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Ovens and 30A fuse/feed

robopj

Hello, I googled and found some info in the old IET forums, which has generated this post.

We need to replace our double oven. For the last 20 years, a 30A trip fuse has provided power to a dual wall socket (kettle 2.2kw, microwave 1.29kw) and the oven with a 5.1kw max rated power consumption. I've discovered this by tripping the 30A fuses in the fuse box to see which appliances were still live. 

It appears that when the kitchen was fitted (20 years ago), the original standalone cooker on/off master switch was converted to a dual wall socket and the then a spur used for the double oven.

According to my maths this is a total of 35.79A @ 240v which is more than 30A, although I'm guessing the times all three appliances have been on at the same time would be infrequent.

ApplianceLoad rating (kw)Amps (at 240v)
Current oven5.121.25
Kettle2.29.166666667
Microwave1.295.375
total8.5935.79166667

Why has the 30A RCD at the fusebox not tripped when they have been on at the same time?

The new oven has a load rating of 6.2kw. This increases the total amps to just over 40A. 

ApplianceLoad rating (kw)Amps (at 240v)
New oven6.225.83333333
Kettle2.29.166666667
Microwave1.295.375
total9.6940.375

I'm guessing this may cause some issues with the 30A feed. Would a more modern 32A be better?

I suppose I could always move the kettle and microwave to other sockets in the kitchen which are on a different 30A circuit.

Please could I have your comments? 

Thank you

Paul

 

 

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    In a word diversity - circuits are usually designed for the current they'll usually have to carry for a reasonable length of time, rather than any instantaneous theoretical maximum.

    Cooking appliance circuits are traditionally rated at 100% of the first 10A, 30% of the remainder, plus 5A if the cooker control unit included a socket outlet.

    So with the old 5.1kW oven - 22A say - the circuit need only be rated for 13.6A  - so there's a fair bit spare for the kettle and microwave.

    Even with the new 6.2kW oven (27A say) you'd be looking at needing just over a 15A circuit as far as the oven is concerned.

    You could argue that a simple oven has less diversity than a conventional full cooker, but even so there's probably a decent margin to play with.

       - Andy.

     

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  • 0

    In a word diversity - circuits are usually designed for the current they'll usually have to carry for a reasonable length of time, rather than any instantaneous theoretical maximum.

    Cooking appliance circuits are traditionally rated at 100% of the first 10A, 30% of the remainder, plus 5A if the cooker control unit included a socket outlet.

    So with the old 5.1kW oven - 22A say - the circuit need only be rated for 13.6A  - so there's a fair bit spare for the kettle and microwave.

    Even with the new 6.2kW oven (27A say) you'd be looking at needing just over a 15A circuit as far as the oven is concerned.

    You could argue that a simple oven has less diversity than a conventional full cooker, but even so there's probably a decent margin to play with.

       - Andy.

     

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