North American Network Operators Group

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Re: rack power question

  • From: Lamar Owen
  • Date: Mon Mar 24 13:44:19 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; at least I've found it to be.
Lamar Owen
Chief Information Officer
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772