multifamily service calculation 120/208 3 phase supply

[mrushing22]

Can someone clear up how to calculate the demand for single phase ranges and dryer on three phase service. I understand how to arrive at the maximum connected between any two phases.For example if I had a 15 unit apartment building and each had a single phase 5KW dryer I end up with 5(total connected between any two phases)x2=10 dryers so is the correct demand 10x5KW=50KW x.5(220.18)=25KWdemand This how I understand it that you apply the demands in 220.18 and 220.19 after you figure the max connected between any 2 phases x 2.If you look in annex D examples example D5a does this and then figures an equivalent 3 phase load. Can any help?

 

[charlie b]

Re: multifamily service calculation 120/208 3 phase supply

That is not what Example D5a does. I think you misread the example, in the following way: When that example divides the 8000 VA for a range by 2, and again by 120, it is trying to size the branch circuit conductors for the range. That part of the example has nothing to do with total calculated load.

You need to keep everything in terms of VA, until the very last step (i.e., when you convert to amps for the service size). A single dryer is 5,000 VA. It does not become ?2 times 5,000 VA,? when it is connected between two phases (as opposed to a 120 volt single phase dryer, or as opposed to a three-phase dryer, if such things exist). A ?VA? is a ?VA,? no matter how many phases are involved.

So for your example, 5,000 VA times 10 units times 50% demand factor equals 25,000 VA. That is the amount to include in the calculations.