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New Oven Appliances - RCBO Ratings

John R.

Installing two new appliances 

  • Microwave Combination Oven 3350W (say 15A)
  • Oven 2990 W (say 13A)

The kitchen already has two radials from the consumer unit to which these will connect, with 20A RCBOs installed.  

The radial circuits are in 2.5mm.sq cable and the length is okay for voltage drop.

The appliances don't have plug tops so need to be hard-wired each into a separate connection plate, so there are no fuses in place.

Would prefer to avoid replacing the 20A RCBOs with 16A ones if possible.  Instruction manuals don't provide any useful information re supply ratings and I can't find anything much to help inform the decision.

16A RCBOs would provide closer protection, but is this really necessary?

  • 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.

     

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