Hi Nigel,
Regarding the isolation transformer, I ordered one of
these. That page says it provides an isolated ground, but it says something about 'secondary neutral to ground bonding' in its data sheet (linked to on that page). I was wondering if they meant earth ground, or just the ground lug on the isolated plug outlets. I guess I'll find out when it gets here.
Re: the scope measurement - I want to measure across the outputs of the H-Bridge. If I connect the ground clip of my scope probe to one side, won't it short it to ground when that side goes high? I'm trying to look at edge rise time / overshoot / ringing so I can optimize an RC snubber for it. When I did this at my last job they told me to use a differential probe.