[asterisk-users] Why Aastra uses 48V whereas other IP Phones use much less, i.e. 5-12V

[Steve Kennedy]

On Wed, Nov 22, 2006 at 06:58:13PM +0100, Huib van Wees wrote:

>    On 11/22/06, Zeeshan Zakaria <[1]zishanov at gmail.com> wrote:
>      Why Aastra phones use more electricity, i.e. 48VDC whereas other
>      phones use much less, e.g. Grandstream and Linksys both use only
>      5VDC. I first thought it was because of PoE, but the ones with 5VDC
>      also run fine on PoE. What is the difference in power consumption
>      then?
>    48V is also a sort of "standard" for telco devices.... if I remember it
>    correctly...

Power is nothing to do with voltage (well it is, but not alone), you
need the current too i.e. V * A.

Pylon electricity lines run at very high voltage (several hundred
thousand volts) or the current going down the lines would heat the
cables and you'd lose a lot of power.

48V is just a telco standard, and most telco equipment (that runs in
racks) is 48V. Probably because 110 (or 220/240 here in EU) is enough to
electrocute an engineer, and 5V/12V would require too many Amps so
wiring would have to be huge to carry the current.


Steve


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