telephone wires

Thread Starter

milee

Joined Sep 20, 2007
15
I was repairing the telephone lines and came to know that there is no electric flow while workin but as soon as i touched the wire with my mouth i got a kind of sudden shock....
therefore i would like to know what exactly had happened when i dealed with the telephone wires...
 

beenthere

Joined Apr 20, 2004
15,819
Phone lines still carry 48 VDC. This is a legacy from the old days. They also carry up around 100 volts AC when ringing. Be careful.
 

thingmaker3

Joined May 16, 2005
5,084
As an apprentice, I was once leaning against a 66 block in a high-rise. Somebody's phone rang. I've not leaned against a 66 block since.

Never assume that "low volts" equals "no volts." Never assume that "low volts" equals "low danger" either. Some of my Union brothers have died because of that mistake. 48 volts may not sound like a lot, but when a screwdriver falls across a pair of 48 volt busses with 120 Amps able to flow, the screwdriver literally explodes. It's not cool, and it's not fun.

I suggest the human mouth is not a good place for conductors.
 

JohnBoy

Joined Oct 30, 2007
7
I was repairing the telephone lines and came to know that there is no electric flow while workin but as soon as i touched the wire with my mouth i got a kind of sudden shock....
therefore i would like to know what exactly had happened when i dealed with the telephone wires...
If you measure each wire to earth ground, one will measure nearly ground potential (tip) and the other will measure approximately -48VDC (ring). When you go "off hook", you complete the circuit through the telephone back to your telco. The telco's switch "sees" the current and returns dial tone to you. Ringing voltage is an interupted 20Hz voltage which can be nearly 100VDC ring to tip. It's less if you're a considerable distance from your telco. You're not likely to get a fatal shock from telco battery. However, considering the possibility of an high induced voltage on the pair it is never a good idea to put the wires in your mouth or otherwise provide a current path with your body.

John
 

bloguetronica

Joined Apr 27, 2007
1,372
I was repairing the telephone lines and came to know that there is no electric flow while workin but as soon as i touched the wire with my mouth i got a kind of sudden shock....
therefore i would like to know what exactly had happened when i dealed with the telephone wires...
Happens the same with 12V. Never touch the wires with your mouth. This is the worse way to get a shock, because the inside of your mouth is pretty conductive and there is the possibility of electricity flowing through the brain.
 

h.d

Joined Oct 22, 2007
150
i know that the voltage of telephone lines is 12-24V but i dont know thats when calling it will be 100 V
thanks for that facts....
 

studiot

Joined Nov 9, 2007
4,998
The international standard is -48 Volts, relative to the second wire which is 'grounded' at the exchange.
You can often find slightly more than this (around the 50 mark) in cities, near to exchanges.
Conversely, especially in large countries like the USA, it can drop considerably below this, where the test point is remote from an exchange or repeater.

If you make measurements relative to local ground (earth) you can measure quite different results.
 
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