adding a spur to a radial circuit

[Joneedshelpwithwiring]

I gather it is possible to add 1 spur to each existing socket on a radial circuit. Can you add 2 single sockets to a double socket and if so do you do it in series or in parallel?

 

[Millennium_Boy]

Yes you can, providing the cable rating is adequate for the MCB rating in the consumer unit, and note any floor area restrictions.

 

[Joneedshelpwithwiring]

So do I connect it in series? Am perplexed as to how it would work. Have read the B & Q brochure which is a little unclear. Re: the floor area think it should be OK as there are 2 radial circuits in a room of 30 sq metres (2 rooms we knocked together)

 

[ban-all-sheds]

All sockets have 3 terminals on them - Live, Neutral and Earth.

Ignoring spurs for a moment, they are all wired with a cable which runs from one socket to the other, connecting L to L to L to L..., N to N to N to N etc.

The only difference between this diagram of a ring, and a radial, is that with a radial the cable stops at the last socket and does not return to the CU to complete the ring.

It may seem as though this means they are in series, but electrically they are all in parallel.

To wire the spur sockets you want you will need to run a length of cable (2.5mm twin & earth, assuming that your existing circuit isn't 4mm) from the L/N/E terminals on the back of an existing socket to the L/N/E terminals on the new one.

It ought to be a simple and straightforward task, but if you've read a leaflet from a DIY shed and you're having problems understanding it then perhaps you should do a bit more learning before you tackle the job, or consider getting an electrician in.

The site that has those diagrams is good one, and I believe that the Which? Book of Wiring and Lighting is useful - I've not looked at it but it gets lots of recommendations.

 

[Joneedshelpwithwiring]

Thank you very much for your help. The specific point I am unclear on (and cannot find information about anywhere) is this. I understand that I should only put one spur on each existing double socket. On one of the double sockets I want to put 2 single sockets. Do I wire both single sockets into the existing double socket so that it will then have 3 cables coming out of it or should I take a spur from one single socket spur to add the next one?

 

[ban-all-sheds]

Thank you very much for your help. The specific point I am unclear on (and cannot find information about anywhere) is this. I understand that I should only put one spur on each existing double socket.

Correct

On one of the double sockets I want to put 2 single sockets. Do I wire both single sockets into the existing double socket so that it will then have 3 cables coming out of it or should I take a spur from one single socket spur to add the next one?

The implication of the highlighted bit in your post is that the existing socket only has one cable wired into it right now, which means that it is at the end of the radial circuit, so attaching 2 more cables to feed two more sockets is actually extending the radial and adding 1 spur, which is OK. Or you could go from one new socket to the next - it all depends on which is easiest for you, really. And in both cases your new sockets can be double ones, which I would advise - there's little difference in cost, there's little more work involved, and you can never have too many sockets.

 

[Joneedshelpwithwiring]

Thank you so so much - you've clarified everything for me. Feel totally confident now. I really appreciate your help!

 

[ekon]

..just re-read this interesting thread. I have just one radial circuit in the house with a 16Amp MCB. There is only the one single socket on this circuit..absolutely sure of that and it's in the kitchen and is intended for a washing machine. We did use it for that purpose but since I built a laundry room we run a dishwasher off it.

Because we can't get at that "radial socket" without completely pulling the dishwasher out I fitted a 13A plug (which is plugged into the "radial socket") to a short length of round 2.5mm cable and ran it to a pattressed double socket which I fitted inside the adjacent kitchen cupboard.. which is accessible. I put the dishwasher's plug (also rated at 13A) into that double socket and run it's power cable back through cupboard sidewall to the dishwasher.

So I have one spare socket in this cupboard and I want to run power outside. I already have a non-RCD but external/weatherproof double socket. If I put another 13A plug on a 2 ft length of suitable
(2.5mm) cable I can run it through the external wall to where I want the external sockets to be sited. I would replace the standard double-socket I'm using at the moment with an RCD protected socket.

I realise that I can only draw around 3100 watts in total ..at any one time.. from all three "operational" sockets (the dishwasher and the two external sockets). Despite trying I cannot find what the dishwasher wattage is (usually about 1000watts?) ..but given that we normally set the dishwasher to go when we got to bed because they're quite noisy things (..yes we have smoke alarms) I cannot see a problem occurring with using all 3 sockets at once. We don't want to run anything "heavy" outside anyway and presumably if we did overload things the 13A fuse in the " radial socket" plug would blow..even before the MCB tripped out.

If I am correct in my reading on here I should strictly be taking the feeds for those extra sockets from the back of the radial socket..on to the back of the next..etc. Using fused plugs at 13Amps only drops the amperage by 3A and I dont think that will be critical given the power loads likely.

Is there anything inherently wrong/dangerous in doing what I have done/propose as opposed to what's been suggested in previous posts?

thanks for reading.

 

[JohnD]

Cyprus wiring might have different rules to UK wiring, I don't know.

BTW instead of replying to a January 2004 post you might do better to start your own.

 

[ekon]

>John..just trying to keep the number of threads down whilst also bringing this interesting post to the top. The first time since the last post in January of this year it's been bumped up..but yes maybe you are right in terms of getting feedback.

As they say "this is Cyprus" and some practices here would make your hair curl..eg "scaffolding"!? on new buildings.

That is why I wasn't too obsessed with the regulations over here..but what is safe and good practice in UK..thats good enough for me.
From what a friend of mine, who was a sparkie in UK all his life ,said to me ..maybe Part P etc was a bit over the top??

I saw this thread as explaining pretty clearly (to me at least) what radial circuits do and can have done to them. Something that might interest others too. I just wondered if my "variant" using sockets, suitable cable and 13A plugs.. instead of working off the backs of sockets.. was in any way dangerous. I don't know what the regs say in UK but if it's in any way dangerous to do what I've done/propose to do then I'll start again.