New sockets off ring main

[JohnW2]

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 ...

Other than presenting a potential nightmare for those undertaking future testing or fault-finding, I would have thought that converting a ring to a 'figure of 8' circuit (by cross-connecting two sockets) can but 'do good', by improving the balance' of a ring with unbalanced loads (i.e. decreasing current in the 'higher current leg), no matter where the cross-connection is applied. Is that not the case?

Kind Regards, John

 

[EFLImpudence]

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

Yes.

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

The cable is the spur. The socket is not on the ring; it is on the spur.

Draw it.


P.S. It is called a Ring Final Circuit; not a ring main.
A spur is a branch of a ring or radial circuit.

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

That would be alright for just one socket - single (possible 13A) or double (possible 26A) - but for more than that you need cable that can handle 32A - the same as the rest of the circuit.

 

[veedee]

Yes.


The cable is the spur. The socket is not on the ring; it is on the spur.

Draw it.


P.S. It is called a Ring Final Circuit; not a ring main.
A spur is a branch of a ring or radial circuit.


That would be alright for just one socket - single (possible 13A) or double (possible 26A) - but for more than that you need cable that can handle 32A - the same as the rest of the circuit.

This is a great teaching moment so thanks.

If you have one socket on the Ring Final Circuit
And want to Add three spurs off the existing socket on the Ring, you'd use 4mm cable as you mentioned earlier.

But how do you screw down all of that cable in the back of the socket? I struggle screwing down 3x 2.5mm cable, I can only imagine the difficulty with 4mm cable.

Is one possible solution to use Wago's?

 

[flameport]

Is one possible solution to use Wago's?

The solution is to extend the ring using 2x 2.5mm² cables.

Extending from a ring using 4mm² cable is technically valid, but isn't something to be recommended or used, unless the layout of the ring has been carefully considered, along with where that 4mm² connects and what likely loads will be connected to it, and that the 4mm² will be installed as method C or equivalent.

In most cases it will be easier, quicker and far less bother to cut the ring in half and make 2 separate 20A or 25A circuits out of it. Those can be extended using the same 2.5mm² cable with no restriction on the number of outlets.

 

[JohnW2]

Extending from a ring using 4mm² cable is technically valid, but isn't something to be recommended or used, unless the layout of the ring has been carefully considered, along with where that 4mm² connects and what likely loads will be connected to it, and that the 4mm² will be installed as method C or equivalent.

That's true, but all but the last of those "unless..." caveats applies equally to installing two or more 2.5mm unfused spurs, each supplying one socket, with origins close to one another on the ring.

In most cases it will be easier, quicker and far less bother to cut the ring in half and make 2 separate 20A or 25A circuits out of it. Those can be extended using the same 2.5mm² cable with no restriction on the number of outlets.

Yes, probably easier and quicker, and with unlimited sockets, so potentially a good choice those who are comfortable with 20A radials (serving thee location concerned) .... BUT, perhaps of more importance/interest to people in this 'DIY' forum is that splitting a ring into two radials creates at least one (arguably two) 'new circuit', hence notifiable work, whereas extending an existing ring or adding spurs to an existing ring is not notifiable.

Kind Regrds, John

 

[EFLImpudence]

In most cases it will be easier, quicker and far less bother to cut the ring in half and make 2 separate 20A or 25A circuits out of it. Those can be extended using the same 2.5mm² cable with no restriction on the number of outlets.

Well, it depends what you mean by 'easier' - e.g. fitting additional MCB for which there might not be space in the CU, or did you mean two 20A or 25A branches of the one circuit?
It seems rather a lot to explain to a DIYer as opposed to simply just "use 4mm² cable".

Also, I note you do not for your method (as you did with the 4mm² spur) list every disadvantage you could think of; not least also ensuring it was method C for the 25A option.

 

[ericmark]

The ring final was designed to save copper after WW2, it did allow 88 meters, now 106 meters, and the normally method was to ensure one uses less than a 100 meter role of cable.

However once installed not that easy to work out how much cable has been used, two basic tools, the low ohm meter, and the loop impedance meter, and from those reading we can calculate how much cable is already used, so we know how much more can be added.

The easy method is a fused connection unit, (FCU) as a 13 amp fuse needs a higher impedance than a 32 amp MCB/RCBO so unlikely to exceed the limits.

To split a ring final into even into multi 16 amp radials may required 3 radials instead of one ring final, using 20 amp radials you may need 4 instead of one ring which needs more room in the consumer unit and more MCB/RCBO's.

But on the other hand if the ring is not be near the limit, and can be split without a problem, but the DIY problem is either of the two meters required are expensive, and it needs some maths.

 

[JohnW2]

The ring final was designed to save copper after WW2, it did allow 88 meters, now 106 meters, and the normally method was to ensure one uses less than a 100 meter role of cable.

The UK knew little about metres back then, and I doubt that the amount of cable in a drum had anything to do with the introduction of ring finals!

However once installed not that easy to work out how much cable has been used, two basic tools, the low ohm meter, and the loop impedance meter, and from those reading we can calculate how much cable is already used, so we know how much more can be added.

You are always talking about this, but I do doubt that, in practice, many domestic ring finals evrn approach the sort of lengths you mention (which are, in any event, only to achieve the guidance figures for VD under the most extreme of loading conditions).

The easy method is a fused connection unit, (FCU) as a 13 amp fuse needs a higher impedance than a 32 amp MCB/RCBO so unlikely to exceed the limits. To split a ring final into even into multi 16 amp radials may required 3 radials instead of one ring final, using 20 amp radials you may need 4 instead of one ring which needs more room in the consumer unit and more MCB/RCBO's. But on the other hand if the ring is not be near the limit, and can be split without a problem, but the DIY problem is either of the two meters required are expensive, and if needs some maths.

As I wrote, I think the main issue for DIYers is that splitting a ring final into (any number of) radials is notifiable, whereas extending an existing ring final, or adding (fused or unfused) spurs to an existing ring final is not (even in Wales).

Kind Regards, John

 

[ericmark]

Yes your correct to suggest doing something which costs £100 plus vat to register the work rather than some thing which does not require notifying seems silly to me too.

 

[JohnW2]

Yes your correct to suggest doing something which costs £100 plus vat to register the work rather than some thing which does not require notifying seems silly to me too.

Indeed - and, whilst it may be £100+VAT in Wales, recently heard from someone (in England) whose LABC was asking for £500+VAT.

Kind Regards, John

 

[veedee]

Awesome thread. Great wealth of info.

 

[ericmark]

Indeed - and, whilst it may be £100+VAT in Wales, recently heard from someone (in England) whose LABC was asking for £500+VAT.

I saw that post, and not convinced those were really the LABC charges, the idea was in England to allow each local authority to set their own fees so to reduce the charges for Part P work.

However in Wales the £100 plus vat does not include the cost of third party inspectors, so if the LABC employ an electrician to do an EICR then the home owner is charged for that on top of the standard fee.

230/(32x5)x95% = 1.365625 Ω but most of the cheap (£50) plug in testers pass at 1.9 Ω so unless the DIY guy has test results of the original installation he has no idea if adding more cable will stop the overload from tripping within the required time.

When I first started the meters and regulation books where kept in the foreman's office, and we were discouraged from using them, but when BS 7671 came in, we started using the meters, and completing the installation certificates, and I was shocked to find out how many large houses were not within the requirements which did not have the 5% safety margin then so 1.44 Ω if using 240 volt the 1.5 Ω, so even if originally within spec, with the volt drop and 5% safety margin could be out of spec now.

The MCB was the real problem, with a fuse a little too much cable would just take a little longer to open, but with the MCB if the magnetic bit does not trip, one is looking at a massive increase in time before the thermal part will trip.

 

[plugwash]

Other than presenting a potential nightmare for those undertaking future testing or fault-finding, I would have thought that converting a ring to a 'figure of 8' circuit (by cross-connecting two sockets) can but 'do good', by improving the balance' of a ring with unbalanced loads (i.e. decreasing current in the 'higher current leg), no matter where the cross-connection is applied. Is that not the case?

A cross connection can certainly make things worse. For example if the existing load is distributed in a roughtly equal manner then adding an interconnect from a place close to the middle to a place close to one end will shift the load towards said end.

 

[EFLImpudence]

A cross connection can certainly make things worse. For example if the existing load is distributed in a roughtly equal manner then adding an interconnect from a place close to the middle to a place close to one end will shift the load towards said end.

Well, yes, it will but that is sort of the opposite of what John said - namely: a bridge across the middle of the ring.

 

[JohnW2]

I saw that post, and not convinced those were really the LABC charges, the idea was in England to allow each local authority to set their own fees so to reduce the charges for Part P work. .... However in Wales the £100 plus vat does not include the cost of third party inspectors, so if the LABC employ an electrician to do an EICR then the home owner is charged for that on top of the standard fee.

Indeed. The £500+VAT we heard about seemed very high, but I think that most LA's in England charge a lot more than the £100 you mention for Wales.

This is what my LA currently says (albeit dates from April 2020). Note that the £350 is the same for a "Full Plans" application (which few people use) or a "Building Notice" (which is what most people use), that the the figure includes VAT and that, in contrast to what you say about Wales, the fee for 'inspections' is "NIL".

Kind Regards, John