Extending ring main right after consumer unit

[JohnL24]

Hi all,

Trying to add two new sockets and having hard time deciding from where to extend the ring main. There is a socket to the right but I can't quite find where it goes and there is no real way to check without ripping into the wall and there is nothing underneath so it means it runs up which would be a huge pain to run the cable down again.

Can I cut directly into the ring main cables coming from the consumer unit and extend the ring main using 30 amp junction boxes?

Cheers.

 

[John D v2.0]

Can I cut directly into the ring main cables coming from the consumer unit and extend the ring main using 30 amp junction boxes?

Yes assuming you're competent to do the work and ideally test the circuit before and after. The junction boxes you mention would need to be Maintenance Free ones not just those basic screw terminal ones as they come loose over time. They need to be rated a minimum of 20A.
Keep an eye on the overall ring length if its a big house it might be close to the limit.

 

[ericmark]

To extend the ring final start point is at centre of ring measure the loop impedance, the loop impedance is what often limits a ring final length, the other is volt drop, we get the figure of 106 meters of 2.5 mm² cable but that is depending on design figures used, close to the consumer unit one can over load a ring final.

In theory you can break in where ever you want as long as either accessible or using maintenance free JB. It is important to test and inspect it is so easy for a ring to be in error split into two radials and since it would still work, but could be over loaded, testing is required. Traditionally 1.44Ω was limit, now 1.37Ω but the cheap plug in testers with loop test normally have lowest pass point at 1.5Ω so to test means test gear costing £100 plus so in real terms not work doing as DIY.

OK I am sure we all do it without the test gear, and just use a multi-meter to test it is a ring, but still it needs some testing, if you don't know how to test, don't do the job.

Can you feed direct from CU using either a 20 overload or a fused connection unit?

 

[AndyPRK]

Another option you could do (people won't like it, and says its against regulations) is to remove the grey insulation off the ring cable under the floor board. (but NOT cut it).

i.e using a blade, cut down the middle about 2" where the bare earth/cpc wire is. Open up the cable.
Take the round 30A junction box and remove the grub screws.
Route the cable thru the junction box terminals. Work out where the insulation on the red and black requires removal (to pass thru terminals) and cut off with blade.

The advantage of this is to haven't changed the resistance of the ring. You haven't cut into the ring. The ring won't fail.
It's also less wires to wrangle into the junction box

Then take 2 cables from the junction box to each socket. (spurs)
Fit grub screws

 

[flameport]

A better option would be to remove one of the existing cables from the consumer unit and route that to one of the new sockets, then add a cable from there to the other socket, and another piece from there back to the consumer unit. No junction boxes required.

Those wonky and unsupported push fit pipe connections under the floor are a massive leak waiting to happen.

 

[ajohn]

In some ways it's often easier to run spurs.

Extending a ring involves cutting into it /breaking the connection some way, running to new sockets and then running back to the other side of the break. The load on the ring should also be evened out but if a cable carries current it warms up, resistance increases which encourages flow down the other leg of the ring.

Depends what you want but if 3 sockets would suite this part is useful as it can be run off a single spur

https://www.screwfix.com/p/mk-logic-plus-13a-3-gang-dp-switched-plug-socket-white/17315

Back boxes are available

 

[AndyPRK]

Did you not see the pic John where the backboxes are already fitted.

If the room is a kitchen then it’s nice to keep the ring.
But when you consider spurs can take 27A, and if you have to add 2 junction boxes just to have a ring, you aren’t improving the situation.

Its easy to say route cables back to the cu. it may not be so easy in practice.

 

[ajohn]

Did you not see the pic John where the backboxes are already fitted

Whoops - looked too quickly and thought the grooves were plaster.

He could break into both ring cables locally and add one spur to a socket to each side of the loop - assuming both cables are there. It's then effectively still a loop.

 

[RF Lighting]

As flameport has said, the only proper way to do this is to pull back one of the legs and actually extend the ring. Junction boxes should be avoided unless there really is no other option. Spurs are also not good especially as you’ve got the opportunity to do the job properly.

Also whoever cut through your skirting board to install those socket boxes wants to be taken outside and shot.

 

[ajohn]

There are millions of junction boxes - screw type including barrier strip that have been around for a very long time without causing any problems. The terminals on the back of socket are just as likely to cause problems and like junction boxes do cause problems when they aren't done up correctly.

As the photo identifies a wire to the consumer unit suggesting no connections off it the OP may be able to use it to pull a new length cable through. Might be a better option to attach something like this to it and pull that through first. The screwfix equiv didn't google but I assume they have similar First test would be that the cable can be pulled a little at each end without loosing it.

https://www.toolstation.com/steel-d...MIrJrC25qL6AIVCLTtCh2Q7w6UEAQYASABEgLODfD_BwE

 

[JohnL24]

Thank you everyone for your responses, really useful tips and information. I think I'll go with the removing one of the ends from consumer unit and taking it to the socket and then returning the other end from the other socket to the unit after. This way no cutting out junction boxes would be required

 

[RF Lighting]

There are millions of junction boxes - screw type including barrier strip that have been around for a very long time without causing any problems. The terminals on the back of socket are just as likely to cause problems and like junction boxes do cause problems when they aren't done up correctly.

I’ve repaired plenty of junction boxes which have failed, some of which have been in very difficult to access places, and some which have required the property to be damaged to access them.

The difference with a fault at a socket is that it’s easy to get to and very obvious where it is, and it is a necessary joint. A junction box is not. Remove the joint and the chance of getting a fault becomes zero.

It’s not always about doing what is allowed or can be got away with, you should be doing things the proper way every time, especially when it’s as easy as the OPs situation.