Calculating amps and load of a system

[nahoku]

Hello,

we are trying to figure out why some of our numbers do not make sense to us. We are building a cluster of computers using Dell machines. Their environmental impact charts specify that each of the machines at min operation requires 250W and at maximum operation 405W. This would then translate to 4.4amps @ 115Volts, if I am using the correct formula. For 100 machines this would translate into maximum draw of 440amps, just simply multiplying the numbers.

Dell provided us with 15 extension cords, each of them is rated as 16amps @ 120 Volts (these are special extensions for the Dell racks, and have a three-prong plug that goes into the wall outlet). This would multiply to a total of 240amps, definitely almost half of what we have been given as a draw from their environmental impact charts. Shouldn't these numbers coincide?

Thanks much!

Geek in need of help

 

[MintJulep]

Your calcs are correct.

Dell has either not throught things out, or is counting on a hefty diversity factor. In general, computers rarely operate at max power draw, and the likelihood of 6.25 computers operating full blast at the same time is remote.

Why did Dell provide 15 cords for 100 computers? Seems like a number that is a factor of an integer would be nice.

 

[nahoku]

Hello - thanks for the reply, cofirming our logic on this to be correct. We are installing the 100 machines into 3 racks (closets) that are connected, and Dell provided us with 5 cords per closet, making it a total of 15. 5 cords have enough outlets to plug in the 42 machines that fit within one closet (I think there's 7 outlets on each cord).

Thanks much again.