I think I should clarify a couple of things. By TVS, I mean Transient Voltage Suppression. Floating supplies can be a wonderful thing, but not if they float too far away from Earth reference. Various forms of coupling can steer them to potentially deadly differences WRT ground. For this reason, it's not unusual to use TVSs, to clamp at least the unreferenced floating Neutral to ground. Let's say you use a 1.5KE51CA, between Isolated Neutral and Ground. It would start conducting around 51 VAC, and clamp your supply. But below that point, there is a leakage current that must be considered.
I just went to the Digi-Key site and pulled the datasheet for the Littelfuse parts. The PDF was too large to attach but it shows that the 51 volt part might have a leakage current of up to a 1 uA. That's not enough to cause a problem, but plenty to confuse an electrician with a Fluke.
Joe
