Ok, I have an existing multi-family dwelling unit building with individual dwelling units within. It has a 240V 3-wire service at 400A There are 6 units on the first floor, 17 units on the 2nd floor and 17 units on the 3rd floor. Currently, there is 1 feeder per floor and taps off this feeder to each dwelling unit panel which is 30A 240V. Due to the age of the panels, as a maintenance upgrade, we are replacing the panels, removing the existing main feeder to each floor and install new in the same conduit but of a larger size. The new feeder on the first floor will be 90A and on the 2nd and 3rd floor 150A. Taps to dwelling unit panels won?t be used, as we will have splices with same size panel feeder as the main feeder. The load centers will all be 60A except for a couple on the 2nd floor which will be 100A due to having electric ranges. ? the units have window a/c units now and they will add the rest of the window a/c units in the future. The a/c units plug into the closest receptacle. I have utility bill info and it can handle the additional a/c units.
Here is my question, we are doing this design work as a maintenance item and while doing it, improving the system by maximizing the existing conduit and doubling the size of the dwelling unit panel. Does all the calculations for feeder sizes and panel sizes need to be done such as 220.83, article 220 part III, etc? I do not think so, but I want to be prepared if the inspector asks. The way I see it, we are not adding any permanently connected load or upgrading the service entrance. This may sound odd, but if calculations are required, the service may not be large enough (by book numbers), the existing conduit my need to be removed and made larger as the feeders are too small (by the book numbers) etc and this is more than what we are trying to accomplish. Based on the utility info (1 years data) and that apartments with a/c now are fine with the existing 30A load centers, the system will work. Any thoughts?
Here is my question, we are doing this design work as a maintenance item and while doing it, improving the system by maximizing the existing conduit and doubling the size of the dwelling unit panel. Does all the calculations for feeder sizes and panel sizes need to be done such as 220.83, article 220 part III, etc? I do not think so, but I want to be prepared if the inspector asks. The way I see it, we are not adding any permanently connected load or upgrading the service entrance. This may sound odd, but if calculations are required, the service may not be large enough (by book numbers), the existing conduit my need to be removed and made larger as the feeders are too small (by the book numbers) etc and this is more than what we are trying to accomplish. Based on the utility info (1 years data) and that apartments with a/c now are fine with the existing 30A load centers, the system will work. Any thoughts?
