nishanf
I'd appreciate some advice on generator sizing.
The home is a recent build in Atlanta, ~9000 sq ft.
The electrician put in a 600amp service with the main disconnect outside and 3 200 amp panels inside.
A 600 amp rated transfer switch is already installed: [URL]https://www.thomsonps.com/Transfer_Switches/TS_870/[/URL]

The 600 amp service appears to overkill. Most of the lights in the home are LED. There is gas heat, gas water, an electric oven, and nothing else beyond ordinary appliances (e.g. no pool/sump/well pumps, etc).
Based on adding up loads and my electric bills, my peak 30min usage during the winter never exceeds ~ 8KW.

During the summer, there are 4 AC units in potential use (3 5 ton and 1 4 ton). LRA is 135 and RLA is 25 for the 5 ton units.

The electrician maintains a 100KW unit is needed to match the service size...this seems inappropriate. The unts beyond 60KW are enormous.

I'm favoring a 48KW or 60KW unit with the use of SMM modules or perhaps a few sure starts on the hvac units.

The 60KW model would likely be the best choice in terms of pure capacity, but I've been warned to stay away from the 3600rpm units.
For that reason, I'm considering the 48KW model, but hate to be undersized.
Any advice?

thanks!

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Peddler
The problem may be that some hard headed local code authorities interpret the cod to be that if you have a 600 amp service you need a 600 amp generator. If that is the thinking they are going with then the 100 KW isn't enough you would need a 150 KW. My opinion is that you could do this whole house with a 48 KW generator and never have a second thought. The 48's are good low speed units that are very quiet and reasonably sized. The likelihood of all 4 AC units running at the same time are slim but even so you would have plenty of capacity. Still if you are going to get it inspected you have to get past the code authorities.
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nishanf
Thanks Peddler.
I don't think inspection will be an issue, and I could always use SMM modules to load shed, I suppose.

I wanted to see if my thinking made sense. It seemed a bit odd to put a 48KW generator with a 200amp breaker on a 600 amp service, but the numbers seem to add up.

Just one more question...would you say the advantage of 1800 RPM over 3600 RPM is so great, that I should not even think about the 60KW model?

thanks!
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Birken Vogt
If the electrician is still around, have him provide the NEC load calculations for the house.
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Peddler
I'm not a fan of that 60KW though for emergency service it may be OK. The 48 is the stronger unit on my opinion.
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Geoff Z
I agree with both the comments above. The NEC load calculation should have already been done to gain approval from the building department. The electrician should simply be able to hand you a copy. I too like that 48kw. I think that whole model line are some of the nicest generators out there. You are asking the right questions and doing your homework. You need to know without a doubt the unit you choose will be approved before you purchase and install.
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