[j-nsp] EX4550 true power consumption

[Chuck Anderson]

On Thu, Oct 24, 2013 at 09:38:43AM -0700, Michael Loftis wrote:
> I don't know anyone that assumes that the peak capability of a PSU
> (especially in network gear) is it's actual consumtion, but thats just
> me.  I do agree I wish they'd publish at least approximate figures.
> It can be a deciding factor in a lot of environments today.  Keep in
> mined 650W is high-line mode (~220/240VAC) - in 120V it's only going
> to be around 325W.

This deserves clarification.  The power usage in Watts for a given
hardware configuration should be the same either way--it is just that
in high-line mode 208/220/240V, you will draw less current in Amps, by
about half for twice the voltage (ohms law approximately, with a Power
Factor Correction thrown in), and because of this the power supply is
designed so that you can consume up to 650W of power only if you use
high-line mode, and if you max-out the supply in low-line 120V mode
you will only be able to consume up to 325W.  This implies that if you
use low-line mode, you won't be able to install as many
modules/optics/whatever-else-uses-power before hitting the max or
losing power supply redundancy (being that both PSUs will be required
to power everything).