That's because there is no rule that says that explicitly. Those who tell you that 'again and again' are offering their own interpretation of the regulation about 'division of circuits'.However after the 17th came out we were told again and again consumer units must have at least two RCD's to comply and no where can I find any rule which says that.
Do they claim otherwise, and can we really expect it to be otherwise? We are, after all, talking about an exam which, by it's very title, is about a set of regulations not about 'electrical skill' or the ability to apply it. If the exam were something like "Electrical Wiring Practices compliant with the 17th edition", it would be very different - but that's not what it is, or what it is called.But the basic point is the same the exam does not in any shape or form test ones ability to interrupt the regulations it only tests if you can remember or look up enough of the regulations to get a pass mark in a parrot fashion. No electrical skill or knowledge is required to pass the exam. General exam skills and ability to read English is all that is required. ... But the whole of the 17th Edition exam is about the ability to read and quite from a book ..
Kind Regards, John