Kitchen wiring layout

As part of the planning for my new kitchen, I looked at the current layout today. I would have helped my dad to rewire it but Part P seems to have put paid to that. I would still like to know what to ask the electrician and get an idea of what he will do. I've done plenty of searching on here and found lots of useful information but not everything yet.
As is usual for a 70s two-bed semi, the current layout is inadequate and in my case badly altered by previous owners. The house has a single ring main with a 32A MCB and cooker radial also with 32A MCB.
The kitchen has two single sockets above the worktop on the ring, one each side of the hob. From one, a spur cable runs diagonally unshielded under the plaster to the cooker hood, with no form of isolation! The other single socket has a spur cable going to a socket under the worktop, itself having a spur cable along the floor to a small CU with RCD under the sink for powering the garden circuit. The cooker outlet (with socket) supplies the electric oven and igniter for the gas hob.
Obviously the diagonal hood cable is a no-no but I was wondering how the cable(s) to the hood could be run. Dropping from the ceiling, as the two sockets above the worktop are wired, would be feasible but where could an isolation switch go? I wouldn't want it behind the chimney. How is it done from below? Keeping to the vertical/horizontal from an accessory rule, a cable dropped vertically from the hood could necessitate an accessory behind the hob? I won't be having units on either side of the extractor. Is putting the cable in metal conduit, a switched FCU to one side of the hob and unswitched outlet behind the hood the best method?
Under Part P, must the approved person do absolutely everything? If I left some nicely chased walls in the (to be) gutted kitchen, where the electrician would want them, I gather he could use them? To save on expensive electrician's time and cost, it would make sense to do as much prep work as possible. Where does Part P draw the line on what is electrical? Could I put back-boxes in?
I expect a new ring main to supply the kitchen would be desirable. The kitchen items on the ring would take a dishwasher, fridge freezer, combi microwave, gas hob, extractor and kettle. The washing machine and tumble drier are in the downstairs loo - but that's another wiring issue.
I expect an electrician would route the cable along the wall in the adjacent integral garage containing the consumer unit. Since the cable would not be coming from the ceiling, would it be acceptable to run cables on the surface (in trunking if necessary) in the void behind base units? This would be on the right level for the hob and dishwasher outlets (accessed from units to the side of these).
Even if the wall was chased horizontally on the line of the above-worktop sockets, how would the dishwasher cable be dropped? The dishwasher will be midway between the cooker and sink-drainer, with the outlet under the drainer. Could the cable do a right angle above the drainer, in the horizontal plane of the above-worktop sockets and vertical plane of dishwasher outlet, even though there is no visible accessory at the point of the right-angle?
Would the following be a valid new ring layout, with S being a switched socket, the bottom two being for the dishwasher (right) and hob (left) mounted under the worktop in accessible cupboards. Everything else is above. The rough location of the appliances is shown, the cooker outlet for the oven is not. Hopefully the ASCII art is readable.
Hood---| (m/w) (kettle) | | ---SS------SS------SS--------FCU----SS-------| -| (Hob) | | (f/f) (Oven} (D/W) | | | |-----------------S-------------------------S
This suggestion ignores adding RCD protection. Is it especially necessary? Is the electrician likely to suggest it?
Lastly, I need to move the garden electrics, as the CU is mounted in the sink unit that is being replaced, and the spur socket from which it is unsuitably wired will no longer be there. As garden wiring is notifiable, even though it is already there, I presume I cannot do the rewiring for that? Would the electrician consider spurring from the bottom-right S above if he did it?
Sorry there's lots here, but thanks in advance for any helpful answers.
James
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James H wrote:

Why? Part P does not stop you DIYing it. The only difference from before is you need to either a) submit a building notice to the council prior to starting work, or b) ignore part P ;-)

Hmmm nice ;-)
What does the garden circuit feed?

Is there a cupboard adjacent to the hood? If so you could have a single socket in the cupboard and simply plug the cooker hood into that.

If you mechanically protect the cable than you can run it in non standard places (or bury it 2" deep if the walls are thick enough).

Nope you can do it all yourself (with building notice, and allowing the council to have it inspected at the stages they want). Councils in general don't seem to have got their act together with this, so you will need to speak to yours to find out how they play it.

Yes you can...

Yup. Possibly a non RCD protected radial to feed the fridge and boiler as well.

Yup probably.

Not quite sure I am am visualising this correctly, but it sounds like you are saying you want to come straight up from the under worktop socket to a cable chase that runs horizontally between two other accessories (one possibly being the isolating switch for said socket), turn 90 degrees and carry on to the switch? If so then it complies with the requirement that the cable runs are in direct line of the visible accessories so sounds ok to me.

Layout looks mostly ok (depending on how to solve the extractor issues). You want to design the cable layout so that you don't end up concentrating all the big loads at one end of the circuit - you want them spread out around the ring, or toward the middle of it. Things like kettles/toasters you can largely ignore since they are short duration loads.

Is there any possibility that someone may in future plug in an appliance that they may use outside? If so then the answer is a definite yes. You have also not mentioned what type of earthing system you have (i.e. TN or TN-C-S with an earth provided along with the supply, or a TT setup with local earth rod). If your earthing is TT then *all*circuits need RCD protection.

Again it depends on what we are talking about. If it is just a single exterior socket for example, then it would not be uncommon to provide that from the ring or a spur from it. Perhaps with the addition of a dedicated RCD if the main supply circuit is not already protected by it. If on the other hand you are talking about a 30m cable run to a collection of out buildings which have power and light circuits then you would be looking for a dedicated submain run from the main CU or even taken as a split feed before it.

Hope that helps...
--
Cheers,

John.

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Thanks for the replies.

Ignoring Part P seems a tempting option, saying it was all done and dusted in late 2004/early 2005, honest guv'nor ;) Looking through the council's building control webpages, they have forms for building work insisting the electrician details are filled in for Part P, with no mention of inspecting DIY. I'm guessing they're one of the many that haven't prepared enough. I'll give them a call.

I'm not having cupboards either side. From my days in a shared house, having to clear the grease off the units either side of the hood wasn't pleasant and put me off having anything near the hood. That said, in those days I would often enter the kitchen to find the fog of a full fry-up in progress with the hood turned off. Nice.
Going deep enough into the walls can't be done so shielding seems the best method.

I don't have a TT earth so I won't need everything RCD'd. The garden circuit just contains a water feature, pair of outdoor uplighters and a floodlamp. I would also like an outdoor socket installed, protected by the RCD of the existing garden setup. That would save having to make the socket in the kitchen nearest the back door RCD protected.
Sounds like spurring off the new kitchen ring using the RCD CU for the garden should be okay.
Thanks,
James
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James H wrote:

If you're using an electric hob, take the fan supply off the load terminals of the cooker control unit, via an unswitched FCU. That way the fan will be on whenever the cooker is on.
Owain
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Nowt to do with electrics, but line the tops of the cupboards with old newspaper. In this way, when you do the five-year-thorough clean all you need do is remove, discard and replace the contaminated newspaper. I've learned the hard way...
HTH
Mungo :-)
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IIRC, It's ok if either deep enough or protected. If this makes it easier, I'd put it in steel conduit.
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*There's two theories to arguing with a woman. Neither one works *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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