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Community Member

VG248 Line Voltage Drop outs with Alarm Systems???

My Security department is using a few analog lines off of a VG248 box. Their alarm panel has a device that monitors the phone line to determine if it has been cut. It does this by monitoring the voltage on the line. The vendor has determined that their box is seeing a voltage drop on this line several times a day. This is generating an alarm for them. I do not know what their threshold is for monitoring this voltage, but I’m trying to find out. Has any one else seen this with this device? Any suggestion how I can verify the line is actually dropping voltage? I do have the latest software on the box. Also I have two separate VG248 boxes, both are doing this, and there are five different alarm panels all doing this…

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Community Member

Re: VG248 Line Voltage Drop outs with Alarm Systems???

I don't have much idea about the alarm systems, but I do have an idea how the voltage drop can be monitored. You can find out the range of impedance on the phone line from you telephone service provider. It will be the maximum resistance to minumum resistance. As the resistance in the line increases, the voltage in the line drops. So with the known range, you can set the alarm system to watch out for the maximum impedance, that is when the voltage drops.

Community Member

Re: VG248 Line Voltage Drop outs with Alarm Systems???

From what we were told by the alarm company, they are looking between 40 and 4 volts. I have no way of telling if my voltages are dropping. From reading the VG248 has an idle voltage of 36v. This should be well within the range.

Community Member

Re: VG248 Line Voltage Drop outs with Alarm Systems???

Here is a bit more info. I put a voltage meter on my line and it reads 36 volts at idle. I put a head set on the line and it drops to about 5.5 volts. This would be ok then. The alarm guy came down and set his alarm panel to dial out and his line dropped down to 1 volt! I put my head set on and it only drops to 5.5 volts. I put an old analog telephone set on the line and it drops to 7 volts. I think there is an issue with their alarm panel

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