Phone line volt/ohm meter check?

[Stephen Tashiro]

Can anyone direct me to web page that tells how to check a residential phone line with a volt/ohm meter? Or should one do such a thing with an ordinary volt/ohm meter?

[Dennis McGarry]

Your standard home phone has two wire, red and green, TIP and RING

U can use any reg. volt meter to check.

If you are cheaking for a break in the line, best to do a continutiy test if possible.

Or if it is a big house, run to a BORG and pick up a tone generator, you clip on part on one end and the other on the other end and see if you get tone..

"Tip" and "Ring" are common terms in the telephone service industry referring to the two wires or sides of an ordinary telephone line (http://www.sawmillcreek.org/wiki/Telephone_line). Tip is the ground (http://www.sawmillcreek.org/wiki/Ground_electricity) side (positive (http://www.sawmillcreek.org/wiki/Electric_charge)) and Ring is the battery (http://www.sawmillcreek.org/wiki/Battery_(electricity)) (negative (http://www.sawmillcreek.org/wiki/Electric_charge)) side of a phone circuit. In the UK these are referred to as the 'A' (earth) and 'B' (battery) wires. The ground side is common with the central office (http://www.sawmillcreek.org/wiki/Central_office) of the telephone company (http://www.sawmillcreek.org/wiki/Telephone_company) (telco); the battery side carries -48 volts of DC voltage when in an "idle" or "on hook" state (nominally -50 volts in the UK). The combination of tip and ring, then, makes up a normal phone line circuit, just as a car's battery needs both connections leads to have a complete electrical circuit. To ring the phone to alert to an incoming call, about 90 volts of 20 Hz AC current is superimposed over the DC voltage already present on the idle line.

[Mike Henderson]

And just a piece of useless trivia, the terms "tip" and "ring" came from the plug that the operators used. The tip of the plug was ground and the ring right behind the tip was negative 48. The two wires from the central office (CO) are called a "loop" because when you went off hook, current would flow from one wire to the other which allowed the CO to detect that you had picked up the phone.

Also, all modern phones (maybe last 75 years) have a diode bridge so that the phone will work even if the house wiring is backwards.

Mike

[Dennis McGarry]

And just a piece of useless trivia, The terms "tip" and "ring" came from the plug that the operators used. The tip of the plug was ground and the ring right behind the tip was negative 48.

Mike

LOL dating yourself there buddy!

Heres one for you, where did the term Debugging in relation to a computer originally come from?

[Mike Henderson]

LOL dating yourself there buddy!

Heres one for you, where did the term Debugging in relation to a computer originally come from?
One of the original mechanical computers implemented in relays failed and they found a bug in one relay. I am pretty old but I didn't work on that computer.

Mike

[Dennis McGarry]

Judges say.... Give it to him.

Originally it was a army systems tech, (really a operator) and her job was to go through the system and remove all the bugs, they would burrow in and eat the wires. When asked about her job replied, "Just debugging the system" and the rest was history.

Youngin's remember now that system back then were the size of a small house today, and all wires connecting the relays and switches... Jewel food corp. headquaters used to heat the offices from the exhust of the mainframe in the systems room. One guys job was to come in everymorning and turn the exhust on to the office areas before the workers came in...

[John Coloccia]

Can anyone direct me to web page that tells how to check a residential phone line with a volt/ohm meter? Or should one do such a thing with an ordinary volt/ohm meter?

What are you trying to test for? If everything's hooked up right you'll read something like 50V across the two lines. That's coming right from the phone company. You can take a spare phone wire (who doesn't have a million of these lying around?), chop off one end, and strip back the wires to make a convenient probe. It's hard sticking multimeter probes into the jack and hitting the two little contacts.

If you short it out, it'll spark. Don't worry, you didn't blow anything up. There's very little energy behind the line voltage. If you happen to be holding on to the wires and a call comes in, that'll get your attention. That's AC, and is more like 90V, or something like that. It won't kill you, but you'll feel it.

[paul cottingham]

A guy on a jobsite had a phone line in his mouth (read -the plug-) when it rang. Said he literally saw stars. He never used his mouth as a third hand again.

In answer to the OP, there is a guy in chicago, mike sandman http://www.sandman.com/ who has tons of good info on telecom. But house telecom is pretty simple.

[Jason Roehl]

Paul, that takes the cake. I've had one in my hand once when someone tried to call, and that 20 Hz/90 V sure lets you know about it. I think it probably feels worse than 120V/60 Hz (I've managed to shock myself with that more than a few times), but I know it's not as dangerous. The most painful I ever got was grabbing a spark plug wire that had a hole in it (it was laying on the exhaust manifold, thus the hole), with the engine running, with my opposite knee touching the bumper. Wow. I could still taste it 6 hours later.

[Jeff Bratt]

Where did the term Debugging in relation to a computer originally come from?

According to this article (http://en.wikipedia.org/wiki/Debugging), the term "bug" (meaning technical error) predates computers. And Grace Hopper said she did not invent the term "debugging", although the story of her and the bug in the relays is true.

[paul cottingham]

Oh, yes, and just to be clear, it -ahem- wasn't me that got zapped.

[paul cottingham]

Can anyone direct me to web page that tells how to check a residential phone line with a volt/ohm meter? Or should one do such a thing with an ordinary volt/ohm meter?
One other thing. The easiest way to check phone lines is to go buy a beater phone, the cheapest plainest handset you can find, and just plug in to each jack then go off hook to check for dial tone. OR clip off the plug and hook up two alligator clips. Get the right kind of clip, and you can squeeze it onto the insulated wires, it'll pierce the insulation, and you can check wiring easily. the wire heals itself.

[Stephen Tashiro]

In my situation, only the end of the wires at the phone jack are accessible. It's at a friend's apartment and his phone doesn't work. The phone company says their line-check (remotely, not by an on-site guy) shows their line is OK. My friend wants to know if there are any sanity checks on the wires that he can do with a multimeter. What voltage, if any, should show between what colors of wires?

[paul cottingham]

48 or so volts, 90 if ringing. There should be only one pair, if not you need to check all permutations, as you have no idea who wired it or how.

[Stephen Tashiro]

48 DC ? I know the idiot-light line tester has an amber light for "AC present", so I assume that's bad.

[paul cottingham]

I -THINK- its DC. I think if you have AC there, it may be an induced current. That is bad I think.

[Jerome Hanby]

The current from your Telco is DC. It starts out at 48 volts, but drops so it will vary based on your distance from the current source. Phone line is typically not shielded, so it's a great big antenna (especially if there are unterminated bridge taps) so it can pick up all kinds of induced signals (not too rare to find a phone where you can detect a local radio station in the background).

If you can disconnect tip and ring from the Telco tie in and short them on the house side of the connection, then you can use your ohm meter from any jack in the house and you should see pretty close to zero ohms (the wire will have some resistance). With that tip and ring connection open, you should read infinity. Unless you like testing the overload protection on your Ohm meter or buying new ohm meters, don't put it on the circuit if you are still attached to the Telco!

If you want to break the problem in half, take an old POTS (plain old telephone set) cut off the plug, strip back the wires and put alligator clips on tip and ring (green and red wires). If you disconnect the house from the Telco and clip onto the Telco connectors, you should have dial time and be able to dial. If you can't break dial time, swap the wires, some older DTMF phones are polarity sensitive. If all works there, you know it's not a Telco problem and you can work back into the house.

If you accidentally or otherwise short tip and ring while you are still attached to the Telco, don't worry about it. It's not a "nice" thing to do, but it's an old school way to busy out a telephone line. Much nicer to use a 600 ohm load, but not a disaster.

Of course, all of this is predicated on you having "normal" Telco service. If it's something "electronic" then YMMV.


I -THINK- its DC. I think if you have AC there, it may be an induced current. That is bad I think.

[Lee Schierer]

In our area, the phone company responsibility ends at the gray box outside the house, unless you pay for a service call or are on a service contract. The gray box has a regular modular plug that connects the house to the line. What I do to determine if the problem is in the house or outside is to plug a working phone directly into that jack outside. If the phone still doesn't work in the entry jack, I call the phone company to get the service restored.

[Jerome Hanby]

In our area, the phone company responsibility ends at the gray box outside the house

Same here, except our gray box is a cylindrical metal can with a screw holding it on at the bottom.

[Stephen Tashiro]

Until I purchased DSL from Qwest, the only phone box on the outside of my house said "Bell System". To facilitate DSL, a technican installed a modern box. When he did this, he left the old box in the line since he said its fuses would give me added protection. The implication was that the new box didn't give me such protection.

My friend lives in a large apartment complex, so I don't think he will be able to get to the phone company's box.

[Jim Koepke]

Until I purchased DSL from Qwest, the only phone box on the outside of my house said "Bell System". To facilitate DSL, a technican installed a modern box. When he did this, he left the old box in the line since he said its fuses would give me added protection. The implication was that the new box didn't give me such protection.

My friend lives in a large apartment complex, so I don't think he will be able to get to the phone company's box.

The installer likely left the old box because it was easier than removing it. I was a telephone installer a long time ago. Things have changed, but not so much so that workers will do more work than they have to. The line protection fuses require a ground wire. They really are not fuses, they are little arc gaps that will make a solid contact if the line is hit by lightning or other high voltage. This is to protect equipment and people.

If it is in an apartment, chances are it is a different type of wire coming into the individual apartments.

It could be a bundle of 6 pairs instead of the usual inside wire of two pairs. This all depends on how old the building and when was the last restoration.

The problem could be caused by another tenet messing with the wiring. Usually the telco box is in a convenient place for an installer to get to without having to find a manager.

Is this a new service, adding an extension or one that worked and stopped working?

jim

[Stephen Tashiro]

The box on my house was on my private residence. My friend lives in a moderately large apartment complex. His phone was working. Then it became intermittent. Then the line went dead.

Yesterday the phone technican came out and my friends line tested bad at the box. The technician fixed it, or so he said. But when my friend put his small idiot-light type tester in his phone receptacle, it indicated "reversed polarity". (I suppose that could be the fault of the apartment's installation.) He swapped two wires and now his phone works. However there is a peristent 60 HZ hum while we are talking.

[paul cottingham]

The phone shouldn't care about reverse polarity. The hum is odd, though.