Planning Kitchen Wall Electrics - Is This Good? [PIC]

[aptsys]

Yes, that may well be true and may be needed in the future.

However, any time both legs of the ring are in the same place, then a ring is, itself, pointless.
If what you say is wanted, use 4mm² for the spur from the position where it stops actually being a ring.

Did I miss a change in the regs?

 

[EFLImpudence]

Did I miss a change in the regs?

No.

 

[John D v2.0]

Yes, that may well be true and may be needed in the future.

However, any time both legs of the ring are in the same place, then a ring is, itself, pointless.
If what you say is wanted, use 4mm² for the spur from the position where it stops actually being a ring.


Plus, of course, other places where it is all that is required.

View attachment 120974

Are you sure that's OK on a ring final? Depending how you look at it you're unbalancing the ring by adding too many sockets (only one unfused spur from each point on the ring) or if you're treating the 4mm cable as both legs of the ring, you're making an extra connection across 2 parts of the ring.

 

[EFLImpudence]

Are you sure that's OK on a ring final?

Yes.

Depending how you look at it you're unbalancing the ring by adding too many sockets

Balancing has to be considered (as it always is, isn't it?) but no more sockets than could be there anyway.

(only one unfused spur from each point on the ring)

Is that a regulation?
Anyway, how far away does the next point have to be?

or if you're treating the 4mm cable as both legs of the ring, you're making an extra connection across 2 parts of the ring.

No, it's just a spur.

 

[John D v2.0]

Balancing has to be considered (as it always is, isn't it?) but no more sockets than could be there anyway.


Is that a regulation?
Anyway, how far away does the next point have to be?

No there are not more sockets, in total, but if they were all in the ring the current split would be different for each. If it's a spur, the current split is identical for all. That's fine if it's at the end of the ring (assumed 20a there anyway) but if it's near one end then less so.

Maybe it's not a regulation, but it's certainly not a general rule that you can substitute arbitrary sections of a ring with spurs in 4mm cable and still have overload protection on the 2.5mm sections of cable.

 

[EFLImpudence]

No there are not more sockets, in total, but if they were all in the ring the current split would be different for each.

Not in all cases.

If it's a spur, the current split is identical for all. That's fine if it's at the end of the ring (assumed 20a there anyway) but if it's near one end then less so.

Less so but it can still be satisfactory.
When extending the ring instead, does anyone consider which is the longer leg and connect the sockets to that side - or is it pot-luck?

Maybe it's not a regulation, but it's certainly not a general rule that you can substitute arbitrary sections of a ring with spurs in 4mm cable and still have overload protection on the 2.5mm sections of cable.

Why not? What difference does it make (considering the points mentioned?

Take a bungalow, as is commonly the case, where the ring runs around the loft with drops from a junction box to each socket.
Would it make a difference if each of the drops were 4mm² to two sockets?

You have said it's fine if at the mid-point of the ring, therefore it must be fine if satisfactorily balanced.

 

[John D v2.0]

Yes subject to all the caveats you mention it would be OK.

 

[John D v2.0]

Sorry failed at quoting

not in all cases.

Which cases? I can only imagine that if there's zero impedence on the section of ring between the two sockets (ie on the same spur/spurred from the same point)

Why not? What difference does it make (considering the points mentioned?

So the extreme example would be a ring with 49m of cable on one leg, all the sockets on 4mm spur from there, then 1m back to the cu. 98% of the current will take the 1m length of cable, causing an overload.

 

[EFLImpudence]

Which cases? I can only imagine that if there's zero impedence on the section of ring between the two sockets (ie on the same spur/spurred from the same point)

I'm not quite sure what you are querying.
There could be several sockets close together, each with a spur, so negligible difference than all from the same point.

So the extreme example would be a ring with 49m of cable on one leg, all the sockets on 4mm spur from there, then 1m back to the cu. 98% of the current will take the 1m length of cable, causing an overload.

Yes, but that's not going to be the case, is it?
You could connect the 4mm² directly to the MCB and have a radial with as many sockets as you wished.

Take these two circuits:

The left is as people are suggesting - extend the ring - it happens that all the sockets are on the short leg.

The right - connect the two 2.5mm² - or use 4mm² - cables and make them parallel. Is that detrimental?
In this case, with the sockets on the shorter leg, it would actually better the balance as the long leg is now shorter.
Obviously, it could be the other way round but it has been agreed that balancing should be considered.

When a 13A FCU is inserted to cover a multi-socket spur, do you think this is to protect the spur cable or the ring?
If the spur, as it must be, then it could be 25A if such were available, so why not increase the cable size?

 

[John D v2.0]

Interesting debate, thanks

I'm not quite sure what you are querying.
There could be several sockets close together, each with a spur, so negligible difference than all from the same point.

I think the difference here is you are looking at things from the point of view, it's possible to design a pure ring badly, so you have to take into account balancing anyway. And if you design this other kind of circuit well taking into account balancing, that's also possible.
My point is that rings work because they are naturally likely to be balanced (no large fixed loads allowed, you're unlikely to have loads of sockets within a few feet that have a heavy load - fan heaters you'd generally have in different rooms, no long spurs unless they're limited to what a socket could take anyway. And even relatively small gaps between sockets on the ring have a reasonable effect on balance.)
With arbitrary spurs leaving the ring, you could have your whole extension wired as a 4mm spur and where do you draw the line?

I'm not quite sure what you are querying.
Yes, but that's not going to be the case, is it?
You could connect the 4mm² directly to the MCB and have a radial with as many sockets as you wished.

Take these two circuits:

View attachment 121006

The left is as people are suggesting - extend the ring - it happens that all the sockets are on the short leg.

The right - connect the two 2.5mm² - or use 4mm² - cables and make them parallel. Is that detrimental?
In this case, with the sockets on the shorter leg, it would actually better the balance as the long leg is now shorter.
Obviously, it could be the other way round but it has been agreed that balancing should be considered.

When a 13A FCU is inserted to cover a multi-socket spur, do you think this is to protect the spur cable or the ring?
If the spur, as it must be, then it could be 25A if such were available, so why not increase the cable size?

Yeah directly to the MCB you are basically the same situation as at the mid point of the ring so it would be fine.

The 13A FCU is to protect the ring as well as the cable (otherwise you could do as you say and take a 32A point load)

Regarding your diagrams, yes, the left situation is better than the right.
The photo I'll post in a sec, but basically you want your loads to be close of half way round the ring (0.5ish) or exactly 0.0 i.e. the MCB.
With the left circuit because of the longer cable it makes a significant difference, even in the case of an extremely long ring with the 3 sockets too close together to want to plug space heaters in to all.

 

[John D v2.0]

Diagram for the above post

 

[EFLImpudence]

I think the difference here is you are looking at things from the point of view, it's possible to design a pure ring badly, so you have to take into account balancing anyway. And if you design this other kind of circuit well taking into account balancing, that's also possible.

So - it's alright when it's alright, then.

My point is that rings work because they are naturally likely to be balanced (no large fixed loads allowed, you're unlikely to have loads of sockets within a few feet that have a heavy load

That applies to my spur as well.
If not, then adding sockets close together by extending the ring is also bad.

- fan heaters you'd generally have in different rooms, no long spurs unless they're limited to what a socket could take anyway. And even relatively small gaps between sockets on the ring have a reasonable effect on balance.

Mmmm.

With arbitrary spurs leaving the ring, you could have your whole extension wired as a 4mm spur and where do you draw the line?

By considering the balancing.
You are just thinking up instances where it may not be acceptable so, in that respect you are correct.

Yeah directly to the MCB you are basically the same situation as at the mid point of the ring so it would be fine.

Well, yes, but the ring part is irrelevant if there is a spur from the MCB.

The 13A FCU is to protect the ring as well as the cable (otherwise you could do as you say and take a 32A point load).

Why, then, is an unfused double socket spur allowed where there could be 26A load?

Regarding your diagrams, yes, the left situation is better than the right.

It is better with your highly unlikely 49:1 ring.
However, your average ratio of 52:3 is also unsatisfactory.
Do people consider that when extending rings?
When it gets to the stage of being satisfactory (by better balance), would my spur also be acceptable?

The photo I'll post in a sec, but basically you want your loads to be close of half way round the ring (0.5ish).

Well, ideally, but that's not how rings are installed.

With the left circuit because of the longer cable it makes a significant difference, even in the case of an extremely long ring with the 3 sockets too close together to want to plug space heaters in to all.

It does. Not sure of the point you are making.


I don't understand your green figures; to what do they refer?

 

[ILikeDIYS]

Started cutting the chases until my Henry hoover cut out (overheat - hopefully will start working again when cooled):

And as I was chiseling the top single socket I found this:

Why on earth is there a curved metal pipe there? Or is it some type of reinforcement? Either way lucky it happened on a socket I can afford to move left as it will be hidden inside a wall unit.

Also on a side-note, Titan wall chaser sucks - the motor keeps stopping the moment it feels a little tension. Much worse than my friends Erbauer I used before.

 

[ban-all-sheds]

Old bit of conduit?

 

[securespark]

only one unfused spur from each point on the ring

Is that a regulation?

In the 14th Edition, it was a numbered regulation:

A38: For ring final sub-circuits complying with A30-33, the total number of spurs shall not exceed the total number of socket outlets and stationary appliances connected directly in the ring.

The definition of "Spur" in the 14th Edition is defined as "a branch cable connected to a ring circuit."

(So presumably that must have included both fused and unfused spurs).


In the 15th Edition, it was moved to the Appendices:

Appendix 5: The total number of fused spurs is unlimited, but the number of non-fused spurs does not exceed the total number of socket outlets and items of stationary equipment connected directly in the circuit.

The definition of "Spur" in the 15th Edition is defined as "a branch cable connected to a ring or radial final circuit."


In the 16th Edition, it was moved to the Appendices of the OSG:

OSG Appendix 8: The total number of fused spurs is unlimited, but the number of non-fused spurs does not exceed the total number of socket outlets and items of stationary equipment connected directly in the circuit.

The definition of "Spur" in the 16th Edition is "a branch from a ring final circuit".


16th Edition AMD 2: 2004:

OSG Appendix 8: The total number of fused spurs is unlimited, but the number of non-fused spurs should not exceed the total number of socket outlets and items of stationary equipment connected directly in the circuit.

The definition of "Spur" in the 16th AMD is unchanged from the 16th.


17th Edition 2001 AMD 1:

OSG Appendix H: The total number of fused spurs is unlimited, but the number of non-fused spurs should not exceed the total number of socket outlets and items of stationary equipment connected directly in the circuit.

The definition of "Spur" in the 17th AMD is "a branch from a ring or radial final circuit".