TELECOM 247

>
> On Fri, 16 Nov 2007 16:58:31 -0000, steveybar
> wrote:
>
>>
>>Ivor Jones wrote in message
>>news:5q5lrnFu6qbgU1@mid.individual.net...
>>> wrote in message
>>> news:8b8a3b8a-e02d-404a-b16a-d231440406df@e25g2000prg.googlegroups.com
>>> : : why telephone offices have -48V sypply ?
>>>
>>> Its 50V actually, to power the exchange (not CO were British here)
>>> equipment, why do you ask..?
>>>
>>> Ivor
>>>
>>
>>Yes, Ive also always wondered why -50v dc, why not -25v or -75v or -100v
>>or
>>.....?
>
> No idea, something historical and probably thought of in the days
> before there was even a Post Office Electrical Engineers Journal
>
>>And whilst we are at it, why is it a -ve value (-50v), and not a +ve value
>>(+50v) ?
>
> Because the +ve is earthed
>
> Now ask why.......
>
> :)