Is my main socket ring too big?

[Paul]

I have a question for those expereienced electricians among us. I am buying a new house, and now that the second fix has been done and the CU installed I can see that there is only a single ring serving the whole of the house sockets. (additional circuits are: lighting upstairs inc smoke alarms, lighting downstairs, electric cooker).

I have serious reservations about this, as I was expecting two rings, one upstairs, one downstairs.

I have done some reading of the uk.d-i-y FAQ, purchased IEE onsite guide to

16th edition wiring regs, had a read on the web and spoken to the NHBC. The general consensus of all these is that the regulation states:

- Ring should not cover more than 100m^2

And thats about it. Now I am pretty confident that with a tumble dryer or washing maching typically pulling up to 2-3KW each (washing machine is cold draw only - Bosch), that all I have to do is boil the kettle (3KW) or have the misses use a hairdryer (2-3KW) on washday and the ring will trip. Thats not taking into account loads from things like Dishwashers, computers, TVs and the like. This concerns me as (a) I have 2 computers I usually leave on

24/7 and they will not like it and (b) I have an alleregy to setting the clocks on everything electronic and can barely cope with twice a year for daylight savings!

Looking at the builders brochure, although their figure of 1000sqft would mean 93m^2, they have taken the main foot print of the building. Calculating with the protruding garage area at the front, and the protruding kitchen area at the rear (all served by the same ring) the foot print is over

100m^2.

My Question: Can anyone tell me a way I can express the single ring being overloaded referencing the IEE regulations?

I know that the 100m^2 figure is just a guide, but there are 34 sockets fed from this ring, and I am sure I will be using nearly every one; its just not up to the job. I am not sure how to prove that though quoting the regulations, which is what I am going to need to do to get the builders to take notice.

Thanks for any feedback

Paul

Email: paul at javajedi dot com

[Andrew Gabriel]

Would be helpful if you gave some idea of the size of the house in terms of number/type of rooms. I'm presuming a 100m^2 house can't have 4 bedrooms and a utility room, but maybe I'm way off?

Washing machine is high power only whilst it heats the water, which is a short time.

Even a full kettle can only be on a short time.

3kW? Is her hair made of asbostos? I never saw a 3kw hairdrier...

No, because you haven't really given enough information to show that it is.

You have got a standard cheap professional installation -- that electrican was probably the cheapest quote the builder could get. If you want a better quality installation, then welcome to the world of D-I-Y...

[Christian McArdle]

The ring should be capable of supporting the expected loads as well as the

100m3 restriction. I can't see how this could be said to be the case. However, rather than an upstairs/downstairs split, it is most important that the kitchen has its own. The loads in the rest of the house without electric heating are likely to be tiny.

Sounds like they've blown the 100m3 anyway.

When partially rewiring my house, I've put several circuits just for the kitchen. One 32A MCB radial powers only the dishwasher, washing machine and tumble dryer. A 16A MCB radial does the fridge/freezer. A 32A RCBO ring powers everything else (except lighting).

Christian.

[usenet]

It's unlikely that all these devices will draw all that power simultaneously. Also, a hair dryer is usually only 750 to 100 watts, nothing like the 2-3kW you suggest.

What you should really do is add up all the things you are likely to have switched on simultaneously and then have a guess at the chances of things which are on intermittently coming on simultaneously. You may well find that the chances of tripping the circuit breaker are not all that great.

As you say the 100m2 is only a guide. 'Diversity' as outlined in the OSG should also be applied, however you can only do this when actual appliances are installed, the builders aren't really able to do it.

Having said all that I too would have expected two rings in a modern house. How big a house is it - i.e. how many bedrooms etc.?

[usenet]

The builder can't tell as it's not really possible to know what will be installed in new houses. If the house has no dishwasher, gas heating and cooking, etc. then one ring main might well be OK.

[Christian McArdle]

I would have thought that you could reasonably assume that a 100m3 house will have a dishwasher, tumble dryer, washing machines, kettle, toaster, oven, fridge freezer, iron and microwave in the kitchen. This is not a studio flat we're talking about. Most old houses of this size would have these appliances, let alone a brand new one.

Whether you can find a specific item in the regs preventing it, it is surely not best practice and easy to conceive of long term overloadings occuring. For the sake of an MCB and a few metres of cable, it isn't too much to ask to do it right. Also, I hope there is a non-RCD side circuit for the fridge/freezer. Very poor practice to omit this on a newbuild, when running cable is so easy.

Christian.

[Paul]

Thanks to all those that replied, some additional information:

- House style is 3 bed, integrated garage at the front (half-in-half-out style). Standard layout, i.e. no utility rooms or study etc downstairs or general fancy bits.

- Accepted that hairdryer was exageration, and kettle is temporal load, but point was if there is a situation that is going to occur on a regular basis, such as washing machine and dryer both on, and the kettle load pushed it over it would trip the breaker.

- It IS the builders expectation that all these things will be used in the property. Primarily becuase the kitchen layout has 3 600mm openings, for dishwasher, fridge and tumble dryer. So these loads at least are expected.

- There is no seperate ring/radial for the fridge, this I guess would have made it more acceptable but as things stand all appliances are on 1 circuit except the cooker and lights which have their own circuits.

- The socket circuit is all on the RCD, so stuck toast in the toaster is likely to drop the lot.. (fridge as well).

I guess what it boils down to, is as some have observed, you would expect 2 rings in a modern house. I especially expect 2 rings given that its a modern

3 bed, at modern 3 bed prices, and its taken me several years to get to the stage where I can buy one!

Apart from the load issue, I am also concerned about the earth. Modern devices have a lot of earth leakage if they have switched mode power supplies, although I believe this is now referred to as "high protective conductor currents". Well, apart from several computers, I am sure that all of video/dvd/hi-fi have switched mode PSU's in generating leakeage. Would this be a problem? (I doubt it, but I am going to ask. I worked for a company once that discovered one day that the top of the fuse box was missing on their consumer unit, as it had melted due to the heat in the main earth bar just underneath it!... lots switched mode PSU's = bad is the message I left with!).

I guess from what I have seen so far, its pretty standard practice, and I have to just live with the re-wire once I move in...

Cheers

Paul.

[Christian McArdle]

Nah. Consumer goods are designed to not require an earth as many markets round the world don't typically have earthed socket circuits. This is why you always get fried by modern televisions, as their surface voltages float off due to the internal 25kV generator. Without an earth to connect the RFI suppression capacitors to, there is no way of generating earth leakage.

Christian.

[stefek.zaba]

I'm afraid you're about right there. It's barely-compliant skimping on the part of the detail specifier (I won't dignify their actions by calling them either an "architect" or a "design engineer"); your floor area is probably just within the 100msq guideline (and it's only a *guideline* anyway, and the Regs aren't legally binding in themselves anyway). But it's poor practice, as you point out; the sage words of p.151 of the OSG, which suggests "consideration should be given to a separate circuit" for washing m/c, dryer, and wushdush to avoid unbalancing the legs of a ring will be answered by the builder as "yup, we considered it [and then thought about the extra 15 quid in materials and 30 in labour it would've cost, and rejected it out of hand]"; and annoying too, since putting in two or three rings (upstairs, down, and kitchen) would've been *much* easier during construction than after the fact.

Still, at least you'll find out all about the quality of the electrical installation when you do the upgrade - and you may be lucky (?) enough to find a serious enough violation of the Regs that you can get the builders to do a proper job (including the upgrade) as part of a hush-it-up deal ;-)

HTH, Stefek

[Lawrence]

Try speaking to builder about being unhappy, if no joy there and you do not mind creating ripples speak to building control at the council. It will probably be worth paying the builder £50 to split the ring main. It will be a darn sight easier at this stage. Otherwise it will be worth making a note of the cable routing for the ring main so you can plan how to split it later.

Much as I appreaciate the desire to have a freezer of the RCD, I would also not want to see the remaining kitchen appliances off the RCD. So if I wanted the freezer separate then I would run a separate cable on its own trip just for the freezer.

Lawrence

usenet at lklyne dt co dt uk

[Andrew Gabriel]

Nothing listed was contrary to building regs. (Maybe something else is, but getting that fixed won't solve original poster's concerns.)

I think that stage was passed before 2nd fix, and original poster said he is past 2nd fix.

Generally, when I rewire, I run two rings in the kitchen. One is not RCD protected, and feeds all the large non-portable appliances like fridge, freezer, washing machine, oven, dishwasher, central heating (if applicable), none of which represent significant electric shock risk, but in many cases represent some risk if their power were to be lost. Socket outlets are all deliberately fairly inaccessible and often unswitched. The second ring is RCD protected and feeds all the readily accessible socket outlets for portable appliances, which are the ones where RCD protection is most important.

[usenet]

Kettle, probably 10 amps, they're rarely 3kW Washing machine, maybe 12 amps Hair dryer -3 or 4 amps Total - 26 amps on a 32 amps circuit, still quite a bit of 'headroom'.

The fridge is pretty irrelevant in consumption terms.

There are really only three circuits, that does seem pretty stingy.

Why should stuck toast trip the RCD?

I think something has got exagerrated and or 'lost in the wash' here, the heating effect of the sort of earth leakage you are talking about would be negligable.

[Owain]

"Christian McArdle" wrote | Whether you can find a specific item in the regs preventing it, | it is surely not best practice and easy to conceive of long term | overloadings occuring. | For the sake of an MCB and a few metres of cable, it isn't too | much to ask to do it right. Also, I hope there is a non-RCD side | circuit for the fridge/freezer. Very poor practice to omit this | on a newbuild, when running cable is so easy.

I hope there isn't a whole-house 30mA RCD installed ...

Seems to me having one circuit where the design current of the circuit is foreseeably inadequate would contravene the Fundamental Requirements for Safety:

130-02-02 All equipment shall be suitable for the maximum power demanded by the current-using equipment when it is functioning in its intended manner

and

314-01-01 Every installation shall be divided into circuits as necessary to: (i) avoid danger in the event of a fault, and (ii) facilitate safe operation, inspection, testing and maintenance

Having only one socket circuit means if there is a fault on that circuit there is no power to use tools etc

314-01-02 A separate circuit shall be provided ... so that such circuits shall remain energised in the event of failure of any other circuit of the installation, and due account shall be taken of the consequences of the operation of any single protective device

This would also restrict the use of a whole-house 30mA RCD. Of particular concern is the fact that the garage socket seems to be on this circuit too.

The circuit is also going to have to be carefully designed. From memory, the Volt Drop of 2.5mm is about 19mV per A per metre cable (depending on mounting method). If we envision a 100m2 house as being a single-storey square 10x10m that means an perimeter ring of 40m. 40metres x 0.019 x 32A design current = about 24V or 10% of the mains voltage unless I've counted fingers wrong. Considering this could be powering the electric lawnmower at the bottom of the garden on an extension lead there is no spare drop really. There is also Zs of the circuit to consider, will it be adequate with the length of cable.

Of course, as the job is being done properly the Design, Installation, Inspection and Test three-part certificate will be signed by a competent person on all three parts, and the schedule of circuits will give cable length, conductor size, and Zs for each circuit, so it will be easy for the builder to demonstrate the Regs are being complied with by supplying that certificate together with copies of the signer's C&G or other qualifications as proof of competence.

Owain

[Chris Oates]

Not normally - at work I run SMPSs and nasty motors on RCDs Neutral currents get a bit weird with harmonics

[Paul]

Thanks for the feedback everyone, positive and negative. I can see there is some division on if its OK, or stretching regs, but clearly the consensus is its a poor solution. I just know now I am going to have to sort it out afterwards anyway, I am just pretty mad that I have such a "just within guidelines" result for the money I am paying.

I did a quick count last night, and I have 18 plugs under my desk alone (a few big loads, lots brick style PSU's) and if nothing else I am sure I am going to have lots of noise on one large ring (I can already listen to my ADSL router PSU on my cheap'n'cheerful unfltered clock radio in the mornings at my current place).

2nd fix has already taken place, and I can't see the builder doing anything now (painters are in). Thanks to Owain for the very detailed reply. I had considered voltage drop due to length of the ring, I will have to get my thinking hat on and do the calculations, this will be a real issue when taking an extension to the back garden if I wanted to use the garage sockets as you pointed out. In reply to your question, the CU is split, the RCD side has a single circuit which is the sockets ring, so I guess yes, the whole house is on a single RCD (except the cooker) and it is probably a 30mA device, I will check next time I am at the site.

As Stefak points out, the ring is supposed to be evenly loaded, but all they have done is run the ring round the ceiling joists on the ground floor pulling it up to the bedrooms and down to the other rooms. As the CU is in the garage, and the first stop on the ring is the kitchen the ring is massivly unbalanced!

I guess all I can do is obtain copies of the electricians certification for the installation to BS7671 when the sale completes. The NHBC warrenty will cover me when all the problems start, I could just do without settling in, then having to consider ripping walls/ceilings/floors apart to get an electricity supply that does not keep tripping...

I can see some people on the group think I am being dramatic, but I am a bit of a gadet freak with plenty of electrical appliances, and can assure you that my concerns are real.

Cheers all, just found uk.d-i-y, think I might be here for a while... very helpful group!

Paul

Email: paul at javajedi dot com

[stefek.zaba]

As the Currant Bun says, "gotcha!" The unbalanced loading on the ring strikes me as a clear violation of good design practice, and is *specifically* mentioned on the page of the OSG wot I quoted (and the note in the margin traces back to reg 433-02-04). I think it's time to put your concerns in writing: a *short* letter - try to keep it down to 1 page of A4 - saying you believe the design of the electrical installation to be inadequate for normal pattern of occupation (don't say "I'm a gadget freak", just say "dushwush, washmash, tumble-drumble" (or rather the more common forms of the names for those appliances!) and other kitchen appliances, plus normal appliances upstairs, make overheating of shorter leg of run to kitchen a foreseeable hazard.

(Also, if the cabling goes up and down between ground and first floors repeatedly in the way you mention, its total length may be getting close to the limits for a 30A/32A 2.5mmsq ring - 88/84m resp. for a normal Type B MCB: and that hacked design contributes materially to the unbalanced loading of the legs of the ring feeding the kitchen. The conventional design of an upstairs ring which would go up once, feed bedroom etc. sockets, and then come down, would be much more appropriate.)

Ask for a response in writing. Have you paid for the house yet? Can you retain money for (a) getting an independent inspection, and (b) rectifying? Make it clear you're questioning the design of the electrics in *all* the houses slapped up to this design, not some wacko requirements which your own current-consumption-obsession produces ;-) If you do want to pursue this you will need a qualified electrical installation designer's opinion to put up against theirsr. If you can face the investment of time and energy, you might find that one of the medium-sized local companies in your area would be happy to do this as a 50-quid inspection-cert job and throw in a couple-of-para amplifying letter as a way of venting their frustration at being undercut by whichever cabling-cowboy got the contract for this build ;-)

Only you can judge, of course, whether it's worth your while raising this amount of stink with the developers, or whether to shrug your shoulders and prepare for a wiring upgrade as you move in.

Good luck with whatever you decide - Stefek

[Andrew Gabriel]

I don't have any regs or tables on me to calculate what that limit is due to, but if it's the earth fault loop impedance, then the RCD effectively overcomes that limit. If it's voltage drop, then the RCD doesn't affect it. (ISTR the OSG has a note to say if the limit is due to earth fault loop impedance against the table entries.)

[Christian McArdle]

I thought it was seriously frowned upon to rely on an RCD for earth fault impedence problems, unless it was a TT system and the problems were due to (relatively) high earth rod impedence?

Christian.

[Andy Wade]

You can debate that one until the cows come home, but it's an academic point in this case. Type B MCB protected rings since are voltage drop limited.

[Mike Tomlinson]

In article , Paul writes

I would expect three; downstairs, upstairs and kitchen/utility.