Hi!
Do you guys know how to measure the current flowing in our telehone lines using a multimeter? I really need it badly.
What's the difference between AC Current and DC Current? What will I use in measuring the current in phone lines?
I'm doing my research regarding the "Electrocution through phone lines." Have you heard of that urban legend?
Thanks a lot.
Urban legend eh? Well,okay,It's probably NOT fatal,but I can assure you it hurts like Hell when you're fiddling with the phone wires,and someone just happens to call at the very second that you are touching the phone line,and are also (unintentionally) well grounded.(wearing only socks on wet concrete-bad move!) -Voice Of Experience.
If your specific topic is electrocution via telephone lines then ..... only the AC ring voltage should be considered. as it can be as high as 90 Volts AC.
So do a search on Telephone line ring voltages.
This does not include lighting strikes.
Joe
The peak voltage will be 48 + (90 SQRT(2)). The ~90 volts will be at 20 Hz.
Tam
you arent going to try to sap enough juice from the telco to power your house are you??
No. Obviously, no one here has ever used a meter. (An oscilloscope would be more useful.)
Before asking elementary-school questions, you should use Google's search engine. Google can help you find a basic electricity tutorial. AFTER that, If you have SPECIFIC questions, they belong in sci.electronics.basics.
Research: Asking someone else to give you all the answers.
Battery voltage can be as high as 56VDC. Ringing voltage can be as high as 135Vrms. Peak voltage could be as high as 245V.
Unless you have a current probe for that oscilloscope, it would be the wrong instrument to measure current in a phone line; a scope is normally a voltage-reading instrument. Also, the instrument used to measure phone line current needs to be totally isolated from the AC line and safety ground. Otherwise, the line becomes unbalanced and the phones don't work. If you do have a scope with a current probe, you're in business. You just have to make sure the combo is calibrated for meaningful measurements. Also, make sure the instrument ground (chassis) is isolated from the power line safety ground. To use a current probe, just clip the probe's sensing loop around one side of the phone line.
For measuring the DC loop current, a (digital or analog) multimeter having a DC current range of 10ma - 50 ma. For measuring the ring current, a (digital or analog) multimeter having an AC current range of 100ma - 200ma. Frequency response of the AC current ranges is a factor because the ringing signal frequency is 16Hz to 20Hz in most areas. Just insert the meter in series with one side of the phone line (doesn't matter which side) and switch to a range that gives you a reasonable reading.
The difference between DC current and AC current (is that redundant?) is that DC flows in only one direction, while AC alternates direction (hence, the term Alternating Current) periodically.
-- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) "In theory, there isn\'t any difference between theory and practice. In practice, there is." - Yogi Berra
Obviously you do not know much (if anything) about electricity or simple electronics. Therefore, please win the Darwin Award by licking all of the power outlets.
There's a show called "Mythbusters" where they approached this very question and as I recall, their results suggested it was indeed possible to be electrocuted through a phone line by lightning. Not likely, but possible under the right conditions.
Google the show and maybe they have that episode online?
As for ringing voltage (ie, no lightning strike), I also recall reading about a documented fatality from a single D-cell battery!! (1.5VDC) in Compliance Engineering magazine many years ago (1998- ish?).
It only takes about 100mA or so, under the right conditions, to stop the heart. You have to work at it (skin resistance, etc...), but if you can do it with 1.5VDC, it stands to reason 90VAC (or 90 volts pulsating DC to be more percise - although by the time it reaches your phone the edges are worn off quite a bit..), will do the job too.
Finally, when I was younger, I once played around with a Secode rotary encoder. You know, like the old rotary telephone dials? Only this one still had the batteries in it. Like an idiot, I was somehow connected to the leads when I decided to "dial" it and got the crap shocked out of me!! And yes, in complete accordance with Murphy's law, I had in fact dialed the "0" for maximum effect.
I immediately set it down, recovered my senses (what little I had left), and opened the test set to find two old, but apparently well- charged 45-volt batteries. They looked like 9-volts, only longer. Lesson learned: Don't assume it's safe, just because it's not plugged in!
About a month later, I got a refresher in that exact subject while repairing a foot switch on a Pace vacuum extractor - where the schematic clearly indicated no line voltage on the foot switch...... Yeah, right.
-mpm
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