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