400amp service entrance 200amp transfer switch
Forget about buying this thing.
It's an &quot;impulse buy&quot;, and that does not work for engineered products like whole-house generators and automatic transfer switches.
It's an Automatic transfer switch
It has a sequenced system which will automatically spin up the generator and then throw the loads over onto the generator.
With an ATS there is a simple rule: The generator must be large enough for the loads to be served.  You are not allowed to have a situation where the generator might come online and immediately bog from overload.   You must prove the generator is large enough.   And the switching equipment must be large enough too!
A &quot;Load Shed&quot; device sits in front of large appliances and automatically disconnects them if the generator seems to be struggling (low voltage or lower-than-spec frequency).  Equipment protected by &quot;Load shed&quot; devices can be excluded from the generator calculation, but it cannot be excluded from the switching equipment calculation.
In point of fact, since you currently have 400A service, the 200A transfer switch will be a &quot;choke point&quot; for your power that will prevent you from using utility power to its full capacity.
How do we arrive at the proper size?
You need to do a load calculation on your house and loads
You say you have an all-gas house.  However, your service panels are ones from a lavishly electric home. In the 400A meter-main, I see a 50A panel going to ???.   In the two large panels, I see no less than fifteen 240V breakers, as well as a subfeed lug kit carrying that panel's entire 150A to yet another, third panel in some other location!
So, the upshot is that all of this needs to be earnestly tallied up, and fed into a proper load calculation.  The load calculation will state how many amps/kVA you will need for a &quot;whole house&quot; generator.
I suspect you will painfully discover that your house really does need 400A service, and you cannot shim the house's loads down to 200A -- let alone 92A.
If you are able to eliminate maybe a dozen of those 240V loads (or move them to the meter-main panel breakers, which won't be on generator)... then you may be able to get your Load Calculation under 200A.  Then with some Load Shed units you may be able to get the &quot;Load to be Served&quot; under 92A... and then.. you could use that generator.
Having 1 generator feed more than 1 panel is problematic, anyway.
The problem is, only one panel can have a pass-through neutral.  All the other panels need to have an isolated neutral, requiring a 3-pole transfer switch.  The bargain transfer switch is only a 2-pole.
The way to solve that, after you have reduced the two large panels to &lt;200A calculated load, is to replace one of the main breakers with a 200A breaker... and have the remaining 150A breaker power nothing at all.  (or perhaps, another panel which is &quot;utility-side only&quot;).
The 200A breaker then feeds ONE &quot;subpanel&quot;.  That &quot;subpanel&quot; feeds both existing large panels.   You stick the generator ATS in between the 200A breaker and the &quot;subpanel&quot; in the normal manner.
I'm putting &quot;subpanel&quot; in quotes because it doesn't actually need to be a subpanel.  As long as the wire from &quot;subpanel&quot; to the two large panels is 200A wire (250 kcmil not 4/0), the &quot;subpanel&quot; doesn't actually need to have any circuit breakers at all.   A subpanel with no circuit breakers is just a box and some lug splices.  &quot;that was easy&quot;
Effectively this will downgrade you from 400A to 200A service, but it will permit use of that bargain generator.
How Harper would do it.
Well if someone held a gun to my head and forced me to use a generator, I'd get a large enough generator for the whole job.
One side-effect is that the generator would be water-cooled (coolant-cooled, to be more precise). I would run that hot coolant through hot-water registers around the house, or one heat exchanger in the forced-air furnace stack... because, hey - free heat!
Or, I'd swap circuits around in the two large panels until one of them only contained loads you would never want to put on generator, and the other one contained loads whose Load Calculation was less than 92 amps. Then, I'd put the ATS on that panel only, and let the other panel just be dead.