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I am planning on installing a Kohler 14kw standby generator for whole house emergency use. My home has 100 amp service. I have gas heat, hot water and stove. Biggest draws would be fridge, dehumidifier, submersible well pump, septic pump.

Should I order generator with the 100 or the 200 amp transfer switch? If I decide to upgrade my service to 200, I wouldn't need to do another transfer switch- just wasn't sure if a 200 amp transfer switch would create any problems with a 100 amp home service.

Thanks!

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There should be no problem going with a 200 amp automatic xfer switch. Good for future proofing. obviously it needs to be compatible with the generator. Preferably get a Kohler switch. BTW, after doing a LOT OF RESEARCH for my son's new house build and found that the Kohler is an excellent choice, we bought it and the 200 amp xfer switch and it works great.

OK, here's the hard part! for a whole house setup, the xfer switch needs to be installed between the meter base and the main panel. That means the main panel is now a sub-panel. Different rules apply. The biggest is the neutral and ground must be separated (floated), that may require some re-wiring the main panel. I'ts not a common practice to float the neutrals in a main panel.

You'll need to get the PoCo involved to pull the meter and drop power. Hate to say it, but this will probably not be an easy install. You'll need to pull a permit and get it inspected. The inspector (IF they are competent) will want to verify the neutrals are floated and isolated from ground. There is a ton of info on the requirements for sub-panels here at SE and on the web.

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You probably don't want whole house transfer anyway

Here's a little secret: most people really don't even need a 100A transfer switch. Why? Because the notion of a "whole house generator" is based on a false premise; namely, that every circuit in your house is equally important. Clearly, your fridge, the sump and well pumps, and the lighting circuit with the smoke alarms are far more important than a random attic lighting circuit or the circuit for the dryer for that matter, and a proper standby power design takes that into account.

This, in turn, means that you wind up with the circuits you want backed up, such as the circuit to your furnace, moved into a subpanel that is powered from the transfer switch, while non-standby circuits (such as an electric car charger, tanked hot water heater, or a random light circuit that isn't used regularly) stay in the main panel.

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    And electric oven (often 30A or 40A 240V), cooktop (20A or so 240V) can be skipped too - when the utility power is out, use the countertop microwave (15A 120V). Living off relatively simple stuff on the day the power is out isn't such a hardship because you won't be worrying about the refrigerator and freezer contents spoiling, etc.
    – manassehkatz-Moving 2 Codidact
    Aug 3 at 2:36

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