> (Scratching head a bit...) I did BE project in communication and hence come
> to know that the telephone ring used in all exchanges is 75V AC RMS, riding
> on -48V DC, to facilitate dialing from ringer (mechanical spring dialing,
> old style) fones.
The 75V AC is activated at the time of ringing.
> Now internal modem derives power from PC power supply only. Given the
> reputaion of indian government service, how safe internal modems are, from
> passing the surge to the Mobo?
The Indian Govt. no longer takes care of telephone services. Its BSNL.
There is nothing as a surge transfer.
> There are protective circuits etc. on modem but mobo power line directly
> connected to exchange one is rather hairy scene to me. Especially when
> polarity reversal is not impossible with exchange(Happens with electricity
> board too...)
Will never happen, neither has ever. There is no concept of polarity
reversal in telephone exchanges. Besides, the exchange supply is completely
*isolated* from the mobo circuitry. Ever tried connecting your telephone to a
220V outlet ?? Your telephone wont be damaged. It'll cost just about 10-15 Rs
to fix the burnt out isolator. Or for that matter, ever tried feeding the
telephone jack 220 V. According to you, the telephone exchange should catch
fire. But never happens. At the most, your card at the exchange would have to
be replaced.
> Just a naive thought...
Never mind. There's always time to learn.
Regards,
Saurabh Garg
--
Linux renders ships, NT is rendering ships useless.
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