Originally Posted By: Dennis Bozek
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Joe… in this house they have two panels at 200 amps a piece. That would be the same as having two units in one house both with a 200 amp panel. In order to run two 200 amp panels, the service feeders must be rated for a minimum of 400 amps.
Take a double house for instance, where the upstairs is rented and the downstairs is rented. In the basement are two 100 amp panels. One for the upstairs and one for the downstairs. The service required to run two 100 amp panels would be 200 amps. There would be no way that you could run both 100 amp panels on a single 100 amp service. It would have to be the upstairs panel of 100 amps plus the downstairs panel of 100 amps....or 200 amps total.
In this picture, there is a main panel with a 200 amp main breaker. If that was the only panel used, then 200 amps on the service loop would be fine. However, there is another panel, protected by another 200 amp breaker. The range circuit in the first panel was more than likely placed there because the subpanel was full. Therefore, they are utilizing two 200 amp panels to run this house. There also looks like there are some addtional branch circuits in the panel that we cannot see. Without knowing everything about this house though, and just viewing the picture Russ gave me, I could only assume what was happening there.
Russ has now told me this house is 4609 sq ft. and I already know they are using a electric oven. Assuming that they have air conditioning, they would need at least 2 air conditioners to cool a house of that size. I also assumed that a house that size surely has a microwave, a disposal, a dishwasher, and at least 2 small appliances. Without adding a electric dryer or any other appliances, my load calculation on this house is 212 amps. Would a single 200 amps service run this house safely?
Did I take 200+200 to come up with 400? Yes I did...but the explanation for doing such is stated above. If the 200 amp breaker protecting the subpanel was only 100 amps, then I would be ok with a 200 amp service. But as you can see...you have two 200 amp breakers with each protecting it's own panel. If I had all the info on this house, all appliances used and what type of energy they are using to run those appliances, I could give Russ a exact number as far as the ampacity required to safely run the load of the house. Right now, looking at the pic alone...I can only assume what I am seeing....and therefore, state that a minimum of a 400 amp service is required.
This information has been edited and reviewed for errors by your favorite resident sparky.