According to Eric R Snow :
On Thu, 09 Feb 2006 21:31:55 -0600, "Martin H. Eastburn"
wrote:

[ ... ]

Is the generator ground earth ground or floating - if you floated your scope
then connect the scope lead to the ground lead as you say.
Otherwise - what would happen is the earth ground in the scope is connected
through the scope ground to the generator ground - and that might not be right.

[ ... ]

I wasn't exact enough when I asked my question. The generator is
actually an alternator. Just a typical one used when the power goes
out. It sits on rubber feet and so is isolated from the ground. I
guess that means it's floating.

No bets. It depends on other interconnections. If it is
running from gasoline, and it is not connected to the house wiring at
all, then it is *probably* floating, at least until you touch some part
of the metal.

The scope will be plugged into the
mains while it's measuring the generator output. The voltage I can
measure with a DVM. But the wave form is what I want to look at.

You would probably be safer to use the differential measurement
setup which I described last night in another branch of this thread.
That way, you don't have to worry whether there is an accidental path to
ground from any part of it.

Good Luck,
DoN.
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