If you don't want to put an mcb/RCBO in a particular slot in a CU...

[Spark123]

One trivial detail was deciding whether to put the spare breakers at the very ends of the busbar(s); or to put all the used and unused breakers in numerical order on the busbar(s).

My preference is to do the latter, probably owing to the oldern days where the wylex boards wanted us to put bigger loads closer to the main switch

 

[PBC_1966]

I clearly stated that I only use DIN rail mounted blanks.

Yes, that's fair enough, but a lot of people don't. I was just saying that a spare MCB or fuse carrier would be preferable to one of those clip-in blanks which "clips out" just as easily, if not more so, than it went in.

 

[Risteard]

one of those clip-in blanks which "clips out" just as easily, if not more so, than it went in.

I would like to see manufacture of them cease.

 

[PBC_1966]

I would like to see manufacture of them cease.

Can't disagree with you on that one.