jim rozen wrote:

But the compressor runs off of 240 volts. Don't you
need to put the scope across both hot leads?

You could use another transformer - any handy 240 to whatever and put a
light load on it. Ground one side of the secondary and hook the other
side to the probe.

If it really is split 240 and not two lines of a three phase service,
looking at only one hot from ground should have very little error in
phase.

Ted