Re: multi-dewelling units calculation
Originally posted by mikeackley: Maybe you have found the answer, without fully realizing it.
I realized it; I?m just not convinced that it is the right answer. I have two reasons. First, 430-24, -25, and -26 (and while we?re at it, -22) all speak of conductor ampacity. When 220-14 points you in that direction, you should expect to find information about motor loads, not conductor ampacity. So the correlation is not entirely satisfactory (meaning, not completely clear). Secondly, the 2002 code points you in a new direction: to 440-6. That paragraph also speaks of conductor ampacity, but it does not add 25%.
My belief is that you always include air conditioning at 100% (assuming it is larger than heating), and never at 125%. HOWEVER, you still need to add 25% of the largest motor, whether it be the A/C unit or some other motor. To be precise, you never include the A/C at 125% and then add 25% of the largest motor on top of that.
To support my position, I cite NEC Example D1(b) (both 1999 and 2002 codes). The A/C unit is included at its nameplate rating (12 amps), and the 25% for the largest motor is added in as a separate line item.