Kitchen wiring query

[Lobster]

I'm about to start wiring up a new kitchen; the plasterer comes back this week and I'd like to have all cables and socket boxes in place before he starts work. Haven't bought the units and appliances yet (think the plasterer would throw a wobbler as I've nowhere to store them in the meantime!)

I intend to fit a built-in fridge and electric oven (one with a prefitted 13A plug). There will be a gas hob immediately above the oven.

The plan is to fit two 13A unswitched sockets below the worktop, immediately behind the oven and fridge units. The oven one will be a double socket to feed both the oven and the hob's electric gas igniter. Each socket will be controlled by a 13A FCU, above worktop height. These will be on the same ring main, with the cables dropped down from ceiling level, buried in the plaster. Sound OK so far?

Questions... First - in the case of the oven, obviously the FCU can't be directly above the socket if the socket is directly behind the oven, ie within the oven kitchen unit. It will be about 30cm to the right of it. Can I take the feed for the socket from the FCU vertically down to below worktop level, buried under the plaster, and from there emerge from the plaster within some conduit and traverse horizontally, to the socket? I realise horizontal cables are normally a no-no, but if they are running surface mounted behind kitchen units? Or is it normal practice to fit the oven socket vertically below the FCU (and therefore behind a cupboard) and have the oven flex wending its way round the back of the cupboard to plug in (which would be quite inaccessible).

Second - how much space is there usually at the back of these built-in units? Is there room to have surface-mounted sockets there? - on the basis that I don't see the point of recessing them if there's no need; and also because if I'm allowed to run horizontal surface-mounted cable behind the units, it would be a bit odd having this feeding flush-fitting sockets. Or do I just need to go buy my units and check?

Thanks for any advice David

[kitchenman]

The problem with fitting points under worktop & behind units is when the fuse blows you will have to remove the appliance.

because sods law says the fuse that blows is the one in the plug, not the one in the switched spur

The other problem is the plug may well stop the appliance going back enough.

Leave plenty of spare cable adjacent intended positions of appliances at floor level

Have plastering done

Install furniture

Put power supplies using surface mounted boxes, in adjacent furniture to appliances.

That way you get it all in the right place

[BigWallop]

OK on that. The rest of my reply is in between your paragraphs so you know what I'm on about. :-))

Sounds OK so far, BUT !!! You will need to protect the cable under the plaster with a metal sheild to stop anyone bashing nails or drilling holes through it. It's a Kitchen area so is prone to having things stuck on the walls at all different heights. It is also needed to fix an earth bond wire to the metal sheild and to the Double Pole Switch end of the cable. An unseen cable is a dangerous cable. You don't want your kitchen fitter to screw or drill through a cable he hasn't seen.

You also don't need Fused Connector Units (FCU's) above the worktop, you need 20 Amp Double Pole Switches to control the remote Un-Switched Sockets. The fuse in the plug-top on the appliance and your ring circuit breaker in the consumer unit will do the rest for you.

If you run the cable behind some protective metal sheild, then you can run it diagonally across the wall from the 20 Amp Double Switch directly to the Un-Switched Socket for the oven.

If you're having the walls plastered, then you can probably fit metal back boxes and flush fit face plates to all your electrical gear. Or am I missing something ? Are the whole walls being plastered from top to bottom, then the kithchen units being fitted ? If so, then the plaster is definitetly going to be thick enough to take inch deep back boxes on all the electrics.

[Dave Liquorice]

Eh, what gives you that idea?

You can run unprotected "horizontally or vertically to and accessory or consumer unit". See the IEE Onsite Guide 7.3.2 Walls.

So you drop down from the FCU to meet the horizontal from the socket and follow that to the socket. On a wall with lots of accessories you have to assume there are cables in any vertical or horizontal line from any accessory.

Variable but as you can run horizontally the "problem" goes away. B-)

[Dave Plowman]

If the fuse blows, the appliance will be faulty and have to be removed for repair anyway.

[rrh]

I'm currently fitting new Wickes units in my kitchen. They have 50mm at the back for services plus a good 135mm or so underneath - plenty of room for cables or pipes.

The wiring regs on cable run locations exist to minimise the danger of accidental drilling through cables etc. It is actually a lot easier to see and avoid cables run across the surface of something than cables buried in plaster. Obviously you don't normally run them on the surface, both because it looks unsightly and because the cables may be exposed to mechanical damage. But if the cables are to be behind fixed kitchen units, I would argue that it is actually better to leave them on the surface as long as they are protected from damage by the units.

You can follow the regs carefully but still end up with silly things. In my kitchen I came totally unexpectedly across a steel conduit buried in the plaster, curving down from ceiling level in a wide arc and disappearing behind a wall unit. At the top it seemed to be some of the old unused wiring conduit of which the house has quite a lot, with two old dead cables in. So I ripped it out...and halfway down the arc found a junction in the conduit with modern-style cable entering from behind. The sheath had been stripped off and the individual cables fed down the rest of the conduit to a point on the the wall where they exited and went back through the wall again to the light switch of the room behind. Arguably regs-compliant since the cables were protected on their run but in my view totally silly to do something as misleading as feeding modern live cable through old conduit which looked unused. Also the conduit would not have stood up to the heavy-duty drilling for the new wall units, cooker hood etc.

Moral: think as well as read regs!

[Lobster]

I agree entirely; though as I'm going to have my installation inspected I am particularly concerned to do things by the letter here...

Thanks all, for some useful replies to my query. So, looks like I should probably have my below-worktop unswitched sockets flush mounted in case they interfere with the backs of appliances/units; but I can have the cables surface mounted (as in, why bother channelling them), running horizontally below worktop level. I've never come across surface mounted cables and flush sockets before; is there a there a recognized way of fitting these?!

Incidentally, my walls are already plastered for the most part; the plasterer is just coming to do a skim coat (plus new ceilings) so it does require work to do the channeling.

Thanks David

[BigWallop]

If the walls already have a base coat plaster, then why not go for some 25 mm X

12.5 mm plastic conduit for the cabling. It will help to keep them neat behind the units and above the worktops it will be hidden (mostly) by the new skim coat plaster and any tiles and things you apply.

They'll also be easier to modify in the future.