Would you explain me more Mr. Smart and associates What to do???? I have new-built , 18-unit apatment, propsed a new 1200A, 3ph, 120/240v, 4wire delta (fed from overhead pole) in los Angeles . Meters are attaced to the main disc.-pull box. are you recommanding that I have to present two calcs, one for 3-phase which is 3-ph. elevator only and one 1-phase load calc for the rest of the building, frankly add both of them for determining final load demand????. Building And Safetey here (to approve the plans) wants red leg delta calc to determine service of pull box based on obtained largest leg Thanks
What I'm saying is you can't calculate the load in VA, then determine ungrounded conductor ampacity with 3? calculation. You have to take the apartments' load in VA and divide by 240V, then take the elevator load in VA and divide by 240V?sqrt(3), then add the result of these two calculations to determine the minimum ampacity of A and C lines. The B (high leg) will just be the result of the elevator load calculation (quite likely this value will be substantially lower, for the sake of discussion, let's say 200A). This will satisfy the calculations.
From there we have to get into the practical application of wiring and equipment. Let's say the A and C lines require 1200A wiring and equipment. If you have one service disconnecting means, it will have to be 3? and rated 1200A. That means your service conductor ampacity for the high leg will have to be 1200A as well (possibly feeder too), even though it will only draw less than 200A.
You could install a fused disconnect and use a smaller fuse for the high leg. This would permit you to use smaller wire for the high leg... but fusing is not my area of expertise. I am not certain if you can get a 200A fuse that fits in a 1200A disconnect. If not, perhaps they make reducing adapter... don't know.
Anyway, consider two service entrances: one 3?, one 1?. You'll likely have to go with a 1200A 1? disconnect because of conventional sizing, but you could go with only a 200A disconnect (and wiring) for the 3?. Price out a 1200A 3? disconnect vs. a 1200A 1? plus a 200A 3? and associated wiring...