Help please with Spurs and Ring Mains (UK)

socket and spur off off that away from the socket,thaen that is within regulations.is the existing spur within reachable distance from the cooker hood?if so then theres nothing stopping you from taking your supply from the outgoig(eg fused) side of the spur.Regs allow for 1 spur from each point on a ring main,but also any point on a ring main,so technically,you could break in six inch away from the socket and be within regulations.Also,are you certain its a ring main?Turn off power,remove socket and ensure you have juice at both reds(CAREFULLY)borrow a multimeter,dont trust a 59p neon screwdriver.Alternatively,fit a plug top to the hood through a 3amp fuse and everybodys safe :-).

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Thank you for you prompt reply

Hmm .... Just as I suspected, hence my asking for advice.

Unfortunately none of your suggestions are convienient so it seems as if I will have to do some demolition work.

Unless .....

Q) Is it permissible to have the spur outlet for the hood and the socket outlet on the same spur ?

Thanks again

You are misunderstanding the recommendation. There's no regulatory reason not to take multiple spurs from the same point on the ring. The limit on spurs is a total limit, and is to stop you just gradually growing the circuit well beyond its original design (there are rarely any spurs on a newly installed ring circuit).

What you do need to consider is that ring circuits are not good for large loads concentrated in one place, particularly near one end of the ring (but a cooker hood is a tiny load), and that you will need a socket with good quality terminals in order to get the 4 conductors in and a deep box to hold all the wiring. However, these points are certainly achievable.

i think you will find you are wrong mr gabriel,i did a c&g course and have my 16th edition wiring regs(c&g 2381)as well c&g 2361/2362 and unless the regs have changed very significantly sind 1997 you will find that one spur is allowed for any one point on the ring.A multiple radial circuit is only allowed after a suitably rated fuse-eg straight from c/u or multiple outlets on fused side of fcu.

I am not sure how true this is,but i have recently heard from others quite high up the trade that ringmains will be phased out in the uk in the next few years,and all circuits will be radial,albeit with larger cables/smaller protective devices,if anybody can confirm??

As for the original poster,there would be nothing to stop him taking his supply through a 5a round pin plug and socket arrangement from his lighting circuit,which will probably easier for him.

That would seem to take us back to the 1950's and before.

AIUI, the "main" reason for the ring was to bring in the Earth conductor from two separate circuits, thus improving the safety of the installation.

cables/smaller

They haven't, but this isn't part of the wiring regs in any case, it's a recommendation in the On-Site Guide.

I don't have the On-Site Guide on me, but I'm pretty sure the wording is simply number of spurs not to exceed number of outlets on the ring.

That's different -- a single spur is only allowed to feed a single outlet or FCU unless the spur is fused.

30A ring circuit was introduced in 1947 as a measure to save copper when it was in short supply after WWII, although it was perhaps another 10 years before it completely displaced radial circuits in new installations. It uses significantly less copper than the radial circuits. Also the number of outlets people required was increasing, which would have directly increased copper requirements for radial circuits, but increasing the number of outlets on a radial circuit required very little extra copper. The ring circuit was also designed such that it was quite easy to convert a house from radial to ring -- some of the cable runs could be used directly without rewiring them. However, I don't think such conversions ever became common -- mostly it would be done when the current installation had deteriorated and needed complete replacement, so reuse of wiring was not an issue.

Although 1947 might seem a long way back, in terms of wiring design it's one of the newest schemes in the world and turns out to be remarkably safe, flexible and expandable when compared with most other current schemes which are older.

I understood rings were introduced because it allowed a relativeley small cable to effectively double its capacity,which i supposed is an offshoot of mr Gabriel's theory.

i certainly hope they dont do away with them,can you imagine wiring 6 or 7 radials for 1 small house?

another thing that always suprises me is the number of properties with a mainsboard under the kichen sink!

ring

Yes, it used exactly the same cable as the 15A radial circuits, but could safely serve very many more outlets. The cable was actually good for 20A anyway, and in making it a ring, we only allow a 50% uplift, i.e. to 30A to allow for uneven loading round the ring.

There's never been requirement to use ring circuits anyway.

20A radial circuits for socket outlets are not uncommon, and 30A is allowed too. Of course, the ring is the most flexible and cheapest to install for anything over a few outlets, so that's what is normally used.

Not come across one of them.

Thank you one and all who have taken the time to contribute on this topic ...... I have read this thread again annd again and find it remarkable that such different interpretations of the regs/codes of practise etc exits concerning what I thought was a basic requirement.

To be absolutely safe I have now decided to provide a supply to the cooker hood by using a junction box to break into a separately fused radial feed, to what was originally an immersion heater but now suplies the central heating boiler. I will use 2.5mm T&E to connect the JB to a switched fused connection unit (with a 3A fuse).

I hope this meets all the requirements of good practise and regs.

Thanks again Jim Burton