Comment by bob1029

Generators are synchronous machines which means they can produce a useful reference frequency without any external source as long as they are spinning at a reasonably correct RPM. This RPM is easy to enforce with mechanical means. This independent operation is also what makes them so dangerous. There is no control signal from the grid back to the generator.

It can be quite safe to plug a generator into an outlet if you take precautions to properly island the system. I had an interlock on my breaker panel that would let me turn on a 50A backfeed breaker if my main breaker was switched off.