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littlespark

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Evening, all.

I've got a kitchen coming up that might lead to more work with a local joiner... first job with him and I want to appear on the ball.

Current set up is 32A MCB on RCD side of a split board, 6.0mm serving a regular cooker switch with only an electric oven coming off it. Hob is presently gas.

The kitchen plan asks for a built in eye level oven and separate microwave combi at the current switch position and an electric hob further round the worktop, so the 32A supply would have to be extended.

The ratings are:

Microwave - 1600W for grill, 900W for microwave. Don't know if these fiunctions would operate simultaneously.
Regular oven - 3650W
Hob - 7200W

Both ovens run off a standard 13A plug, but to have these on the rfc along with kettle, toaster, washing machine and whatever else may be a push.

My plan was to have one of the ovens on the rfc, the other sharing the cooker circuit with the hob. Possible uprating of the mcb to 40A
 
TL;DR
2 ovens, 1 hob on single circuit?
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James

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I personally hate diversity calc's on cooking appliances in the kitchen

the whole idea of diversity is that appliences will not all be on at the same time.
however I for-see a situation of a large dinner party or a Christmas day when unusually but not unforeseeable all of them are on at the same time.

it is unlikely to cause cable damage but could cause a breaker to trip.
at that point the customer thinks that the electrix are under spec and or faulty, that causes you problems.

I personally prefer to over spec rather than use the guidance in this particular circumstance.

years ago, you would get away with it because of the time taken to blow a fuse or fuse wire but now with breakers tripping faster and more uniformly it can cause more issues than you expect.
 

littlespark

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Ideally, I would give them all a dedicated supply from the board, but wrong end of the house. At least the kitchen rfc only serves the kitchen and not the rest of the downstairs.

Both ovens are designed to be plugged in, so i might just give them a single socket each, on the ring... (not a double to serve both) and see what happens. Leaving the hob with 32A all for itself. (31.5A for a 7.2kW appliance. That's pushing it already!)
 

James

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Ideally, I would give them all a dedicated supply from the board, but wrong end of the house. At least the kitchen rfc only serves the kitchen and not the rest of the downstairs.

Both ovens are designed to be plugged in, so i might just give them a single socket each, on the ring... (not a double to serve both) and see what happens. Leaving the hob with 32A all for itself. (31.5A for a 7.2kW appliance. That's pushing it already!)
lets face it, at least when you are in the middle of cooking a big dinner using both ovens, you are probably not doing the laundry and running the dishwasher, toaster and kettle at the same time.
but you can see why i dont like diversity in the kitchen?
 
Applying diversity you're getting a design current of 24.4A, well within your 32A. The diversity allowance for cookers has been around for a long time, you would expect it to have been thoroughly tried and tested by now wouldn't you?

Are any forum members finding they are getting nuisance tripping as a result of overload on cooker circuits where diversity has been correctly applied?
 

davesparks

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the whole idea of diversity is that appliences will not all be on at the same time.
however I for-see a situation of a large dinner party or a Christmas day when unusually but not unforeseeable all of them are on at the same time.
That is just part of how diversity works, it is not just the fact that not all appliances are on at the same time. Especially with cooking appliances.
It is the cycling of the thermostats which plays the biggest role in diversity for cooking appliances.

Plus if you've ever cooked a meal such as Christmas Dinner you'll know that you don't cook everything at the same time, for the same length of time.
 

Ian1981

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The whole Christmas Day cooking dinner and every thermostat is on scenario just doesn’t exist, the whole diversity application is a time proven method applied to cooking appliances for as long as I can remember.
 

Midwest

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We had an 8kW range cooker, where the three ovens cooked all run simultaneously. Clamped it once going full pelt, never got more than 14A.

If it were me, I’d be thinking of separate radials, but I can only see you showing full load of one oven? The combi microwave, as far as I’m aware, can run the grill and microwave at the same time, which comes in around 11A, that’s why I would be thinking of it’s own supply.

Doesn’t the guidance in app 15 recommend separate supplies for cooking loads over 2kw? What’s the rating for the other oven? Could they use the existing 32A supply?
 

Marvo

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That is just part of how diversity works, it is not just the fact that not all appliances are on at the same time. Especially with cooking appliances.
It is the cycling of the thermostats which plays the biggest role in diversity for cooking appliances.

Plus if you've ever cooked a meal such as Christmas Dinner you'll know that you don't cook everything at the same time, for the same length of time.
Also the fact that there's a substantial time delay before an MCB trips if there's a marginal overload....and even longer if the OCPD's are fuses
 

Lucien Nunes

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Under normal conditions a B32 won't trip at 40A and will take 20 mins at 50A. During that time Ib>In so it's incorrect to rely on that buffer zone at the design stage. But if you follow the normal diversity procedures and make In>Ib based on the load with diversity applied, you've complied with the regs, for practical purposes the circuit will never be overloaded, and you've still got the buffer zone of the OCPD fusing factor to render a nuisance trip exceedingly unlikely. Even if everything is turned on at the same time, the Simmerstats and thermostats will be cycling happily before the 20 mins is up.
 
Doesn’t the guidance in app 15 recommend separate supplies for cooking loads over 2kw?
I read that guidance as 'don't put cooking loads over 2kw on general purpose socket circuits' (or is that what you meant?)
Post automatically merged:

Personally I'd put everything on the 6mm 32A circuit, and follow the guidance on p190 OSG.
 

littlespark

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As I said before, I’d rather run radial circuits, but the manufacturers have put moulded plugs on the 2 ovens.
The non microwave one is 3650w, but that’s at full pelt.
I’m thinking to put the microwave on the rfc, and the other oven on the cooker supply where I joint it to extend to the hob position
 

Midwest

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Of all the appliances, I think the microwave combi will run at full steam, using the grill & microwave, albeit the grill will cycle on/off. That could be a bit of a draw on that part of the rfc. What does the manufacturer say? I wouldn't plug the ovens into the rfc either, even allowing for diversity, but thats just me. Being a bit conflicting, from what I posted earlier, but just doesn't seem right.
 

telectrix

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Of all the appliances, I think the microwave combi will run at full steam, using the grill & microwave, albeit the grill will cycle on/off. That could be a bit of a draw on that part of the rfc. What does the manufacturer say? I wouldn't plug the ovens into the rfc either, even allowing for diversity, but thats just me. Being a bit conflicting, from what I posted earlier, but just doesn't seem right.
don't seem right my nan plugging the iron into a light socket, but she came to no harm, apart from a burn mark as she could not understand how it was hot when it hadn't been on the coal fire.
 

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