To be clear, this is meant as "The minimum feeder conductor size shall have an allowable capacity, after the application of any adjustment or correction factors, not less than the maximum load to be served." The adjustment and correction factors have nothing to do with Article 220. They refer only to (2017) 310.15(B)(2) and (3).
Cheers, Wayne
I've had to read this a few times, so you saying in escense, after finding load amount, that number stays static, and as you apply the adjustment or correction factors to the wire size, you keep adjusting that wire size until after the adjustments (per 310) the load capacity of conductors now match your predetermined load? Thus the seaming oversized conductors found by my illustration for 215.2(A)(1)(a) when compared to that of (b), (a) was not calculated correctly, the factors found in 220 need to be applied to both prior to the adjustments found in part (b) from your statement.
It seem that the code may acknowledge there maybe a difference in results between the 2 methods when it says to use the largest of the 2.
So see if this is a better understanding, Example: Start with a XXAmp load (L), by itself says Z for conductor size, but after applying adjustments (c) that conductor no longer has an XXA capacity but now is L-c, (with adjustment) and L not=(L-c). So now using an educated guess you recalculate using a larger value for L call it L1, in the end L1-c must equal L. L=(L1-c), and then you use L1 ampacity for determining conductor size
It also seems that 220 calculations would come before that of the adjustments referenced in 215.2(A)(1)(a) or (b) in order to get to the value of (L)?
Article 220 is "
Branch-Circuit, Feeders, and Service Load Calculations." From that it would appear Article 220 would definitely have something to do with getting to the conductor size, in that it gets you to the load requirements. 215 does directly makes reference to 220 requirements in determining feeder size. However I don't see any mention of 310 in Article 215. Or is this a case of "all other relevant code" requirements seen in many code articles?
Article 220 applying to both 215.2(A)(1)(a) and (b). Let's see if this looks better:
If feeder is only serving the lighting load, in a dwelling unit load is at 3VA per sqft before any adjustment if you are dealing with 2500sqft you have before adjustment 7500VA. 220.42 application also applies. 1st 3000VA at 100% 3000/240 is 12.5A, leaving 4500VA at a factor of 35% leaving 1575VA/240V is 6.56A so now (a) provides 19.06A non continuous load at 100%. Lighting loads supplied with 120/240V and you have 31.25 amps as a starting point. If none of that load is continuous then for 215.2(A)(1)(A) you use only 100% or 31.25A. Lighting in a commercial space could fit definition of continuous load and then would be calculated at 125% 23.825A
Now if you use 215.2(A)(1)(b) you apply adjustments to that for simplicity say your only adjustment is that found in 220.42. 1st 3000VA at 100% 3000/240 is 12.5A, leaving 4500VA at a factor of 35% leaving 1575VA/240V is 6.56A so and now (b) provides 19.06A adjusted. Then apply adjustment from 310 If this is applied to feeder size general rule you would size feeder to the larger of either methods. This illustration feeder would be sized to 31.25a. 19.06A, In a residential unit. If an adjustment made per 310 for temp 310.15(B)(2)(a) 75° column, ambient temp 87-95° give adjustment of .94 it is now 17.916A. That is less than minimum allowable ampacity of 19.06A, so must size up, if use conductors rated to start with rated 20.4A by the adjustment of .94 you now have 19.176A which meets minimum ampacity required.
Does this look better?
