Kitchen redesign and electrical constraints

[LooneyTunes]

CharlesElliott said:

You can calculate what you think the max load will be (although then you need to know what the 'actual' draw of a cooker or appliance will be, rather than the rated draw), or you can use diversity rules, or some combination of your choosing. But as a starting point, the diversity rating for a domestic cooker is 10A + 30% of the remaining rated value......which is approx 17A or 50% of a 32A rated appliance.

We're talking ovens, not cookers.

[CharlesElliott]

LooneyTunes said:

We're talking ovens, not cookers.

Do you see a specific difference? The diversity table refers to Cooker circuits, which is why I used that word, but I don't believe it affects the substance of what I said. Hobs, ovens and grills (or combinations thereof) could all be on a 'cooker circuit'.

[LooneyTunes]

CharlesElliott said:

LooneyTunes said:

We're talking ovens, not cookers.

Do you see a specific difference? The diversity table refers to Cooker circuits, which is why I used that word, but I don't beleive if affects the substance of what I said. Hobs, ovens and grills (or combinations thereof) could all be on a cooker circuit.

Of course there's a difference!

An oven is a single appliance that lacks granular user control over the individual elements. Accepting that when it is up to temperature the element(s) will be intermittently on, whilst it is getting up to temperature and/or in certain operating modes it is entirely possible (likely even) that it will draw the full rated load.

A cooker, on the other hand, typically comprises an oven and a hob. It is far from certain (indeed, unlikely) that all elements (the oven elements and all rings) would be used simultaneously at full power, so applying diversity calcs against the theoretical max draw seems reasonable.

Look at it from a different perspective, when else would you not expect the chosen MCB to be at least capable of supporting the largest single load on a circuit? Sure, it might not support every load on a circuit being at full power constantly, but that's what diversity calcs are designed to addreess? ETA: and in this case the oven is the only load proposed on the radial.

I think those posting that you can apply diversity to a single appliance on its own radial aren't correct. I'd also be concerned that anyone choosing to choose a smaller MCB might also then decided that the cabling could be smaller too...

Edited by LooneyTunes on Monday 26th August 15:08

[Mr Pointy]

CharlesElliott said:

LooneyTunes said:

We're talking ovens, not cookers.

Do you see a specific difference? The diversity table refers to Cooker circuits, which is why I used that word, but I don't believe it affects the substance of what I said. Hobs, ovens and grills (or combinations thereof) could all be on a 'cooker circuit'.

I too beleive this is correct - the diversity calculations apply to hobs, cookers (hob & oven in one enclosure) & ovens.

I didn't mean to say thet the diversity calculations couldn't be applied to three individual radials only that doing so could lead to a higher potential current draw than if all three were on one circuit. Of course there is less chance of tripping on Christmas morning but I don't think that's a widespread problem anyway. On one circuit (24A draw with diversity) you could fit something like a 32A MCB & have a 10kW shower (a 42A load) & not take out the 100A fuse. If the radials weren't sized with diversity you would need 3x 32A MCB (or even 2x 32A & a 40A) which means you could theoretically pull 96A when cooking. Of course it's extremely unlikely, but you could.

You'd also need more runs from the CU & they would almost certainly need to be significantly thicker copper.

[Chumley.mouse]

Heres a bit of perspective….. our house still has the old kitchen ring main , its the only circuit that still has to be rewired as we will be doing it when a new kitchen is installed.

The oven , induction hob, fridge , freezer , dishwasher, microwave, kettle , toaster and anything else that is plugged in is all on it. It has never tripped in the 5 years we have been here ( even on Christmas day ). The oven and hob are on 13a plugs , The hob plug does get a bit warm when more than 2 rings on .

[CharlesElliott]

My general points were intended to look at load across the CU and through the DNO fuse. If you only have one load connected to a final circuit then of course it should have an individual MCB / RCBO that is rated appropriately.

But if you have three ovens, whilst each should have a 32A breaker, I would not consider the total draw to be 96A at a practical level. If you do assume that, then with other loads in the property, you must go to two or three phase.

ETA: Do the ovens rated at 6300W actually have more than one oven compartment as I haven’t been able to find a single compartment oven rated at that level.

Edited by CharlesElliott on Monday 26th August 15:48

Edited by CharlesElliott on Monday 26th August 15:49

[mrmistoffelees]

CharlesElliott said:

ETA: Do the ovens rated at 6300W actually have more than one oven compartment as I haven’t been able to find a single compartment oven rated at that level. They are nearly always 3200W max.

Edited by CharlesElliott on Monday 26th August 15:48

It's two double ovens, for a total of four. These ones: https://www.neff-home.com/uk/productlist/ovens-com...

And the hob is: https://www.neff-home.com/uk/productlist/hobs/indu...

[matchmaker]

The supply cutout may say 100A on it, but may not have a fuse of that size in it.

[LooneyTunes]

mrmistoffelees said:

CharlesElliott said:

ETA: Do the ovens rated at 6300W actually have more than one oven compartment as I haven’t been able to find a single compartment oven rated at that level. They are nearly always 3200W max.

Edited by CharlesElliott on Monday 26th August 15:48

It's two double ovens, for a total of four. These ones: https://www.neff-home.com/uk/productlist/ovens-com...

And the hob is: https://www.neff-home.com/uk/productlist/hobs/indu...

Linked from that page, for the oven manufacturer specifies:

Connection Rating: 6300W
Fuse Protection: 32A
https://media3.neff-international.com/Documents/sp...

NEFF clearly don't believe that diversity calcs are appropriate for those ovens.

Mr Pointy said:

If the radials weren't sized with diversity you would need 3x 32A MCB (or even 2x 32A & a 40A) which means you could theoretically pull 96A when cooking. Of course it's extremely unlikely, but you could.

(edit to fixed messed up quote)

True, but there are other things that the OP could do to limit total draw to the kitchen and nuisance tripping of the whole house (such as the secondary CU he mentioned) but if I were the client I wouldn't be wanting individual cables/breakers undersized vs the manufacturers instructions.

Edited by LooneyTunes on Monday 26th August 17:05

[guitarcarfanatic]

Does your EV charger allow a CT clamp to be fitted? Most do - this will self modulate the car charger power draw based on what else is being used around the house.

[b14]

In case it helps, we're in the middle of a full renovation and our kitchen is basically going to be the same spec as yours - two double ovens plus a large induction hob. 7.4kw EV charger. Our sparky that is wiring the entire house has said that we're fine on 100 amp DNO fuse. Obviously the CU is being specced to fit from brand new since it's an entirely new wiring arrangement throughout the house.

If we had a heat pump he said we'd need three phase, but he's comfortable as is on 100 amp fuse. Slightly puts paid to our idea to put in a heat pump for our pool but we'll worry about that first world problem later.

[tendown]

BS1361 shows that a 100A cut out fuse will take 200A for several minutes - I don't think you need to worry

Or probably more helpfully about 150A for a few hours....

Edited by tendown on Monday 26th August 19:29