New sockets off ring main

[Spence129]

I need to add 3 new sockets off of a socket, the current socket is on the ring main and won’t be used. So will use a blank plate. I know I can only have 1 spur, but can I create a mini ring, so the blank plate socket will have 4 live, 4 neutral and 4 earth, I’ll connect earth to backplate and then join the 4 live and 4 neutral, so one cable will go through the new sockets, and one from the last socket back to the blank plate socket. Is this acceptable?

Thank you!

 

[robinbanks]

join the 4 live

Using how many connector blocks? One 4 port wago (for example), or two 2 port ones?

(I'm asking if you're proposing extending the ring, or creating a spur that is a ring that attaches to another ring in only one place)

 

[Spence129]

Using how many connector blocks? One 4 port wago (for example), or two 2 port ones?

(I'm asking if you're proposing extending the ring, or creating a spur that is a ring that attaches to another ring in only one place)

I assumed I can only add one socket on a spur so was thinking I should extend the ring? I assume that means I need to use 2 2 blocks?

 

[EFLImpudence]

I need to add 3 new sockets off of a socket, the current socket is on the ring main and won’t be used.

Ok.

So will use a blank plate.

Why?

I know I can only have 1 spur,

The cable is the spur and you could have more than one from the same place.

but can I create a mini ring,

No.


Easiest way is to connect a 4mm² T&E cable to the existing socket and run to as many new sockets as you want.

 

[Spence129]

Ok.


Why?


The cable is the spur and you could have more than one from the same place.


No.


Easiest way is to connect a 4mm² T&E cable to the existing socket and run to as many new sockets as you want.

So if I run 4mm cable I can just spur the 3 sockets?
The reason I’m using a blank plate is because the current location will be covered by kitchen end panel and space may be a little tight.

 

[ericmark]

I have used either a grid switch 4 unit plate with two sockets to split ring final, or a twin back box again splitting the ring.

But the main point is inspecting and testing, a old ring final has a limit of 88 meters, when the permitted volt drop was 4% and now 106 meters now it's 5%, as to how much volt drop matters is up for debate.

The loop impedance should ensure with a 5% safety margine it will trip with a short circuit, so 1.37 ohm, so the first step is to find out the last certificate and see how close you already are to the limit.

 

[EFLImpudence]

So if I run 4mm cable I can just spur the 3 sockets?

Yes.

The reason I’m using a blank plate is because the current location will be covered by kitchen end panel and space may be a little tight.

Ok.

 

[robinbanks]

Easiest way is to connect a 4mm² T&E cable to the existing socket and run to as many new sockets as you want.

The way that reads, you appear to be advocating that you can run an unlimited number of sockets on a unfused spur so long as the cable is 4mm?

I don't think I've ever seen anyone else advocate this, the usual advice being a sole socket (single/double) on an unfused spur..

Is the assertion that it's impossible to overload a 4mm cable before the ring final's protection device trips?

 

[EFLImpudence]

The way that reads, you appear to be advocating that you can run an unlimited number of sockets on a unfused spur so long as the cable is 4mm?

You can. Think about it.

I don't think I've ever seen anyone else advocate this, the usual advice being a single socket on an unfused spur..

Unfused spur of 2.5mm², yes.

See: Appendix 15B.

 

[robinbanks]

You can. Think about it.

Oh, I get it (from the perspective that if it was a radial right from the CU it'd be 4mm), it's just I do wonder how much mental resistance to the approach one would encounter given that no one ever talks about it

 

[EFLImpudence]

it's just I do wonder how much mental resistance to the approach one would encounter

Does it matter? Would that resistance be valid?

given that no one ever talks about it

Talk more about it. It shouldn't take long.

 

[ericmark]

We were advised that we should check for fig of 8 wiring, I can see the point if the join is near the origin, but not near the centre, this has been talked about before, and we considered that if the suggestion in the appendix is followed and non portable equipment over 2 kW has dedicated supplies it is unlikely to cause a problem.

So there are two common ways which could cause overloads, supply to outbuilding and washer/dryer, it is rare for an immersion heater to be connected to a ring final.

The problem is the DIY guy will be unaware about the warning in the appendix, so easier to say no more than one spur per socket on a ring final.

 

[veedee]

The cable is the spur and you could have more than one from the same place.

So if you have a socket on a ring circuit, theoretically, you could have 10 spurs from that one socket on the ring?

The only limitation seemingly being, how many wires you can squeeze/screw into the socket connections blocks?

Easiest way is to connect a 4mm² T&E cable to the existing socket and run to as many new sockets as you want.

I am confused.

Socket A is on a ring circuit.

With One 2.5mm twin and earth cable coming in from the previous socket and One 2.5mm twin and earth cable going from Socket A to the next socket in the ring.

If I wanted to add 3 new sockets, what would need to be done with the 4mm cable and what do i do with the existing 2.5mm cable that's already in socket A?

Apologies if this comes across like i am high jacking the thread.. This is just fascinating to me

 

[robinbanks]

If I wanted to add 3 new sockets, what would need to be done with the 4mm cable

Add it to the terminal connectors along side the 2x2.5mm cores already there forming the ring

and what do i do with the existing 2.5mm cable that's already in socket A?

Leave them there; they're the "from last accessory" and "to next accessory" of the ring

The concern outlined by Eric above (which makes sense and is fairly often talked about) surrounds relative resistances of the two sides of the ring; if you were to do this "4mm and 3 sockets"
off of a socket that was 1m away from the CU and the rest of the ring was 49m of cable, and you plugged in five 1.5kw kettles to your spurred sockets then you can end up with the lions share (49/50ths) of 32A flowing down the 1m of 2.5mm side of the ring, and that exceeds the current carrying capacity of the wire, but not the breaker, in all installation methods. Whether the subsequent heating and rise in resistance of the 1m section would cause things to even out before a serious problem occurred, I haven't worked out.. but a spark looking at the job could make a call on whether this situation is likely to arise (how evenly loaded are each side of the ring, and how likely is it that this spur will contribute disproportionately to the load on the ring), whereas a non aware person may not..

Keeping a ring doesn't solve the problem, by the way; it you put 3 doubles immediately adjacent each other, 1m from the CU and then had the same 49m on the rest of the ring you've still concentrated the load on a point where the two sides carry disproportionate currents

 

[veedee]

Add it to the terminal connectors along side the 2x2.5mm cores already there forming the ring


Leave them there; they're the "from last accessory" and "to next accessory" of the ring

So I run the 4mm cable from the existing socket on the ring to the new socket.

Is the new socket also on the ring main or is this a spur?

If this is a spur, why not just use 2.5mm cable?