Having read the replies to my question a while back, I'd like to run the following calculation before the group: Appliance maximum power in kW: Oven => 2.3 Hob => 6.3 Micro => 3 Total = 11600W
11600W / 230V => 50.43A.
According to diversity rule
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(30% of remainder: 40.43 x 0.3 = 12.13)
10 + 12.13 + 5 (for socket) = 27.13A which is inside 32A, so this load is fine on a 32A MCB (and suitable cable etc).
If there are any errors, please let me know.
Antony
PS With the amount I cook, it will probably never matter, but I allegedly owe it to the next owners... :)
You can't bring the hob into this equation Antony. The hob will need its own supply as it is a heavy load appliance. The only types of loading you should supply with a ring final circuit ate loads which can safely be fused with up to a 13 Amps fuse.
230 V / 13 A = 2,990 W
The oven and hob make up a total loading of nearly 9kW on their own, which can safely be supplied through a radial circuit of 10 mm csa' at 40 A safety breaker.
It can be possible for all these appliances to be on at he same time, so they should be rated in your design as such where ever possible. Diversity is only a ruling on a single free standing stove, not separated cooking appliances.
The Regs spefically allow a split hob and oven to be treated as a single cooking appliance, and in a domestic situation the '10A + 30% of the rest' is an appropriate diversity guideline. (It would NOT be appropriate in a commercial kitchen, where sustained peak usage would be notably higher). The 8.6kW of oven and hob gives a 'diversified' figure, starting from the raw 8600/240 = 36A of 10 + (26*0.3) = 10.8A. Arranging for a microwave to share the same dedicated circuit - the 'old fashioned' way being to use a cooker control unit with an integral 13A socket - adds 5A to the diversified load; but that's a slight 'abuse' of the justification for the 'add 5A' guideline, which is based on the idea of the cooker-control-unit socket being used for a kettle - a high peak load which doesn't last more than 5 minutes. In practice it's no bad idea to use the headroom on a proper cooker radial for the third cooking appliance, rather than the ring which your dishwasher, dryer, washing machine, toaster and similar might all be using; but a peaked-cap Regs-n-Whitfield literalist won't like that argument.
**BUT** that diversified load calculation tells you what it's reasonable to consider the cooker circuit load to be on the whole CU. It does NOT mean you size the cooker radial to the lower, 'diversified', figure, either in cable size or in MCB rating. Rather, you size the cooking radial according to the sensible design load - 10mmsq + 40A MCB being the bound-to-be-OK sizing, 6mmsq needing more careful consideration. That way, the cooking-appliance final circuit is fine for existing appliances and likely future replacements.
What's the difference in diversity between 4 rings and an oven in a free standing stove and 4 rings and a hob as two separated appliances? They are going to be used in exactly the same way.
Personally I would put the microwave on the ring (and *not* have a socket on the cooker control unit) and use a 32A for the cooker bits. The cooker control switch should be within 2 metres of *both* the hob and the oven.
Well if my question created some discussion amongst the esteemed members of this NG, then it can't have been a silly one. I'm doing what Owain suggested above, primarily because I understand what he's saying, and I trust him!
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