Well, first of all the fact that the gear is rated for 1600 amps does not mean that it is served by a transformer capable of supplying 1600 amps. But letís take for granted, for now anyway, that it is.
1600 amps times 480 volts times 1.732 (the square root of three, a term that always finds its way into three phase calculations) gives you a total of 1,330,000 VA, or 1,330 KVA. If all the loads were resistive (i.e., no motors, no inductive lighting ballasts, no welders), you could use this value as though it were the same as watts. Thus, in your building of 183,894 square feet, you have 1,330,000/183,894, or about 7.2 watts per square foot.
If there are inductive loads, and this is likely, you would get watts from VA by multiplying VA times the power factor. Letís assume a power factor of 0.90, just for discussion.
1,330,000 VA times 0.9 is 1,197,000 watts. Then, 1,197,000/183,894 is about 6.5 watts per square foot.
Charles E. Beck, P.E., Seattle
Comments based on 2014 NEC unless otherwise noted.