How do I determine how big a service panel I need?

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  #1  
Old 03-22-05, 09:16 AM
Wendell
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How do I determine how big a service panel I need?

I presently am connected to the power grid through a 100 amp service panel. I know I need a bigger one--if for no other reason than I am out of breaker slots.

Presently, the total amperage of the breakers already in that 100 amp box adds up to 470 amps. I am using just under 1000 KWH per month. That drives my shop and a hot tub. But, now my wife wants air conditioning (it will take a 1 ton and a 5 ton unit) and a swim spa (add another 100 amps).

It sounds like maybe I need a 400 amp panel, but is there a "scientific" way to determine how big a box I need?

Thanks for your thoughts and advice.
 
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Old 03-22-05, 04:07 PM
Pendragon's Avatar
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I've found that the total of the breakers in your box means nothing...

Are you saying that ALL you have running is a spa and shop (a few tools, lighting, etc), or is that for everything in the house (Except AC, which you don't have yet)?

I would say either 200 amp service, which would likely require a new drop from the power company, or maybe a subpanel to run the a/c's (why 2?) on.

Maybe one of the resident electricians can give you a more specific answer.
 
  #3  
Old 03-22-05, 05:21 PM
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You need to perform a demand load calculation. Adding up the breakers in your panel is a usless exercise.

Here is a link to demand load calc.

http://www.selfhelpandmore.com/homew...calc/index.htm
 
  #4  
Old 03-22-05, 05:30 PM
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Anything above a 200 amp service for residential is usually for a large custom home or a mansion. You can calculate just to be safe, of course.
 
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Old 03-22-05, 05:49 PM
Wendell
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The 100 amp panel runs everything: 2300 sq foot house, shop, and hot tub.

Yes, I will have to rebuilt the entire connection to the grid. The present line is buried, too small for more power, and is connected at a transformer with two other houses. There are several solutions, but none is perfect or cheap. The closest pole has a high tension drip serving an adjacent subdivision underground. I will have to put in a vault in the street to intercept that line, a new transformer, and new trench and line to my house. The pole where I presently take power (not the closest) cannot take another transformer without setting a new pole across the street from it to carry a tie back--to support the weight of new transformer and heavier wire to the pole that drops to my underground. Complicated I know. But I've got to rebuild the whole thing anyway since the present buried cable goes right where the pool will go.
 
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Old 03-22-05, 06:30 PM
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I got lucky for mine, my house only shares a transformer with 1 other, smaller home, and the way homes are, no others will be able to feed from it. I had 200 amp service from the start, also underground, but with above ground street poles I only had to pay for the service line from the pole to my house, anything required before that is the power companys money, they had to install a larger transformer since only 1 home had been on it before and after ivan, they installed an even larger transformer!
 
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Old 03-23-05, 10:51 AM
Wendell
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Thanks, everyone. That link Joed provided to the site with the formula for doing the load calc helped very much.

BTW, the reason for the two ACs is the design of the house with two wings with a central great room with cathedral ceiling, leaving no attic through which to run an air conduit.

Wendell
 
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Old 03-24-05, 10:56 AM
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my 2 cents

here my way of calculating
i take area of house x 80%
ex
L x W = Y x 80%
40 x 30 = 1200 x 80% = 960 amp rounded to 100 amps

cheers

pg
 
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