What size electrical cable for oven and hob?

[Russell griffiths]

9 hours ago, mjc55 said:

That's interesting - why do you say that?

As I said I’m no electrician, but if something needs a feed instead of just plugged into the ring then give it its own feed, it’s a new house so easy to do and minimal cost. 

[Spinny]

I posted an overlapping topic here where same points were raised.

I started by using an online cable size calculator of which there are several, for example...

 https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html?ad_position=&source=adwords&ad_id=756345223846&placement=&kw=cable size calculator uk&network=g&matchtype=p&ad_type=&product_id=&product_partition_id=&campaign=ROAS_Cable&version=finalurl_v3&gad_source=1&gad_campaignid=22639595510&gbraid=0AAAAAD-6GhlR4kPPUV4W9EpyDAKmslWFR&gclid=EAIaIQobChMIjbnsqKXgkwMVDJNQBh3_pS37EAAYAiAAEgKbAPD_BwE

 

Obviously these cable calculators are misleading/wrong because they completely omit the diversity allowance in the regs. (Not sure whether this is a deliberate play to sell more cable ?)

 

In reality I suspect most cables run through a mixed route e.g. mine go through a sound insulated wall cavity, a ceiling void, and through a channel in a chased and plastered wall.

 

A domestic kettle is 3kw or 13A of course, and presumably draws that continuously until the water boils. Commonly used on any power socket on a 30A ring main using 2.5mm.

Interesting to reflect that 3kw is the same as my single oven which will commonly be used to cook at 160-220C, so I imagine would draw full power until that temperature is reached - I guess perhaps 10-20mins. I guess for two ovens or a double oven you could have around 6kw or 26A whilst both on so would justify a dedicated circuit and may debatably be 4mm ? A single oven would seem to be more than fine on a dedicated 2.5mm ?

 

 

[-rick-]

1 hour ago, Spinny said:

Obviously these cable calculators are misleading/wrong because they completely omit the diversity allowance in the regs. (Not sure whether this is a deliberate play to sell more cable ?)

 

I think they are just answering a different question and expect someone who is working with electrics to know what they are looking for. They are just talked about current carrying capacity of the cable. Up to you to work out how much current your devices will need.

 

1 hour ago, Spinny said:

In reality I suspect most cables run through a mixed route e.g. mine go through a sound insulated wall cavity, a ceiling void, and through a channel in a chased and plastered wall.

 

Yep so some derating required.

 

1 hour ago, Spinny said:

A domestic kettle is 3kw or 13A of course, and presumably draws that continuously until the water boils. Commonly used on any power socket on a 30A ring main using 2.5mm.

 

13A socket is not rated for 13A continuously. But kettles are only on for a few minutes before they boil.

 

1 hour ago, Spinny said:

Interesting to reflect that 3kw is the same as my single oven which will commonly be used to cook at 160-220C, so I imagine would draw full power until that temperature is reached - I guess perhaps 10-20mins.

 

I would guess a lot less than that. My oven seems to warm up pretty fast and it's not a fixed install (got a 13A plug on the back) so isn't the most powerful.

 

One of these threads triggered me to look up the ratings of fixed install ovens and for single ovens they are all saying they need 16A breakers. So if they are installed on a dedicated circuit with a 16A breaker there is no diversity applied. (Electrician will still do calcs for sizing upstream components).

 

1 hour ago, Spinny said:

I guess for two ovens or a double oven you could have around 6kw or 26A whilst both on so would justify a dedicated circuit and may debatably be 4mm ? A single oven would seem to be more than fine on a dedicated 2.5mm ?

 

Sounds about right (caveated that insulation/distance derating might drive requirements higher), though my own thought is to always use 4mm as that allows the potential to switch from a single to double in future without rerunning wires. (4mm might not be enough for a double if big derating factors are required).

 

I missed that your ovens are fixed installation in the other thread. If they don't come with a 13A plug (and are therefore fused) they need a dedicated circuit (as the dedicated circuit provides the fuse).

[Spinny]

OK looks like I have a 10mm for the hob, two 4mm for the ovens, 2.5mm ring main tails, and a 2.5mm spur to the extractor.

(Had thought the oven cables might be 2.5mm as the labelling is obscured and 4mm is only 1mm thicker than 2.5mm externally)

Can't find the consumer unit ends for the ovens at the moment but they must be tucked up somewhere.

 

Island has ring main, and a seperate 4mm for the quooker tap, plus a lighting cable for the LEDs.

 

I have a kitchen radial with 9 double sockets and a single on it, as they seem to have moved away from ring circuits everywhere.

 

Ideally I need to find a vertical double socket because of limited room to recess into the kitchen island end panel, if anyone has seen any ?