According to Steve Kraus :
It does seem unlikely; if your main breaker is closed, your genny
should stall immediately when it tries to power the neighborhood.

I think unless you have some sort of huge generator the load presented by
the outside world will look to the generator as pretty much a short to
ground.

Precisely.

A friend of a friend suicide-corded his generator into his house,
and the generator promptly smoked within seconds of firing up.

He forgot the main breaker.

[It managed to fire up because the generator is automatically
not connected during startup, and "engages" when the motor is
up to speed. At which point it started belching smoke and stalled
out.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.