wiring an electric oven - again

hello everyone
I have a question regarding wiring an electric oven (3.7KW). the hob will be gas.
AFAIU, wiring it into an existing 30A ring circuit is out of the question, since it already has microwave and a washing machine (2.2KW) on it, as well as other appliances like TVs, kettles, computers etc (the existing ring covers the whole floor).
so it looks like I have to use a new MCB and a new circuit for the oven alone. the question is whether I should run a single piece of cable to it or create another ring circuit that would have the oven and maybe a microwave on it. is ring suitable for the oven and the microwave? how do I fuse connections to this new ring?
another question is what thickness of cable I need to use. for a radial circuit it probably has to be 4.0mm and for a ring 2.5mm should be enough?
4.0mm is not easy to come across (screwfix doesn't seem to stock it), so it goes up to 6.0mm which is probably an overkill. the distance from the CU to the oven is 10-15m.
thanks a lot in advance for any suggestions.
/ijon
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That would be because rings use 2.5 mm and 20A radials use 2.5 mm, not much call for lots of 4 mm these days.

How many spare ways in the cu? Run radials in 2.5 mm with mcbs. You should use a radial for a fixed 16A load really.

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My cooker has it's own circuit - 6mm cable running about 12m via a 40A circuit breaker.
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On Sat, 17 May 2008 16:35:53 +0100 someone who may be ijon tichy

I would suggest installing a proper cooker circuit, with at least a 30/32A protective device and suitably sized cable. That gives most flexibility for the future in terms of cooking. Someone may want to install a halogen hob.
An additional ring main is a separate issue.
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ijon tichy wrote:

Agreed, a 16A point load that could be present for a reasonable duration is also not really suited to a general purpose circuit such as you have.

Ideally you want a new 16A radial for the oven alone. Then you will need no further fusing on the circuit to protect the oven. The microwave will probably be a smallish load, and can go on a normal socket on the ring.

2.5mm^2 is adequate unless you have to run through thermal insulation on any high temperature areas on the way to the cooker.

4mm^2 is not a very useful size because although it has a higher current carrying capacity, it does not have a larger earth conductor to match. Hence there are often times where one might want to use it, but have to use 6mm^2 just to get a more substantial earth.
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thanks for all the replies, guys, especially John and Dennis.
replying to Dennis' question, I only have one spare MCB left. 8(
John Rumm wrote:

these new ovens are weird. I think as long as they have the circular element around the fan and top grills, they fall below 3KW. as soon as the bottom heating element appears, they go above. ~2.5KW for the fan element plus 1KW for the bottom.

yeah, this is probably the route I am going to take. 16A radial is just 2.5mm then? AFAIK, this kind of setup is used for hot water cylinders (20A), with corresponding unfused DP switches (red ones)?

no, it will be away from the heat, buried under the plaster though. can I put a thick rubber flex between the oven's terminals and the end of the radial with a switch? this is probably a meter from the oven itself.

I see. thanks very much again for all the explanations and suggestions.
/ijon
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ijon tichy wrote:

Single ovens often come with a plug on them these days - fully intending that they be plugged into a normal socket. The load of an oven is not as great as you might expect - especially when you take into account the effect of the thermostat that will switch the load on an off once it is up to temperature.
A double oven is another matter though and will normally be better supplied from its own radial.

Yup, you can fit a cooker point (the type without a socket), and a cooker flex outlet. Ideally heat resistant rubber flex should be used for the final connection - although T&E is often substituted.

Under plaster is the same as clipped directly to the surface from the point of view of the current carrying capacity of the cable.
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John Rumm wrote:

the oven I am referring to is just a powerful domestic single oven (neff b1442), but it is still 3.7KW. this is not uncommon, since recently I came across a siemens single oven that was 3.8KW.

it looks like I still have to do the radial for mine.

yeah, I will use the flex, assuming I can buy a couple of meters of it in Maplin.
thanks!
/max
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You will need the radail circuit. And 3.8kW single ovens do seem quite common. I used 2.5 T&E for the last one but the CU was only a metre from the oven.

City Electrical Factors usually do well in stocking and cutting the flex by the metre that you need.
Adam
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ijon tichy wrote:

Yup, so radial it is then. Some can be as low as 2kW...
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John Rumm wrote:

just finished laying the radial. 2.5mm T&E for ~12m. should be plenty I think just for the oven.
thanks for the contributions!
/ijon
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