Apartment demand factor

[new_ee]

I have a 12 unit apartment that has a 36360VA (151.5A single phase 120/240) load on each unit panel. Im using a 41 demand factor based on table 220.32 for the service size. Im coming out with 1813.8 A total load and then 743.7 A load after applying the demand factor.

My question is really about the individual unit panels. What does the individual panel (and feeders to the panel) have to be rated for? The total load of 152A or the 743.7/12 units 62A?

 

[charlie b]

Re: Apartment demand factor

An easy way to look at it is to look at one service or feeder at a time. You use whatever demand factors apply to the loads that are powered through that service conductor or that feeder.

In other words, when you are looking at the service to all 12 units, you add up the loads on all 12 units, apply the 41% demand factor, and get the 743.7 amp service load.

Then you look at the feeder to a single unit. You will note that the table from which you got the 41% (i.e., Table 220.32) does not have an entry for "1 unit" or "2 units." Therefore, the demand factor of 41% would certainly not apply to the feeder to a single unit. In fact, that entire article, 220.32, does not apply to a single unit. You must size the unit feeder for the 151.5 amps.

You do have an alternative, though. You can use the standard calculation process, and you can use the optional method of 220.30, and size the unit feeder for whichever of these two gives the smaller answer.

 

[new_ee]

Re: Apartment demand factor

Thanks. I was headed in that direction (I think). What do you mean by standard method? The method I have already used (adding up the loads on the panel)?

[ July 26, 2005, 04:48 PM: Message edited by: new_ee ]