3 family House with detached warehouse.

[SpotOn]

Hello everyone newbie here,

I have always worked on single family homes and am working on my first multi family home project.

The Building has one house panel, three apartments each with
*Electric heat (heat pump)
*Electric Hot water
*8 kw range
*Electric Dryer
*Misc exhaust fans etc.
*Standard 3 VA general load, 2 appliance, 1 laundry

AND there is a 3600 sf detached warehouse being fed from this service

The service to the building is three phase 120/208
each dwelling unit will have 120/208 single phase
the warehouse will have 120/208 three phase


I have never had to do a calculation for a multi family home and am wondering how to go about sizing the "house panel"
in CT we are still on the 2005 NEC. article 220.84 says the house loads shall be calculated in accordance with part three.
Do i take the common area square footage to get the general lighting load? Do i still need to have small appliance circuits etc or just the connected loads?

I also noticed in 220.55 it states that "where two or more single-phase ranges are supplied by a 3-phase, 4wire feeder or service the total load shall be calculated on the basis of twice the maximum number connected between any two phases" . Does this mean I need to double the calculated size? for example if I have a range on A & B, one on B & C and one on A & C each range is 8kw I need to calculate each range at 16 kw before the demand factor adjustment?

Another question i have is for sizing feeders for the individual units. I'm assuming those feeder are sized at 100% and no demand factors are to be used, is this correct?

Thank you in advanced for any help
Best Regards,
Jon

 

[Dennis Alwon]

The easiest way for me to explain this is tell you to look at Annex D examples in the back of the code book. Specifically you want Example D5(a). At the end of the example is also a description for 3 phase feeding single phase ranges

 

[david luchini]

I have never had to do a calculation for a multi family home and am wondering how to go about sizing the "house panel"
in CT we are still on the 2005 NEC. article 220.84 says the house loads shall be calculated in accordance with part three.
Do i take the common area square footage to get the general lighting load? Do i still need to have small appliance circuits etc or just the connected loads?

Yes, the house loads would be based on the common area square footage for lighting load, and any other loads that are supplied by the house panel. There is no need for SA circuits, etc, in the house load calculation.

I also noticed in 220.55 it states that "where two or more single-phase ranges are supplied by a 3-phase, 4wire feeder or service the total load shall be calculated on the basis of twice the maximum number connected between any two phases" . Does this mean I need to double the calculated size? for example if I have a range on A & B, one on B & C and one on A & C each range is 8kw I need to calculate each range at 16 kw before the demand factor adjustment?

If you are using 220.84 for the Dwelling Unit calculations, then you would not use 220.55. Note that using 220.84, you need to use the nameplate rating of the Range, and other appliances. If you have a 12kW range, you would use 12kW in the 220.84 calculation, not the 8kW from 220.55.

If you were using 220.55 for the multiple ranges, you would have a maximum of one range between any two phases, so twice that would be 2. The 220.55 demand for two ranges is 11kW. You then take 11kW divide it by two for the "per phase" demand (5.5kW) and multiply by 3 for the 3 phase demand...total demand is 16.5kW. Example D5(a) in Annex D has a good example of this.

Another question i have is for sizing feeders for the individual units. I'm assuming those feeder are sized at 100% and no demand factors are to be used, is this correct?

For each dwelling unit feeder, you can use the basic method in part III of Art. 220, using the demand factors allowed therein. Or you could use the Optional Method in 220.82, with its demand factors.

 

[SpotOn]

Thanks for the help!! I needed a push in the right direction.