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From: (John R. Levine)
Subject: Re: How to tell if PABX is suitable for modems?
Date: 26 Feb 1999 11:23:50 -0500

>I've never heard of a modem being damaged by being plugged in a digital
>line.  Most digital phones use 5-24 volts in combination across 2 to 4
>wires.  The modem has only one pair.  A regular phone line is 55 volts
>and ringing is 105 volts.

I've actually had a modem fried by plugging it into a digital PBX.
The voltage is OK, but the current seems to be a lot higher and that's
the problem.  It was a pain, I was in Australia and modems are really
expensive there.

Now I have a swell little doozit called an IBM Modem Saver, about the
size of a pen with an RJ11 plug on the end and some LEDs.  You stick
it into the jack and it tells you OK, reverse polarity but OK, or
excess current.  Costs about $30 from telecom suppliers.

John R. Levine, IECC, POB 727, Trumansburg NY 14886 +1 607 387 6869, Village Trustee and Sewer Commissioner,,
Member, Provisional board, Coalition Against Unsolicited Commercial E-mail

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