At issue is how the generator is internally connected, and
the possibilities of accidents.... and on whether or not you
are willing to bet your life that the generator is connected
the way you think it should be, and that it hasn't any faults.

For instance, you scope's ground wire is connected to earth
ground through the power cord.

Your generator should also be grounded, but if it isn't, an
accidental connection between the generator's hot lead and
the scope's ground, could cause the generator to be elevated
120V, or more, above the scope's front panel.

As I stated earlier, I use a filament transformer for such
measurements. Its fidelity is very good, and most are isolated
for several hundred volts... actually many of the older
filament transformers are good for 3000V.

-Chuck Harris

Robert Simpson via groups.io wrote: