The big problem with what you propose it that it's too easy for something to go wrong.
Here's a few sentences I found on this subject. I'm sure if you search you can find much more: (bold is mine)
WARNING: Improper connections to a building's electrical system can allow the generators electrical current backfeed into the utility lines. Backfed power may electrocute utility workers or other individuals who may contact the lines during a power outage. Consult with the utility company or a qualified electrician.
Improper connections to a building's electrical system can allow electrical current from the utility company to backfeed into the generator when power is restored. This utility backfed power may cause the generator to explode, burn or cause fires in the building's electical system.
I'll second both points made by Bill above. From much personal experience parallelling large generators in a past life (Navy), you DO NOT want to have a generator online but no way to synchronize when the utility power comes on.
I believe I've seen moderatly (Profitably) priced residential grade power transfer equipment sold in kit form which is just made for this purpose. Safest way to go.
As an electrician, at my house, I might think I can get away with an outlet arrangement as you described, but I know to go yank the utility meter before I hooked up. Then there is the question of which loads to connect, etc. The generator won't run everything. This is not necessarily as easy as the home owner presumes it is.
What about grounding issues?
Just way toooo many things to go wrong. Too much risk and liability, as you have no control over the home owners actions after you're gone.
There are 10 types of people. Those who know binary, and those who don't.
you DO NOT want to have a generator online but no way to synchronize when the utility power comes on.
Allow me to relate a little story which happened at a British telecommunications facility some years ago.
In replacing the control modules for the generator set, somebody somehow managed to miswire the synchronizing circuitry and clearly didn't check it before putting it in service.
When they came to parallel two generators, the sync circuitry did it's job in matching speed and locking the gensets together. Unfortunately, they were synchronized out-of-phase when the connection was made.
I understand they were retrieving engine parts out of the roof for some time......
I guess I should have told you that most everyone out here turns the main breaker off in the panel before they do all this unfortunately there are knuckle heads who don't and who think they can power the whole house. Now this is not a 100% guarantee of not powering up the grid. I feel like I am the only one who has seen this done. Home Depot and Lowes were selling these things including male dryer plugs and 10-3 SO by the truck load during the last Hurricane and I know that most of these folks were not taking the time to install transfer switches. And we all know that a 6kw portable generator ain't the cleanest power to be had soooo back to the original question even if you do use a transfer switch has anybody had or heard of any issues with heating up the neutrals or any weird stuff going on.
Square D for sure and I'm sure a few others manufacture just what you're looking for. A small 2 or 4 circuit sub panel is fed from the main and the outside generator plug, it's an either or proposition (the panel is fed by utility or geneator)and has to be done manually, but it's legal and safe. How can any of us trust anyone during a power outage to be methodical, etc. This does the job, the geneartor can be wheeled back there and you can sleep at night.