Sizing a device for multifamily dwelling

[Blakeehunter]

Hello everyone new here and have a question I'm looking to resolve.
Good evening, I had an electrical question for you. I am currently working on a multi family apartment complex. I did a load study for each unit and determined the load for each unit and then sized my service accordingly, my question involves the capacity of the service, we will be using #2 alum SEC due to availability, we will be installing 100 amp disconnects with 100 amp breakers. The loads do not require 100 amp capacity, some 60 some 70 some 80. The meter sockets are 4 gain . So would my service need to be sized for 400 amps or the actual calculated load ?

 

[WA_Sparky]

Sizing a device for multifamily dwelling

You may want to change your feeder size, #2 AL seems to be rated for 70A. The feeder should be rated for the Over current protection serving the panel. 100A feeder using AL is #1/0 according to my chart. (Voltage drop calculation will need to be done for long distance feeders and my result in upsizing feeders).

My standard practice has been:

Size panels based on demand load.

Size service = (sum of all Dwelling unit connected loads)*nec 220.84 factor [based on number of units] + demand load of house panels.

Hope it helps.

 

[mopowr steve]

You may want to change your feeder size, #2 AL seems to be rated for 70A. The feeder should be rated for the Over current protection serving the panel. 100A feeder using AL is #1/0 according to my chart. (Voltage drop calculation will need to be done for long distance feeders and my result in upsizing feeders).

My standard practice has been:

Size panels based on demand load.

Size service = (sum of all Dwelling unit connected loads)*nec 220.84 factor [based on number of units] + demand load of house panels.

Hope it helps.

Actually (If memory serves me right) if those are dwelling units and the feeders solely feed from service disconnect and the panel with no other loads before it then the feeder can be sized same as service conductor as #2 AL.

 

[topgone]

Actually (If memory serves me right) if those are dwelling units and the feeders solely feed from service disconnect and the panel with no other loads before it then the feeder can be sized same as service conductor as #2 AL.

#2 AL is good for 90 amps right? Are you not skimping on wires?

 

[Little Bill]

#2 AL is good for 90 amps right? Are you not skimping on wires?

There used to be a table (Table 310.15(B)(6) that could be used for single phase 120/240V for dwelling units. It allowed smaller conductors than was allowed by the ampacity tables. #2 Al was good for 100A service. I don't have my 2017 handy but now, instead of the table, you use 83% of the service size. So 83% of 100A is 83A. So it's about the same thing as #2 Al is good for 90A and that will cover the 83A derived from the 83% rule.

 

[mopowr steve]

Thanks Bill

 

[WA_Sparky]

Thanks for the update

Thanks for the update

Sorry for the bad information. Thank you guys for correcting me. This is why I like this forum. So much knowledge available in one friendly place, cheers.