Calculation Question for Upcoming Masters Exam

[Jnorton195]

An office building to be constructed will have two hundred and fifty, 20 Amp, 120 Volt duplex receptacles installed. Determine the MINIMUM number of 120 Volt, 20 amp circuits required to supply the receptacles.

This question is on my study material and my answer was:

250 X 180 VA = 45000 VA - 10000 VA = 35000 VA X .5 = 17500 VA + 10000 VA = 27500 VA / 2400 VA = 11.45 (12) branch circuits.

The study material I'm using is not using the Table 220.44 Demand Factor and is dividing 45000 VA by 2400 VA to get 18.75 branch circuits.

Can someone help me understand why the demand factor from Table 220.44 wouldn't be used? Or if it is an incorrect solution on the author of the study material?

 

[JoeStillman]

The demand factor of 220.44 applies to the aggregated load of all the branch circuits, but not to the branch circuits themselves. Your demand calculation is correct, but can only be applied to the service calculation, not the individual branch circuits. Note that article 220.44 falls under Part II - Feeder and Service Calculations. The relevant Code Article is 210 - Branch Circuits, 213.23 Permissible Loads.