Extending a ring main

21 Dec 2009
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United Kingdom
I have just added a new room alongside my existing lounge and wish to extend the ring main from the lounge to the new room. The wires in the lounge are inaccessible so the easiest way to do this would seem to be as follows:

- Convert an existing 2 way 13 amp outlet in the lounge into a junction box.
- Break the ring in the junction box and loop two new wires through the wall to form the extended ring.
- Replace the 2 way 13 amp outlet with a new box alongside the junction box using a spur from the junction box (clearly connected to only one side of the ring).

Is this an acceptable way of extending a ring main i.e. would it pass a NICEIC inspection ?

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Assuming the double socket is directly wired to the ring with two cables, run a new cable from here to a new socket, to next, to the next, etc, etc, then run a cable from the last new socket back to the lounge.

At the lounge socket join a new cable to an old cable with line crimps.
Then connect the remaining new cable and the remaining old cable to the actual socket itself.

Before doing any of this confirm the cables at the lounge socket are directly part of the ring.

Ring circuits shouldn't exceed 100 m square of floor area.
Ron- If you are getting a plasterer in to do the new room after you've done the sockets, tv, lights, bt and internet stuff I'd not worry too much about the odd chase in the old room.

You could run 2 x cables 2.5mm TE out from the existing lounge socket.

You would disconnect one side of the existing cabling and terminate that to one of your new runs with choc blocks (and nicely placed at the rear of the back box). The other new cable takes up the now spare position on the existing socket (from where you took off and joined the cable).

You then have a fully functioning ring with access to the only junction (the cables on the choc blocks) via taking off the socket.

You will have to make sure there's enough depth in the socket back box to take the total of 4 cables, 2 old, 2 new and the choc block.

Tesing would be a good idea, have you a martindale socket tester, and a multi meter for basic continuity ?
Thanks Guys ... as a qualified electrical engineer but not C&G qualified and NICEIC certified, I feel that I am competant to do the installation myself. However, my building control guy has said that he won't issue the completion certificate without a NICEIC certificate and registration. So, I really have no option other than to get an electrician in to approve what I have done (I've found a local company who is willing to do this for under £200 .. which is still IMO a waste of money).

So, without reading the whole of BS7671 Ver 17 and Part P, is there a small checklist of things to do in order to make sure that my installation will be approved ? I have the diagram in Appendix 15 of BS 7671 and will be following faithfully the guidelines for ring main arrangements.

Question for Sparkwright .. if I crimp wires, how do I then insulate them ? Presumably not tape but heatshrink could be a possibiity, I suppose. Chris5's suggestion of a choc box seems like a good one.

BTW .. I do have a good quality digital multimeter.

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for 2.5mm cable and 1.5mm cable you get insulated crimps, if you want a bit of belt and braces then heat shrink them too.

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