Single and Multifamily Dwelling Units Calculations (Optional methods 220.82 & 220.84)

[PabloQG]

Hi all, first post in the forum.

Probably this has been asked thousands of times, but I can't find an answer.

When calculating feeders for multifamily dwellings, is it correct to apply both methods from 220 Part IV, or are they mutually exclusive?

For example, using the image below: Is it correct to calculate the feeders that go from the Meter Enclosure to the 100A panels using 220.82 for each panel? (Assuming that they comply with the requirements of 220.82(A) ). That is, treat each 100A Panel as an individual dwelling unit.

After doing that, is it correct to calculate the Main feeder using 220.84? If not, what would be the proper method to calculate the Main feeder?

 

[Dennis Alwon]

That is how I would do it.

 

[PabloQG]

Thanks!..I thought so, but didn't knew if it was entirely correct or if there is any other consideration.

Now, after sizing the feeders according to 220.82, and main feeder according to 220.84, is it correct to apply the 83% rule (310.15(B)(7)) to the main feeder? That would really let the ampacity of the main feeders below the connected load, but I can't find any prohibition to do so, as long as the service rating is between 100A and 400A.