rack power question
Lamar Owen
lowen at pari.edu
Mon Mar 24 17:40:52 UTC 2008
On Sunday 23 March 2008, Justin Shore wrote:
> There are a few things to remember. Code only permits you to load a
> circuit to 80% of its maximum-rated capacity. The remaining 20% is the
> safety margin required by the NEC. Knowing this that means that the
> 12Kw specified above require 7x 20a 120v circuits or 5x 30a 120v circuits.
Cord connected loads can be 50A easily enough; something like a NEMA L21-60P
can give you 18KW in one plug (after 80% derating); if you could use 277V the
L22-60P is available to get you almost 40KW on one plug (again, after the 80%
is factored in; it's almost 50KW at 100% rating). Hubbell makes 60 and 100A
plugs and receptacles if 40KW isn't enough. PDU's for these are more scarce,
but I'm sure Marway would build to suit.
We have a few of the older Hubbell 50A twistloks here that were used for some
sort of signal processing equipment back in the day.
> Also remember that many of the larger servers (such as the Dell 6850s or
> 6950s) are 240v and will require a pair of dedicated circuits (20a or 30a).
The 6950 can run on 120VAC. That is one of the primary reasons we bought
6950's with Opterons instead of 6850's with Xeons; I only had 120VAC capable
UPS's at the time.
With router densities going way up, and heating going along with them, this
facilities issue can even impact the network operator.
> I would also recommend that you look into in-row power distribution
> cabinets like the Liebert FDC.
We have Liebert PPA's here. Two 125's and a 50.
> Grounding is a topic that is worthy of its own book. Consult an
> electrician used to working with data centers. Don't overlook this
> critical thing.
Ground reference grid. See Cisco's 'Building the Best Data Center for your
Business' book and/or Sun's Blueprint series datacenter book for more good
information. Also be thoroughly familiar with NEC Article 645.
While this discussion might seem out of the ordinary for a network operator's
group, it is a very good discussion.
Another good resource for datacenter/commcenter information is
www.datacenterknowledge.com; at least I've found it to be.
--
Lamar Owen
Chief Information Officer
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC 28772
(828)862-5554
www.pari.edu
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