One for the electricians

[saff]

I'm still in the planning stages of a new kitchen.

There is an existing 32A cooker circuit which at present serves a built in oven. The hob is gas. We plan to replace the oven and move it to another location and replace the gas hob with an induction hob.

The current (pun intended) 32A circuit is on 6mm T&E. What sort of power could I reasonably pull on that cable given that the hob may be around 7Kw, lower powerful ones are available and the oven can be around 4Kw, again lower power models available. Is 11Kw a realistic power draw on 6mm?

I know 10mm would be the preferred option but it would be a royal pita to rewire or add a new circuit.

Thanks for any guidance.

 

[renault12ts]

11kw is just a tad too much for 6mm...sorry, 10mm has to be the way to go.

 

[saff]

11kw is just a tad too much for 6mm...sorry, 10mm has to be the way to go.

Thanks for that. What would be a more fitting power draw for 6mm given that I can get lower power appliances?

 

[renault12ts]

Probably a max of 10. And, it also depends on how long that cable run is.

 

[m80]

A shade over 10Kw is max in an ideal instalation.
A bit more specialised but you need consider,
the type of protection although this isn't the greatest concern but closer rated breakers allow for greater current,
the length of the cable run,
and the route it takes and it's ability to disipate the heat created by the loading that is in insulation the cable needs to be derated.

As above at least 10mm.

 

[saff]

OK cheers for that. 10Kw sounds fine as a max. The cable from the 32A breaker to the outlet, which will become the feed for the hob is I would guess 7m in length and runs in dry cavity wall and uninsulated ceiling void. A further (approx) 4m clipped to a plaster wall within a space behind the kitchen units to then feed the oven.
How does that sound?

 

[saff]

Oh also the breaker is a Hager B32 and the RCD is a Hager 63A covering the cooker, ring main, boiler and shower. If thats of any use.

 

[Chrishazle]

How about running a new cable for the new oven location leaving the existing one for the hob? I'd think twice about downsizing the induction hob - we have a 70cm one, daughter has 60cm, it really seems small after ours.

Also re induction hobs, many have 4 rings - 1 small, 2 medium and 1 large. However, our AEG electrolux 70cm has 4 equal areas, 2 front and 2 back. Power availability is restricted in that, if you have say the left front on full power (IIRC 3Kw) the left front will only go to 5, if you try to go further it turns the front one down - clever! Another good point is that if, for instance, you have a fish poacher long enough for a full salmon, you can put it across 2 areas and have both on at the same time. I far prefer our hob to daughters (?Neff or Bosch, not sure which).

This is the current version of our hob : Induction hob - HK764403FB | AEG

 

[saff]

Cheers Chris. Running a cable from the breaker in the consumer unit is a no-no really. My plan is to extend the 6mm, after dropping off for the hob and then on to feed the oven. Some ovens are supplied with a 13A plug and while I don't really want to do it this way there are low-wattage ovens out there.

 

[Smart320]

Had the same dilemma at last home. We ran a new feed for the new double oven/ microwave and used our old feed for our induction hob, which previously handled our single oven and ceramic hob. New induction hob ( KitchenAid with 2 smaller rings , linked for long griddle pan and one very large ring ) had a high max power rating and electrician said he would not take a risk , also did not want issues when running all rings at max. Never had any problems afterwards.

 

[zipdip]

Well you are still looking at what you will buy,without doubt the induction hob is the big user,if you can curb the power output of the built in cooker you could be ok to use 6mm cable,after all some cookers come with a plug so you can just use the ring main,but I suspect your new cooker will not have a plug,given diversity you might be able to spur off the 6mm cable and put a RCD in line then connect the cooker,the thing is nobody I know has all four rings on full blast on a induction hob and the same with a cooker.double over,they draw more a the start then settle down,of course we do have some electricians on here and I suppose they will disagree,another thought how far is the consumer unit from the kitchen that could help when the experts are making their calculations.

 

[Dryce]

As has been said induction hobs can be quite smart.

And some models will allow you to configure a lower maximum power setting to limit the total demand from the supply even if all zones are active. The electronic controller effectively derate the zones if all are switched on maximum.

 

[190]

...running a cable from the breaker in the consumer unit is a no-no really. My plan is to extend the 6mm, after dropping off for the hob and then on to feed the oven

If you are intending to extended the cable with a junction box of some sort then it needs to remain accessible for inspection. The reason being that in theory screw type connections can loosen over time with many heat/cool cycles. A buried or boxed in cable joint is only permitted if it's considered to be a permanent joint e.g. crimped or soldered. Soldering sounds odd on such heavy cable but that's what I understood the regulations to say.

I've just gone through the electrics with a new kitchen installation and the other concern I had was provision of a means of isolation. While you can get away with feedings things like an integrated fridge, dishwasher and in my case a gas hob from a switched socket mounted inside an adjacent cupboard an integrated oven should be fed via an accessible isolation switch on the wall. I'm not sure where that leaves the single ovens that can run of a normal BS1363 13A plug top.

 

[saff]

If you are intending to extended the cable with a junction box of some sort then it needs to remain accessible for inspection. The reason being that in theory screw type connections can loosen over time with many heat/cool cycles. A buried or boxed in cable joint is only permitted if it's considered to be a permanent joint e.g. crimped or soldered. Soldering sounds odd on such heavy cable but that's what I understood the regulations to say.

I've just gone through the electrics with a new kitchen installation and the other concern I had was provision of a means of isolation. While you can get away with feedings things like an integrated fridge, dishwasher and in my case a gas hob from a switched socket mounted inside an adjacent cupboard an integrated oven should be fed via an accessible isolation switch on the wall. I'm not sure where that leaves the single ovens that can run of a normal BS1363 13A plug top.

Thanks for this 190. There is an isolator switch on display which will cover both hob and oven and the junction box will be accessible in a cupboard beneath the hob.

 

[ricky s]

Could I ask to weather there is any Part P certification compliance anywhere here within this thread??, albeit better this project be deemed a 2018 17th edition design, with the 18th edition looming upon us all on the 1/1/19 and all that entails..ugh?. more install, more testing, more paperwork, bigger invoices, more grief! I do hate my job, roll on retirement or the lottery. Sod Part P. they cannot police it anyway, total jobsworth community. Hmm, sounds like I am bitter and twisted here...probably! But best of luck with your kitchen fitment mate, go for it.

 

[190]

As an experienced Electrical Engineer that gave up practicing nearly 20 years ago I had a look at the Part P documentation, just out of interest. I thought there was very little useful or practical information in it. Just a lot of Bureaucracy. To do an Electrical job right you need to look at BS 7671

 

[AltonAnt]

It may be worth mentioning that some of the German hobs I've fitted have jumpers inside to set the max current and whether or not 3 phase is being used which is more common in Germany.
This will obviously be restrictive though if you have you use all rings e.g. our ceramic hob is rated at 6.6kw and the double oven at 5.5kw.

You don't fit a new kitchen every day so it is worth the effort to get it done properly.

 

[Delderek]

zipdip has mentioned diversity factor, when calculating cable size, which I believe takes into account that appliances will not all be working at maximum current at the same time. There are proper formulas to use.