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.