Discuss 2 cookers 1 halogen hob in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Benny_Boy

Evening chaps,

Been having a think about this:

Doing an extension soon which has an existing 6mm to iso for cooker.

The kitchen's being ripped out soon and a micro- combi 3.6kw and single oven 3.3kw are going in with a 10.5kw halogen hob.

EDITED for clarity:
It actually looks like diversity actually allows all three of these to be on a 32A breaker on 6mm!


But I'm not proposing that, I'm having the ovens on the existing 6mm and a new swa buried to the hob.

p160 osg

I've told the chappie that he's got to have a separate feed for the hob as I didn't feel comfortable thinking about christmas dinner when those rings will be drawing 35-45A for an hour or so!


I'm thinking the hob in 4mm swa, (I thought 6mm at first but it seems no need)to an adaptable box then to outlet. on a 32A breaker



Does that sound reasonable?
 
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p = vxi
10.5kw = 43amps and you want to use a 4mm 32A mcb bang breaker trips but before that the cable melts
10mm 45A mcb nothing reasonable here mate
p=vxi
 
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I'm glad you changed your original comments spsparks - too harsh! As for your revised thoughts on this, again too OTT.
4mm swa will not melt in this instance, even though we do not know the exact reference method. It takes quite a lot of over-rated-current before a cable melts, and the actual draw in this application is perhaps borderline, but not unreasonable - especially as the OP is asking our opinion for confirmation of his thinking. Do you understand how hobs like this work, and what the actual current draw is likely to be in reality?
I myself am not sufficiently knowledgeable to give a definitive answer to him, but let's hear what others have to say on the subject.
 
p = vxi
10.5kw = 43amps and you want to use a 4mm 32A mcb bang breaker trips but before that the cable melts
10mm 45A mcb nothing reasonable here mate
p=vxi

it's hardly a shower is it.

10.5kw @230 = 45.6

after diversity (it's a hob) = 20.7A =Ib
4mm SWA ref method d = 43A (although ambient temp is more likely to be 10 not 20 degC)

this gives me an Ib of 20.7A, an In of 32A, and an Iz of 43A.

You see what I mean?
It's very rare that a hob is on full power on all rings at once.
I just wondered if any forum members would have done it differently, ie used a different diversity factor. My design complies with BS7671, just that a lot of it comes down to common sense. Always good to get a second opinion if something feels a bit wrong, as I often find domestic cooking appliance diversity does.
 
Evening chaps,

Been having a think about this:

Doing an extension soon which has an existing 6mm to iso for cooker.

The kitchen's being ripped out soon and a micro- combi 3.6kw and single oven 3.3kw are going in with a 10.5kw halogen hob.

Now am I right in thinking diversity actually allows all three of these to be on a 32A breaker on 6mm? (provided no socket)

p160 osg

I've told the chappie that he's got to have a separate feed for the hob as I didn't feel comfortable thinking about christmas dinner when those rings will be drawing 35-45A for an hour or so!


I'm doing the hob in 4mm swa (it's got to go outside)to an adaptable box then to outlet. on a 32A breaker



Does that sound reasonable?

If your designing to the OSG pg 160 then what your proposing would not be recognised It states that a load of 15kw can be supplied by a 32amp protection Device but your 3 units will be 17.4Kw so over the loading limiting.
 
If your designing to the OSG pg 160 then what your proposing would not be recognised It states that a load of 15kw can be supplied by a 32amp protection Device but your 3 units will be 17.4Kw so over the loading limiting.
No, I was putting the oven and the micro-combi on the existing 6mm and running a 4mm swa outside, buried, for the hob with separate iso. Should have made that clear.:rolleyes:

I've actually told the chap that I'm running 6mm swa with a 40A mcb but got home and had a quick look in BRB and it looks for all the world like 4mm swa, and 32a mcb are ok to me.
 
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If your designing to the OSG pg 160 then what your proposing would not be recognised It states that a load of 15kw can be supplied by a 32amp protection Device but your 3 units will be 17.4Kw so over the loading limiting.

Not quite so.... That 17.4KW will probably never be seen, Both of the ovens will have heating elements that cannot be utilised together, such as grill and main oven element, or fan element. The micro will also have heating elements/functions that can't be utilised together.
So much more likely that the age old cooker diversity factor regarding the 15KW will hold true for this little set up too....

Even the hob, when all the rings are being used, will be individually switching on and off via the thermostats. Full load will only ever be seen for a few minutes at a time at worst!!!....
 
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would anyone actually hook up all three to one outlet on 6mm 32a mcb?

I ask the question in earnest because by calc it seems for the lot Ib is 29.8A

Having looked at p160 osg it certainly looks me like 15kw would be the accepted max load cooker on a 32A breaker

Don't think I'd fancy it, some might.
 
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If it comes within the 15KW rating ...why not?? Do you know that the cooker diversity factor has been around now for around 60+ years, and has been proving it's self to be a rock solid in all that time!!!

Why is it that these days everything has to be bigger and bigger?? Cut out fuses must have 100A, must have 25mm meter tails, Must have 10mm cooker cable, ....Most of it brought about by guesstimating or some sort of fear in there abilities to produce accurate calc's ....
 

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