But why.
A proper automatic transfer switch is <$300
I think this could make an interesting discussion. What are the options?
In a pinch, a lot of folks backfeed their panel, either through a dryer plug or dedicated circuit. Problem is, with no interlock, you could backfeed the transformer and hurt a lineman or neighbor. Definitely illegal and dangerous.
There's the whole house transfer switch. It goes between the meter and the panel, switches from generator to utility automatically. Good for pad mounted permanent generators and an option for portables, though my understanding is it's not code compliant with portables. These are generally good to 200A, but I think 320A/400A versions are available, but much more expensive.
There's the meter socket transfer switch. Good for 40A. Easy install, inexpensive. But for the same reasons a 7.5kw portable can't serve a 200a transfer switch, I'm not sure how these are code compliant.
Dedicated generator switch panels tie into breakers at the main panel, giving you the option to switch 6-12 circuits individually from generator to utility. Code compliant, but seems "messy" to me. Only allows for certain elements in the house to be on generator power.
There's the main panel with automatic transfer switch built in. Generac sells one that is rebranded from Eaton or somebody. It a 40-space 200a panel with about 20-30 breakers on the switch side, and about 10 on the utility power only side. Requires replacing the main panel. Good for pad mounted generators. Not sure what options are available for 320/400a service.
Dedicated sub panel with transfer switch or interlock. Variation on the fancy panel above. Have one main panel that is utility power only, and a second (sub?) panel that's switchable. This could work cheaply with 320/400a service, but means anything on the first panel can't receive generator power.
What else?