Wiring an induction hob & electric oven

[Rogercranstoun]

I'm planning to fit a 7.5KW induction hob which I would like to connect to a radial 6mm T&E cable through a 40 amp mcb at the consumer unit. Is this OK or should I reduce the mcb to 32 amp?

Also, the 5.7KW double oven I want to install has the possibility to be connected to a separate radial 6mm running through a 40 amp mcb. Is this OK, or should I also reduce the mcb to 32 amp?

And, is it OK to make the final run to the hob and oven in 4mm?

Thanks :

 

[holmslaw]

..

 

[Rogercranstoun]

I'm planning to fit a 7.5KW induction hob which I would like to connect to a radial 6mm T&E cable through a 40 amp mcb at the consumer unit. Is this OK or should I reduce the mcb to 32 amp?

Also, the 5.7KW double oven I want to install has the possibility to be connected to a separate radial 6mm running through a 40 amp mcb. Is this OK, or should I also reduce the mcb to 32 amp?

And, is it OK to make the final run to the hob and oven in 4mm?

Thanks :

Thanks for this....you've raised a key aspect.

To reduce heat lost in the kitchen, I've dry lined the walls and run the cable behind and filled the 25mm gap with foil-faced 'kingsmill' board. Also, I've placed mineral wool insulation in the ceiling void where some of the cable also runs.

Is this a serious problem?

Has this compromised

 

[holmslaw]

..

 

[Rogercranstoun]

Thanks for this....you've raised a key aspect.

To reduce heat lost in the kitchen, I've dry lined the walls and run the cable behind and filled the 25mm gap with foil-faced 'kingsmill' board. Also, I've placed mineral wool insulation in the ceiling void where some of the cable also runs.

Is this a serious problem?

Has this compromised

Unfortunately, you may or maynot have a problem thats impossible to advise on without inspecting. Your best bet is to get advice from a local spark.

If I use 32 amp MCB with 6 mm in this situation, what's the worst that can happen? Is it that any increase in the cable temp will 'blow' the MCB or could it be more serious?

The thought of having to run fresh cable is daunting as all surface decoration is complete.

 

[holmslaw]

..

 

[EFLImpudence]

In insulation 6mm² cable is rated at only 23A (23A).

So the cable could overheat, i.e. be damaged, catch fire or melt, without tripping the 32A breaker which only responds to over-current.

In such a situation you would fit a 20A mcb which actually will be satisfactory for the oven and MAY be satisfactory for your hob with each being on a separate circuit.

What do the fitting instructions for the hob state?

 

[Rogercranstoun]

In insulation 6mm² cable is rated at only 23A (23A).

So the cable could overheat, i.e. be damaged, catch fire or melt, without tripping the 32A breaker which only responds to over-current.

In such a situation you would fit a 20A mcb which actually will be satisfactory for the oven and MAY be satisfactory for your hob with each being on a separate circuit.

What do the fitting instructions for the hob state?

Thanks for both your advice so far. Nothing in the fitting instructions for the hob to guide me I'm afraid. The only indicator is on the back plate that shows 7200w.

So, the oven seems OK on 20A mcb. If I also fit another 20A mcb on the 6mm hob radial, how will I know if that's safe?

 

[EFLImpudence]

If I also fit another 20A mcb on the 6mm hob radial, how will I know if that's safe?

It will be 'safe' but if the hob draws more than 20A then it could be detrimental to the mcb, not to mention the inconvenience of frequent tripping.

The normal calculations for cookers work out alright but one of the regulations states that manufacturers instructions should be taken into account.

Is there nothing like 'this appliance must be connected to a 30A supply'

 

[Rogercranstoun]

If I also fit another 20A mcb on the 6mm hob radial, how will I know if that's safe?

It will be 'safe' but if the hob draws more than 20A then it could be detrimental to the mcb, not to mention the inconvenience of frequent tripping.

The normal calculations for cookers work out alright but one of the regulations states that manufacturers instructions should be taken into account.

Is there nothing like 'this appliance must be connected to a 30A supply'

All the instructions state is that it should be connected by a 'qualified person'. I contacted neff, but they only say the same. There are no specs shown for the cable rating or the fusing. The only clues are 7200w shown on a base sticker (along with the model references) and the label on the flex which shows a black and brown tied together, blue and grey tied together + a single y/g earth. The sticker attached to the flex also shows 220-240v 2L+2N, if that helps.

 

[EFLImpudence]

7200w shown on a base sticker (along with the model references) and the label on the flex which shows a black and brown tied together, blue and grey tied together + a single y/g earth. The sticker attached to the flex also shows 220-240v 2L+2N, if that helps.

That will be the European method. Just connect as normal,
Brown - live
Blue - Neutral
G/Y - Earth.

Assuming maximum derating for the cable - 23A CCC

7.2kW @ 230V = 31.3A

Then for cookers etc, we apply 'diversity' because not all on at the same time.

10 + [(31.3 - 10) x 0.3] = 16.4A

So should be ok on 20A mcb

But I would advise getting an electrician to confirm in case anything is not apparent from here.

 

[Rogercranstoun]

7200w shown on a base sticker (along with the model references) and the label on the flex which shows a black and brown tied together, blue and grey tied together + a single y/g earth. The sticker attached to the flex also shows 220-240v 2L+2N, if that helps.

That will be the European method. Just connect as normal,
Brown - live
Blue - Neutral
G/Y - Earth.

Assuming maximum derating for the cable - 23A CCC

7.2kW @ 230V = 31.3A

Then for cookers etc, we apply 'diversity' because not all on at the same time.

10 + [(31.3 - 10) x 0.3] = 16.4A

So should be ok on 20A mcb

But I would advise getting an electrician to confirm in case anything is not apparent from here.

The appliances will be on separate 6mm radials, so does 'diversity' apply as each will be run through separate MCBs from CU's RCB side.

The one clue I received from neff technical team was that the Oven is rated to pull 25A max.

Does this change matters on the cooker or will 6mm through 20A MCB be OK for this appliance even with the insulating aspect?

For the hob, is 6mm 32A MCB OK or should I really change the cable to 10mm through 32A MCB? It might just be possible to pull the 6mm through the wall insulation, dragging 10mm behind it; and then connect to the 6mm in the ceiling void, repositing it on top of the mineral wool.

Both appliances are to be operated through separate 45A cooker switches: I read somewhere that 10mm is to large to fit into these switches?

Grateful for you comments to date.

 

[PrenticeBoyofDerry]

Can you post the make and model of the hob?
it could help!

 

[Rogercranstoun]

Can you post the make and model of the hob?
it could help!

It's a Series 5 Neff T44T43N0GB with electronic touch controls, LED display for each cook zone and a FlexInduction panel; a rectangular large scale zone for bigger cooking.

 

[EFLImpudence]

The appliances will be on separate 6mm radials, so does 'diversity' apply as each will be run through separate MCBs from CU's RCB side.

Yes, I know.
I was only writing about the hob and its circuit.
The oven will definitely be alright.

The one clue I received from neff technical team was that the Oven is rated to pull 25A max.

Yes, not very helpful - 5700/230 = 24.78A
When diversity applied to oven:
10 + [( 24.78 - 10) x 0.3] = 14.43A

Does this change matters on the cooker or will 6mm through 20A MCB be OK for this appliance even with the insulating aspect?

No change.

For the hob, is 6mm 32A MCB OK

NO

or should I really change the cable to 10mm through 32A MCB? It might just be possible to pull the 6mm through the wall insulation, dragging 10mm behind it; and then connect to the 6mm in the ceiling void, repositing it on top of the mineral wool.

10 would be better but I doubt you will be able to drag it through.

Both appliances are to be operated through separate 45A cooker switches: I read somewhere that 10mm is to large to fit into these switches?

You will need the deepest back boxes.
50A cooker switch is the size of a double socket but vertical.

I have given you the figures that apply in your situation but you do not seem to have grasped it yet - no disrespect, it's not your job.

I still recommend you get an electrician - at least to have a look.