuvax.nwu.edu Organization: The Hole in the Wall Hollywood California U.S.A. Lines: 156 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 571, Message 1 of 9 In article <10692@accuvax.nwu.edu>, drears@pica.army.mil (Dennis G. Rears (FSAC)) writes: It's Deja-vu telecom time again. > It seems as if each telephone cable contains four wires (red, > green, black, and yellow). For one line only the red and green wires > are used. The black and yellow wires are only used for the second > line. If only one line is installed in a jack why do the yellow and > black wires have to be attached? I suspect it doesn't. You are right, a telephone line requires two wires or "one pair" in telco speak. The first pair are the Red and Green and the second pair are the Yellow and Black. For a one line installation, you only need to connect the first pair (Red and Green). The second pair is often not connected through anymore - standards have gone to hell since divesture. The telco used to connect the second pair (Yellow and Black) when installing so that if they popped in a second line they wouldn't have to hunt round the premises to splice all the second pairs. > The modular jack that goes into the phone has four wires in it. Why > is that, if only the red and green are required for service? Just in > case you have a two line phone? There are several reasons for this besides a second line. At the end of this posting I am including something I posted in November 1988 in response to an inquiry just like yours. > Why is the jack that goes from the telephone headset to the > telephone a different size than the jack that goes from the phone to > the wall jack? Is it to idiotproof the process? Also why four wires > into the headset? Does the phone itself do anything to the signals > before it sends it to the headset? If the proper size jack was put on > the headset could you plug that into the wall jack and receive calls? Because it serves a completely different purpose. It idiot proofs it to some extent. But I have had customers plug the handset into the line jack and then call and complain that the line cord wont plug into the handset jack - this really has happened. Notice that a handset jack has and uses two pairs (four wires). It uses two wires to talk (Transmitter) and two wires to listen (Receiver). Ok, so the line jack is two wires (talk and listen on the same pair) and the handset has split talk and listen into separate pairs. Inside the phone instrument there is a device called a network that magically sends the voice signals to the right place. Yes, you could Micky Mouse a handset to work directly on the line, but the line voltage would soon kill the receiver magnet and the sound of your own voice would blow the wax out of your ears etc. So that is what the instrument stuff is for, if it wasn't needed, someone would have been selling handset to line cord adapters years ago. The Linesmans "Butt-set" has the network built into the handset as does the AT&T Trimline phone. > What do the two wires (red and green or yellow and black) carry? Is > one positive and negative like electrical wires? Yes, as a phone line is about 48V DC when "on hook" (hung up) and between 3 and 9V DC when "off hook", there is a DC voltage there. The normal voltage polarity is Green = + and Red = -. Some phone systems will reverse the polarity when a call goes through (rare these days). If the polarity is wrong, no biggy, some old 2500 sets may no longer dial, so flip the Red and Green and everything will work again. They phone wires also carry audio signals, Voice and Touch Tone. They also carry the ringing signal 40-150V AC. > In the case of my second line I bought a double wall phone outlet. I > installed the first line (R&G) to the top outline and installed the > second (B&Y) line to the bottom outlet. The first line worked the > second did not. The second line was live as I have a jack wired right > into at the NIU. I then disconnected the wires from the NIU for the first > line and reconnected them to the NIU for the second. That got the second > line working. That says to me that there must be something physically > wrong with the Yellow or Black wires. That seems strange to me as all > four wires are in the same cable and if there was a physical break in the > cable it would affect all the wires, not just one or two. Any thoughts > of this? Yes, you could have a break in just one wire in a cable. This is not uncommon. I have had this happen with long runs of cable, this is a good reason to install more pairs than you need. If you have a "bad pair", just mark it as such and progress. But as you are a domestic installation I would physically check the wire from the NIU (Protector) to the jack. There may be a connecting block or jack along the way that has not spliced the Black and Yellow pairs. One word of warning. Some lazy installers will often place the Black and Yellow under a screw in a a junction box/jack but will not strip the wires. It will look like two wires are connected under a screw head, but as they still have insulation, they are not. And now if you are still fascinated by all this stuff, here's more of the same. This is a posting from a couple of years ago that kinda covers the same ground. Newsgroups: comp.dcom.telecom Subject: The other pair of wires. Message-ID: Date: 9 Nov 88 10:11:08 GMT Sender: chip@vector.UUCP Lines: 54 There has been a fair amount of discussion about what you will find on the second pair of phone wires in a residence. Here is a list of what you might/could find: The first pair will always carry a regular phone line. These wires are usually Red and Green, they can be White with a Blue Stripe and Blue with a White stripe. They are referred to as Tip and Ring. The Green or White/Blue wire is Tip and the Red or Blue/White is Ring. Tip is Positive and Ring is negative. ( Yes I know the voltage thingy is more complex than that, this is not for experts. For folks with Rat Shack meters, what I have said is true) Ok, now the first pair is out of the way, let's look at the second pair. They are usually Black and Yellow or White/Orange and Orange/White. These wires can have several things happening to them, but not all at once. First of all, there can be nothing on the wires, and they may not be connected anywhere. Next, the Yellow wire can be grounded. This is rare these days, but you will find it on old installations. Another old thing you will find is AC voltage for lighting the dials of old Princess phones. If you look around, you will find a wall transformer wired into the Yellow and Black wires. If the transformer says, "Bell System Property" etc. That's it. If you no longer have a rotary dial Princess with a lighted dial, pull it. Talking of old, old style multiline "business" phones. Yes, the ones with the buttons that light up and flash, they needed a hard wire signal to know that a line was off hook. This was known in "Telco speak" as "A-Lead control". If a single line phone was used as an extension on one of these systems also known in "Telco speak" as "1A2", the second pair (Yellow and Black) were shorted together when the phone went "off hook" to let the system know that a line was in use so all the right blinky lights came on. If you used a phone without A-Lead control, it went into hold when you hung up - most inconvenient. These days, if the telco uses the second pair, it is usually for a second line. Looking back to the first paragraph, the Black wire is Tip and the Yellow wire is Ring, usually known as Tip 2 and Ring 2. Yup, that makes the first pair (Red&Green) Tip 1 and Ring 1. Now, when discussing PBXs and modern "Key Systems", the second pair can often carry "data", stuff controlling the phones. More details available upon request. Available for Bar Mitzvoth weddings and barbeques. Julian Macassey, n6are julian@bongo.info.com ucla-an!denwa!bongo!julian N6ARE@K6IYK (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495