As a general question, you know answer as well as I do. However, when there are two layers of insulation between live conductors and touchable matter (as in metal encased Class II items), we do not necessarily earth that metal (indeed, as we know, many a Class I item comes with instructions that one "MUST NOT" earth it).Why do we earth anything at all then?
Maybe that's realistic, but I was responding to your comment about what was "reasonably foreseeable", and I'm quite sure that it is very much "reasonably foreseeable" that some silly people will fiddle in CUs in ways which they shouldn't. As you go on to agree ...I think a general principle of most safety standards is that it is simply not considered possible/reasonable to protect "idiots with tools".
Exactly my pointI do see your point though that the temptation to "mess around" in a partially-live CU is much greater than in most other domestic electrical situations and the risk to people doing that is increased by the use of metal enclosures. ...
One of the many (in my opinion) stupidities of the regulation, that it does not require any "containment of thermal events". Provided only that what little material is left is deemed to be 'non-combustible', you can have as many ~12mm diameter holes as you like in the front, bottom and sides of a metal domestic CU!Whether that outweighs the benefits in terms of better containing thermal events I could not say....
Kind Regards, John