Cable size for hob and oven

Hi

I am in the process of redoing my kitchen and getting a separate hob and double oven, for cable sizing would you use the example calc below for each item, which was a response to a question last November:

"The rule of thumb for cooker circuits is:

32A MCB or 30A fuse
6mm flat Twin+Earth cable


Applying diversity:

9400w

9400/230 = 41Amps maximum

Formula: 10A + 30% of rest + 5A for any socket outlet

10 + 0.3 * 31 + 5 = 24.3A

We only need to cater for 24.3Amps or only 19.3Amps if no socket outlet.

If its a short run from the cooker to the consumer unit then you could get away with 4mm cable.
I would use 6mm cable just incase you get a bigger cooker in the future or the cable run is long"

Thanks
Nick

Hey...at last someones done some research first!

Yes, that is the correct way to size a cooker supply. Stick with 6mm and a 32amp breaker.

Don't forget to read about Part P in the Wiki because the work is notifiable.

If it were me I would have to spend the extra couple of pennies for the larger cable then you know you are fine. But then I work in a cable factory so it might be more than pennies difference in the shops.

Based on your comments I assume you've wired your ring final in 4mm and your lighting in 2.5mm?

You seem to have the responses you were looking for so i hope you don't mind my question! is it really acceptable to apply diversity and assume the whole cuurrent isn't demanded? I no its allowable but do most electricians apply it?

ashm said:

is it really acceptable to apply diversity and assume the whole cuurrent isn't demanded? I no its allowable but do most electricians apply it?

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Yes we do.

Take a single fixed load like an 8.5kW shower. When you turn it on it will draw 8.5kW. Because it's a fixed single load the circuit must be designed to carry the full load current and diversity can't be applied

An oven and hob is a mixture of smaller separate loads, the rings, the grill and the oven(s).

In normal use only some of the loads will be used at any one time. Maybe the grill + 1 ring, the oven and a few rings and so on. So in normal use it's very unlikely the oven and hob will draw anywhere near it's full load current so diversity can be applied.

When it comes to Christmas things change. All of the rings + the oven(s) and grill could all be in use at the same time. But as they are all thermostatically controlled even then it's unlikely it will be drawing its full load.

And if it does draw it's full load once again, it's very unlikely the protective device will trip in the middle of cooking Christmas dinner because of the overload trip characteristics of protective devices.

When the supply companies design the infrastructure that feeds your house, after applying diversity they base their calculations on around 20amps per dwelling. So at Christmas when everyone in your area is cooking Christmas dinner at the same time, there is more chance of a local power cut than your cooker tripping

harrisonline said:

If it were me I would have to spend the extra couple of pennies for the larger cable then you know you are fine.

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I agree.

9.4kW cooker = 41A - cable for that.