Wiring for a seperate hob and oven.

[rolandk]

Hi there!
I have an existing hob and double oven both electric. The hob is rated at 6Kw and the oven 2.7K. They are supplied by 6mm cable with a 30amp MCB at the consumer unit. The cable run is around 7-8 meters mainly in the ceiling and down in a stud partition wall, no insulation involved. The cable goes into the switch unit for the oven then is looped out to the switch unit for the hob.
Reason for the post is I've just tried to replace the switches with more modern units but there is no room in the terminals for two 6mm conductors and no space in the new back boxes for three cables at the cooker switch. I hesitate to ask but can I put the supply cable into a suitably rated junction box and take two 6mm cables from there to the oven and hob switches! Or more fundamentaly is the 6mm cable big enough? We never had the MCB trip and I read a bit on here about diversity etc. We are in the process of refitting the kitchen so would it be worth us uprating the cable. By 'us' I mean the Part P registered sparks when I find one locally! I know my limits!!
Thanks, Roland

 

[Taylortwocities]

One of these, maybe? PRW217

 

[rolandk]

Spot on thanks! Do you reckon the 6mm supply cable is OK to stick with? It occured to me that the 2.7Kw loading of the oven could be handled by 2.5mm from the switch rather than the existing 6mm?

Cheers, Roland

 

[holmslaw]

..

 

[Steve]

Yes, fit a dual appliance outlet, and connect one of the cables to a single socket, and plug the oven into this. Or a fused connection unit.

 

[Taylortwocities]

Seems to me that is what he has got at the moment, if you read his OP.

 

[Steve]

Seems to me that is what he has got at the moment, if you read his OP.

Nope, cant see it.

All I can ascertain is that he has two switches above the worktop with seperate cables to the two appliances. No mention of fusing or under-counter arrangements.

 

[rolandk]

Sorry guys if it wan't clear in my original post but the is no additional fusing after the cook or hob swiches. Now I see what's being said - the current arrangement has a 2.7Kw oven protected by a 30amp MCB so it anything went wrong with it it wouldn't be just the sunday joint roasting!!
I kind of assumed because it was wired this way when the house was built it had to be right but I'm learning fast!! I can get a 13 amp FCU/socket installed for the oven no prob but shall I stick to the existing single 6mm feed for both oven and hob or go to 10mm. Especially asI now checked the hob again and it's 6.6Kw not 6 as I thought! Getting a new CU installed too when I find a sparks who doesn't want the shirt off my back!!! Like £600 just to change the CU and test or is this the going rate!

Thanks, again Roland

 

[Steve]

6mm is fine.

Remember, the hob wont always draw 6.6kw, in fact the only time it might is if someone wangs all the rings on full, it'll be drawing full load for a couple of minutes until the rings start cycling.

£600 for a new CU - depends whats involved. Parts can easily top £100-200 alone if a "true 17th edition" board is fitted.

Dont get it done by a £200 fly-by-night bloke. I did, it wasnt pretty.

 

[rolandk]

Thanks Steve,

I know what you're saying I don't want a cheap job, just value for money! Just that for a 10 way edition 17 CU he reckoned a days work so it just seemed a bit steep. I wouldn't mind being on £500 a day! I will say though since I've been looking on here it's opened my eyes to how complex all this is with regs etc these days. Hats off to the good sparks who can keep up to date with all this!

Cheers,
Roland

 

[Steve]

For the 17th edition it depends what RCD method you use. For 10 RCBOs, you're looking at £200, plus about £20-30 for an enclosure.

For twin RCDs and 10 MCBs you could probably half that, maybe £100.

And a day's work is about right, look at paying £200-300 for this. 200 oop noorth and 300 darn sarf.

But all in, £400-500 wouldnt be unfair for all RCBOs.

 

[chippy5]

I'm a kitchen fitter and when we upgrade clients consumer units the sparks we use charges us 350 a job (some he wins some he losses) it takes him about half a day. the most common extra is that to have a Part P installation both the water and Gas (if applicable) have to be earthed back to the board in 10mm earthing cable this can be a problem to do some times the best way is low level conduit run round the outside of the house

 

[rolandk]

Steve,
it was twin rcb's and 10 Rcb's but it sounds like the quote is in the right ball park. Sparks must be really busy round here, it's a hell of a job to get them over just to do a quote!

Just the clarify on the cable size, there is only one 6mm cable shared by the oven and hob, not one each. With a total possible 9.3Kw is the 6mm still OK?

Cheers

 

[Steve]

Just the clarify on the cable size, there is only one 6mm cable shared by the oven and hob, not one each. With a total possible 9.3Kw is the 6mm still OK?

Yes, because the cable is protected by a 32A MCB. The laod is not excessive, and you can diversify it, being a cooker load, because it wont ever actually pull full load.

the most common extra is that to have a Part P installation both the water and Gas (if applicable) have to be earthed back to the board in 10mm earthing cable

WTF has this got to do with part p? Part p says nothing about the installation of bonding.

I think you mean 17th edition of the WIRING regs, which does specify methods of bonding. But as did the 16th edition.

 

[chippy5]

according to my sparks you earth the main incoming supplys then you don't have to cross bond all exposed pipe work. check with your electrican to see if he wants this done. You can run the cable yourself, might save you a bit of money