New separate ceramic hob and oven

[PrenticeBoyofDerry]

My angle is that the load even after diversity, would exceed the cable safe current carrying capacity based on my many assumptions.
Cable within insulation in cavity wall derating to 23.5A.
Hob at 7.9kW
Oven at 5.75kW (based on flex captivity)
Giving 13.65kW Load, simple diversity calcs leave me at 27A

 

[EFLImpudence]

Even using 230V (on the likely 240V Wattage quoted) I make it 24.8A

Using 240V it is 24.1A which converted to 230V comes to 23.1A


Leaving that aside, I have seen oven instructions call for 2.5mm² while calling for a 16A fuse so perhaps we had better wait until the OP tells us what it is.

 

[ANGLER]

The bungalow was rewired by the ELECTRIC BOARD/Anglia Electricity in 1993. This included the cooker circuit.
Approx 10+ years ago, we have had the cavity walls insulated.

 

[EFLImpudence]

What is the make and model of the oven?

 

[PrenticeBoyofDerry]

The bungalow was rewired by the ELECTRIC BOARD/Anglia Electricity in 1993. This included the cooker circuit.
Approx 10+ years ago, we have had the cavity walls insulated.

By installing the cooker cable within the cavity, they have used very bad practice and with the insulation present this would create the derating that I have mentioned.

 

[PrenticeBoyofDerry]

Even using 230V (on the likely 240V Wattage quoted) I make it 24.8A

Using 240V it is 24.1A which converted to 230V comes to 23.1A

I have 13.650kw/240V =57A
(57Ax0.3)+10 =27A

Leaving that aside, I have seen oven instructions call for 2.5mm² while calling for a 16A fuse so perhaps we had better wait until the OP tells us what it is.

Yes that would be helpful

 

[EFLImpudence]

I have 13.650kw/240V =57A
(57Ax0.3)+10 =27A

(47Ax0.3)+10

 

[PrenticeBoyofDerry]

(47Ax0.3)+10

Bugger was doing full load calc. Yes 24A but still exceeding 23.5A

 

[ban-all-sheds]

with the insulation present this would create the derating that I have mentioned.

If it was blown polystyrene granules it could be creating a problem more severe than derating...

//www.diynot.com/forums/viewtopic.php?t=134950​

Approx 10+ years ago, we have had the cavity walls insulated.

Do you know what they used?

Did they ask you if there were any cables in the cavities?

 

[ANGLER]

I only recently discovered that the 6mm cable was in the cavity. My previous range cooker had a Total hob rating @ 230v 8.53kW and a Max. Elec load @ 230v 15.6kW.

The new AEG BE300360KM Built-in Oven 0.79 kW/h/Output 16 Amp.

 

[EFLImpudence]

Found this:

I can't find the actual rating. They don't seem to like giving it these days.
There should be a sticker on the oven somewhere - inside the door?

So, would seem to be usual 15A/16A appliance.

16 x 240 = 3.84kW max.

+ 7.9 for hob = 11.74kW = 49A

so design current of 22A.

 

[ANGLER]

Does this suggest upping the cable size to 10mm, with the cable clipped to the wall and plastered over. This is instead of being cavity fed?

 

[EFLImpudence]

No. 4mm² would be fine if you did that.

I don't think there is a problem as it is.

 

[PrenticeBoyofDerry]

Does this suggest upping the cable size to 10mm, with the cable clipped to the wall and plastered over. This is instead of being cavity fed?

It is not ideal for cable to be routed withing the cavity, especially as this is a thermal insulated cavity. As it seem the demand (with diversity) is less than cables current carry capacity (CCC), that should mean the cable will not overheat.
I am never totally happy having a cable protected by device that is greater than the CCC of the cables, when factoring diversity to achieve a satisfactory outcome. But saying that being said it is a tried and tested method.
I think the concern now would be the possibility of any reaction the cable could have with the insulation. I think with age of the installation of cables and the insulation you should be Okay. I would have thought that cables manufactured in 1990s had no longer have the chemical reaction with polystyrene and that 10 years ago, they were no longer blowing in polystyrene but using mineral wool. Yet it does need some further investigation.

 

[ANGLER]

Thankyou for your help and education