Re: Want to move to all 208V for server racks

[Lamar Owen <lowen () pari edu>]

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.