[133098] in North American Network Operators' Group
Re: Want to move to all 208V for server racks
daemon@ATHENA.MIT.EDU (Lamar Owen)
Sat Dec 4 11:06:39 2010
Date: Sat, 4 Dec 2010 11:05:56 -0500
From: Lamar Owen <lowen@pari.edu>
To: nanog@nanog.org
In-Reply-To: <20101203075436.GX1583@angus.ind.WPI.EDU>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Friday, December 03, 2010 02:54:37 am Chuck Anderson wrote:
> Here's a question for you. How do you calculate the total current &
> power capacity of a L21-20 or L21-30, and how do you do the
> calculations in order to balance the load between the phase legs?
> This seems like it would be a trivial thing to do, but given that the
> three legs are 120 degrees out of phase with each other, I don't think
> you can just do normal addition.
You would be correct. A pretty good three-phase calculation reference can be found at http://www.3phasepower.org/3phasepowercalculation.htm
It is vector addition, and with the angles involved you end up multiplying and dividing by the square root of 3 a lot.
Also see the wikipedia article, and here's a few others:
http://www.gavinelectrical.com/content/threephase.htm
http://www.servertech.com/uploads/documents/0000/0236/3-Phase_Power_in_the_Data_Center.pdf
That last PDF is directly related to this discussion, and a good read.
