Yes, I suppose that is correct - but nothing to do with the diversity aspect. ... More to do with some sockets and plugs being not really fit for purpose. ....... Yes, perhaps it is just the fuse holder and rivets.
It's interesting that this discussion is becoming rather wider and more complicated than the diversity ones usually are. To be sure I'm understanding, can you confirm that the following are your view....
1... Given that a 30A cooking appliance is generally taken to represent a 16A after-diversity load, do I take it that you would be perfectly happy for it to be supplied via a "16A" (unfused) plug/socket fed by a circuit protected by a 16A MCB, despite the fact that 30A would probably sometimes pass (for 'non-extended' periods of time) through the 16A-rated plug/socket?
2... By analogy with the above, if a hypothetical "13A" unfused plug/socket existed, do I take it that you would be equally happy for a 20A Cooking appliance (13A after-diversity') appliance to be supplied via that "13A" unfused plug/socket (with a hypothetical upstream 13A MCB), despite the fact that 20A would probably sometimes pass (for 'non-extended' periods of time) through the 13A-rated plug/socket?
3... That if the Plug/socket in (2) above contained a 13A fuse (any with any rating of upstream MCB), you would then probably not be so 'happy'.
If the above, particularly (2) and (3), are all correct understanding of your views, then, as I said, it sounds as if you problem [with (3)] would relate solely to the plug fuse and it's connections.
... Hence the frequent discussions about how much current they can cope with. .... Having said that, I have seen a plug that has been fitted through a plug-in timer to an immersion which has been there 'for ever' with no ill effects.
Others overheat for no apparent reason.
Yes, I think most of us have seen both of those 'extremes'. Unless there is a surprising amount of manufacturing and/or environmental variation, that seems to suggest that there is no fundamental reason why BS1363 plugs/sockets cannot satisfactorily carry 'full currents' for long periods of time, and that when such service does result in problems, one perhaps needs to look at how well they have been installed (and/or look for unusually harsh environmental conditions)
If you mean a true 16A load which cycled on and off - the diversity being solely time related - I would not be keen.
Fair enough, but I wonder whether you are perhaps making a distinction which isn't necessarily all that 'real'. Given that not many (at least, 'traditional') cooking appliances have any 'modulation' of the heat-producing components (elements etc.) most of the diversity with them is also "soley time-related", with a finite (certainly not zero) probability that all parts of the potential maximum load will be drawing full current simultaneously at times.
Hypothetical though it is, I'm not sure that I would be particularly concerned by the concept of a "20A" (13A after-'diversity') electric kettle supplied via a 13A fused plug, pretty safe in the believe that it would never be used for more than very brief periods at a time (even though drawing 20A continuously during those periods). The 'diversity' I would be then be thinking of would then be the time-diversity over periods of, say, 30 minutes - i.e. the average current over any 30-minute period of even 'improbably heavy use' would undoubtedly be well under 13A.
Kind Regards, John