Hob/Oven question!

[Kemikal]

Hello,

I know this comes up all the time, but I've looked around and have found conflicting answers and differing scenarios, so I had to ask as I've had a little electrical experience but I'm by no means a expert.

Ok, we've decided to opt for an induction hob and separate double oven, and in our naivety bought without looking, and now it comes to installing it we've struck a snag.

The hobs is a Kenwood KHC604-Ind rated at 7,400w and the oven is a NEFF U12S53N3GB rated at 4,900w.

From what I've found out - and please correct me if I'm wrong - it goes a little something like this...


7400/230 = 32.17 amps

4900/230 = 21.3 amps


...and as we only have a single 32A cooker outlet plate connection, can't both be run from it.

This is what I'm not sure of. I've seen a number of people advise that if diversity is applied to the oven it will be (10+30% of remainder) 13amps and can therefore be connected to the normal kitchen circuit? I'm a little dubious as I would have thought that if this is the case it would have a normal plug? (The manufactures instructions say that diversity can't be applied to the hob).

Logic is telling me that we'd have to run a second circuit from the fuse box around the kitchen (approx 10m) and install a new connection point to accommodate the oven (is it just that simple?), but if there is a way that we can run both from the existing single point, we'd love to hear it.



Thanks for your time, any advice would be more than welcome.

 

[EFLImpudence]

Well, the oven actually comes to 13.39A so …

A normal cooker circuit with a 32A breaker is good for 15kW of appliance with an integral socket at the cooker switch or 19kW without socket.

Connect them both to the existing circuit; all will be well.

 

[Diyisfun]

P = IxV
P= Watts
I = Amps
V = Volts

So its p/v

 

[EFLImpudence]

I have just realised you divide by 230.
If the Wattage was quoted at 240 by the manufacturer this will lower the amperage but the oven should still not be plugged into the socket circuit.

 

[Kemikal]

Thanks for answering my question - and sorry for the scepticism - but will the 2 appliances not be drawing too many amps?

I think I'm more asking HOW can the 2 be connected without a problem?


Thanks,

 

[PrenticeBoyofDerry]

I think in reading the manufacturers instruction of the hob, you are mistaken by believing diversity cannot be applied to the circuit. I think the part that states diversity cannot be applied to this unit, is referring to the cooker control unit, which makes sense. As you would want the CCU to be able to handle the full current of the MCB.
So applying diversity, will allow a 32A circuit to supply both hob and oven.

 

[EFLImpudence]

Cooking appliances have numerous elements which cycle on and off because of their thermostats.

Consequently they do not draw the maximum current.
The diversity formula has been used for decades and would seem to work very well.

7400 + 4900 = 12300 / 240 = 51.25A

41.25 x 0.3 = 12.375 +10 = 22.75A

So your 32A MCB gives plenty of leeway even on this figure.


OR


That's just how it works.

 

[Kemikal]

Ooh, I'm not sure, the book says...

"IMPORTANT: This appliance must be connected to a suitable double pole control unit adjacent to the cooktop.
No diversity can be applied to this control unit.
The control unit must be capable of breaking the full load current of the appliance."

So, the cooker control unit is the connection on the wall I take it? (I have a switch for the cooker and a plug socket with a switch, if that helps.)

So does this mean that I can apply diversity to both the hob and oven bringing it down to around 29A and connect them both to the same single 32A connection point behind the existing cooker?


Sorry if this is all really simple stating the obvious stuff...

 

[PrenticeBoyofDerry]

Thanks for answering my question - and sorry for the scepticism - but will the 2 appliances not be drawing too many amps?

I think I'm more asking HOW can the 2 be connected without a problem?


Thanks,

7400w + 4900w =12300w/230v
=53.48A
(53.48-10) x 0.30
=13.044A
13.044+10 = 23.04A
add 5A for socket outlet on CCU if applicable.

 

[Kemikal]

Cooking appliances have numerous elements which cycle on and off because of their thermostats.

Consequently they do not draw the maximum current.
The diversity formula has been used for decades and would seem to work very well.

7400 + 4900 = 12300 / 240 = 51.25A

41.25 x 0.3 = 12.375 +10 = 22.75A

So your 32A MCB gives plenty of leeway even on this figure.


OR


That's just how it works.

Sorry buddy, i was typing when this came through... so all is good, even though it's an induction hob? I've read so many conflicting answers that i really need to be sure as we have 4 children and would frequently be running 2 ovens and 2 hobs!

 

[PrenticeBoyofDerry]

Ooh, I'm not sure, the book says...

"IMPORTANT: This appliance must be connected to a suitable double pole control unit adjacent to the cooktop.
No diversity can be applied to this control unit.
The control unit must be capable of breaking the full load current of the appliance."

So, the cooker control unit is the connection on the wall I take it? (I have a switch for the cooker and a plug socket with a switch, if that helps.)

That will be you CCU, and that is what the MI is saying you cannot apply diversity to.

So does this mean that I can apply diversity to both the hob and oven bringing it down to around 29A and connect them both to the same single 32A connection point behind the existing cooker?

You can offer diversity to circuit bringing it to a little under 30A.
The use of a CCU rated above 32A would be adequate but the 45A rated ones are generally used.
So 32A circuit would be fine, I would opt for two CCUs one for oven one for hob, using a dual outlet plate to divide the two cables to each appliance.
I would only have one of the CCUs with a socket outlet though, as this would take you beyond the 32A allowed on the circuit.

 

[AndyPRK]

That's a lot of unnecessary work to fit a 2nd cooker switch which isn't required. And in that case not sure where you plan to use a dual outlet plate?

 

[JohnW2]

"IMPORTANT: This appliance must be connected to a suitable double pole control unit adjacent to the cooktop.
No diversity can be applied to this control unit. ... The control unit must be capable of breaking the full load current of the appliance."

That will be you CCU, and that is what the MI is saying you cannot apply diversity to.

Indeed - and, as you said in an earlier post, that seems perfectly reasonable, and something which I think very commonly gets forgotten/overlooked.

Diversity is a statistical/probabilistic concept, based on the fact that anything approaching the 'full load current' of the cooker will very rarely flow, and that the average load over any reasonable period of time will be much lower than that 'full load current'. However, it is implicit in that concept that any current up to that 'full load current' (certainly well over the calculated after-diversity current) can, and occasionally will, flow.

Those occasional and short-lived currents well over the 'after-diversity current' are not a problem for the cable or OPD (fuse, MCB or RCBO) but are an issue in relation to any switches, since it could just be that it was called upon the break the current at a point in time when (by 'bad luck') the current flowing happened to be something well over the calculated after-diversity current (potentially as high as the 'full load current' of the cooker).

Given that most CCU switches seem to be rated at 45A or 50A, this presents a potential problem for cooking loads greater than about 10.4 - 11.5 kW which I suspect is not always considered.

Kind Regards, John

 

[JohnW2]

That's a lot of unnecessary work to fit a 2nd cooker switch which isn't required.

As I've just written, it might not be unnecessary, since one shouldn't really apply diversity when considering switch ratings.

Kind Regards, John