Indeed, but it problem about that Law is that is says that no matter was decision one makes, it will prove to have been the wrong one!The discussion about FCUs, double-pole isolation, single pole isolation or even no isolation at all, is all well and good until you remember Sozdt's Law, something with which we are all VERY familiar!
In this case, on the face of it one would think that installing a DP switch (which, as I said, is what I would normally do and advise) would be foolproof, but Mr Sozdt has a nasty habit of finding a way of proving us wrong!
Kind Regards, John