we recently moved a bunch of POTS lines from Verizon to MCI, and we also ordered five additional new MCI POTS lines. We had the ported POTS lines connected to modems and faxes. Since the port, the modems all drop the calls and so do our fax machines. We also tried using the five new POTS lines but same results. PBX tech says he has dialtone but something is slowing down the lines and he says it is probably a line voltage problem and MCI needs to come out. My manager disagrees and says the tech is incompetent. I'm not at this site so I can do no testing myself. Has anyone ever experienced a similar problem? thanks for your input.
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line voltage on POTS lines
- Thread starter coniglio
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There are two types of pots lines loop start and ground start. These days, most lines are loop start. The POTS phone line, with all phones on-hook, should measure around 48 volts DC. This drops down to the 3 to 9 volt range when a telephone on the line goes off-hook. An off-hook telephone typically draws about 20 milliamps of DC current to operate, at a DC resistance around 180 ohms. The remaining voltage drop occurs over the copper wire path and over the telephone company circuits where there is usually 200 to 400 ohms of series resistance to protect from short circuits and decouple the audio circuits. To ring your telephone, the telephone company momentarily applies a 90 VRMS 20 Hz AC signal to the line. Even with a thousand ohms of line resistance, this is still a bit of a shock, so be careful when you are probing around trying to find a POTS line.
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You either have a sealing current problem, current powers the phone devices or a signaling problem or a disconnect supervision problem--all of which the problem resides with the telco. You biggest problem will be convincing the telco that they have a problem.
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if their copper trnuks, or if their on a channel bank, i would connect a butt set to the demark and test.. if you don't have a but set any analog phone will work on a loop start line, for ground start you'll need to touch a ground to the tip (top) side of the line and remove it.. since it's a fax/modem line it will be loop..just like a home line. fyi.. i will not put loop start lines on a pbx..
john poole
bellsouth business
columbia,sc
john poole
bellsouth business
columbia,sc
This might sound real funny, but are the fax machines not picking up? and the fax maintenance vendore stating that the machine is not getting enough voltage to "ring" the fax machine? Put a telephone on the line and if it rings you should be getting enough power to trigger the fax machine.
or check the auto answer button on the fax machine and make sure it's on.
John
or check the auto answer button on the fax machine and make sure it's on.
John
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MCI tech and PBX tech are meeting at the site this morning so hopefully they'll be able to figure this out between the two of them. It's the PBX tech who's mentioning the voltage problem. We're also having a problem with some modems as well as the fax machine. We'll see what happpens...I'll let you know. Thanks, all.
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MCI tech said the DB level on MCI's lines was twice what it should be. Their DB level is -13 and PBX's is -20. I don't pretend at all to know what these numbers mean but at least now the problem has been identified and is being resolved. Thank you all for your input.
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