Why has my ring been split?

[paulg1]

I'm adding a stud wall to a dining room to form a new study and walk in cupboard instead. While I have the floor up (I'm also insulating between the joists) I was planning on adding a pair of new sockets on the new stud wall.

However, when investigating a little more it turns out that the dining room isn't on the main downstairs ring - it's on it's own little circuit with a 20A breaker on the consumer unit (cable is 2.5mm). Stranger still it looks like the room was originally one ring - but one of the sockets has a cable cut where it enters the back box so now the room is composed of 2 radial circuits.

Why would someone do this? It seems absolutely intentional. Maybe the cut cable was damaged in some way and it was easier to turn it into 2 radial circuits? The 20A MCB does look like it was put in at a different time to all the rest.

I'm thinking I should get an electrician in to turn it back into a ring (and add the sockets), but curious as to why it would be like this?

 

[securespark]

A 20A circuit for one room is plenty.

Are there two or more conductors in the MCB for the dining room sockets?

Have you found the other end of the cut cable?

 

[paulg1]

Are there two or more conductors in the MCB for the dining room sockets?

I can't see easily as it's all hidden behind walls / floorboards. I could take a look tomorrow if you think it's useful.

Have you found the other end of the cut cable?

Yep - it's goes straight to the next socket in the room where it is wired in as normal. The socket with the cut cable actually has two cut cables - the other one goes a meter or so and then is just hanging in the void under the joists around where a fireplace used to be. Maybe it used to feed an electric fire?

 

[sparkwright]

Sometimes if a section of cable on a ring circuit becomes damaged, it is far easier to disconnect the damaged cable completely, and make the wiring into one or two 20 amp radial circuits.



However, if a cable is disconnected, it needs to be disconnected at both ends.

There should be no 'live' cut ends anywhere.

 

[flameport]

I'm thinking I should get an electrician in to turn it back into a ring

Unless you are intending to wire things like it's 1949 and have a single ring circuit for the entire house, forget about rings.

 

[sparkwright]

Unless you are intending to wire things like it's 1949 and have a single ring circuit for the entire house, forget about rings.

But rings are good. You can have a 32amp circuit instead of a 20amp one by using just a few extra metres (usually) of 2.5 mm2 cable.

 

[SUNRAY]

But rings are good. You can have a 32amp circuit instead of a 20amp one by using just a few extra metres (usually) of 2.5 mm2 cable.

And often a ring uses less cable than 2 radials

 

[ericmark]

The 13 amp socket with take 2 or 3 cables of 2.5 mm², 4 mm² or 6 mm² it varies make to make, and with 2.5 mm² with a ring final you can have up to 106 meters of cable. With a home wired from side to side, the load on two ring finals is reasonably even, the loop impedance is likely less to an up/down split, and should a ring final fail, there is no temptation to run extension leads up or down stairs. The 13 amp socket and ring final have been downgraded with thinner cable when we went metric and poorer cooling for the fuse when with added finger protectors to the line pin so can't disparate the heat as well any more, they are designed, so the plug is in free air, so the fuse can cool, so should not be used in airing cupboards and the like, however often ovens are arranged, so cooling fans also cool the plug.

Although we can install radials, a 2.5 mm² radial using the same formula as with the ring final and a 20 amp over load is limited to around 32 meters. So for every ring final you need three radials. To use over 2.5 mm², you risk it not fitting in some makes of socket, and the whole system becomes less flexible, I know I have two kettles plugged into the same ring, and with a kitchen I know the appendix says over 2 kW non-portable should be a dedicated circuit, but that would mean dedicated circuits for cooker, washing machine, dishwasher, and drier, all having a dedicated circuit, but we get away with the ring final with just the cooker on a dedicated circuit.

If we returned to the old 15 amp socket, that would mean likely 6 radials just for the kitchen, with 16 amp RCBO's at £30 each, one can see why we go to just 2 or 3 ring finals to cover the whole house. It works out far cheaper. I will admit when ring finals are used without the required inspection and testing, there can be dangers, but that would be like saying faults can cause car accidents if they are not MOT'ed, so that does not really hold water.

To wire the house without using the 13 amp socket system would add a massive extra cost to wiring homes, so really except for small areas like a garage, we don't really have much option. Specially when our regulations don't permit the use of German sockets.

As to DIY the big problem is the socket tester, in the main they are designed for Europe even if they do have a 13 amp plug with them, as the pass point for the loop impedance is around the 1.9 Ω rather than 1.38 Ω so to test one needs to hire expensive equipment. So I can see the reason for using FCU's and fused radials when DIY extending.

However, most DIY people would not know how to inspect and test anyway, I know the minor works and installation certificates are a free download from IET website, and using them acts as a good check list, but you can't sight not doing inspection and testing as a reason for not using ring finals.

However, when one finds a fault, often the only price effective option is to downgrade to a radial circuit, find spur from spur, easy option is to downgrade to a radial.

 

[boringoldcodger]

I can't see easily as it's all hidden behind walls / floorboards. I could take a look tomorrow if you think it's useful.

That isn't what securespark was asking. He's interested in whether the (20A, I think you said) MCB in the CU (aka fusebox) has 2 (or more) wires in it.

 

[Mottie]

I’m really surprised that Andy @HERTS P&D hasn't been drawn to this thread!

 

[ebee]

That isn't what securespark was asking. He's interested in whether the (20A, I think you said) MCB in the CU (aka fusebox) has 2 (or more) wires in it.

Although that`s only one possible clue, a 16 or 20A radial could have more than one set of conductors in it just like you`d expect with a ring.
In fact I was once discussing four conductors in a 32A MCB Fuseway on a consumer unit - to wire a ring final as two rings on one breaker in the central portion of a house rather than one larger simple ring design.
One fellow was adamant he would "correct " it by by making a joint of connecting one leg of each ring to make it become one larger ring.
I pointed out that this would only increase R1, R2 & Rn therefore Zs and not be of any benefit but I am unaware if he was convinced.

It was one of those "Ten Penny Shots" type of things, our old Junior School Head used to quiz us with as he burst into a lesson of every class each week for a gen knowledge quiz. I think it had some benefits with us schoolkids.

 

[HERTS P&D]

I’m really surprised that Andy @HERTS P&D hasn't been drawn to this thread!

I did see it but as it was on a Sparky thread, I thought the usual suspects wouldn't see it.

But I did want to mention that he should of used Lube!



Andy

 

[securespark]

I have to admit I was tempted, but I resisted!

 

[securespark]

Unless you are intending to wire things like it's 1949 and have a single ring circuit for the entire house, forget about rings.

So today I'm gonna wire things like it's 1949.....

 

[pete01]

I'm gonna party like its 1999