Existing Load for multifamily

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odyssey1

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Pulaski Va
Hello. I read this forum all of the time, and it has helped out a lot.

I am working on a multifamily apartment building. there are 11 apartment units per floor. There are two panels per floor that feed the 11 apartment units. The individual units do not have their own panels, as this building used to be a hotel. The owner would like to add supplemental heat to each unit (around 500 watts per unit). My question is, could I use 220.83 to determine if I have enough capacity in the panel, or is 220.87 the only way to determine if I have capacity? The owner is in a time crunch, and the 30 day testing may put them in an bind.

On the other hand, it seems that if you knew all of the loads in each unit and the square footage, you could calculate the service load the same way you would for new construction using article 220.

Thank you for your help!
 
I would do a load calc for the building. Only 500W of supplemental heat? I can't imagine that really doing much.
 
You didn't state the number of floors, but since you said 11 units per floor, you're looking at at least 22 units. With that size of service, there's a fair chance POCO has demand data. However, you'll probably still have to do some load calc's if apartment electrical "features" or panel loads are different.
 
Thank you everyone for your help so far.

Here is some additional information. Everything is existing. There are two panels per floor that feed the apartment units. I will take just one of the panels ('A') as an example: Panel 'A' is a 120/208volt 3 phase 4 wire. It feeds 6 apartment units. Panel 'A' contains 5 circuits for each unit: (1) lighting and receptacle circuit, (2) small appliance circuits, (1) range circuit, (1) Heat Pump circuit. 500 Watts of supplemental heat will be added to each unit for a total additional load on panel 'A' of 3kW.

To determine if panel 'A' has enough capacity for the additional load, the AHJ is requesting a 30 day metering to determine the maximum demand per NEC 220.87, exception.

Since this is an existing dwelling unit, can I use 220.83 to calculate rather than meter to determine if panel 'A' has sufficient capacity for the additional heat? The only problem that I can find with this is that each unit does not have it's own panel, and this is a multifamily application.

Alternately, could I use article 220 to calculate the existing load on panel 'A' using (3VA/square feet)x(500 square feet)=1500VA/unit for the general lighting load, 1,500VA apiece for the small appliance loads, nameplate rating of range-8000VA, and MCA of HP-3000VA = 15,500VA total. Using 220.84 I could use a demand factor of .44 to give a total of 6,820VA/unit, or 40,920 total for panel 'A'.

Would either of these methods be acceptable to determine the existing load without having to meter panel 'A' for 30 days? It seems like if all of the loads were captured, you would get a pretty accurate picture of the demand.

Thank you again
 
minimal load

minimal load

Is not 500 watts per apartment negligible? That is less than someone using a hair dryer? Such a small load could be installed on an existing circuit?
 
odyssey1 said:
...Using 220.84 I could use a demand factor of .44 to give a total of 6,820VA/unit, or 40,920 total for panel 'A'. ...
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I say you can use 220.84.

The problem is, some air-brained inspectors believe because there is a section that is titled "Determining Existing Loads" in Article 220 Part IV, that is the only applicable section in Part IV for an existing installation. As such, you have to do a Part III calculation to get around it.
 
Would the inspector allow you to pull a permit and start work now under the assumption that when you provide recorded data in 30 days it will have sufficient capacity? Let him hold back final until your load recordings are finished?
 
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