which can be "remedied" by using a 3 prong to 2 prong ground isolator
In my business that action is a safety violation. It is more dangerous than working on a live circuit with no lock-out-tagout. Either can get you fired on the spot.
I had Tektronix provide a 'basic scope use class' just three weeks ago to supposed 'seasoned' bench technicians.
You may ask, why so severe?
277VAC does not feel very good when you touch the scope chassis when someone well trained is scoping a 3-phase 480VAC signal. When the boss gets the sh#t knocked out of him because his techs don't know how to use a scope - expect hell to break loose. (The 'boss' knows more about test equipment usage than all of his technicians combined.)
Isolation transformers are also unacceptable for such measurements. Connecting the scope chassis to anything except a point already grounded, at a minimum, affects the signal displayed. ISO xFmrs should only be used to prevent external noise or transients from interfering with measurement or prevent DUT generated transients from leaking to the mains or others systems.
When scoping a floating potential, the only acceptable options are the differential method or the use of a differential probe. Even the portable scopes affect the signal unless each channel is designed as a differential probe. We have those, too.
Anyone only having the test equipment training provided in physics or engineering classes should attend some current real-world equipment safety and usage training.
Am I being an ass? Yes, you can become that way after mopping up the leftovers and attending a couple of funerals.
On the lighter side: I am serious when I say the scope chassis will become part of the circuit under test when you connect the ground clip to a floating point. I've seen too many false positives/negatives in diagnosis and testing caused by this.
Folks should just read the manuals supplied with the equipment.
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein
"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg