Kitchen appliance isolator

[Peter]

The IEE Wiring regs do, that is why you dont plug in an immersion heater or storage heater etc etc

Peter

[Richard Savage]

My previous reply to your point above seems to have dissapeared into the ether. Copied here:

Sorry, didn't mean to omit that vital element from the equation.. What exactly is meant by 'next to' the appliance? I suspect that my '3 FCUs under the sink' solution will be chosen whether or not it qualifies.

Ta

Richard

[Stefek Zaba]

Piffle (in the domestic situation). You're seriously suggesting that the Regs somehow forbid having a washing machine, built-in microwave, wall-mounted convector heater, yada yada, sitting in a room, disconnected from the mains by virtue of being unplugged!? That they're supposed to have the Magic Green-n-Yellow Wire continuously attached from the moment they cross the threshold? Ye cannae be serious, jimmee...

[Stefek Zaba]

Sigh. So unfused spurs don't exist, right? Nor is it permissible to design a circuit where the nature of the load means an overload will not arise using circuit protection only for short-circuit conditions, but not for overloads? And I'm hallucinating when I see a 20A MCB 2.5mmsq entry in the Conventional Cricuits table (7.1) of the OSG?

Hint - those are "rhetorical questions". Meaning, their factual answer stands in stark contradiction to your simplistic, and plain wrong, claim that "2.5mm is limited to a 16a mcb"). Yes, to use 2.5mm on circuits with protective devices rated over 16A needs a bit of thought, sometimes (gasp) some calculation of earth loop impedance in the cases where there isn't a precomputed Table in the OSG for us. And your advice at least errs on the side of caution. But accurate and complete it surely ain't...

Stefek

[Capitol]

A rather different approach may be to use plug in 13A remote radio controlled switches on the ring, as sold by LIDL on occasion. These are made by Mandolyn International Ltd and will handle about 3KW. I can't find a UK website with a quick search, but they are identical to the US units in the attached link, except for the connectors.

I believe the switching is relay, and so far I've never broken one in domestic use. If the relay is rated for US currents, which is likely, then the 13A connectors are going to overload before the inside.

I don't know if these are two pole, but Lidl could tell you. A word of warning however, IME some (not all) of these units sometimes forget their coding! and need reprogramming. This effect is worse if the units are disconnected for a period of some weeks.

Just a thought.

Regards Capitol

[Peter]

Well regs say so sockets are for portable appliances if said appliance is fixed then it should be wired via a switched isolator one exceptionn given is a clock.

Peter

[Peter]

Yes that is ok it just means adjacent to and accessible Peter

[Peter]

The context in which the reply was given was reduction of cable size from

6mm to 2.5mm this has to be fused down, there is a limit to the amount of sockets on an unfused spur you cannot spur all the kitchen appliances onto a single 2.5mm cable sorry if this was not clear.

Peter

[Dave Plowman (News)]

Please explain how you'd achieve this on a normal kitchen appliance supplied with a mains lead with 13 amp plug?

[Dave Plowman (News)]

Sounds like someone is trying to write their own regs.

Most would say the only fixed appliance you'll commonly get in a kitchen is a large cooker that can't run off a 13 amp plug.

What possible reason could there be for requiring earth continuity with the appliance unplugged? All the water connectors are non conducting, for gawd's sake.

[Richard Porter]

I think if you re-read the OP you'll find it doesn't mention a cooker at all. It mentions a hob, presumably gas, which has a mains ignition circuit so a 3amp fused plug or spur is adequate.

[Stefek Zaba]

Agreed - a single 2.5mmsq feeding many sockets, not-fused-down, where the protective device is (say) a 32A MCB, is indeed a Bad Thing and should Not Happen. But a 6mmsq "backbone", with short 2.5mmsq feeds (unfused, connected via junction boxes say) to individual single or even (though it's sillier) double sockets, would be compliant, though not a Conventional Final Circuit. Each such single appliance-feeding socket (a) would be protected against fault current by the upstream 32A MCB - here the "short" feed is important to keep the earth loop imedance low, so that operation of the MCB in the required 0.5s can be guaranteed, and the temperature rise in this faulting cable can be kept within limits; (b) would be incapable of producing an overload for the rating of the short length of 2.5mmsq cable, since you can't pull a sustained 27A out of a single socket (RefMeth1 rating of 2.5mmsq), hard to do so even out of a double, and the actual connected load - single white-goods appliance - will in fact pull no more than rating plate says, prolly 2kW = 8A at peak water-heating time for a "modern" dishwash, possibly the full 3kW = 12A for an older/fancier/faster water-heating appliance; (c) closer-rated fault-current protection will be provided by the plug in't fuse. It's actually a completely direct analogue of the "normal" unfused spur in 2.5mmsq taken off a 32A 2.5mmsq-both-ways ring: the ring is fused at higher than the rating of the spur cable, but the combination of plugfuse and circuit-MCB provide fault protection for the spur cable, while overload is "designed out" by fitting only one power take-off point, either single or double socket.

Having said all that, and certain as I am that design calcs would sanction such a layout in the right circs, I'd still shy away from installing a circuit like that in an ordinary domestic setup: it's simply too unintuitive for a subsequent householder or inspecting/minor-worksing electrician to feel comfortable with. Having had, in the previous house, a period of enthusiasm for FCUs with directly-wired-in appliances, and then been inconvenienced when repairers have needed to reliably disconnect the appliance or wheel in a spare, I've come to appreciate the wisdom of the standard arrangement with FCU to act as control switch for easy-to-operate isolation, feeding a conventional 13A socket (unswitched for preference) at the back of the appliance.

Stefek

[Peter]

I bet all of those built in kitchen appliances are supplied with moulded on plugs!!

Peter D

[Dave Plowman (News)]

Why use an FCU if there's a conventional plug? Wouldn't a simple 20 amp DP switch be neater and less confusing?

[Peter]

you dont its classed as portable

Peter

[Peter]

Most people are not qualified to know different

the same reason the metal sink is earthed its called bonding

Peter

[Peter]

I agree here sorry if I misunderstood what you saiid before :)

Well then we agree

Peter

[Peter]

Yes I did suggest this too

Peter

[Stefek Zaba]

Piffle (again). There is *NO* requirement for kitchen sinks to be bonded. *NONE*. Supplementary bonding is required, for good sensible reasons, in bathrooms/shower-rooms, based on the greatly reduced impedance of a wet, unclothed body compared to a dry, clothed-and-shoe-wearing one. There's electrician's folklore which extends the idea of bonding to kitchens, but that's all it is: most of the population doesn't prance about barefoot, naked, and wet in a stone-floor-no-DPC-kitchen - which is the sort of behaviour needed to make the extra shock risk significant enough to need supplementary bondage. The OSG is quite explicit on this point - section 4.6: "there is no requirement in BS 7671 to supplementary bond the following: kitchen pipes, sinks, or draining boards; metal furniture in kitchens; metal pipes and wash hand basins in domestic locations other than bathrooms. Note: [it goes on to say in smaller print] metal waste pipes in contact with earth should be main bonded back to the main earthing terminal."

Just why this myth has arisen is uncertain. One very likely candidate is the "Electrician's Bible" - Whitfield's "Electricians Guide" - which, ignoring the wording of the Regs and the OSG, shows a diagram where supplementary bonding is applied in a kitchen to prevent "a severe shock which could otherwise occur between the live case of a faulty electric kettle and an adjacent water tap". (There's plenty to argue with in this example, but I'll leave it for now). Other explanations include the fact that the incoming water main often rises up in the kitchen, with the main stop tap being under the sink: so it's the right place to do the main bonding for the incoming water service, and all that lovely green-n-yellow-magic-safety wire is just begging to have extra connections added to it ("let's do the sink while we're at it"). Only the most cynical would add the creation of chargeable work to the uninformed customer anxious about their safety to this list of reasons.

Factually, bonding the sink isn't an unambiguous safety gain - it would be nice to say "well it's not required, but it can't do any harm". Bonding will generally create a lower-resistance path to earth: so unless you can be sure that all fixed AND PORTABLE appliances with which the user might be in contact are also bonded to the sink, you're in fact increasing the shock current which will flow between a faulty appliance or other source of live potential and the sink, through the user's body. There's a strong counter-argument, of course, that with a low-impedance earth any fault direct to the extraneous-conductive-part will make the fuse/MCB blow that much quicker and more reliably; my point is that there is a balance to be weighed up between that protection and the increased risk of the sink becoming a better return path for shock from faulty appliance through a person's body. And since supplementary local bonding for portable appliances (Mr Whitfield's famous kettle, hand mixers, table-top microwaves, yada yada yada) is wildly impractical, half-hearted extra bonding can even make things worse. The more use there is of plastic pipework, the less appropriate bonding becomes (as the IEE Regs and OSG themselves spell out for the bathroom case); and regardless of pipework details, more appropriate protection against shock in the kitchen environment is provided by RCD/RCBO.

Stefek

[Stefek Zaba]

Yes, it would - better all round, saving the hassle of the "wrong" fuse blowing. Only justifications for an FCU would be if you were feeding multiple socket locations, or "can't find a 20A DP sw in old-georgian scroll-effect brass, but can get an FCU in same this rainy Sunday" (or whatever weirdo decorative demand has been laid down by the domestic authorities ;-).

But you're quite right, the 20A DP switch wins in practically all respects.

Stefek