New Oven Appliances - RCBO Ratings

If the manufacturer's really don't specify anything then you only need to protect the cabling, so 20A/2.5mm2 is likely to be OK (but not guaranteed since some installation methods e.g. in thermal insulation, might not be automatically OK as the cable Iz can be <20A). I suppose you could even involve the fixed load approach and not have to provide overload protection to the cables at all.

There's certainly precedent for separate ovens and hobs to be connected to a common 32A circuit.

   - Andy. 

Worth noting which radial the washing machine and dishwasher are on. 

The average dishwasher in a UK domestic dwellings is 10 to 15amps

The average Washing machine in a UK domestic dwellings is 5 to 10amps

Thus it is possible that the oven, washing machine and dishwasher COULD be use simultaneously

The kitchen has a dedicated ring main in addition to individual radials for the boiler, two ovens and the induction hob.

The washing machine and dishwasher are separately supplied from the 32A ring main, as is the fridge.

I might take the view that 20A RCBOs provide for the opportunity to swap out appliances in future, but then appliance ratings tend to reduce over time rather than increase.

Certainly the protection needs to cover the cables, but whether there's any actual requirement to have 16A rather than 20A CBs because these may better match the appliances remains uncertain.

It's a bit of a quandary.

The breaker is there to catch a catastrophic "dead short" sort of fault - it is not credible that the 16 amp oven  wakes up one day and decides to draw 20% more or whatever it is. (and if somehow magically it did, why would we care - the thermostat would just cycle with a duty cycle with a slightly shorter on time? Element faults to earth that might be dangerous would be caught by the RCD part of the RCBO)

  It is important to catch dangerous damage, like a cable drilled while hanging a knife rack, or being burnt due to being trapped behind a hot hob or something, but that is something that will be detected by almost any rating of breaker... 

I'm firmly in the camp of leaving the 20A breakers as they are, and letting them run cooler in the board.  Breakers run too near the limit have a short and hot life.

'close' protection is rarely needed at the MCB/RCBO end of things.

Mike.

It is the end of the day and I am tired, but I do not understand the question. What advantage is expected from down-rating the RCBO?

That's a fair point, I didn't explain the rationale for the question.  The reason I asked the question was because a retired electrician mate said that 16A would be "better", admittedly without providing an explanation as to why.

Generalised, the question is about whether it's necessary / advantageous to rate circuit protection to align with the expected maximum load.

The answers above rather support my initial decision to use 20A RCBOs, this being more than adequate to protect the cabling.