#### erickench

##### Senior Member

- Location
- Brooklyn, NY

- Thread starter erickench
- Start date

- Location
- Brooklyn, NY

- Location
- Connecticut

- Occupation
- Engineer

220.42 is one of the demand factor of Part III. I think the demand factor in 220.42 could be applied to the service or feeder that serves the multifamily dwelling for the total load of all the dwelling units.

- Location
- Seattle, WA

- Occupation
- Electrical Engineer

When calculating the service to the building as a whole, you start from scratch, and do not simply add the results of the individual unit calculations. Make a list of all the loads in the entire building, and apply the appropriate demand factors. Specifically, when using Table 220.42, you use the square footage of the entire building.

- Location
- Brooklyn, NY

- Location
- Seattle, WA

- Occupation
- Electrical Engineer

- Location
- Brooklyn, NY

Okay, but do you at least agree that the subfeeders to the apartments should be sized according to NEC 220.42? Then I would apply the optional calculation method.

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- Location
- Connecticut

- Occupation
- Engineer

I don't quite understand what you are asking. The subfeeders to the apartments could be sized EITHER according to the method in 220.40 or the optional method in 220.82.Okay, but do you at least agree that the subfeeders to the apartments should be sized according to NEC 220.42? Then I would apply the optional calculation method.

A 1500sf apartment would have 4500va lighting per 220.12. Using 220.42 the feeder to the apartment would include 3525va lighting plus the additional loads in 220.40. Per the optional method in 220.82, 4500va of lighting plus the additional loads listed would be added together and applied with the first 10kVA at 100% and the remainder at 40%.

- Location
- Brooklyn, NY

What I'm saying is I just don't consider it appropriate to use the standard method to size the service conductors for a multifamily building. To me the demand factors just wouldn't be applied properly but that's just my opinion. If I were a designer I would use the standard method to size the subfeeders to each apartment panel and the optional method to size the service conductors. This to me make's more sense. But that's just a matter of preference.I don't quite understand what you are asking. The subfeeders to the apartments could be sized EITHER according to the method in 220.40 or the optional method in 220.82.

A 1500sf apartment would have 4500va lighting per 220.12. Using 220.42 the feeder to the apartment would include 3525va lighting plus the additional loads in 220.40. Per the optional method in 220.82, 4500va of lighting plus the additional loads listed would be added together and applied with the first 10kVA at 100% and the remainder at 40%.

Last edited:

- Location
- san jose, Costa Rica, code NEC USA

Hello,

When calculating the service to the building as a whole, you start from scratch, and do not simply add the results of the individual unit calculations. Make a list of all the loads in the entire building, and apply the appropriate demand factors. Specifically, when using Table 220.42, you use the square footage of the entire building.

It would be possible to use the optional method part IV just for the calculation of the feeders of each dwelling, and then use the standard method for the calculation of the service conductors that supply all the dwellings?

Thanks in advance,

Regards,