Yes.  Originally the concept of an "electron" wasn't known and experiments
in the 19th Century seemed to point to "positive" things moving to
"negitave" things.  I'm old enough that my early cars were
positive-ground...as is all telephony still.

. . . J o n a t h a n 

-----Original Message-----
From: wireless-boun...@wispa.org [mailto:wireless-boun...@wispa.org] On
Behalf Of Tom DeReggi
Sent: Thursday, March 18, 2010 6:26 PM
To: WISPA General List
Subject: Re: [WISPA] -48vdc Gigabit switch

While on the subject.... Anyone know why the concept of  positive ground
was implimented? What was accomplished by not doing negative ground like
everything else typically does?

Tom DeReggi
RapidDSL & Wireless, Inc
IntAirNet- Fixed Wireless Broadband


----- Original Message -----
From: "Jeremy Parr" <jeremyp...@gmail.com>
To: "WISPA General List" <wireless@wispa.org>
Sent: Thursday, March 18, 2010 3:11 PM
Subject: Re: [WISPA] -48vdc Gigabit switch


> On 18 March 2010 14:48, Cameron Crum <cc...@dot11net.com> wrote:
>
>> You could always reverse the leads for a +48 switch or pull 12v or 24v
>> off one or two of the batteries.
>>
>
> No no no, *DO NOT* do this! -48vdc, but its very nature, is positive 
> ground.
> If you plug in a +48vdc device with the polarity reversed it will boot
up,
> and will probably link up via  UTP patch cable to another device. If you
> plug in a STP patch cable, or a console cable with a ground, you will 
> likely
> let the magic smoke out. Recharging the magic smoke reservoir can be an
> expensive procedure.
>
>
>
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