New Kitchen - Double oven circuit questions.

your_eviltwin · Jun 24, 2020

Good even,

I am having a new kitchen installed and i just wanna double check a few things, having spoken to a few sparkys at work i seem to have the just of it, however im looking for clarity before
getting quotes.

Back ground.

The kitchen is a complete rewire so that it will now have its own ring. (the house is old and ALL sockets runn of 1 ring main).

Moving the oven to other side of the kitchen plus installing a "double" this time round,

Current Oven selections are
3kW - Combi Oven
2.8kW - Oven.

My first question is, how should the ovens be wired?
One supr off a 40Amp breaker then Oven Switch to both?
One supr off a 40Amp breaker then 2x Oven Switchs chained that isolate either oven
Or 2 40A supurs to sockets to ovens? - Ive yet to see a CU that supplies 2x40A breakers.

the second question, size cale is needed for the run to the oven, ( ~10m run throught celing and wall) and what size cable for the flex to connect up to the ovens - looking through the manul is seems they suggessted 2.5mm^2 and thet seem small.... but then im no sparky.

davesparks · Jun 24, 2020

It depends on the personal preference of the electrician doing the installation.
They may prefer to install a seperate supply for each oven or they could equally install a single supply to feed both.

Whichever option they choose they almost certainly won't install a 40A supply, the size will be calculated to suit the power ratings of the appliances.

Your comment about CUs not being supplied with enough 40A MCB's doesn't make sense, you specify which MCB's you need when you order the CU. And these days it is increasingly likely to be RCBO's anyway.

If the ovens aren't supplied with a pre installed flex then a suitably sized heat resisting flex will be suitable.

Markyd · Jun 24, 2020

The sparky who is doing the work will tell you everything you need to know

your_eviltwin · Jun 24, 2020

davesparks said:
Whichever option they choose they almost certainly won't install a 40A supply, the size will be calculated to suit the power ratings of the appliances.

Thank you for this information.

davesparks said:
Your comment about CUs not being supplied with enough 40A MCB's doesn't make sense, you specify which MCB's you need when you order the CU. And these days it is increasingly likely to be RCBO's anyway.

IT is likley that i ill be moving my CU, it is also increassanly likely that a mate will install this for me so i was doing some "Window" shoping ScrewFix to see what is avalable. when I made the observation.

I was keen to use RCBO's origanally, cost depending.
I did the calcs (asuming a 230V supply) and the Ampere came to 12.1 and 13.05Amps, would i asume then the likley choose would be 2x 16A RCBOs if we where to put in two circuits?

davesparks · Jun 25, 2020

your_eviltwin said:
IT is likley that i ill be moving my CU, it is also increassanly likely that a mate will install this for me so i was doing some "Window" shoping ScrewFix to see what is avalable. when I made the observation.

I was keen to use RCBO's origanally, cost depending.
I did the calcs (asuming a 230V supply) and the Ampere came to 12.1 and 13.05Amps, would i asume then the likley choose would be 2x 16A RCBOs if we where to put in two circuits?

Unless your mate who will be doing the work is a qualified electrician I strongly recommend you don't attempt this as a DIY job but get a qualified electrician to do the work.

In fitting a kitchen there is a lot of work that you can, relatively safely, DIY, the water plumbing, kitchen fitting, tiling, decorating all spring to mind.
But the electrical installation work is the one task that I smich harder to do safely without training, and has the very real chance of killing someone if you do it wrong.

I haven't done the calculations but those ecurrents appear to be correct for a straightforward conversion from the power ratings you have stated.

I am not prepared to comment on what size circuit breaker, cable or installation method you should use as I do not feel comfortable giving a DIYer advice when I don't know their level of electrical knowledge or skill.

your_eviltwin · Jun 25, 2020

davesparks said:
Unless your mate who will be doing the work is a qualified electrician I strongly recommend you don't attempt this as a DIY job but get a qualified electrician to do the work.

Rest assured I'm not doing any DIY with the electrics and Yes my mate is an electrician. Due to timings there is a chance he might to be able to do the work

So the wife and i are currently working out our budget (just incase) plus he has only been able to advise over the phone thus far therefore I was hoping to get a general idea so as not to be ripped off

So far the builders have all given different approaches and quotes which has it's left me a tad dismayed.

But given the info I have recived tonight I feel confident I will know if I'm being taken for a ride if I have to get some in.

pc1966 · Jun 25, 2020

The likes of Screwfix, etc, have various pre-populated CUs for sale. But really it makes sense to look at your current installation (plus the planned new stuff) and install a CU configured to match (and with a couple of spare slots for any future additions). You can always buythen with the bare minimum fitted and add whatever you need afterwards.

As already said, this is not a DIY job!

Going for RCBO is what most folk here would recommend if you can afford it, and these days the cost premium is quite small. It means in the (hopefully unlikely) case of a circuit tripping on an earth fault it only impacts on the one circuit. Also many "18th edition" board has a Surge Protection Device fitted which is also a good thing to have.

I quoted "18th edition" as really there is no such thing and it is a marketing step! Most of the current requierments (such as a non-combustible enclosure for domestic use) were already in place by the end of the 17th edition of the IET regulations.

radiohead · Jun 25, 2020

Surely you'd be asking your mate these questions if he's an electrician?

G1ZQC_David · Jun 27, 2020

Rather than me try to explain diversity, here is the Guru of the Electrical world, Mr John Ward, explaining it all, please watch till the end, it makes really good viewing.