Telephone Wiring

[Bob]

You could add to that 90VAC when the phone rings.

Bob

[new]

While wiring in a new phone jack I got zapped. I measured 55vots accross b&y zand R&G pairs.

I eventually went to outside telephone interface and plugged into test jack and found it coming from phone company.

There is no way this is normal is it?

[Noozer]

Why not? 60 volts at idle, 90 volts at ring.

[Jeff Wisnia]

AC or DC?

Were you using a digital or analog meter?

Do your phones work OK?

Most standard phone lines are 48 volts DC with no phones on that line "off hook".

I wouldn't worry much about measuring 55 volts.

You can feel a shock from much lower voltages, particularly if something like the sharp end of a wire drags through the dry outer layer of your skin.

HTH,

Jeff

[new]

Thanks for the fast response Bob. This is a constant 55 volts so it is not involved with the ring (and it is on both pairs anyway).

I had thought I had an old pricess transformer around but when I went out to the jack I was suprised.

Again: is this normal?

[new]

An analog meter and AC voltage.

[spamTHISbrp]

Yes, normal and expected.

In the US while the line is idle one of the pair is at approx. ground, and the other at approx. -48V DC.

Ring voltage is a 20Hz sine-wave of 90VAC on the -48V line (peak V is

90-48, or +42V, and -peak is -48 -90 or -138V).

Dave

[Jeff Wisnia]

Well, you will only have AC voltage on a phone line during a "ring", but even though your meter is set to measure AC it will probably still give you a reasonably accurate reading from DC voltages.

Anyway, I think enough folks have responded to assure you that what you measured is normal enough.

Jeff

[Stubby]

[Pat]

As others have said, voltage sounds about right. But you shouldn't feel it under normal circumstances. You will get quite the jolt sometimes if the phone rings while you are playing witht he wires.

You have voltage on both sets of wires. Do you have 2 lines coming in to the house?

[Chris Lewis]

According to Pat :

Heh. For reasons I won't go into here, I had to splice a telephone line while sitting on a concrete floor in our detached garage, and I was too lazy to sling something non-conductive underneath me.

That _hurt_. Even without ringing. Was unable to grasp/twist the wire.

The SO could hear me swearing over 100' away in the house.

Finally gave up and sat on a piece of plywood.

[Pat]

Huh. I always work on phones barehanded and never had a problem. Trying to remember if I've ever worked on them barefoot, too, but can't think of any time I did that. Never had a problem. Bared wires with a jacknife, pulled off cut insulation with my teeth, etc.

Maybe it's just me. My mother always said she wanted me to be well grounded, but I don't think this is what she meant.

What's the consensus. Do most people feel the voltage out of a phone or not?

BTW, my father (an electrician) always said that ringer voltage was esp. dangerous because it was close to the voltage of your heart. I don't have any idea if that is true or just an old wives tale.

[Stubby]

It's dangerous because it is AC and muscles respond to changes of voltage.

[Chris Lewis]

According to Pat :

So do I. But have you ever done it whilst in shorts sitting on bare concrete?

Ordinary shoes/carpet make a _big_ difference.

Generally speaking, if you're reasonably grounded (bare legs on concrete ;-), most people start feeling things at around 35-40V.

I assure you, your heart doesn't run at 90V.

Ringer voltage is perhaps somewhat more, um, "memorable" for two reasons. One is that it's closer to DC, which is inherently somewhat nastier than the same voltage in AC. The second, more important one, is that you're firmly grasping it thinking all is right with the world, and _zap_ out of nowhere, you get hit.

Since your muscles are already gripping it, the ringer voltage tends to keep you gripping it even harder. Longer duration contact. Maybe a whole ring cycle before you can let go.

In contrast, you don't usually have anywhere near as good a connection to line voltage when things start to hurt, and short of a "fall into" or a misguided "firm grab", the muscular reaction tends to knock your hand or finger _away_. Grab that switched off switch leg firmly, and have someone flip the switch on. That's very much different, and vastly more likely to be lethal than a mere "graze".

[glenn P]

Actually DC can be just as dangerous as AC. The heart muscle "clamps" instead of going into VF. If the current vector goes across the chest, it can be more dangerous than AC mains.

Yes, the "close to the voltage of the heart" is an old wive's tale (in fact I haven't ever heard that tale myself). The ion channels that produce the muscle contraction aren't working anywhere near telephone ringer voltage.

[Beachcomber]

The on-hook voltage is DC and is going to be around 40-50 volts and the current is near zero. You can feel this under certain circumstances. The voltage drops dramatically when the phone goes off the hook to perhaps 9 volts or so. Standing on a ground is not usually a problem around telephone wires unless you are in an electrical storm. The loop (off hook) current is limited by a resistor at the phone exchange to about 20 ma or so, even if the wires are shorted together.

Long lines in rural areas might have higher loop current, but again, phone wiring is not considered dangerous except with the thunderstorm exception.

Ring voltage is going to be higher, anywhere from 90 volts AC or higher, but normally not with enough current to kill you unless you are at the top of a telephone poll and the shock you receive causes you to fall off and break your neck.

Remember, transformers only pass AC and block DC. (Telephone audio signals are considered AC even though they are really varying DC. - A transformer is said to pass the AC component of the DC as long as it is not overdriven or saturated).

Capacitors block DC and pass AC.

Beachcomber

[Jim Redelfs]

Probably. Someone probably rang your phone at JUST the right time for you to get really ZAPPED. Either that or you were WELL grounded when touching the live wires.

Dialtone is -48-52VDC. I've never metered it at 55, but I suppose its possible. We VERY rarely disconnect a working pair before working on it.

You'll notice inside the S/NI/D it says something like [to avoid shock, you should disconnect the service prior to working on it]. Good advise, I guess.

[Jim Redelfs]

Agreed.

An electric chair uses DC somewhere in the neighborhood of 2,000-volts.

[unknown]

At one time "westinghouse" meant "electrocute"?

[Jeff Wisnia]

I used to think it described a place where you went to "west" after a long day's work.

I remember the stories about the Edison (DC) and Westinghouse (AC) rivalry and how Edison argued that AC was more dangerous. Edison even went so far as to electrocute an elephant to support his case.

Don't watch this if you're an animal rights type:

Jeff