I'm going to try to undertake some measurements on something a bit closer to a 'cooking appliance', and over a longer time period, and will present some figures in due course!
'Due course' as come ...
.... OK. Although it was all the data I had to hand at the time, my previous attempts to illustrate ‘diversity’ with data relating to heating a large (insulated) cylinder of water with an immersion heater was not very analogous to cooking appliances, and my attempts to ‘scale it down’ to much shorter time periods went all wrong!
I have no electric cookers, ovens or hobs, so I have undertaken experiments using a 1,700 W deep fat fryer, which I switched on from cold and ran for an hour or so at ‘chip frying temperature’. Whilst this is probably not an ideal model of a hob, it’s probably not a bad model of the likely behaviour of an oven. What I found is illustrated in the graphs below.
Note that, following plugwash’s comments, the 'average power' over 15-minute periods has now been calculated correctly - i.e. as the RMS (rather than mean) of the data during that period.
[ note also that the few brief periods of ‘low' (<1,700 W) consumption result from the fact that, although data is collected once every ~12 seconds, the stored data I have toi work with are ‘1-minute averages'. Hence, if the element was only ‘on’ for part of a 1-munute period, the indicated coinsumption will be a corresponding fraction of 1,700 W ]
As can be seen, the average (RMS) power consumed by the 1,700 W appliance fairly quickly settles down to around 600 W, meaning that the heating of cables etc. will be approximately the same as with a load drawing ~600 W continuously.
Scaling that up to larger cooking appliances (or collections of cooking appliances), assuming that they 'behave' (in terms of on/off thermostatic cycling) similarly to the fryer, if one had 11 of my fryers (total of 18,700 W, about 81.3 A at 230 V) turned on from cold simultaneously, they ought to settle down to a total average load of about 6,600 W (about 28.7 A at 230V).
Hence, if my fryer is ‘typical’ of cooking appliances, a collection of cooking appliances whose maximum loads represented a total of 81.3 A (at 230V (18.7 kW) should result in an average effect on (i.e. heating of) cables which is the same as would be achieved by a load constantly drawing about 28.7 A at the same voltage (i.e. roughly a 6.6 kW load).
This is very similar to (in fact, a bit more 'conservative' than) the conclusion one would come to by use of the standard domestic cooking appliance diversity calculation, which would say that the after-diversity current for a total cooking appliance load of 81.3A would be about 31.4 A.
Hence, both my empirical observations and the standard diversity calculation indicate that a total cooking appliance load of 81.3 A (about 18.7 kW) should be OK on a '32 A circuit'.
If (as would nearly always be the case in domestic practice), there were some 'staggering (i.e. not absolutely everything switched on from cold simultaneously), then the average power consumption would be likely to be a bit less than these figures suggest.
Edit: for anyone reading this, please note that I may well fairly shortly be posting some revisions to the above!
Kind Regards, John