[time-nuts] Where does 28V come from?

J. Forster jfor at quik.com
Tue Jul 21 14:39:59 UTC 2009


The higher voltage is used to get a longer range for the subscriber loop
in the pre amplifier days w/o using heavier wire. Remember, there is LOT
of copper in a POTS netrork.

They probably studied the problem very thoroughly in the late 1800s,
trading off cost for safety (electrocution danger). There was no PVC or
Teflon, just wax and dry paper.

I seem to remember the positive ground was for corrosion protection.

-John

=============


> Most wireless sites will be 28 volts also. Some are switching to the telco
> standard of -48 which when measured is actually around -56 volts. One
> reason for going to a higher voltage is, you can use smaller conductors to
> get same amount of power out.
>
> Not to steal the thread, but any one know why the telephone company choose
> to use a negative voltage? Where as the positive is referenced to ground?
> When I was a kid I was told it was because they discovered that the
> battery terminal would corrode if it was done that way?
>
>
>
>
>
>
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