I suppose you ought to ascertain what the manufacturer has to say about that, but I see no real reason why not - the only 'active' components (which might conceivably be fussed about orientation) are the MCBs/RCBOs and, when fitted to a 3-phase board, they are often/usually 'horizontal' (as opposed to the 'vertical' in the usual single-phase CU orientation), anyway.
Yes, but that was written long before this wretched business about 'non-combustible' CUs (with self-closing 'non-combustible' front panels) appeared on the scene. As I said, that issue would, these days, be my only uncertainty.
It is undoubtedly preferable/desirable that the main switch should be vertical, but I do not recall having seen any regulation which requires this.
That's also on and off.
It is, to you and me. But maybe not always to joe public.
I've said, a number of times, that there are some people who shouldn't do anything to electrical installations except work the switches.
Be that as it may, the point raised relates to an issue (consumers being able to easily isolate the entire electrical installation in the event of an 'emergency') which householders need to be able to do as easily as possible - so, given the vast spectrum of degrees of knowledge about 'matters electrical' within the general population, doing that should be made as simple and straightforward as possible - particular given that the need to isolate could arise when the householder was in a state of panic, and maybe also in the dark and smoke.
Install the CU upside down!
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