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Posted By Topic: Upgrading oven & Hob

Sep 06 2019 17:30

me again, I thought I would do this a new topic, but just want to get thoughts of you guys the pros. we are replacing an old range oven with which is wired with 6mm on a 32mcb. would that be sufficient to run a induction hob and under bench oven. my sparky said he would have to run it on 2 separate circuit's. Just thought maybe would have got away with 1. he did mention the inductions are hungrier

Sep 06 2019 17:57

I know at times we question the decisions that trades people make, particularly with regards to quotes and the likes.

If you are doubting your electrician, would you then be doubting your plumber or builder with their decisions?

Sep 06 2019 18:22

Um yes.

Not all trade people are equal. I guess I’m just a tight arse. Why run another circuit and cable if you don’t need it. But I’m happy to play by the rules. If if they say you need to then you need to. I’ve just seen new builds with oven and hobs on 1 switch. Anyway all good.

Sep 06 2019 19:11

Hob and oven on one switch is possible. But it depends on the model. Some models might use the full 32A just for the hob.

He's just trying to eliminate the possibility of you calling him on Christmas day because they keep tripping out.

Sep 06 2019 22:45

I do this all the time. Totally acceptable to use existing 6mm cable used for old range for new hob/oven set up. Most of them come with pre terminated tails that you can run to a junction box behind.
I know you can buy some pretty powerful hobs now but remembering max demand for cooking appliances is 50% of the connected load. Even if you had a hob and an oven that drew max 12KW, your only talking 26amps max demand which is fine on 32amp mcb.
Ideally it would be nice to have a seperate circuit for both if it was a new build but going through the effort of running another circuit in a older house when you don’t need to??

Sep 06 2019 23:17

Haydos - It's not 50% for the final subcircuit, that's only when calculating the maximum demand for the whole installation. It's diversity that applies when calculating the maximum demand for cooking appliances on final subcircuits.

And he's asking about connecting the induction cooktop and an oven to that circuit. So your 12kW cooktop plus a 3kW oven, makes it 15kW total, which puts it into the 40A circuit bracket for the final subcircuit.

That's why I said that it depends on the model.

Sep 07 2019 05:55

I can tell you now. The specs for the hob 7.4kw and 3.2 oven. I’ll check with the sparky again. Would be nice to keep on existing circuit but like you say would t really want it tripping I would be popular with the wife.

Sep 07 2019 07:11

Most of the freestanding ranges that I replace are rated at 10-12KW anyway. That is more than the hob/oven that is replacing it.
At the end of the day it’s the sparky’s decision. If he wants to run another circuit then let him. I personally just don’t see the point. It’s totally fine.
And yes you might trip the breaker if your have all 4 elements screaming and the oven on fan bake. It’s the same as any other circuit. you might trip your PowerPoint circuit if you have 3 oil heaters running. It’s called max demand. There are obviously variables but in an existing house, on existing mcb and existing cable I would just change it.

Sep 07 2019 10:25

interesting you expecting us to impart our knowledge despite you not telling us the size of the units. that's like asking how much to send a parcel but you don't say where to or how big the parcel is....., have you checked the cabinetry to see whether an induction hob could fit in, that'll be the biggest hurdle, the last two i did took several hours to drop the oven down etc

Sep 07 2019 12:06

OK so that's 7.4 + 3.2 +10.6 kW
+ 46 A

Diversity is allowed as per C2.5.3 ; where Table C 5 gives an assessed MD for the circuit of 32 A

The 6 mm T&E has a CCC of 40 A for "partially surrounded, but only 25 A fully surrounded.
Given the reasonably high chance that at least some of the run is or will be fully surrounded, plus the fact that this hob is at the lower end for induction hobs and is likely to upgraded in future; I'd be wanting to split the circuits.

Sep 07 2019 12:26

Um, a digital error has occurred in your post Aleck, most people will work it out! :-)


Sep 07 2019 20:29

Cheers everyone. Appreciate the expertise and advice. We will get the sparky to run the oven and hob on seperate circuits.