Cable sizing advice please

[kandgmitchell]

Our daughter is moving into a Edwardian terraced "do'er upper" shortly. It has a kitchen but it's a poorly assembled bunch of cheap units with previously a gas cooker. We want to tidy it up and install an electric hob and oven I acquired 2nd hand locally, hardly used.

 

The electrical inspection revealed that the mains lead water pipe isn't earthed and I can see there are only a few ring main sockets, no oven outlet or the like. The mains incomer is adjacent the front door so I've got to run cables from there right through the house to the back kitchen to feed the new oven and hob plus an earth cable for the lead pipe (it'll be mdpe eventually but I'm older now and these things take time). Now I can run these myself which allows us to get some carpets down on the first floor leaving a sparks to do the work either end.

 

I have enough 4mm earth cable and a cable with twin 6mm + 2.5  conductors, left over from my own house build for this. However are these sufficient? 

 

The oven draws a max 2.3kW and the hob 4.8kW - 5.8kW according to the instructions.

 

Thanks

[Nickfromwales]

9 hours ago, kandgmitchell said:

Our daughter is moving into a Edwardian terraced "do'er upper" shortly. It has a kitchen but it's a poorly assembled bunch of cheap units with previously a gas cooker. We want to tidy it up and install an electric hob and oven I acquired 2nd hand locally, hardly used.

 

The electrical inspection revealed that the mains lead water pipe isn't earthed and I can see there are only a few ring main sockets, no oven outlet or the like. The mains incomer is adjacent the front door so I've got to run cables from there right through the house to the back kitchen to feed the new oven and hob plus an earth cable for the lead pipe (it'll be mdpe eventually but I'm older now and these things take time). Now I can run these myself which allows us to get some carpets down on the first floor leaving a sparks to do the work either end.

 

I have enough 4mm earth cable and a cable with twin 6mm + 2.5  conductors, left over from my own house build for this. However are these sufficient? 

 

The oven draws a max 2.3kW and the hob 4.8kW - 5.8kW according to the instructions.

 

Thanks

4mm2 earth cable was retired a good few years ago, so I fear you’re quite unprepared for this. 
 

Please consult a sparky, as the fuse-board aka CU (consumer unit) is very likely in need of an upgrade to make this safe for your little bundle of joy  

[kandgmitchell]

Yes I'd allowed for a CU upgrade in the budget and of course part of being prepared is asking the questions before doing the job......

[Carrerahill]

23 hours ago, kandgmitchell said:

Our daughter is moving into a Edwardian terraced "do'er upper" shortly. It has a kitchen but it's a poorly assembled bunch of cheap units with previously a gas cooker. We want to tidy it up and install an electric hob and oven I acquired 2nd hand locally, hardly used.

 

The electrical inspection revealed that the mains lead water pipe isn't earthed and I can see there are only a few ring main sockets, no oven outlet or the like. The mains incomer is adjacent the front door so I've got to run cables from there right through the house to the back kitchen to feed the new oven and hob plus an earth cable for the lead pipe (it'll be mdpe eventually but I'm older now and these things take time). Now I can run these myself which allows us to get some carpets down on the first floor leaving a sparks to do the work either end.

 

I have enough 4mm earth cable and a cable with twin 6mm + 2.5  conductors, left over from my own house build for this. However are these sufficient? 

 

The oven draws a max 2.3kW and the hob 4.8kW - 5.8kW according to the instructions.

 

Thanks

Just to be clear, you’re looking to add an oven and hob circuit, and possibly a proper dedicated kitchen ring as well.

 

If it were me, I would install either a 2.5mm² ring final circuit or a 4mm² radial for the kitchen, depending on exactly what I was intending to supply. This would typically be protected on a 32A RCBO or MCB on an RCD split board.

 

For the oven, at around 2.3kW it only draws roughly 10A, so in theory a 16A supply on 2.5mm² radial would be sufficient, but personally I would install a 20A supply on 4mm² radial to give some headroom for future changes or upgrades. That way you are not limiting yourself later on if the appliance specification changes. I would then run the 20A feed into a fused connection unit, fit a 13A fuse, and then run out to the oven on flex. My usual approach is to remove the factory plug and hardwire the appliance via an isolator, even though I appreciate this can technically affect the warranty, as I prefer to control the quality of the flex and terminations myself. I generally do not like heavy loads running for long periods through standard 13A sockets, particularly where socket quality is questionable, because cheaper sockets can degrade and overheat at sustained loads around 2kW or more. I also do not like the idea of sockets being hidden behind appliances for years on end, so I always prefer them to be accessible in adjacent cupboards where possible, ideally unswitched sockets with a separate above-counter isolator depending on the setup.

 

For lower power appliances I often use MK unswitched sockets at low level controlled via MK grid switches, which keeps things tidy and accessible while maintaining good isolation control.

 

For the hob, assuming a full load of around 25A, I would normally install a 32A or 40A supply, and in most cases I would lean towards 40A using 6mm² cable if available, as that gives better long-term headroom. That said, a 32A circuit on 4mm² is still perfectly acceptable depending on the installation constraints. I would run the hob circuit into a double pole isolator of suitable rating, and I generally prefer to size up, so I would usually specify at least a 40A isolator, often 50A, using brands like MK, Schneider or Hager.

 

All isolators should be installed in accessible positions rather than hidden behind appliances, so in practice I would normally mount metal-clad fused connection units inside adjacent cupboards in a location where they can always be reached easily, even after the kitchen is fully fitted.