kitchen rewiring

[Fred]

Hi,

I have read here about the advantages of having a radial just to the freezer, but would you have to put a note on the socket to say it was on a different circuit to the rest of the sockets in the kitchen or do you rely on any electrician double checking the power is off before they go to work?

I thought I had also read the suggestion to put the kitchen on a separate ring to the rest of the house, but I have had a quick look through the faq and wiki and haven't spotted it this morning. What would be the advantage of this? I think it was to do with loading but a cooker and hob would be on their own radial, so these would not affect kitchen loading. What other heavy loads are there in a kitchen? True a kettle may be rated at 2 or 3kw but it is only on for short periods.

I'm thinking the current drawn by toasters, bread makers, and food processors and other small white goods are neither here nor there. Is it perhaps more of an issue where the dishwasher, washing machine, and tumble dryer are all in the kitchen? I guess a tumble drier must be rated about 3kW and the water heaters in washing machines and dishwashers must be about the same, though used for shorter periods?

We have a kitchen desperately in need of renovation, with a laundry/utility room next door with the washing machine and tumble dryer in that. At some point soon, SWMBO insists that they are smartened up. Would it be a good idea to have the laundry and kitchen on their own ring when we get the work done or would you even go as far as having the laundry on its own?

TIA

[Jim]

There's no harm in sticking a label on it, but I don't believe there is any specific regulation to say this must be done.

In our rewire that I'm just in the progress of we have:

• radial for the kitchen sockets * with the fridge on a switched fused spur with the switch mounted above the cabinets and an unswitched socket behind the fridge. * the cooker hood on another fused spur.

• separate radial for the tumble drier and washing machine

• a separate 16A radial for the dishwasher

• a 40A oven supply.

And everything on separate RCBOs because it's 17th edition.

But then we've committed to replastering so the extra cost was minimal.

The reasoning behind using a radial rather than a ring was AIUI twofold

a) if all the load is down one end of the ring it doesn't actually work as designed. b) kitchen sockets are prone to faults where grime gets into them and it's less likely for a radial circuit to partially fail in an unsafe fashion.

I suspect this is vastly over-engineered! I should mention, it was all specified by the electrician who will be commissioning it.

[NT]

None of what you mention is a requirement. Kitchens (and usually the rest of the floor) run on just one ring are very common, and despite carrying well above 30A at times they're quite happy about it, since the overcurrent is only short term, and no damage results. Diversity is the key.

In an ideal world, and you may as well if rewiring now, a kitchen would be split over 2 rings, and those rings can happily supply the rest of the floor too. A non-RCDed freezer socket on its own feed is another advantage, but its more about seeking perfection than a necessity.

NT

[Tim Watts]

Jim wibbled on Friday 23 April 2010 12:47

For the record, my kitchen design is:

(All RCBO - fridge, freezer take their chances with the rest of them)

1 x 32A ring for 2xfull sized appliance spaces + 4 sockets (High probability of combi oven and kettle here). The actual ring is extrememly small so I have a further design consideration to balance the lengths of the legs reasonably well. 2 x 20A could have been argued for here, but my CU is getting rather full and I prefer 32A flexibility - 4 very large loads are pretty much guaranteed to load balance according to diversity. 2 are less so. 1 x 32A ring for the rest of the kitchen, shared with the dining end, utility/back hall and one bedroom. This is purely from a geographical POV. Due to the layout of the worktops, it is less likely that this ring will see massive point loads, though I could have a combi oven and a kettle on this ring instead of the other. 32A radial cooker. I'll be having gas, so this will sport a 13A socket for the gas cooker instead via the cooker isolator (32A radial is permitted standard circuit, though rare).

Then

1 x 32A ring for the other two bedrooms and main hall - geographic convenience and balances well.

1 x 32A ring upstairs (dormer, so is not very big). Could downgrade to 20A radial but as the sockets are in fact in a circle a ring makes sense.

2 x 10A lighting circuits on a whole house front/back split.

Misc outdoor circuits.

That's probably overengineered, except for the large local grouped load on the first ring - without getting really silly with excessive chasing and cable runs, that was the most practical compromise.

[Fredxx]

Personally I would have thought 2 rings into the kitchen would mean a convenient way to create loads splits. Also what's wrong with using unswitched plugs below surface and switch above surface for dishwasher etc?

Do they have to be RCBOs? I thought as along as they are covered by an RCD, all would be OK. Though I guess it's simpler to use individual RCBOs rather than a consumer unit with split RCDs, also with a limited number of RCDs. Just that RCBOs are still very expensive.

Do you experience nusiance tripping from kitchen appliances? Perhaps I'm lucky, but the only thing in the past few years to trip an RCD has been an iron.

A ring has a set of rules that the IET are happy with and aware of the consequences. Generally, unless the consumer unit is in/next to the kitchen, the plugs are likely to be clustered together in the middle of the ring. I'm sure it's not difficult to spread out outlets to spread the load.

Not really my experience, especially under counter. It's far easier to remove appliances when required using plugs and sockets.

[dennis]

If its very short you could use thicker cable and it wouldn't cost much extra. A 4 mm2 radial (32A?) could do the job.

[John Rumm]

There is certainly no harm in having a label - and if the socket was going to *not* have RCD protection[1], then a label to highlight it should not be used to power devices outside would be good.

[1] Under the 17th edition this will mean mechanical earthed protection or deep burial/surface routing for the cable.

Its mentioned in passing but there is no dedicated article for it as such AFAIAA.

Indeed - kettles etc are usually mostly ignored on the grounds that they are very short term loads.

Yup these are the big users - its quite easy (at least in theory) to gobble 6kw of the available capacity with just these three. Don't forget that many single ovens (at around 1800 - 2200W) are also often just plugged into a socket.

In older properties kitchens were often just included on a "downstairs" ring circuit - but then the potential load was far lower. These days kitchens are still included this way in smaller properties, but often separated out on larger ones (especially those with utility rooms). The splits can make sense as kitchen and downstairs and upstairs, but equally can work as kitchen and "rest of house" or kitchen + upstairs and downstairs etc.

Unless you are running a large family laundry room (e.g. two WMs and a TD) then I would probably leave it bundled with the kitchen. However this is a good argument for having a kitchen separate from the rest of the house. A dedicated circuit for freezers etc is a "nice to have" as well.

[Ian Middleton]

Well my kitchen done in 2006 has..

32A MCB protected radial for induction hob. 32A MCB protected radial for oven and microwave. 32A RCD protected ring for kitchen sockets and this includes fridge and freezer. 32A MCB protected ring for fixed appliances, in our case dishwasher, washing machine, tumble drier and under floor heating.

Did think about putting fridge and freezer on non RCD protected ring but....well never got done. Not had any false trips, so OK for now....

[John Rumm]

Nothing wrong with that, and quite common.

They don't have to be RCBOs - it depends on how much discrimination you require between circuits. If the object of the exercise is to ensure a fridge is separate from other appliances then it really needs its own (or no) RCD/RCBO.

They are much cheaper than they were. Not so long ago MCBs were £5 - £8 each and you could pay £50 for a RCBO. Now you are often paying £20 - £25 for a RCBO and as little as £2 for a MCB.

We have a newish tumble drier that exhibits quite high leakage at times and has caused trips - certainly when we still had a whole house RCD shortly after moving in.

Even if not, one can add some cable length to one leg if required to get a better balance.

I don't think that assertion is necessarily true. Open circuit conductors or high resistance connections are faults that occur on the termination side of the sockets, not the users side. So while you may damage socket by filling it with crud, it ought not make any difference to its performance connecting bits of a circuit together (unless it routinely gets very hot!)

I don't think he was arguing against plugs and sockets, but was suggesting that a radial is preferable with kitchen plugs and sockets.

Sounds quite sensible really.

[NT]

Given that the kitchen has almost all the high power loads that will run on plugs, do you not think it would be better to run the usually 2 rings, upstairs and down, both into the ktichen to divide the load? If you have one ring just for kitchen, its shedding close to none of the peak load.

NT

[ARWadsworth]

Given that the kitchen has almost all the high power loads that will run on plugs, do you not think it would be better to run the usually 2 rings, upstairs and down, both into the ktichen to divide the load? If you have one ring just for kitchen, its shedding close to none of the peak load.

NT

That could result in a massive waste of cable and a possible volt drop problem.

Adam

[John Rumm]

While there are no hard and fast rules, and it is wise to be open to the options presented by particular house layouts etc, I would be less keen in mixing it up this way since to work safely in the kitchen you may end up having to turn off all the power circuits in the house.

There is some advantage to having circuits group geographically related things together as well as logically related ones.

[Tim..]

Surely the more sensible approach would be a separate ring for just the kitchen (whether fed by ring or radial), and then convential rings for both up and downstairs ?

Tim.

[John Rumm]

In most cases, yes unless the property is large - in which case an extra one for the utility room can be good, or small in which case one for kitchen and one for the rest can be ok etc.

[Fred]

Our (few) trips have been caused by the iron as well. I wonder why these are prone to do this?

[Fred]

I hadn't thought of specifying radials. I know there is usually a radial for an electric cooker but had not thought of one for the washing machine, tumble dryer, and dishwasher. I thought that in the UK we were encouraged to use rings everywhere and radials were for lighting and Europeans ;)

That's an interesting thought. We would need the heavy users in the middle of the ring but would that fit with the geography of the kitchen? If not, I guess a radial might be a better idea. Another reply mentioned 4mm^2 T&E* for this purpose. I wonder how bulky it is to handle (connect to the backs of sockets etc)?

Is a kitchen quite unique in that you can plan ahead where loads will be on the ring? After all, isn't the idea of having plugs and sockets to give you the versatility of plugging what you like, where you like?

Since these big loads are only found in the kitchen, perhaps balancing is less of a concern in the rest of the house?

*good to use it for something, I understand it isn't used for much else because of its small CPC.

[Fred]

I didn't know that about ovens, thanks.

I think you are right that with the big appliances taking such a big load, it might be a good idea to give the kitchen its own supply.

Thanks again.

[John Rumm]

You can use whatever makes sense in the circumstances. Lots of radials means a wide consumer unit...

If you want a 32A protected radial then you need 4mm^2 T&E, ordinary 20A radials you can do in 2.5mm^2 usually. 4 is quite bit harder to work with - especially when you want a branch (i.e. three sets of cables in a single accessory). However with deep backboxes and a sensible choice of wiring accessory its doable.

A kitchen is slightly different in that you usually have a good idea of where the big loads will be. The small stuff will move about, much as it does on any other circuit, but there are only usually a limited number of places to locate a DW, TD, WM etc.

Well, in some ways more of a concern... in a general domestic ring, you will have lots of diversity, lots of small loads, and things will get moved about to a certain degree.

With a kitchen you need to think about the layout a bit. If its 20m from the CU then it hardly matters, anywhere is near enough "in the middle". Ig however the CU is in the kitchen right next to where you expect to locate 6kW of load, but you need another 30m of cable to cover the rest of the sockets, than a bit more planning is needed if you want to do it in one ring.

This is often a sticking point, and can limit circuit length. One could argue less so in these days with RCD protection being far more common, although its still good to design circuits that are intrinsically safe without having to rely on the RCD for fault protection.

[John Rumm]

Another reason for a dedicated circuit is a kitchen tends to have more than its fair share of things with mineral insulated heating elements - these can exhibit high earth leakage, which will make RCD trips more likely. A separate circuit with its own RCD will tends to reduce the liklihood of a nuisance trip in the first place, and mitigate its effects more should it happen.

[Fred]

Thanks. I had almost been talked into using a beefy radial for the washing machine and tumble dryer. Like you said before, they are big loads, so I thought it might be no different to giving a cooker its own radial. However if we go for a worst case scenario of 3kW each,

6000/240=25A so we are definitely in 4mm^2 territory. I'm not planning on any branches but if the wire is bulky and stiff and a pig to handle, I'm tempted to go back to the idea of a 2.5mm^2 ring.