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2 single ovens and an induction hob?

acalmenvoy

Will the existing wiring ( Cooker switch to 32amp fuse in fuse box) be enough or we talking major rewiring, both ovens are 3.5KW each and the hob is 7.4KW total connected load?

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Risteard81

2011 wrote: »

Agreed and already stated. However it can only be applied to a point. I have shown why I think the rating of the MCB would be exceeded under quite unremarkable circumstances. How about you show how it won’t be?

Simple, the design current under very normal conditions exceeds the rating of the protective device.

I only applied 25% loading for the hob which is very generous in terms of diversity and it was still an issue.

The design current doesn't exceed the rating of the protective device. It is the total connected load which does. Incidentally these are often quoted for elements which cannot even be simultaneously energised. I'm at work so will prove you wrong with quotes from published books on the matter later.

2011

Risteard81 wrote: »

Not only is diversity acceptable

Agreed and already stated. However it can only be applied to a point. I have shown why I think the rating of the MCB would be exceeded under quite unremarkable circumstances. How about you show how it won’t be?

It is fully compliant with the Wiring Rules. Why would you think otherwise?

Simple, the design current under very normal conditions exceeds the rating of the protective device.

I only applied 25% loading for the hob which is very generous in terms of diversity and it was still an issue.

Risteard81

2011 wrote: »

This does not apply when started cold. Stats only switch off when the set point is achieved.

For a few minutes only. Time is an important factor when designing.

It is fine and completely compliant to have an oven and induction hob sharing a 32A cooker circuit. That is an irrefutable fact. 15kW of cooking load is the maximum for a 32A cooker circuit owing to diversity. Fact.

Risteard81

2011 wrote: »

Just because you have not had an issue with your setup does not mean it is acceptable.
As already stated I accept that diversity can be applied to some extent but this is a bridge too far. Let’s look at the maths as it is quiet simple:

2 ovens switched on from cold = 6 kW is 26 amps at unruly power factor before a stat even kicks in. If I switch on just one ring of the job (assuming 4 rings of equal rating) that is another 8 amps at unity power factor. This is a total of 34 amps which exceeds the rating of the MCB which is against the regulations.

How likely is it that someone would switch on 2 ovens and one ring from cold? Very likely in my opinion. Would you get away with it? Most likely yes but it is against best practice and I would strongly advise against it. It is best to comply fully with the National Wiring Rules.

Not only is diversity acceptable - it is essential for economic design. It is fully compliant with the Wiring Rules. Why would you think otherwise?

2011

Risteard81 wrote: »

It won't be drawn simultaneously as the thermostats will cycle the elements on and off

This does not apply when started cold. Stats only switch off when the set point is achieved.

2011

Risteard81 wrote: »

It's actually likely fine. 15kW of appliances can go on a 32A circuit owing to diversity. I have an oven and 7kW induction hob on a 32A circuit with 6mm^2 cable here. It is fully functional, safe and compliant. I probably wouldn't add a second oven though personally.

Just because you have not had an issue with your setup does not mean it is acceptable.
As already stated I accept that diversity can be applied to some extent but this is a bridge too far. Let’s look at the maths as it is quiet simple:

2 ovens switched on from cold = 6 kW is 26 amps at unruly power factor before a stat even kicks in. If I switch on just one ring of the job (assuming 4 rings of equal rating) that is another 8 amps at unity power factor. This is a total of 34 amps which exceeds the rating of the MCB which is against the regulations.

How likely is it that someone would switch on 2 ovens and one ring from cold? Very likely in my opinion. Would you get away with it? Most likely yes but it is against best practice and I would strongly advise against it. It is best to comply fully with the National Wiring Rules.

Naturally if the power factor is not perfect (it generally isn’t) or more rings are switched on with the 2 ovens the current could be far higher.

Risteard81

YellowBucket wrote: »

With cooking appliances you'll definitely get scenarios where most of the load could be drawn simultaneously, even if it's only christmas day or some dinner party, you'll find someone won't be too happy if their MCB trips in the middle of some complicated dish.

We have ours on 2 x 32A circuits.

It won't be drawn simultaneously as the thermostats will cycle the elements on and off

Cerco

GreeBo wrote: »

Once its an induction hob I would always give it its own circuit.
When you can join zones for larger pots etc its just not worth it.

Maybe my house is different but it would be rare that the oven and hob wouldnt be on at the same time.

Maybe, but I can imagine a regular scenario of the vegetables on the hob with the roast in the oven. Probably two rings in use. But then many roast their veg so it depends. Personally I would go for the two circuit option. It’s a once off cost for lasting peace of mind.

GreeBo

Once its an induction hob I would always give it its own circuit.
When you can join zones for larger pots etc its just not worth it.

Maybe my house is different but it would be rare that the oven and hob wouldnt be on at the same time.

YellowBucket

With cooking appliances you'll definitely get scenarios where most of the load could be drawn simultaneously, even if it's only christmas day or some dinner party, you'll find someone won't be too happy if their MCB trips in the middle of some complicated dish.

We have ours on 2 x 32A circuits.

Lenar3556

Risteard81 wrote: »

That's an imagined problem which simply doesn't happen in the real world. Diversity works.

It does when you are dealing with a diverse enough loading profile. But a bit of a stretch in this case. He is talking about over 60 amps of cooking there. Is it a house? If there is need for two ovens it follows that they are both expected to be on at the same time. And it’s not unreasonable to expect to have some hob going along side them.

Risteard81

3d4life wrote: »

Expect cooking complexites on Christmas day if everything off one breaker.

That's an imagined problem which simply doesn't happen in the real world. Diversity works.

3d4life

Expect cooking complexites on Christmas day if everything off one breaker.

Risteard81

It's actually likely fine. 15kW of appliances can go on a 32A circuit owing to diversity. I have an oven and 7kW induction hob on a 32A circuit with 6mm^2 cable here. It is fully functional, safe and compliant. I probably wouldn't add a second oven though personally.

2011

acalmenvoy wrote: »

Thanks for the reply, would the diversity factor be applicable here?

It would but you are still looking for too much.

acalmenvoy

2011 wrote: »

That is too much for one circuit. The hob alone is about right for a 32A MCB.

Thanks for the reply, would the diversity factor be applicable here?

2011

That is too much for one circuit. The hob alone is about right for a 32A MCB.