load calculation with 3 phase supply

[surfwyoming]

I am calculating a 100 room condo that is supplied with 3 phase power.
I have 2 small appliance circuits, 900 va lighting load, 20 amp ac/heat 120 volt, and a 20 amp 240 volt cook top. I add all these up and use demand
factors.
My question is do I use 208 times 1.71 or just the 208 to get my individual loads and therefor my total load.

 

[charlie b]

Add the loads in terms of VA first. If you only know a load in terms of its current, then convert it to VA, and add it to the rest. For an individual load, you convert to VA by multiplying by the voltage it requires (i.e., 120 or 208), and if it is three phase you also multiply by 1.73 (that's a bit closer than 1.71).

After you get the total VA, and after you have taken advantage of any available demand factors, then and only then do you convert back to amps. Since the system is three phase, you divide the total VA by 208, and then divide the result by 1.73.

Welcome to the forum.