[j-nsp] AC power distribution for the MX

[Richard A Steenbergen]

On Mon, Apr 19, 2010 at 04:22:58PM -0400, Ross Vandegrift wrote:
> Hi everyone,
> 
> Juniper docs claim this about the power system for an MX480: "Each
> inlet requires a dedicated AC power feed and a dedicated 15 A (250
> VAC) circuit breaker."  This seems silly - so long as we're
> careful not to overload any circuits and pull from diverse panels, why
> would they care?
> 
> Does Juniper have a good reason to require this, or are they just
> trying to prevent people from plugging all four PEMs into the same
> circuit and thinking that they are redundant?  Any suggestions for
> good AC distribution gear?  APC AP9570 looks like what I'd use if left
> to my own.

You're right this isn't required at all. I think the point they're
trying to drive home is that you shouldn't just plug them all into a
single 15A breaker and assume everything will be good forever. Each
power supply only does 1.7kW anyways (in 200-240V mode) so a dedicated
15A would be way overkill (unless you're talking about the new power
supplies for fully loading a box w/Trio cards or something). Maybe they 
meant a dedicated 15A at 110V. :)

Obviously the draw is relative to the number of cards you have running
too, i.e. you should be able to run a MX480 with a single DPC on a
single circuit no problem. When doing your power calculations don't
forget that the fans can suck a decent amount of juice when they kick
into high speed mode, so be sure to check the draw under those
conditions too (unless you don't mind tripping breakers when it gets
hot).

If you're feeding off a 30A 208V the AP9570 is a good choice (assuming
you don't want metered, switched, or anything fancy like a zero U bar). 
If you're feeding off a 20A 208V, the AP9566 is about as cheap as it
gets, and works quite well. This is what I run in my basement at any
rate. :)

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
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