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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?

Parents

  • 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.

     

Reply

  • 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.

     

Children
  • in reply to John R.

    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.

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