Re: Why -48V for telephone lines, and not positive?

From: Paul Burke (paul_at_scazon.com)
Date: 12/01/04 

Date: Wed, 01 Dec 2004 08:37:48 +0000

Winfield Hill wrote:

> JeffM wrote...
>
>>>when this stuff was invented
>>
>>Yup. Stroger Switches were invented in 1884--by an undertaker.
>
>
> Do you think they used -48V back then?
>

I would imagine that the requirements for long(ish) distance
communication had been worked out long before, by the Morse telegraph
companies (you know, the clerk heroically tapping away with the arrow
stuck in his back, dies as the cavalry rides over the hill), though IIRC
they used single wire, earth return circuits. The polarisation to avoid
corrosion of the wires would have come out of that.

Paul Burke

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