New kitchen electrics - one for the sparkys

[howzy]

I have an old oven switched via standard "cooker" isolator switch in the wall. This has a 6mm cable to a 30A mcb in the CU. 20 year old install when house was built. No spare ways on the CU which is on the other side of the house from the kitchen. I'm changing this to a 5 zone induction hob rated 7.29Kw at the same position. Then I'm adding a double oven rated 5.8Kw on other side of kitchen. Considering diversity, is it reasonable to run another 6mm from the live side of the existing isolator switch, terminate it with another isolator at the new oven position, upgrade the mcb to 40A and connect the new oven to the new isolator

 

[SeanT]

If the 6mm cable is run within a wall as opposed to clipped, then you can't fit the 40 amp isolator - if it's clipped then you need to know how far it goes - bear in mind that if connecting the new bit of 6mm to the live side then this will need to be clipped rather than buried too, or uprated to 10mm.
I'd say that considering diversity if you were cooking a decent sized meal you might have the oven on full whack and two or three larger rings on, so might end up drawing around 10kW - a good 40 amps plus - anyway - and there is always the possibility that someone might want to use it all, it's quite feasible - in which case you are going to be drawing 13.1k - ie. about 57 amps - you might by then be able to cook on the 6mm supply cable from the CU (and the oversized 40 amp breaker won't go)
Basically, you'd be better off with 10mm, and at least a 45 amp mcb (allowing for your bit of diversity), if the 20 year old CU will even take it.
I'd let the 6mm with the 30 amp mcb alone, and find another way of powering this oven - or fit a gas hob if you have a gas supply nearby - they are better anyway....

 

[Adam_151]

I certainly don't like the sound of that!

take it back to the CU, theres aways someway you can make space for now, got two lighting circuits? whats the load on them?

 

[jockspark]

diversity for a cooker 10amps + 30% total load

 

[Taylortwocities]

Is that a cooker or an oven

The GUIDE is (as you say) 10amps + 30% total load for each device. So same again for the hob and for the oven.

Per the above, I would have two circuits, one for hob one for oven otherwise you could end up with cold turkey on Christmas Day

 

[SeanT]

Admittedly in this case it's a double oven, however I fail to see how you could apply any diversity calculation to a single fan oven that doesn't allow you to have the grill on at the same time - it's gonna be drawing maximum current a lot of the time??

 

[Taylortwocities]

Indeed. thats why the diversiity stuff is a guide.
There's a preamble in the OSG that basically says its up to the designer to decide if diversity applies, and to what level.

Me, I dont like raw turkey with my sprouts

 

[howzy]

Great information. Cheers. On that basis how would I install a simple freestanding cooker? Some I've seen are rated 10.7Kw (oven & induction hob freestanding combo) and on that basis probably could not be installed into most houses without some fairly serious upgrading work. Or am I misunderstanding something?

 

[SeanT]

You'd use the diversity calculation above and come up with 23 amps as the current.

 

[howzy]

Interesting - so application of a diversity factor is apparently okay on a freestanding oven&hob combo at 10.7Kw, apparently enabling install on existing set-up, but not on the two separate appliances (built-in 1.5 oven & induction hob) as mentioned before at 5.8Kw & 7.3Kw respectively. Isn't the risk of everything being on at the same time the same? I'm interested to know what drives the different approach between freestanding and built-in. It seems a more conservative approach on the built-in pair.