Single Family Dwelling Main Service Disconnect

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comjos

Member
Location
Pikeville KY
I have a question that I should know but here goes. In completing the Standard Service Calculation the Demand Load was 230 amps the Minimum Service Required is 250 amps. According to the NEC with the main disconnect within an enclosure to be derated at 80%. Should the main be (1.25% x 250 = 310) or next higher 350 ampere OCPD? I get a little confused in terms of the Service Calculations and the main disconnect.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
comjos said:
I have a question that I should know but here goes. In completing the Standard Service Calculation the Demand Load was 230 amps the Minimum Service Required is 250 amps. According to the NEC with the main disconnect within an enclosure to be derated at 80%. Should the main be (1.25% x 250 = 310) or next higher 350 ampere OCPD? I get a little confused in terms of the Service Calculations and the main disconnect.
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I don't understand what you are saying regarding the Demand Load being 230A and the Minimum Service Required being 250A. Can you explain this a bit more... and/or show us your calculations???

Calculations under Article 220 take continuous and non-continuous loading into account. If you did yours properly and got 230A, that is the minimum size service required. Your disconnecting means rating is permitted to be the next size up (when calculated load is less than 800A and does not correspond with a standard ocpd rating). You are also permitted to go to a higher rating if you also upsize your service conductors to match.
 
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hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
Wow I wouldn't want to pay that electric bill, I hope you made a mistake or the electric is cheap in that area, here with all gas heating and appliances we rarely see caculation above 75 amps for the most part. but we also are paying about 0.16 cents a KWH for the first 700 KWH's and I'm not sure how much for after that but I think its up there.
 
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comjos

Member
Location
Pikeville KY
I actually used Mike Holt's Service Entrance calculation spreadsheet. This is the correct figures for the dwelling. In fact I haven't included the in-ground pool heater or pump. I have attached the load sheet. The rates are around $.08/ Kwh at this particular house.
 
Dennis Alwon

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
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Retired Electrical Contractor
comjos said:
I have a question that I should know but here goes. In completing the Standard Service Calculation the Demand Load was 230 amps the Minimum Service Required is 250 amps. According to the NEC with the main disconnect within an enclosure to be derated at 80%. Should the main be (1.25% x 250 = 310) or next higher 350 ampere OCPD? I get a little confused in terms of the Service Calculations and the main disconnect.
Click to expand...

If the service calculation is 230 amps then a 250 amp service is fine as long as all the loads are not considered continuous load.
 
C

comjos

Member
Location
Pikeville KY
Here are the revised ones. I really like this forum and to be able to discuss electrical questions and issues to very knowledgeable people. Sincere, not trying to brown nose. :D
 
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