Service Calculation for a Dwelling Unit

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steve66

steve66

Senior Member
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Illinois
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Engineer
220.52a requires 1500 VA to be added to the load calculation for each small appliance circuit.

Does this include the load for the refrigerator and microwave oven, or do I need to add those in separately per 220.14A?

The examples in appendix D don't seem to add anything for refrigerators or microwaves, so I think its included in the small applicance branch circuits.

Thanks:
Steve
 
I would say that the load of a refrigerator and a portable counter mounted microwave would be included in the 1500 VA load of the small appliance branch circuits.

Chris
 
210.52(B)(1) says the two or more 20-ampere small appliance branch circuits shall serve receptacle outlets for refrigeration equipment. Exception No 2 permits refrigeration equipment to be supplied from an individual branch circuit rated at 15 amperes or greater.
 
construct said:
210.52(B)(1) says the two or more 20-ampere small appliance branch circuits shall serve receptacle outlets for refrigeration equipment. Exception No 2 permits refrigeration equipment to be supplied from an individual branch circuit rated at 15 amperes or greater.
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So are you saying that you must include the refrigerator as a specific appliance in your service load calculations?

Chris
 
Maybe if you put the refrigerator on a separate circuit you count it, and if you put it on the SA circuit it's included?

Sounds kind of strange, but the handbook says if you provide 3 SA circuits, you have to count 1500 VA for each of them, for a total of 4500 VA. (I'm not sure I agree with that.)

But having the refrig. on a separate circuit might be considered similar?
 
Sounds kind of strange, but the handbook says if you provide 3 SA circuits, you have to count 1500 VA for each of them, for a total of 4500 VA. (I'm not sure I agree with that.)
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There was a change in the 2008 NEC for section 220.52(A) and (B) to clarify that each of the small appliance branch circuits and laundry circuits must be counted at 1500 VA not just the required circuits.

Chris
 
steve66 said:
Thanks. Does anyone else feel different?
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Not really, but maybe in a nit picky way. I'd accept a portable microwave on the SABC, while a counter mounted one I'd want counted as a separate load.

Personally, I start by counting everything likely to be used, such as a microwave, or disposal, and if it shows a service too large a size for the budget, start trimming things from there as needed.
 
Volta said:
Not really, but maybe in a nit picky way. I'd accept a portable microwave on the SABC, while a counter mounted one I'd want counted as a separate load.

Personally, I start by counting everything likely to be used, such as a microwave, or disposal, and if it shows a service too large a size for the budget, start trimming things from there as needed.
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I'd also agree, a permenantly installed microwave would be added to the load.

That's exactly where I was at: I had calculated about 210 amps each for 18 apartments. But since I started this post, I found the optional method drops the calc. down to about 170 amps per apartment.

Steve
 
Google "City of Naperville Load Calculation". One of the city inspectors put together a spread sheet to determine the residential electrical load calc. One of these calculations needs to be filled out prior to permits so that the right size service is provided. I hope this helps.
 
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