# Telco AC Voltage



## ce2two (Oct 4, 2008)

mattb84 said:


> This is my first thread. Thanks is advance for your experience. We are installing a telephone entry system with remote programming capability among other systems. The issue, however, is an AC voltage oscillation on the telephone line. The voltage fluctuates from 19v to 240v on the telco main with everything disconnected. This is affecting modem connectivity and or cause board failure. I have contacted the telco company but would like to steer them in the right direction if anyone has came across this before. Of course we must wait for the issue to be resolved before getting paid...


 Hope your not dealing with VERIZON :no: I wish u luck my friend?


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## hbiss (Mar 1, 2008)

_The voltage fluctuates from 19v to 240v on the telco main with everything disconnected._

What the hell is a telco main?? How are you measuring this and what are you using to measure it? 

-Hal


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## oldtimer (Jun 10, 2010)

hbiss said:


> _The voltage fluctuates from 19v to 240v on the telco main with everything disconnected._
> 
> What the hell is a telco main?? How are you measuring this and what are you using to measure it?
> 
> -Hal


 telco.............Telephone Company.


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## TOOL_5150 (Aug 27, 2007)

oldtimer said:


> telco.............Telephone Company.


LMAO. I am sure that Hal knows that telco means telephone company.

~Matt


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## B4T (Feb 10, 2009)

hbiss said:


> _The voltage fluctuates from 19v to *240v* on the telco main with everything disconnected._
> -Hal


Are you sure about that..


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## TOOL_5150 (Aug 27, 2007)

B4T said:


> Are you sure about that..


Hey buba.. that line in italics posted from hal is a quote :thumbsup:


~Matt


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## B4T (Feb 10, 2009)

TOOL_5150 said:


> Hey buba.. that line in italics posted from hal is a quote :thumbsup:
> ~Matt


I got it now.. thanks


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## Edrick (Jun 6, 2010)

The line from the Telco is giving you 240? With the building isolated? The lines have somewhere around 40v of power regularly for the light up keypads and what not and 90v when ringing


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## hbiss (Mar 1, 2008)

Ok, not to scare this guy off but we do need more information. To the OP, are you saying that at the DEMARC (the "box" supplied by the telco where you connect your wiring) you have abnormal voltages across the telephone line T to R? Normally there will be 48vdc across an open line and when ringing there will be approximately 90vac at 30Hz along with that DC voltage. 

If you connect a telephone or butt set to your line and it has the 19-240vac as you allege you most certainly will hear a BAD hum and when the voltage gets up above approximately 60 volts it will ring! So, what happens when you connect a phone to that line?

-Hal


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## ce2two (Oct 4, 2008)

hbiss said:


> Ok, not to scare this guy off but we do need more information. To the OP, are you saying that at the DEMARC (the "box" supplied by the telco where you connect your wiring) you have abnormal voltages across the telephone line T to R? Normally there will be 48vdc across an open line and when ringing there will be approximately 90vac at 30Hz along with that DC voltage.
> 
> If you connect a telephone or butt set to your line and it has the 19-240vac as you allege you most certainly will hear a BAD hum and when the voltage gets up above approximately 60 volts it will ring! So, what happens when you connect a phone to that line?
> 
> -Hal


All homes at the neg.D, a.k.a demarc or the primm,located below resi. elect. panel ,you have a constant 48 volts D.C. ....240 volts (huh)???? sounds more like an alien on the telco line:laughing:work with telco,ask them to do a loop back ,intrusive testing,noise ,crosstalk.etc....
RED AND GREEN PAIR MOST USED COLORS USED THROUGH OUT TELCO INDUSTRY...SINGLE LINE?


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## mattb84 (Mar 19, 2011)

Yes i am refering to AC voltage across tip and ring at the demarcation box. I would imagine noise but, oddly, there is none. I assume the voltage is being induced from a transformer, adjacent line, or some other system. The voltage constantly osscilates in a very predictable pattern from 19VAC to 240VAC. It is something I have never seen. Never more than 10 VAC on a phone line while not in use.


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## hbiss (Mar 1, 2008)

Betcha you are using a digital volt meter (VOM) right? 

-Hal


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## mattb84 (Mar 19, 2011)

Yes I am. Just Purchased a new meter. Do you think that could be it? If there is no voltage issue I have to figure out what else could be causing the board failure.


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## 76nemo (Aug 13, 2008)

mattb84 said:


> Yes I am. Just Purchased a new meter. Do you think that could be it? If there is no voltage issue I have to figure out what else could be causing the board failure.


 
Hal's pointing towards capacitive voltage picked up by your high Z DMM.

Try a low impedance meter and report back to us. I'll be real surprised if you have 240V anywhere in your line..............


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## hbiss (Mar 1, 2008)

mattb84 said:


> Yes I am. Just Purchased a new meter. Do you think that could be it? If there is no voltage issue I have to figure out what else could be causing the board failure.


Usually high loop current is responsible for that sort of thing. It should be from 15-25ma DC. You measure it using a standard phone, your meter in series with either tip or ring. Go off hook and see what you get. You can use your new meter for this. There are loop current regulators out there that you can use to reduce high loop current.

To cover all your bases it would also be a good idea to install a surge protector on the line and properly bond it to the service ground. One that clamps at 120V should be good. 

-Hal


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## mattb84 (Mar 19, 2011)

Ok so armed with my old analog meter I have some more results. We have still been unable to connect to the telephone entry remotely. On hook voltage is 50VDC. Off hook voltage is 6VDC. Tip and ground tests less than 1V. These numbers are good but where I think the issue lies is when checking between Ring and ground 4VAC. The telephone company refuses to do anything about this saying it is within spec.


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## hbiss (Mar 1, 2008)

Again- what is the off hook loop current? 

Other than possibly indicating a long loop or high loop current those numbers are ok. Tip is ground back at the CO so tip to ground should be essentially zero and ring to ground should be essentially tip to ring, both with a couple of miles of wire factored in, if that DC imbalance is what concerns you. 

-Hal


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## cgray2 (May 31, 2008)

does the system have a good ground , should be less than 25 ohms measured with a megger clamp on meter


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## K2500 (Mar 21, 2009)

cgray2 said:


> does the system have a good ground , should be less than 25 ohms measured with a megger clamp on meter


Ohms with a clamp on?


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