You are maing it too complicated
You are maing it too complicated
Please let me start over.....
I have 360 total pieces of PC equipment that draw 2 amps each at 120 volts.
That is a total of 720 amps.
I cannot fit more than 37 of these PCs in a row under a busway. Hence, 74 amps per busway.
The busways are RATED for 100 amps. I dont need to fuse them at 100 amps.
74x120=8880 VA
8880/208x1.73=24.6 amps (a three pole 30 breaker, should be bumped to a 40)
8880/480x1.73=10.7 amps (a three pole 15 breaker, will probly get a 20)
24.6 amps per leg=73.8 total on one busway to cover my 37 MAX PCs.
12 busways X 74=888 total available amps. More than enough to cover my total expected load.
So, can i get away with 10 KVA freq converters instead of my original calculation of 40 KVA?
The only real problem I can see with this route is ensuring that the loads are always balanced, so not to trip the 30 or 40 amp breaker, correct?
First off, the converters need to be sized for the load not the breakers. You could have 500A busses, with 500A breakers and only 74 amp converters. The converter protection is independent of this and per the manufacturers instructions. So get that out of the way.
You have 37 units at 2 amps each on one leg of one bus. Since you don't explain what the output of the converters is I will explain assume the following from previous posts. If this is not the correct assumptions, please write back again.
If you have a 3 phase inverter, required to feed 74 amps per phase on a 3 phase bus, the next thing you need to know is whether the loads are continuous, or if you want head room for design comfort. If you want either of the above then modify the 74 amps accordingly (i.e. 74x125%=92.5) and use that amperage as a base.
The rest is straight forward. 74 amps x 208 volts x 1.73 (which is the square root of 3 and represents the phase angel between the phases) = 26,628 va End of story. You had it all, but got hung up with all the little stuff. If all 37 loads are not expected to be at full usage for a minimum of 3 hours at a time, and a computer is not going to, then it is not a continuous load and you don't need the 125%. The calculations of the load requirements are competely independent of the calculations for feeder circuits, bus sizes and overcurrent protection. Whatever reference you were making to balanced loads also has nothing to do with these calculations. If you are putting 37 loads on a phase and can't put any more on then that prevents overloading. While the entire system and electrical grid is more efficient with balanced loads, it has nothing to do with the above calculations per phase.
BTW, if you actually mean that you can only fit 37 units total on a 3 phase bussway, then that obviously changes everything, and that is why I say that you have not described your actual situation comprehensively. If we are not giving the correct responses, please try describing the exact installation, wihtout trying to determine sizes or solutions.
37 units at 2 amp divided by 3 bus phases is 9 12 with 1 left over. So 13 x 2 = 26 amps maximum per phase 26A x 208V x 1.73 = 9356 va again doesn't allow for continuous loads.
Still don't know exactly what you need to accomplish. Hope this helps and doesn't confuse more. Keep it simple.
