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Old 10-05-2009, 11:44 PM   #1
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Why is there no sparks when shorting a phone line?


I was working with a live phone line the other day and came to the realization that despite there being 50ish volts on there, there are no sparks or burns when causing it to short out by error. In fact, I would expect to maybe get a small shock when putting my finger in a jack or touching the two wires. None at all.

Is the voltage I read with a meter the actual voltage, or is it some form of phantom voltage or something?

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Old 10-06-2009, 05:18 AM   #2
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Why is there no sparks when shorting a phone line?


Try holding both of those wires when an incoming call is ringing the phone!

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Old 10-06-2009, 05:59 AM   #3
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Why is there no sparks when shorting a phone line?


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Try holding both of those wires when an incoming call is ringing the phone!
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Old 10-06-2009, 06:34 AM   #4
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Why is there no sparks when shorting a phone line?


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Try holding both of those wires when an incoming call is ringing the phone!
As kbsparky said hold both wires then use your cell phone to dial your number you will fell the spark
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Old 10-06-2009, 07:28 AM   #5
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Why is there no sparks when shorting a phone line?


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Try holding both of those wires when an incoming call is ringing the phone!
That will ring you're bell!!
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Old 10-06-2009, 09:06 AM   #6
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Why is there no sparks when shorting a phone line?


Voltages of up to around 70V are across the phone line when an incoming call ring signal arrives or if an old fashioned non-touch tone phone is dialed.

There can be visible sparks if you are playing around with loose wires just right, but since the current (amperage) is very low the sparks are small.

The feeble current rings the bell because the bell coils have thousands of turns of wire to "magnify" the magnetic field enough to physically move the clapper.
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Old 10-06-2009, 04:19 PM   #7
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Why is there no sparks when shorting a phone line?


I need to go try this now. I'm of the very curious type.
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Old 10-06-2009, 05:13 PM   #8
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Why is there no sparks when shorting a phone line?


I feel a small tingle sometimes with the 50vdc [actually 4 ea. 12v batteries in series under charge will give you 4x14.4v, if you were close to the central office].
All the phones have to be on-hook, of course, otherwise the voltage is just a few volts.

If somebody calls you while you're touching the phone line [and for sure they will] you will be shocked, guaranteed, and it's nasty because the freq. is so low you can almost feel the rising and falling of the waveform.

If lightning hits the line while you're doing this your shoes will get holes in the bottoms, but that will be the least of your worries.

Last edited by Yoyizit; 10-06-2009 at 05:16 PM.
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Old 10-07-2009, 12:22 AM   #9
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Why is there no sparks when shorting a phone line?


Yeah working on phone or electrical lines during a storm is probably a bad idea.

Though would lightning actually go through a phone line? Would figure since it's soon thin it would burn before it even gets to you. I don't want to put that to the test though.
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Old 10-07-2009, 12:34 AM   #10
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Why is there no sparks when shorting a phone line?


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Yeah working on phone or electrical lines during a storm is probably a bad idea.

Though would lightning actually go through a phone line? Would figure since it's soon thin it would burn before it even gets to you. I don't want to put that to the test though.
don't ever underestimate lightning. It could simply melt a line or it could ride the outside of the line and not harm the line at all. It's tough to figure out lightning with it's 10 million to 100 million volts (although I have read up to 1 billion) and hundreds of thousands of amps.

When a person gets struck by lighting, sometimes it simply passes over their skin, sometimes it passes through the body. Why? I have not a fricken clue. When you deal with voltages and current that high, it is well beyond simply testing it to see what it does.
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Old 10-07-2009, 01:47 PM   #11
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Why is there no sparks when shorting a phone line?


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Though would lightning actually go through a phone line? Would figure since it's soon thin it would burn before it even gets to you. I don't want to put that to the test though.
30,000A for long enough would melt the line between the strike and the load. Check out Onderdonk and Preece for IT ratings.
One load is the central office. An off-hook phone is not much load.
Once the line arcs over, the voltage is limited by the arc but I think the current in the arc is pretty much 30,000A.

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Last edited by Yoyizit; 10-07-2009 at 01:58 PM.
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