I definitely agree with you on the lighting circuit. It was nothing more than lazy on my part suggesting otherwise! I personally install a serperate circuit (not necessarily a ring) for the kitchen appliances because in my limited experience i have found them to be the main RCD nuisance tripping issue. So an unprotected way with an rcbo in is the way to go for me.
I also appreciate what you are saying about the parallel paths/ring main only feeding 1 point (is it one point? or is it 5 because of the feeds coming off? or is it 10 because of the flex outlets? another argument that we could go round in circles on!).
As previously mentioned the client has ALOT of kitchen gadgets, and has specified she wants a minimum of 8 sockets (4 2gs) across one side of the kitchen, the other side has the immersion, fridge, freezer, washer, dryer, dish washer). The price for a 20a and a 32a breaker is the same, the only issue is the additional 6/7m run of 2.5 to the grid that would be the extra cost.
As for carrying out the testing i would of course test it as a ring? How else would you test 2 x 2.5 cables being supplied from the same OCPD that were interconnected? Do you appreciate what i am saying about the grid switch having effectively 5 x SFCU in it?
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Firstly immersion heater, on a new install/rewire it goes on its own circuit everytime, no question. The rest of them you'll just have to use your own judgement. I doubt very much the combined current of the sockets and appliances in the kitchen at any one time will exceed 32amps.
I know i'm not the best at transferring the thoughts in my head into written words but I think it would help you to see what I am trying to say if you consider an upscaled version of this.
You have a circuit coming from your CU as 2 x 2.5 cables terminating at a single enclosure containing 5 protective devices, you say this is a ring and will operate as a ring and be tested as a ring.
Compare this to a circuit coming from a DB as 2 x 25mm cables terminating at a single enclosure containing 5 protective devices (another DB). Is this a ring?
I know 4.0mm would be ridiculous in one of those switches so wouldn't contemplate that but if I felt it needed more than a 20amp circuit i'd be looking at 2 x 2.5 radials personally, either 16 or 20 amps.
And I always fit RCBO's for every circuit that needs RCD protection, in my opinion having 2 RCD's doesn't give adequate protection against the problems of nuisance tripping. And yes I have lost a couple of CU changes because of this stance, but i've also won a couple based on this after explaining the pro's and cons of each way in as unbiased a fashion as I can.
I am hoping someone else will give their stance on this soon
I had allowed a separate circuit for the immersion, in a petty cider fuelled way i was trying to make it look worse than it was because i couldn't conjure up any more kitchen appliances!
Your example of the parallel paths feeding a DB was a good one and i do definitely see what your saying! The only difference i can see is that you in the DB example you are terminating both ends of the cable in the same terminals at either end, whereas with the grid switch i would have been terminating a 2.5 feed into either end of the 5 Fused Switches, therefore putting a load between each feed.
I had considered the 2 x 20a radial for the exact reason you are talking about. However i had been reluctant to feed two circuits into one grid switch, again i appreciate that this is no different than most stairwell/landing light arrangements however it just felt a bit queer!
In an ideal world i would use RCBOs, the only time i have seen this done though is in small commercial premises (i just did some work at a restaurant that had this set up). Hopefully a dual RCD board should be more than fine for protection because nuisance tripping won't be occurring on any of my jobs
Voltz, i don't believe i blamed the board for anything! The one i touched felt crap, end of! May of been a faulty effort, may of been a fake! There seems to enough fake electrical components knocking around these days for it to happen. However i will be buying one next time a friend wants a cheap job doing and giving it a go because as you said, you can't all be wrong and i have read enough of your replies to know you are more than clued up!
