Oven nightmare

[JunJun]

Hi,

I've stupidly bought an oven without doing enough research, that has a power rating of 4.4kW. Its too high for the current cooker outlet, which is fed from a ring main shared with all the other outlets in the kitchen. The shop won't take it back so now I'm stuck with a 50kg paper weight taking up a large portion of the kitchen floor.

Ok, so the plan is to add a new ring main for just the cooker. Am I correct in thinking it can be wired with a normal loop of 2.5mm twin and earth to the consumer unit? I plan to run the cable myself, which is the most difficult bit, and get an electrician to connect it all up.

Thanks

 

[JohnD]

Your plan is wrong on all three counts.

Describe the run between the CU and the cooker, and provide a photo of the CU with the lid open, we may have some suggestions.

 

[JunJun]

Your plan is wrong on all three counts.

Please elaborate.

 

[JohnD]

see revision.

 

[mikeyd]

2.5mm rings are only used to supply sockets. You need to run a single cable (radial, not ring) from the consumer unit to a cooker switch, then on to a cooker outlet plate. You could get away with 4mm but I would strongly advise you use 6mm, which is the usual for a cooker circuit. Make sure you run the cable in safe zones and you should also get the electrician on board first so he can tell you if he is OK with you running the cable in.

 

[JunJun]

Ok, image of consumer unit attached. I was under the impression a normal 2.5mm fed ring main can carry up to 32A; 4.4kW is ~18A which seems well below the a ring mains capacity. Anyway, to answer JohnD's question, the plan was to run it as:

CU -> double pole switch -> Oven -> CU

I've just visualised it and I can now see how its wrong lol but theoretically it would still work.

Sorry I'm just a bit fed up with it all, a sparky I've used before and did good work in the past has failed to turn up again. If any electrician in or around the Manchester area want to do it, you're more than welcome to.

 

[JohnD]

It must be a radial circuit, not a ring.

You could chase out the wall if you want to, and cement in the deep wall boxes. It will be dusty. Don't run the cable. You may be able to have it clipped it to the wall behind kitchen units to redce the amount of chasing and replastering. Show us the route and we may have more suggestions. There are rules about where to run a concealed cable.

 

[JunJun]

It must be a radial circuit, not a ring.

You could chase out the wall if you want to, and cement in the deep wall boxes. It will be dusty. Don't run the cable. You may be able to have it clipped it to the wall behind kitchen units to redce the amount of chasing and replastering. Show us the route and we may have more suggestions. There are rules about where to run a concealed cable.

Thanks for the info. Chasing the cable isn't an issue, I've fortunately got a basement where all the existing cables coming from the CU are pinned to some wooden boards on the ceiling, these then go up through the floor boards. The plan was to follow the existing cables, up through the floor and surface mount it to the wall behind the cabinet where the oven is going to be located. I don't know if this is acceptable but the switch could go in the cupboard, again surface mounted, above where the oven is.

 

[JohnD]

So you have a gas hob?

 

[JunJun]

The hob is standalone and is on the opposite side of the kitchen cut into the worktop. The oven is mounted eye level in a tall cabinet with a cupboard above and below. There's a big air gap behind, plenty of room for the cable.

 

[JohnD]

If you're running an electric oven circuit, it may be worthwhile including sufficient capacity for an electric hob (or cooker) if you want one in future. You can provide a switch and connection unit, out of use until required.

It is preferable not to have cables or switches behind or above ovens where they may get hot, and the switch should be to one side and in clear view, in case of emergency. Typically mounted about 150/200mm above the worktop, like your sockets.

 

[ericmark]

Cable rating depends on where it is run, so although we may say 2.5mm² is 20 amp cable that is open to change. It could be down to 13.5A or as high as 27A higher if not thermoplastic cable. I would agree with others if doing the job then may as well use 6mm² so future proof.
The problem electricians have is the forms require them to sign that they have designed, installed, and tested and inspected, there are forms which allow three different signatures, but these can't be used with the scheme providers you would need to register the work with the LABC the latter is a silly price.
So you need an electrician to design and he can then tell you he wants a channel here or a hole here and you can prepare the job for him and agree to plaster up after he leaves, but he has to agree to it all.

The rules on a ring final are in part recommendations, and they state to ensure you don't overload a circuit for an extended time any fixed appliance over 2 kW should have a dedicated supply, this is not adhered to very much with washing machines, tumble driers, dish washers and oven often being put on the ring final, however the immersion heater does seem to get a dedicated supply. But with a kitchen sometimes although two parallel cables are used they are used to feed a single grid switch so technically they are not a ring final so it could be regarded as a dedicated supply and also since the designer has considered the loading the 2 kW limit does not apply.

It all gets a bit technical but the point is an electrician may well see and easy method which even with pictures we can miss. Including some cookers can be configured to use different amounts of power.

So get that electrician first, and then decide what to do, you may find there is an easy option you and us have missed.

 

[EFLImpudence]

You could get away with 4mm but I would strongly advise you use 6mm,

It's not a question of getting away with it; 4mm² is adequate for a 32A circuit - method C.

which is the usual for a cooker circuit.

Only in the past because of BS3036 fuses and their derating factor - and, of course, not realising things have changed.

 

[ban-all-sheds]

Your plan is wrong on all three counts.

Please elaborate.

Cooker circuits are not rings.
They are not done in 2.5mm².
New circuits are notifiable and you cannot ask an electrician to sign off your work and lie to say he did it.

 

[securespark]

Is the 32A breaker that is unlabeled spare?