Sizing for house about to be rewired

djMaxSeptember 18, 2011

I'm doing a bunch of rewiring in a 6,000 square foot house. Last update was probably 1960, so while it's not a total disaster we will be running new wire often. It has 1 kitchen with a couple wall ovens and 4 heating zones which will be upgraded to AC as well. So the big question - 200 amp service or 400 amp? My guess is that getting NStar (my power co) to upgrade to 200 is not too hard. The service is underground and though it looks like 100 now, they probably are compelled to give me 200. 400 - I bet they charge and charge a lot. Simple load calculators say we need 180A, which seems too close to 200 to feel good about, but not sure if they assume only incandescent, etc.

Thanks very much for any thoughts.

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If the calculations correctly show 180, then 200 should be sufficient. Will you later be adding non-storage electric water heaters or charging for an electric vehicle? Price the various options. Consider the 400 amp.

    Bookmark   September 18, 2011 at 1:55PM
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I guess what I'm after is knowing whether those calculators are generally overkill. We may be adding non-storage gas water heaters, but does that hit electricity hard too? Electric vehicle... not likely in MA. :) But all good things for me to keep in mind. I'll price them both.

    Bookmark   September 18, 2011 at 4:44PM
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With a house that large, you may have trouble limiting your usage to 42 breakers. Yes, you could put in a subpanel to get extra slots for breakers, but nowadays, I would generally look at a couple of 200A panels (400/320 service), and be done with it.

    Bookmark   September 18, 2011 at 6:38PM
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Ron Natalie

I agree with what's been stated. But if you're going to the effort of a whole house rewiring, there's no reason to not sit down and calculate the loads PROPERLY. Other than that we're just making conjecture.

Frankly, I'd still put a 40A or whatever circuit into the garage. Even if you don't ever get an EV someday someone will put a welder or a pottery kiln or something out there.

It was after that incident that I decided I better get the building and plumbing codes and learn them as well as I knew the electrical code just in case. Found two cases that saved me some heartburn on those as well.

Tankless or not gas water heaters take only a few amps (and just have a 15A plug on them). All you have is control logic and a blower for the combustion air/gasses.

Kurto is right. Having multiple panels will probably be obligatory just for the number of poles you need. In my 7000 sf house, I've got three. The main panel only has a few circuits, the feeders to two other subpanels elsewhere, and some random stuff out in the hangar and garages.

Compared to the rest, getting the power company to drop in a 400A service isn't that big a deal in most places. The scary one for me was the 80KVA generator which is way overkill but the moron engineers who the architect employed were not able/willing to do a proper load sizing (80KVA = 400A fully loaded). I also sent a rather testy letter with two pages of code deficiencies after I got my plans back.

Fortunately my guys who were doing the actual work see this far too often (code violations in the architects plans) and would have never built the house wrong.

    Bookmark   September 19, 2011 at 8:13AM
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