Cooker wiring distribution

[iep]

Appreciate I'll be getting an electrician in to do this but looking to understand what I'll be asking them to do.

We currently have a standard electric cooker (hob and oven in one freestanding unit). It connects to an outlet on the wall behind it via a simple, unswitched, twin outlet wall plate. The wiring back to the fuse box from the wall plate is 10mm twin and earth via the cooker switch in the wall and is protected by a 50A RCBO. Oven is connected directly to the wall plate with no other in-line fuse. I'm assuming this is normal and safe (though I wonder what is protecting the cooker cable before it gets to the fuse inside the cooker).

In our new kitchen, we're going ot have a built in hob in the same location as the existing cooker and a built in oven about 2m away in a tall cupboard. Oven requires 16A. Total current for hob and oven is well within the 10mm cable capacity (and also below the 50A RCBO limit).

To build in a bit of future flexibility (maybe add a microwave above/below oven later on), I was thinking to ask for a 4mm twin and earth spur from the original cooker outlet plate over to a new/second outlet plate for the oven. I'm assuming this would need to be fused locally to the main outlet plate (at level appropriate for the 4mm cable spur) and then again at the new outlet for the oven?

Attempt yo draw it all out below:

Thanks.

 

[EFLImpudence]

We currently have a standard electric cooker (hob and oven in one freestanding unit). It connects to an outlet on the wall behind it via a simple, unswitched, twin outlet wall plate. The wiring back to the fuse box from the wall plate is 10mm twin and earth and is protected by a 50A RCBO. Oven is connected directly to the wall plate with no other in-line fuse. I'm assuming this is normal and safe (though I wonder what is protecting the cooker cable before it gets to the fuse inside the cooker).

The RCBO is protecting the cable.
It is unlikely there is a fuse inside the cooker.

In our new kitchen, we're going ot have a built in hob in the same location as the existing cooker and a built in oven about 2m away in a tall cupboard. Oven requires 16A. Total current for hob and oven is well within the 10mm cable capacity (and also below the 50A RCBO limit).

Any domestic appliances you are likely to buy will be well within the cable capacity.
32A RCBO and 4mm² (installed Method C) is all that is required.

To build in a bit of future flexibility (maybe add a microwave above/below oven later on),

You have all the future flexibility you will ever need.
10mm² is often used as the main supply cable to flats.

I was thinking to ask for a 4mm twin and earth spur from the original cooker outlet plate over to a new/second outlet plate for the oven. I'm assuming this would need to be fused locally to the main outlet plate (at level appropriate for the 4mm cable spur)

You could just reduce the rating of the RCBO to 32A.
Nothing locally would be required.

and then again at the new outlet for the oven?

Nope.

 

[AndyPRK]

Does the oven come with a 13A plug on it?

 

[iep]

Does the oven come with a 13A plug on it?

Nope, it's a 16A hard wired one. I gather needs an electrician to install.

 

[iep]

The RCBO is protecting the cable.
It is unlikely there is a fuse inside the cooker.


Any domestic appliances you are likely to buy will be well within the cable capacity.
32A RCBO and 4mm² (installed Method C) is all that is required.


You have all the future flexibility you will ever need.
10mm² is often used as the main supply cable to flats.


You could just reduce the rating of the RCBO to 32A.
Nothing locally would be required.


Nope.

Jeez, I see what you mean. If I'm doing my diversity calc correctly I should only ever need ~26A

Hob = 32A
Oven = 16A
Micro/combi/whatever = 16A
Total = 64A

So, ((64A - 10A) * 30%) +10A = 26.2A

Is that right? In that case, the 32A RCBO makes sense even if I were to add a full second oven further down the line. Seems almost too easy

Thanks again.

 

[AndyPRK]

If you just had the oven remotely, people say its impossible for a oven to fail and go overload so you don't need any extra fuses/MCBs.
Also the add on extension is less than 3 meters, so that supports not requiring additional protection.

If the oven and microwave had plugs with fuses in them, that would also protect overload, and even 2.5mm cable could be used. (2.5mm rated to 27A)

So you could almost use whatever cable you want! 4mm or more common and future proof 6mm.

 

[EFLImpudence]

Jeez, I see what you mean. If I'm doing my diversity calc correctly I should only ever need ~26A

Hob = 32A
Oven = 16A
Micro/combi/whatever = 16A
Total = 64A

So, ((64A - 10A) * 30%) +10A = 26.2A

Is that right?

That is correct.

In that case, the 32A RCBO makes sense even if I were to add a full second oven further down the line. Seems almost too easy

Yep.

 

[EFLImpudence]

Also the add on extension is less than 3 meters, so that supports not requiring additional protection.

Where does the 3m come from? You are surely not misreading 433.2.2 as another here frequently does?

So you could almost use whatever cable you want! 4mm or more common and future proof 6mm.

The use of 6mm² would more correctly be called "past proofing" as it was/is required with a BS3036 30A fuse but not a 32A MCB/RCBO.

 

[AndyPRK]

what size cable do new build houses use for cooker circuits? It's not 4mm.

 

[pete01]

A lot of sparks would put a 32 amp radial circuit in using 4mm but wont use 4mm for a 32 amp cooker circuit.....strange that

 

[pete01]

what size cable do new build houses use for cooker circuits? It's not 4mm.

6mm?

 

[EFLImpudence]

Just habit.

 

[iep]

Thanks for all the input on this. Really helpful. Sounds like I'm just asking for a 6mm spur from the original outlet plate. Nice and easy.

Cheers!