[asterisk-users] Cisco power injector with GXP2000 phones

[Kristian Kielhofner]

On Dec 6, 2007 10:44 AM, Jon Pounder <JonP at inline.net> wrote:
> Quoting Salvatore Giudice <Salvatore.Giudice at VoIPSecurityTraining.com>:
>
> > The electricity is carried on different pins in a cisco poe injector. Just
> > because they both support the same standard doesn't mean they were
> > implemented the same.
> >
>
> I didn't even know the gxp2000's could handle poe - anyone care to
> share what voltage/current they expect on what pins ?
>
> even if I could just move the existing powersupplies back to the
> punchdown panel that would unclutter desks and make centralizing ups
> power that much simpler.
>

  Not a good idea.

  The Grandstreams expect 48V just like every other POE device.  Their
power supplies are 12V.  Simply splicing them inline with an ethernet
cable won't work.  To boot, some older Grandstreams use 5V power
supplies.  That obviously won't work either.  48V is nice because it
is high enough voltage to not suffer distribution loss over cable runs
but low enough to not cause major harm and still qualify as "low
voltage" under many codes, laws, etc.

  The biggest problem is that any properly implemented PoE device
negotiates PoE.  The other pairs of ethernet are not just live,
supplying 48V DC to anything.  That's why I refuse to use "passive"
PoE.  Just seems dangerous!


-- 
Kristian Kielhofner