That suggests to me that (1) there is an earth leakage fault in the oven, (2) the condensation is causing a second (but temporary) earth leakage fault in the extractor, and (3) it requires the combination of both faults to exceed the trip current of the RCD.
I'm non the wiser, Harry. The RCB covering 5 MCB circuits, including the cooker, trips. most probably due to steam/water/condensation from above. It will reset and supply current to the oven clock but if I try to use the oven it will trip again. Wait overnight and all will be well.
If that RCB also covers the hood, then it is most likely leakage in the hood, causing the trip.
The only way for you to determine which, is to disconnect one item completely at a time and make further tests using the oven to see if it trips.
Note that I do mean disconnecting completely, both L and N from the circuit, or unplugging - because leakage L to E, or N to E can both trip the RCB.
Another possible complication is that leakage on more than one item, is additive. You might for instance have some leakage on the oven, which alone may not be enough to cause a trip, but add a little more leakage from a hood, it pushes it over the limit and then it trips.
The correct instrument for finding such leakage is a 500v insulation tester.
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