Extending ring main

[DIYSOS2018]

Hi folks

Looking to extend my ring main as currently have a spurred socket coming off an existing spurred socket.

Based on the existing sockets placement I think it should be an easy enough task but just want to check my understanding of things is correct.

Drawing one (forgive the poor art) is current setup, and drawing 2 is proposed setup.

thanks

 

[EFLImpudence]

Just replace the spur cable with 4mm² twin & earth.

 

[DIYSOS2018]

Just replace the spur cable with 4mm² twin & earth.

thanks but I don’t follow how that helps as I’m still spurring off a spur?

 

[EFLImpudence]

Yes, but the cable is then adequate for the 32A of the ring circuit MCB.

 

[sparkwright]

To clarify, the cable between 'socket one' and the 1st 'spurred' socket is the one that would need to be replaced with 4mm2 cable.

If, in addition, the cable between the 1st spurred socket and the 2nd spurred socket was also 4mm2, this would make adding a third spurred socket in the future easier.

 

[DIYSOS2018]

Thanks both for the replies. Can either of you humour me though. If I went with the original plan of extending the ring main using 2.5mm2 cable per the rest of the ring main would that suffice?

 

[sparkwright]

Yes, that would be fine, probably the more logical thing to do, particularly from a testing point of view perhaps.

 

[DIYSOS2018]

Great thanks

I’ll be honest I’m still not quite following the unlimited spurring off an already spurred socket so long as 4mm2 has been used but I’m not a spark

 

[sparkwright]

One 2.5mm2 cable on it's own is not allowed on a 32amp circuit.

Two 2.5 cables in a ring ARE. That's a bit like a 5mm2 cable - if such a thing existed.

If you spur a cable DIRECTLY from the ring, and use a cable rated at 32amp, such as 4mm2 or greater, you have in effect extended the ring, rather than having a weedy single 2.5mm2 spur cable which will only be cable of supplying one socket.

A 13 amp fused spur can supply an unlimited line of socket, if fed from the ring, or a single spur from the ring.

Not the most scientific explanation, trying to keep it simple and easy.

 

[DIYSOS2018]

Really helpful thanks sparkwright

So playing devils advocate here. Going back to photo 1, my current setup. Rather than mucking about with extending the ring main, or stripping back and re running 4mm2 cable, would running a second line of 2.5mm2 cable from socket one and the spurred socket give me what I need?

 

[sparkwright]

I don't understand why in diagram 1 the socket marked 'spurred socket' is wired directly to the ring...

 

[DIYSOS2018]

I think your looking at ‘2’. They seem to have uploaded in the wrong order but the diagram number is over at the far left of the page.

 

[sparkwright]

Oh I see.

Yes, you could do that.

At 'socket 1' you would then have 4 cables.
Electrically it would be safe to join all four cables to safe, but wouldn't be a true ring, more like a figure of 8, and a potential nightmare for testing and fault finding in the future, so I would advise against that.

So you would therefore have to join one old cable and one new cable together - in connectors in the socket box, or a maintenance free 30amp junction box under the floor.

And connect the remaining old cable and remaining new cable direct to the socket.

 

[DIYSOS2018]

Is there a simple drawing that can explain your figure of 8 reference for me? And also the bit about the connectors?

 

[sparkwright]

Using the connectors will make the circuit a complete ring (with just one spur).

Every socket will have two cables (expect where the spur is).

This way you will be extending the ring (expect for the one spur).

If at 'socket one' you had all four cables directly all joined together, it wouldn't be a true ring. At this point you would have an interconnection, making the ring into a figure of eight.

Using the connectors makes it a true ring.

Draw it out with the four cables joined together.

Then do a drawing with the two cables jointed, and the other two connected to the socket.

If you trace all round the diagrams with your finger you'll see one works out to be a nice continous ring, albeit with one spur.

You should see the difference.