TELECOM 247

> Mike wrote in message
> news:2vqdnYxTO44cQ6DanZ2dnUVZ8tHinZ2d@pipex.net...
>> 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.......
>>
>> :)
>
> OK - why.....
>
> and why not have used +50v and earthed the -ve ?
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