Extending ring main

17 Feb 2021
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United Kingdom
Hi after some help.i an having a conservatory built.and to power and light it.i want to feed it from the downstairs ring 3 sockets one interval light and one outside light.from what I have read I can't extend the ring from the sockets and have to break into th the wiring with a junction box is this right. Do I need to do it at both ends of the ring .my sockets are fed from above. So can I break into the ring just above the socket and use a wagi box
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The rule book says your allowed 3% volt drop for lighting, and 5% for everything else, I would not expect an inspector to worry about volt drop, however in the main a conservatory means the LABC can stick their noses in, so dotting i's and crossing t's may be required.

There are many ways to extend a ring final, but in theory first step is to measure the loop impedance to see if near the limit or not, that is all well and good for an electrician with a loop impedance meter, but without that meter the safe option so not to exceed the impedance limits is the fused connection unit (FCU).

Since it is from a ring final, you can't really have a new circuit even if by definition a circuit is "An assembly of electrical equipment supplied from the same origin and protected against over current by the same protective device(s)." as that would not make sense in English to have a final final. So you can with the exception of special locations fit a fused spur from a ring final without notifying, and the limits for a 13 amp fuse is 2.42 Ω so unlikely to exceed the limit when the ring final is 1.44 Ω, so the FCU is likely the best option.

Using a grid system you can have a single socket and a fuse in a double socket back box, which is how I extended a spur. IMGP7387.jpg I use Screwfix LAP range. There is enough room for two fuses and a socket so could take both lights and sockets from that, and still have a socket. The advantage is your unlikely to exceed the loop impedance limits.

If actually extending the ring, the limit for lights is 16 amp, so you could use a switched FCU as the light switch and a 3 amp fuse.
Thanks Eric for your reply .this is what I was planning. For extending ring and doing the same on the other side of the room to continue the ring.do you think that is practical
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I don't understand your diagram.

Where is the second cable that must be attached to the existing socket and where does it go?

Why do you need a junction box?
Sorry not very clear on the drawing. Hope this gives a better idea.will do a more detailed drawing if still not clear.i thought you have to tap Into the circuit wiring to extend the ring .with a junction box at either end
Yes that would be alright - as long as you remove the existing cable between the living room sockets making sure it does not go anywhere else in between.

Can you not access the cables at the living room sockets so that you do not need junction boxes?

Junction boxes must remain accessible unless you use Maintenance-Free ones.
16162589172188430870517929731939.jpgthe two sockets in the lounge ar fed down the wall with 2 cables.was going to put cable joints in wagi boxes
You can't just connect another cable to each socket without finding out where the two cables go.

Well you could but that wouldn't be extending the ring.

Is it a bungalow with loft above?
No it's a small terrace.sorry a bit slow grasping this.do you mean taking the live cable out from the first socket.and the live in cable from the second socket.and then feed the new sockets to the sockets I have taken the cable out .so I end up with 2 cables in lounge sockets
If your socket box is a 35mm one you would have room to extend the ring from there.
Disconnect one cable from the back of the socket, run your new pair of cables round your extended ring. Connect one into the socket and the other join to the previously disconnected cable with Wagos.
Hi Timbo ithanks for your message is this what you were thinking of

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