Whats the alternative to adding a spur if the ring main hasn't enough slack
to reach the new socket? Could I break the ring with two junction boxes
and add two wires to extend the ring to the new socket, if thats ok what
about a double wired spur?

I don't really understand the theory behind this spur thing, is it the
rating of the wire from the ring to the spur or is it just that if you have
too many spurs they you'll probably have too many sockets for one ring?

Can somebody please clarify this for me?

Many thanks
Roger

Whats the alternative to adding a spur if the ring main hasn't enough
slack
to reach the new socket?

Best is to replace the entire cable to the next socket. If this is
impractical, then extend the cable using crimped connections. If there isn't
much extension needed and you do it right, you might only have to extend one
of the cables.

Christian.

Roger wrote:

Whats the alternative to adding a spur if the ring main hasn't enough slack
to reach the new socket?

This doesn't make any sense: Why do you want an alternative to a spur?
If you want to add an extra single or twin socket then just take a spur
from the nearest socket on the ring with a length of 2.5mm cable (as
long as it isn't already feeding a spur somewhere else.)

Could I break the ring with two junction boxes
and add two wires to extend the ring to the new socket,

Yes, that'd be fine.


if thats ok what about a double wired spur?

Buh?

--
Scott

Where are we going and why am I in this handbasket?

In message ,
"Roger" wrote:

Whats the alternative to adding a spur if the ring main hasn't enough slack
to reach the new socket? Could I break the ring with two junction boxes
and add two wires to extend the ring to the new socket,

That's possible (make sure your newsreader is using a monospaced font
such as Courier):

Old:

----SKT----------------SKT-----

New:

----SKT----JN JN----SKT-----
| |
+-SKT-+

(In fact you could have as many new sockets on your new loop of ring as
you liked)

if thats ok what
about a double wired spur?


Not alowed:

----SKT------JN--------SKT-----
||
||
SKT

(If you only need one extra socket, it is perfectly acceptable to run it
with one length of 2.5mm2 and only stick one double socket on the end)

Although you might think it's ok, running a double length of 2.5mm2 (or
indeed a single 4mm2) from just one juncion box isn't in the standard
layouts and so isn't allowed unless you are qualified to prove that the
loadings are ok in your situation. The thing with the "standardised
ring" is that all the calculations have already been done and so long as
you stay within the stated limits (2.5mm2 cable, 32A breaker, 100m2
floor area, one outlet per spur, balancing etc.) it will "comply".

I don't really understand the theory behind this spur thing, is it the
rating of the wire from the ring to the spur or is it just that if you have
too many spurs they you'll probably have too many sockets for one ring?


It's not the latter as you are allowed as many sockets on a ring as
you think necessary. It is a little bit of the former as the 2.5mm2
cable normally used for rings and spurs is only rated at 21A if run in
insulation (27A "clipped direct"). As a ring is generally fused at 32A,
a spur is, partly, protected from overloading by the fact that the most
you can get out of a double socket is 2*13A.

It's also to do with the loading on the ring itself. One of the things
you are supposed to do when designing a ring circuit is to ensure that
demand is "balanced" in both legs of the ring. For example, it might
look ok to have a ring with this topology:

+--SK1---SK2--+
| |
-+ SK3
-+ |
| |
+--SK5---SK4--+

but if SK1 and SK2 are in your living room running the telly and video,
and SK4 and SK5 are in the kitchen running the washing machine and
tumble dryer then the load can hardly said to be balanced - a greater
proportion of the current for SK4 and SK5 will want to go "down"
directly towards SK5. This runs the risk of overloading the cable in
that part of the ring.

Now imagine the situation where the ring *is* balanced (it doesn't have
to be exact, perhaps the washing machine is on SK3), but where someone
wants to add a few sockets. If you allowed them to add as many sockets
on spurs as they liked, they could end up sticking a whole chain of
sockets connected to (say) SK5. You could argue that using a double
run of 2.5mm2 or a single of 4mm2 cable allows you to carry 32A+, but
the rules limiting you to one double socket (or fused outlet) per spur,
and only as many spurs as outlets in the ring ensure that the load on
the ring isn't put (too much) out of balance.

Does that help?

Back to your original idea, the use of junction boxes to split the ring
is fine, but make sure they are accessible so that at some (unknown)
point in the future you could, if you needed to, check the screw
connections. General wisdom in this ng says that "under a floorboard"
counts as accessible but "plastered into a wall" isn't :-)

As mentioned above though, if it is only one socket you need, there's
nothing stopping you sticking a junction box "in" the ring and wiring a
conventional 2.5mm2/one socket spur from there.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Anything worth doing is worth overdoing.

Martin Angove wrote:

As mentioned above though, if it is only one socket you need, there's
nothing stopping you sticking a junction box "in" the ring and wiring
a conventional 2.5mm2/one socket spur from there.

I think if I was doing that I'd put another socket in where the junction
box goes. If you have to join the cables may as well get an extra socket
out of it rather than a blanking plate.

In message ,
"blah" wrote:

Martin Angove wrote:

As mentioned above though, if it is only one socket you need, there's
nothing stopping you sticking a junction box "in" the ring and wiring
a conventional 2.5mm2/one socket spur from there.

I think if I was doing that I'd put another socket in where the junction
box goes. If you have to join the cables may as well get an extra socket
out of it rather than a blanking plate.

Depends on the cable run though. If the cables are under the floor or
above the ceiling (very common) there may not be a suitable place to
mount a socket. Come to think of it, apart from putting the extra socket
bang next to an existing one (in which case, why not spur off that) I
can't think of the sort of cable run which would allow you (easily) to
insert a socket in the ring unless it is entirely surface-run. If this
was possible in the OP's case I don't think he'd have bothered asking
the OQ!

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... I did it. I killed them all.

In uk.d-i-y, Martin Angove wrote:

Depends on the cable run though. If the cables are under the floor or
above the ceiling (very common) there may not be a suitable place to
mount a socket. Come to think of it, apart from putting the extra socket
bang next to an existing one (in which case, why not spur off that) I
can't think of the sort of cable run which would allow you (easily) to
insert a socket in the ring unless it is entirely surface-run. If this
was possible in the OP's case I don't think he'd have bothered asking
the OQ!

Not that rare, actually: the point is, once you've opened up the ring
at Socket A by disconnecting the cable which runs on to Socket B, you
have the full length (in principle!) of the run between A&B to play with,
making it likely enough that you can find somewhere to put the new
on-the-ring socket using all or most of the cable which previously
ran A-B. Then you put in two new cable runs, either from new-to-A to
reinstate the ring with a spur off to the-new-socket-you-actually-wanted,
or incorporate the new-socket-you-actually-wanted into the ring by
running the first new cable from the may-as-well-be-a-socket-as-a-juncbox
to the new-socket-you-actually-wanted, and the second on from the
new-socket-you-actually-wanted on to A.

(Next week: Stefek explains "one song to the tune of another" in no less
than 2,000 words ;-)

Cheers, Stefek

In message ,
wrote:

In uk.d-i-y, Martin Angove wrote:

Depends on the cable run though. If the cables are under the floor or
above the ceiling (very common) there may not be a suitable place to
mount a socket. Come to think of it, apart from putting the extra socket
bang next to an existing one (in which case, why not spur off that) I
can't think of the sort of cable run which would allow you (easily) to
insert a socket in the ring unless it is entirely surface-run. If this
was possible in the OP's case I don't think he'd have bothered asking
the OQ!

Not that rare, actually: the point is, once you've opened up the ring
at Socket A by disconnecting the cable which runs on to Socket B, you
have the full length (in principle!) of the run between A&B to play with,
making it likely enough that you can find somewhere to put the new
on-the-ring socket using all or most of the cable which previously
ran A-B. Then you put in two new cable runs, either from new-to-A to
reinstate the ring with a spur off to the-new-socket-you-actually-wanted,
or incorporate the new-socket-you-actually-wanted into the ring by
running the first new cable from the may-as-well-be-a-socket-as-a-juncbox
to the new-socket-you-actually-wanted, and the second on from the
new-socket-you-actually-wanted on to A.

Ok, point taken. Bit of a problem if your cables are buried in plaster,
but good point nonetheless.


(Next week: Stefek explains "one song to the tune of another" in no less
than 2,000 words ;-)


Or perhaps you could extol the virtues of the swannee whistle when
played in conjunction with a kazoo :-)

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Behind every succesfull man is woman with nothing to wear

Bloody hell! thats brilliant, the best answers I've ever had on a ng.

Thanks very much guys, I think I really understand now what its all about.

BTW in the end I put in one spur from a junction box on the ring and wired
another into the ring, bit difficult getting the wires in and out of the old
conduit, but worth it to keep down my total spurs.

Once again thanks very much for all the advice and explanation.

Rgds
Roger

"Roger" wrote in message
...
Whats the alternative to adding a spur if the ring main hasn't enough
slack
to reach the new socket? Could I break the ring with two junction boxes
and add two wires to extend the ring to the new socket, if thats ok what
about a double wired spur?

I don't really understand the theory behind this spur thing, is it the
rating of the wire from the ring to the spur or is it just that if you
have
too many spurs they you'll probably have too many sockets for one ring?

Can somebody please clarify this for me?

Many thanks
Roger