Kitchen appliance isolator

[Richard Savage]

My mythical kitchen is slowly creeping towards installation - I bought the hob last week!

Now planning the wiring and am mindful of the need to be able to isolate the power to washing machine, dishwasher, hob ignition and extractor hood. I _really_ do not want to fit fused spur isolators above the worksurface so I was going to fit all three (running hob and extractor from the same isolator) in the space under the sink. However, this is going to make for quite lengthy, parallel, cable runs and I was wondering if I could incorporate a single isolator for the whole of the ring on the appliance side of the kitchen.

Is it possible? And could it be done discretely - I don't want something that looks as though it could have designed for use by the CEGB.

Alternatively (and probably simpler) would a cooker isolator (switch only), spurred off a socket on the kitchen ring, feeding the four under surface sockets for the appliances be acceptable? And could I wire those sockets in series with a suitable weight of T+E? I'm thinking that the sequence would be:

====SKT====Ring======= | Switch ------ W/M --------- D/W----------Hob--------Extractor

TIA

Richard

[Grunff]

I was in a similar situation, and decided to solve it by placing sockets (surfacemount metalclad) inside the base units adjacent to appliances. A hole at the back of the base unit is used for passing the plug through. Works well, as long as you don't mind sockets in your base units.

[Dave Plowman (News)]

I'm curious about why you feel the need for any of this? All the appliances - with the possible exception of the cooker hood - could surely be unplugged for isolation? And if you needed to isolate the entire ring, what's wrong with the MCB in the consumer unit?

[Chris J Dixon]

If it is necessary to isolate an appliance quickly, sockets behind the appliance could be hard to reach with the appliance in place.

Chris

[Dave Plowman (News)]

Every appliance I've seen has got an on/off switch.

But if you're going to the effort of re-wiring to include isolator switches, why not simply situate the sockets where they are accessible without removing the appliance?

[Christian McArdle]

Put in whatever switches you like. Provided that the appliance is connected via either an FCU or a plug and socket, then there is no requirement for switching.

Just ensure that on a 32A ring, the switch must be double pole and rated at:

one single socket = 13A (20A more likely to be found) one double socket = 20A more than one socket = 32A (45A more likely to be found)

Alternatively, a 13A FCU may be used to switch for any number of sockets, provided the expected appliance load is below this, which it isn't.

Personally, I used a 3 x 20A DP grid switch to switch my tumble dryer/washing machine and dishwasher independently, all fed off a dedicated

32A radial circuit. I used a junction box to drop the 6mm incoming to 3 x 2.5mm that would fit the switch terminals. As each switch only controls one single socket which will be fused in the plug, this is permissible for both short circuit and overloading.

Finally, the cable run mustn't be done in 2.5mm cable after the switch if the third option (more than one socket not limited to 13A) is used. You must use at least 4mm, probably 6mm cable, which will be a pig to install, as getting 2 x 6mm into a wiring accessory will not be easy/possible. You may have to drop to 2.5mm in a large junction box just outside the socket (which is permissible as you are allowed to assume 20A max from a double socket or

13A max from a single).

Christian.

[Richard Savage]

Thanks to all (i.e. the usual helpful few!)

To try and answer some of your questions:

The units will all be built in and spread around an 'L' shaped area of worksurface interspersed with drawer units.

I think that the drawer units really make access to sockets behind unreasonably fiddly and I'm not prepared to have FCUs or appliance sockets above the worksurface.

There is only one 'cupboard' providing the possible option of locating 3 FCUs and then running radials to sockets close to each appliance. This under the sink which is approx 2/3 from the top of the upright in the L. This is why I said something about lengthy cables in the original post.

If it was my choice I would not provide any isolation, but just put single, possibly switched, sockets close to each unit and use the MCB in the CU as an isolator.

It is only the installers who said that each appliance must be supplied by an FCU/socket pair and cannot simply be plugged into the kitchen ring.

I understand what you say (Christian) about using 6mm cable - I had feared as much!

The CU is some distance from the kitchen and, needless to say, hidden in an under-stairs cupboard. In any case is it acceptible to have the MCB as the only way of isolating the kitchen appliances, especially the hood? If it is it might be easier to show SWMBO how to test the RCD which is separate from the CU and thus more accessible!

A big red emergency off button has a certain appeal - is that feasible (only half joking)? Some sort of remote test switch for the RCD would have the desired result. Have I heard/read about kitchen over-heat sensors that can trip the power supply to the kitchen? Presumably they trip a suitably rated contactor? The ones supplying the last mainframe room that I worked in used to stick on!!

Cheers guys

Richard

[Peter]

Well the MCB is only single pole !

Regs require that the means of isolation be double pole and readily accessible, if the socket is behind the washer then it is not.

Peter

[Peter]

This is not allways double pole and what about repairs to said appliance ?

Peter

[Peter]

Sorry you cant do this 2.5mm is limited to a 16a mcb !

Wire the appliances on the ring using 20A dp switches above each appliance with a socket below, the Hood should be on a switched fused spur (3Amp fuse) and the cooker in 6mm with a 45A DP switch within 2mtrs of Hob

Peter

[Stefek Zaba]

I think the strict requirement you mention applies only to electric motors - and I don't think washing machines count! For domestic appliances, functional switching as provided by the front panel is accessible, while isolation and switching-for-mechanical-maintenance are (I claim) adequately provided for by removing a plug from a socket. I'm sure we could argue the toss about corner cases where two faults (a live-to-casing *and* an earth continuity fault) make it dangerous to move a washing machine or similar to get at a socket hidden behind it; but domestic installs are typically designed under a single-fault assumption. Better practice is indeed to have either an FCU in an accessible position, mayhap as part of a gridswitch, or at least have the socket in a next-door base unit so that isolation doesn't require movement of the appliance; but I'm not convinced that the letter of the Regs is violated by the common arrangement with the socket at the back of a gap between applianceses...

Stefek

[Peter]

No ! it is not and the Hood will need to be fused down via a 3AMP switched fused spur, now that you have said that the appliances will be built in they are classed as fixed for the regs and MUST have a means of isolation next to the appliance that is double pole.

Peter

[Stefek Zaba]

So, does your sense of aesthetics rule out using grid-switch FCUs in the relatively-distant cupboard? That'd take up only one double mounting box; and with FCUs controlling the spurs to each dedicated socket, providing closer protection for the cables, the runs from there to each socket can be in 2.5mmsq.

The "Big Red Switch" does have appeal, but isn't feasible with a ring (not without bizarre contact arrangements to switch both sides of the ring *and* preserve continuity of the rest of ring when you bypass the relevant section). Unless, that is, you have a truly dedicated kitchen ring, and can replace the twin 2.5mmsqs running back to the CU with a single 4mmsq or 6mmsq (6mmsq is safe bet, 4mmsq needs calcs on permitted length), and you put a 45A cooker-style isolator at the point where the thicker incomer fed out into two arms of the kitchen ring...

[Richard Savage]

'Tis indeed a dedicated kitchen ring. But I don't think that a Big Red switch will meet the aesthetic requirements of SWMBO. She has already vetoed red with aluminium edging as the colour scheme for the units ;-)

Richard

[Dave Plowman (News)]

I'm aware of that.

Which regs? The appliance switch provides the isolation in event of a problem. For servicing, you unplug it.

[Dave Plowman (News)]

Then make sure the one you buy has got a double pole switch. And when the appliance is moved for servicing, you unplug it.

[Richard Savage]

Similarly sorry. Come what may there will be no switches above the surface! In one instance (the W/M) that is for aesthetic reasons, in the other it is because the hob and sink are either above or below the units (the D/W and hood). Oh, and it is a gas hob (as mentioned in the initial thread) so we're only worrying about ignition power. The ovens are on the other side of the room with their own feed.

Please keep the comments coming, being able to argue the toss with bods who understand the problem is sooo much more satisfying than trying to discuss it with SWMBO.

Rgds Richard

[Dave Plowman (News)]

Bollox. It can be on a 3 amp fuse plug. Or run off the lighting circuit with no additional fusing.

[Peter]

Fixed appliances must be earthed when you remove a plugtop from a socket outlet you remove the earth therefore a double pole switch should be provided maintaining the earth bonding.

Peter

[Richard Savage]

Well, FWIW the installation notes for both units (W/M and D/W) make no mention or distiction between free standing and building-in with regard to permanent earth connections. The only mention of permanent earthing is where the 13A plug is removed and the unit hard-wired into a permanent connection. In that instance, as you say above, the switch must be double poled with a min 3mm gap between poles and must not 'break the yellow and green cable at any point'. No mention of permanent earth when using a 13A plug.

Richard