Rings and spurs

[STI]

One of those nights where you get a question in your head and it keeps churning arond. Can someone clarify and help.

1. If you add a spur to astandard 2.5mm ring you basically take a supply to a socket outlet using a single piece of 2.5mm t&e from the nearest point on the ring. Now if i wanted to extend the ring to include this spur why cant i just run another cable back to the socket that supplied the spur.

The only reason i could come up with not to do this was that potentially one of the conductors on what was the spur could come off and if doing checks with a meter continuity would still show as in tact. Am i correct are there other reasons not to.

2. When i look at the diagrams in the regs book and on site guide for adding a FCU to feed a spur so more than one outlet can be attached they all show the FCU as wired into the ring. Why is this, why cant you just run a single cable to the FCU then add your outlets. I would have thought the fuse in the FCU would prevent the supply cable to it from being overloaded.

Thanks and heres to a better nights sleep

 

[Chri5]

A add in to the ring is always better than a spur socket, and running 2 x TE cable to the nearest ring outlet is a very standard way of doing it.

A spur is only allow one x d/ socket due to the limits of a single 2.5mm TE cable being circa 26 amps (subject to distance and installation method).

So say you don't limit a cascade of socket from a spur via a 13amp fused outlet.

If say you had 3 singles from a double spur you have a potential demand of 3 x 13a + (the double socket at 2 x 13a)= 65 amps on 1 x 2.5mm TE

Hence why you must fuse at 13 amp.

You MUST assume the sockets may be run at full tilt / 13amp per single due to the fact than any appliance might be plugged in. So if you argued that it's only 50w demand appliances that cannot be considered.

 

[PrenticeBoyofDerry]

but a spur can be a multi-socket outlet, the regs states somewhere, not to hand so going blind on this one.
A spur can feed one outlet, whether it be single, double or multi.

 

[PrenticeBoyofDerry]

1. If you add a spur to astandard 2.5mm ring you basically take a supply to a socket outlet using a single piece of 2.5mm t&e from the nearest point on the ring. Now if i wanted to extend the ring to include this spur why cant i just run another cable back to the socket that supplied the spur.

You can providing you connect your cables correctly, might be a squeeze for room in the back box though!

 

[STI]

A add in to the ring is always better than a spur socket, and running 2 x TE cable to the nearest ring outlet is a very standard way of doing it.
A spur is only allow one x d/ socket due to the limits of a single 2.5mm TE cable being circa 26 amps (subject to distance and installation method).

So say you don't limit a cascade of socket from a spur via a 13amp fused outlet.

If say you had 3 singles from a double spur you have a potential demand of 3 x 13a + (the double socket at 2 x 13a)= 65 amps on 1 x 2.5mm TE

Hence why you must fuse at 13 amp.


You MUST assume the sockets may be run at full tilt / 13amp per single due to the fact than any appliance might be plugged in. So if you argued that it's only 50w demand appliances that cannot be considered.

Chris5 Thanks for the reply. To make sure i have not misunderstood, are you saying that to add to a ring you just run two cables back to the nearest socket.In other words how i asked if it could be done in my first question. I thought you had to break into the ring ie disconnect one cable from the existing socket, extend this to the new socket then run another cable from the new socket back to the one where you disconnected the cable from.

I understand the loading principles of sockets on the spur but that doesnt explain (or at least i cant see it yet ) why a FCU needs to be on the ring. Surely if this is fused at 13a then it will trip once the current goes above that point whether it is attached to the ring or just on a single piece of 2.5mm spurred from the ring.

 

[STI]

1. If you add a spur to astandard 2.5mm ring you basically take a supply to a socket outlet using a single piece of 2.5mm t&e from the nearest point on the ring. Now if i wanted to extend the ring to include this spur why cant i just run another cable back to the socket that supplied the spur.

You can providing you connect your cables correctly, might be a squeeze for room in the back box though!

Hi PBD, Yes i thought the space might be an issue as well as getting 4 conductors into each terminal. But what do you mean by connecting the cables correctly other than p-p n-n and e-e?. what about the issue of a lost contact at the new socket not showing up as a break as the ring would still effectively run through the old socket.

Thanks
Steve

 

[ban-all-sheds]

1. If you add a spur to astandard 2.5mm ring you basically take a supply to a socket outlet using a single piece of 2.5mm t&e from the nearest point on the ring. Now if i wanted to extend the ring to include this spur why cant i just run another cable back to the socket that supplied the spur.

You can. Obviously though you can't just connect it to the socket terminals, you'd need to join it to one of the circuit legs using choc-block or crimps.

The only reason i could come up with not to do this was that potentially one of the conductors on what was the spur could come off and if doing checks with a meter continuity would still show as in tact. Am i correct are there other reasons not to.

No - you're not correct, you are worryingly wrong, because if you'd extended the ring you'd no longer have a spur.

I'm starting to worry that you really don't understand the fundamental topology of a ring.

2. When i look at the diagrams in the regs book and on site guide for adding a FCU to feed a spur so more than one outlet can be attached they all show the FCU as wired into the ring. Why is this, why cant you just run a single cable to the FCU then add your outlets. I would have thought the fuse in the FCU would prevent the supply cable to it from being overloaded.

You can and it would.

Why, when you looked at the diagram on p362 of the regs did you not see the spur at 9 o'clock?

Chris5 Thanks for the reply. To make sure i have not misunderstood, are you saying that to add to a ring you just run two cables back to the nearest socket.In other words how i asked if it could be done in my first question. I thought you had to break into the ring ie disconnect one cable from the existing socket, extend this to the new socket then run another cable from the new socket back to the one where you disconnected the cable from.

Of course you do

I understand the loading principles of sockets on the spur but that doesnt explain (or at least i cant see it yet ) why a FCU needs to be on the ring. Surely if this is fused at 13a then it will trip once the current goes above that point whether it is attached to the ring or just on a single piece of 2.5mm spurred from the ring.

OMG.

Hi PBD, Yes i thought the space might be an issue as well as getting 4 conductors into each terminal.

But what do you mean by connecting the cables correctly other than p-p n-n and e-e?. what about the issue of a lost contact at the new socket not showing up as a break as the ring would still effectively run through the old socket.

So you have no idea how an FCU is wired, and how it works.

You think this is a ring:

And you're working as an electrician.


God help us all.

 

[Chri5]

but a spur can be a multi-socket outlet, the regs states somewhere, not to hand so going blind on this one.

Are you saying I could add one of these without the plug and without fusing ?

 

[STI]

1. If you add a spur to astandard 2.5mm ring you basically take a supply to a socket outlet using a single piece of 2.5mm t&e from the nearest point on the ring. Now if i wanted to extend the ring to include this spur why cant i just run another cable back to the socket that supplied the spur.

You can. Obviously though you can't just connect it to the socket terminals, you'd need to join it to one of the circuit legs using choc-block or crimps.

BAS obviuosly i did not explain my question and note it was a question clearly enough. Your response means it should be wired how i thought but other than that it doesnt answer why it cant be done how you show in your diagram lower down. Thats what i am interested in knowing.

The only reason i could come up with not to do this was that potentially one of the conductors on what was the spur could come off and if doing checks with a meter continuity would still show as in tact. Am i correct are there other reasons not to.

No - you're not correct, you are worryingly wrong, because if you'd extended the ring you'd no longer have a spur.

My question was can i extend the ring as asked. Absolutely agree if i have extended the ring then i dont have a spur. But again i was trying to obtain clarity as to why it couldnt be done the way i asked. So yes if it could be done in the way i asked you would have a ring connected to a ring, whats wrong with that other than it doesnt conform to the normal description of a ring. The current would still flow around two cables(4 at one point if it could be done the way i asked) just like a ring. I then went on to ask that can this not be done because if the conductor breaks at the extended socket then it effectively reverts to being a spur but any continuity measurements would still show a ring exists on the circuit.

I'm starting to worry that you really don't understand the fundamental topology of a ring.
I do i just like to explore other ideas

2. When i look at the diagrams in the regs book and on site guide for adding a FCU to feed a spur so more than one outlet can be attached they all show the FCU as wired into the ring. Why is this, why cant you just run a single cable to the FCU then add your outlets. I would have thought the fuse in the FCU would prevent the supply cable to it from being overloaded.

You can and it would.

Why, when you looked at the diagram on p362 of the regs did you not see the spur at 9 o'clock?
Got me on that one i missed it i looked at the diagram in the electricians guide to building regs page 54 and my notes.

Chris5 Thanks for the reply. To make sure i have not misunderstood, are you saying that to add to a ring you just run two cables back to the nearest socket.In other words how i asked if it could be done in my first question. I thought you had to break into the ring ie disconnect one cable from the existing socket, extend this to the new socket then run another cable from the new socket back to the one where you disconnected the cable from.

Of course you do
I am assuming sarcasm here. I still like to explore other ideas and will continue to do so. Its not a sign of incompetence just interest.

I understand the loading principles of sockets on the spur but that doesnt explain (or at least i cant see it yet ) why a FCU needs to be on the ring. Surely if this is fused at 13a then it will trip once the current goes above that point whether it is attached to the ring or just on a single piece of 2.5mm spurred from the ring.

OMG.
What ? given my initial question was based upon the diagram on page 54, my notes and i am sure but cant currently find it there is another diagram showing an FCU as part of the ring why the eye roll, My thoughts are correct it doesnt need to be on the ring. Thank you its been clarified no need for the eye roll.

Hi PBD, Yes i thought the space might be an issue as well as getting 4 conductors into each terminal.

But what do you mean by connecting the cables correctly other than p-p n-n and e-e?. what about the issue of a lost contact at the new socket not showing up as a break as the ring would still effectively run through the old socket.

So you have no idea how an FCU is wired, and how it works.

Yes I do this reply from PBD was nothing to do with the FCU it was back to my original question on adding a socket to the ring.

You think this is a ring:

And you're working as an electrician.
No my question was why couldnt that be a ring

God help us all.

No God help us all when people stop asking questions and we all think we know it all.

 

[OwainDIYer]

You cannot join all four conductors together in the socket to extend the ring. If you do you don't have a ring, you have a figure 8 (two rings joining together) which is not allowed

You join one side of the ring to one side of the extension at the socket, and the other side of the ring to the other side of the extension using connectors/crimps.

If space is tight in the back box, which it usually is, it may be worthwhile swapping the double socket on the ring for 2 x single sockets in a dual box.

 

[ban-all-sheds]

Asking questions?

Long before, way before, you got to the stage of working as an electrician you should have cone to understand what a ring is, and how an FCU works.

I'd judge a DIYer incompetent if he didn't know those things, let alone someone charging money for their professional skills and expertise.

 

[PrenticeBoyofDerry]

Hi PBD, Yes i thought the space might be an issue as well as getting 4 conductors into each terminal. But what do you mean by connecting the cables correctly other than p-p n-n and e-e?. what about the issue of a lost contact at the new socket not showing up as a break as the ring would still effectively run through the old socket.

Thanks
Steve

As already mentioned, you can not connect all the cables in to the socket outlet terminals, you are extending the ring final circuit, so you need to connect the individual legs of the ring circuit to form a ring.

 

[holmslaw]

..

 

[STI]

Asking questions?

Long before, way before, you got to the stage of working as an electrician you should have cone to understand what a ring is, and how an FCU works.

I'd judge a DIYer incompetent if he didn't know those things, let alone someone charging money for their professional skills and expertise.

So where have i said anything that says i dont know what a ring is or how to wire up a FCU or how it works. I have questioned in one case the accepted concept of a ring and in the other i wanted clarity on something that didnt make sense exactly because i did understand how it worked. and you pointed out a diagram on PAGE 362 that put my concerns to rest thank you.

Sadly BAS we appear to have a fundamentally different outlook on life. I like to explore in the safety of a forum, classroom, discussion other idea's. If people dont question the accepted we do not evolve. If Pasteur had just looked at a bunch of mould and accepted the current thinking he would have thrown it away and we wouldnt have penecillin. If NASA had just looked at space and said we cant breathe up their so no point going we wouldnt have many household items we do today and if wilbur and wright had just accepted that we dont have wings we wouldnt have the travel and life experiences we do today. We would still be using horses as the main form of transport, we would still be using drums and fires as long distance communication methods we would still be passing knowledge only by word of mouth etc etc. But people questioned the accepted and we evolved.

I will continue to ask questions every day, i will continue to challenge the accepted way of doing things and my knowledge will grow. I will also encourage others to ask questions so that they can learn too.

There is not one electrician out there who knows everything, if they are professionals they will admit their weak points and ask questions of colleagues reference manuals etc to get their answers. As do i.

 

[PrenticeBoyofDerry]

Are you saying I could add one of these without the plug and without fusing ?

no not one of them, I just remember seeing something in the regs regarding multiple socket being spurred. Not something I have ever fitted.
Now I have looked, it's in appx 8 of the osg, but all the 3 gang accessories I can find are fused.

Have you looked here?
//www.diynot.com/wiki/electrics:extend_ring