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Joined: Jan 2003
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iwire Offline OP
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I was reading this and I remembered getting some good belts off of phone lines.

Isn't the ring voltage greater than 70 V?

Bob

[This message has been edited by iwire (edited 05-28-2004).]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Aug 2001
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Idle line voltage is typically 48 to 50V DC, and the ring voltage is low-frequency AC superimposed on that. Voltages vary depending upon line lengths and the number of bells connected, but ringing voltage can actually exceed 90V.

Quote
The electrical outlets in your home pack a whopping 15 amps; your humble telephone carries less than a tenth of a milliamp.
Well, I'll skip over the 15A angle as we all know that the current that actually flows depends upon the resistance.

But the second statement there is just untrue. The standing DC current when a phone is off-hook can be over 100mA. The ringing voltage can certainly pack a similarly dangerous level of current to someone immersed in water.

So let's put it this way: If I was soaking in the tub I wouldn't want anyone to come along a drop a phone in there with me..... [Linked Image]

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Bob,a phone guy once told me years ago that it was 90v DC.


Russell

Joined: Jun 2003
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I have heard the same as Russell. One time years ago I had my helper hold onto the phone wires while I was testing a two line system. He got belted twice before he said 'no more'. [Linked Image]

Pierre


Pierre Belarge
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CRW Offline
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An alarm guy told me he used to strip the wires with his teeth becaue they were so small. He stripped an incoming phone line once when a call came in and got rapped in the mouth with 90V and it wasn't fun.

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Agreed.... 90VDC on the ring. I've felt it, it's a good belt. Definitely could get electrocuted in a bath tub.

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No, ringing supply is AC, usually at a low frequency of around 20Hz.

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As a long time "phone guy" I have to agree with most of what's been said.

The battery voltage on an idle pots line (basically open circuit) should be 48 to 50 volts DC. It will drop when a phone goes off hook and the voltage then will depend on the length of the loop and size of the wire (as always)the particular phone and number of phones off hook at one time on that pair.

The ideal loop current is around 20-35ma. Less than that may result in transmission (low volume) problems and more than that can cause operational problems with some electronics particularly modems. I don't remember exactly but I think the TELCO guarantees a minimum of 20ma with no upper limit. So for short loop lengths you can see excessive loop current though 100ma would be extreme.

The ringing voltage is nomally 90 volts at 30Hz superimposed on the 48 volt DC battery voltage. Not sure what the ring current is though it's not that much but, yes you can get knocked on your a** if you are not careful. Something other than 30Hz may be used in some areas dependent on the ringing schemes used though the switch over to "standard" customer supplied phones pretty much eliminated party line and other selective ringing schemes.

The article alludes to using the phone during a storm. Even more than the above I would be concerned about lightning and other stray voltages entering the house on the phone lines. Most TELCO protectors clamp at a minimum of 300 volts or more and I wouldn't want to be in a bathtub talking on a corded phone at the time!

-Hal

Joined: Feb 2002
Posts: 2,233
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Bob,

When I use to work for the alarm co. our telco lines use to carry 120 v DC. When you got hit by them you knew it. We use to have to solder each connection for the alarm co. and when you touch the solder to the hot wire and lean on a metal garage door, it really wakes you up. ( Take it from me. I did it.)I use to have several funny stories about Telco guys and our Burglar Alarm (BA) lines. There was the guy who was using his teeth to strip the wire, and we told him to watch out for the BA line. Well, when he found it, his head flipped back real fast. He then asked us what was in there. We told him that it was 120VDC. He alsmot broke his neck or at least get whiplash. There was another time a Telco guy told us about the lady who called into the CO ( Central Office) She was going to go on vacation, and she wanted the Telco people to come out and "Water" her Ground rod. It seems when the original installer went out there he couldn't get a good reading on the telco line. So he threw a bvuckey of water on her ground rod to get a better reading. It worked and he told her to throw a bucket of water on her ground rod once a week. She did but now she wanted to go on vacation and she wanted some to go out and water her ground rod. I have a few more.

Harold

Joined: Dec 2001
Posts: 2,492
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Quote
An alarm guy told me he used to strip the wires with his teeth becaue they were so small.
My sports teacher at school once did that with 220V wires. He moved into a new house or apartment and hung new light fixtures. Standing on the ladder he noticed he forgot the knife and decided to strip the wires in the ceiling with his teeth. Of course he had shut off the breaker before. Meanwhile his brother had noticed his radio didn't work. Went to the panel, "stupid, can't work without power" and on went the breaker...
He says he fell off the ladder from the jolt, luckily he didn't hurt himself too badly.

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