As I understand it the basic principle of UK wiring is that every cable has a fuse to protect it. Your main circuits are protected at the consumer unit then the cable to each appliance is either protected by the fuse in the plug (if plugged into a socket) or by a fused spur (if a wired directly without a plug connection). How do you protect the cable on an oven that's above 13A? The ovens I'm fitting are rated at 14.4A and 13.75A so can't go on a plug. However, together they're comfortably within the 32A rating for a 2.5mm ring circuit so don't need individual connections to the CU. I can see that 45A cooker connection isolators and 20A cable connection plates but they don't appear to be fused.
You risk overloading the ring with that sort of load. Two new ctts needed 16a breakers with 20a local isolation in 2.5mm. No point running both off a single new ctt, two new ctts just as hard as running one in this case.
It's a new build/self build so all new circuits. I am doing some parts of the installation and a qualified electrician is doing other parts and inspecting and testing. In the kitchen there is a 10mm 40A circuit for the hob with the sockets and appliances to be divided between a 32A ring and a 20A radial both serving only the kitchen.
I'm thinking if the run from the DP isolator to the oven is done in 4mm then all cables are protected by the MCB at the Cu
You can't put things over 13amp on a ring final cct. 16amp circuits for each. I would avoid 20amp radials in kitchens and utilities.
The supply for the second oven is the issue as the 20a 2,5mm radial could be swapped for a 16a MCB to run the first. A local 16a MCB off the ring might be the answer - the 9.6A dishwasher is on that circuit but other than that the only high power device would be a kettle (and with an induction job the plan is for a stove top kettle anyway - quicker than a standalone kettle with the power the hob can throw out) The other option is a local CU with 16A MCBs from the 10mm hob supply but that would have less diversity.
What would be the best solution in that case assuming additional cables can't easily be run now? The kitchen has 1x10mm and 3x 2.5mm cables. The loads are: 10.8Kw hob 2.3kw dishwasher 3.4kw oven 1 3.3kw oven 2 plus sockets.
An extra cable is going to be really difficult now. There's 102A (50+32+20) rated supply to the kitchen and the house only has 100A. Surely there must be some safe, sensible and regs compliant way to connect the appliances even if it's not 100% best practice.
There really isn't any other way. You also need to check if your current consumer unit is beefy enough for this extra load. You need to sort this out with the spark who is going to help you,
Why not put a 2 or 3 way unit on the end of the 10mm, I seriously doubt a hob is going to draw 50 amps.
How did you get that mate? I got 67a with the small shops diversity factor applied. 10800 10800 100% 3400 2720 80% 3300 1980 60% =15500 / 230 67.3913a
He has a 10mm feeding just a hob with a 40A MCB protecting it. I suggested putting a 2 way unit on the end instead of the hob. You could then feed the hob with a 40A mcb and the oven with a 16A. 10mm will carry 50 amps, however even if all four/six rings are used in one go they will be clicking in and out at different times so the hob will never use its full draw and also the oven ratings are probably for the grill and oven element combined, which cant happen. I didn't bother using diversity or the regs, just a bit of common sense. You used to wire ovens and hobs all the time like this, a 32A 6mm to a switch/outlet plate and then 2x4mm to oven and hob, worked perfect.
Times change, and so do kitchen habits. It's not unusual to see pairs of double ovens, and even pairs of jobs these days. Are we looking at double ovens? Are we looking at a six ring hob? Diversity guidelines are old and outdated, particularly the one for domestic cookers which takes the first 10amp and 30% of the remainder. This is what permitted cookers to be placed on a 32amp device. These days though, while this is fine for smaller homes, one with a large kitchen built for entertaining will require thought when it comes to diversity. I would think you may get away with using the 10mm for the hob and one oven, and the radials 2.5 for the other. Then a single ring. Better planning would of seen a couple more feeds. The OP says it's tricky to run extra now. In reality, I hope that's true. I hope it's not laziness or cost saving.
Thanks for the replies. It's not about cost. There was supposed to be an additional 2.5mm radial but it only got half pulled somehow and the walls are now sealed up. I'm not sure the diversity is completely outdated. The hob rating must be for all 5 rings on "boost" but that's really not the way you cook. I suppose I might fire up two pans of boiling water at the same time but if anything else is on it would be at a gentle simmer by then. The highest power settings on induction are vicious - you don't use them often or for long. Likewise I would be surprised is the ovens run at full power for long (it could be that the only time they draw full pier is in pyrolytic mode which you don't use when you're coming on other appliances. When cooking it's a quick burst of continuous power to heat up (5 minutes?) then short bursts of power to maintain temp. An immersion heater used to heat a 100l tank of water is a very different kind of load. Main oven on its own radial, second oven off the 10mm would work.
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