- Location
- Massachusetts
I will agree that for dwelling units these terms probably do not apply. The NEC does a reasonable job at providing guidance for determining the minimum size service for resi- and commerical loads.
I don't use the NEC for the work I do, it is all engineered.
It seems in this case your design would be less the the normal NEC minimums. I am not at all saying what you engineer does not work perfectly, just that in this case the NEC would provide a larger service then the method described here.
Basically, think of demand as what is the actual running load. Motors are the easiest to think of. Say you have a 5 hp motor 208V 3ph motor, the rated FLC is 16.7A. But the pump connected to the motor will never draw more than 87% of the motor power, and therefore the running load is 0.87 x 5Hp. So, when running it will never draw more than 14.6A. That is the demand (running) load.