The rules for feeder and service load calculations differ from those for branch-circuit calculations. Do you know the differences?
With branch circuits (Art. 220, Part II), you’re basically determining what the various loads will be for a given structure. That is, X amount of lighting load, X amount of receptacle load, X amount of specific loads based on the occupancy or some other factor.
But you size each of your feeders based on the sum of the branch-circuit loads it supplies. The calculated load of each feeder can’t be less than that number [Sec. 220.40], after applying the load factors permitted by Part III or required by Part IV of Art. 220. This rule for feeder sizing also applies to service sizing [Sec. 220.40], thus Part III addresses feeders and services almost without distinction between the two.
As might be expected, Part III is filled with demand tables and rules for using them. Before moving on to those, we need to address the Informational Note of Sec. 220.40. It’s really two notes. In Part 2, we’ll discuss why glossing over this Informational Note is a mistake. The first note contained in this note is of particular importance.
