When I rewired my house, I put in a few spurs to feed low power things
like table lamps. I probably didn't need to, but all these spurs are
single sockets.

Now I want to turn one of them into a double socket to feed a WMC and
a TD, so I'm not happy about having a single 2.5mm cable feeding them.

I have two options: either break into the ring and extend it (using a
JB behind the existing double socket that the spur comes from), or
simply double up the cables to the spur.

The latter seems more sensible, but there is something at the back of
my mind that says it is wrong.

Any thoughts?

--
Nigel M

On Mon, 23 Jan 2006 13:29:23 +0000 someone who may be Nigel
Molesworth wrote this:-

When I rewired my house, I put in a few spurs to feed low power things
like table lamps. I probably didn't need to, but all these spurs are
single sockets.

Now I want to turn one of them into a double socket to feed a WMC and
a TD,

Washing machine and tumble drier presumably.

so I'm not happy about having a single 2.5mm cable feeding them.

Are you intending to operate both of them in such a way that they
draw 13A almost continuously for an hour or so?

I have two options: either break into the ring and extend it (using a
JB behind the existing double socket that the spur comes from),

A junction box presumably. Will this junction box be located in the
wall?

or simply double up the cables to the spur.

The latter seems more sensible,

To you perhaps, but not to me.

but there is something at the back of my mind that says it is wrong.

There is something in the front of my mind that says you need to
learn rather more about electric wiring before doing any more work
yourself.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Mon, 23 Jan 2006 14:59:08 +0000, David Hansen wrote:

Will this junction box be located in the wall?
Yes, behind the socket - not nice.

or simply double up the cables to the spur.
The latter seems more sensible,

To you perhaps, but not to me.

I'll ignore your comments about learning more about wiring. I've
re-wired several properties, all have improved on the wiring by so
called professionals.

So why would you say that doubling up the cables to a spur (rather
than extending the ring using a JB) is a bad idea?

Remember that according to the regs I am not obliged to use more than
2.5mm for a double socket on a spur.

--
Nigel M

Nigel Molesworth wrote:

When I rewired my house, I put in a few spurs to feed low power things
like table lamps. I probably didn't need to, but all these spurs are
single sockets.

Yes, spurs can feed one single or one double socket, the assumption
being that the load on a double socket won't in practice exceed 20 A.

Now I want to turn one of them into a double socket to feed a WMC and
a TD, so I'm not happy about having a single 2.5mm cable feeding them.

Well it should be fine unless the cable's completely surrounded by
thermal insulation. All the Table 4D5A ratings of 2.5 T&E equal or
exceed 20 A. If you think the load will exceed 5 kW for long periods
then you should use two single sockets (in the ring or on separate
spurs) and not a double.

I have two options: either break into the ring and extend it (using a
JB behind the existing double socket that the spur comes from), or
simply double up the cables to the spur.

The latter seems more sensible, but there is something at the back of
my mind that says it is wrong.

Inserting the new socket into the ring is the better option, since it
will ensure better distribution of current in the two legs of the ring
(unless the spur point is exactly at the ring's mid-point).

The regs require you to ensure that the sustained load current in any
part of a ring under the actual intended conditions of use won't exceed
the as-installed cable rating, said rating not to be less than 20 A.

--
Andy

On Mon, 23 Jan 2006 16:04:26 +0000 someone who may be Nigel
Molesworth wrote this:-

Will this junction box be located in the wall?
Yes, behind the socket - not nice.

You are going to put a junction box behind a socket outlet;
presumably by removing the box it is currently fitted to, making a
(deeper) hole, installing the junction box, re-fitting the box and
then fitting the socket to that? Bearing in mind the requirements
for being able to inspect joints, how do you intend to make the
connections within the junction box?

I'll ignore your comments about learning more about wiring.

I suggest that you do not, until you have learnt some more. At the
moment ISTM that you are at the stage where a little knowledge is
dangerous.

So why would you say that doubling up the cables to a spur (rather
than extending the ring using a JB) is a bad idea?

1) conductors in parallel are not appreciated by the IEE. Since you
do not appear to understand why, I suggest that you find out.

2) it is unnecessary. Unless you intend the duty cycle I suggested
and which you snipped (or there is a particular combination of
insulation and/or ambient temperature) the existing cable is
probably capable of meeting the duty cycle [1].

3) if the existing cable is incapable of meeting the duty cycle the
next size up should be used.

4) such an arrangement is non-standard and will confuse anyone
coming across it later. You do understand the bits about considering
future maintenance/new work in the Wiring Regulations?

5) getting four conductors into the terminals of most sockets is
going to be interesting. If you do get them in then, other than in a
deep double box, you are unlikely to be able to fit the socket back
on the wall. Apart from anything else, this is unlikely to meet the
requirement for good workmanship.

Remember that according to the regs I am not obliged to use more than
2.5mm for a double socket on a spur.

Incorrect. That is a minimum cable size. The actual size depends on
the precise installation.

[1] while heating, a washing machine and tumble dryer may draw 13A.
However, they do not do so continuously. The worst case would be
starting both going at the same time, so they both draw 13A for say
20min (likely to be less), after which the heating element in drier
may cycle on and off but that in the washing machine is unlikely to
come on again until it is loaded again.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Mon, 23 Jan 2006 17:24:47 +0000, David Hansen wrote:

3) if the existing cable is incapable of meeting the duty cycle the
next size up should be used.

This is what I had in mind, 4mm or 6mm.

I don't see why you find it necessary to insult me, what purpose does
it serve?

--
Nigel M

On Mon, 23 Jan 2006 16:21:31 +0000, Andy Wade wrote:

Inserting the new socket into the ring is the better option, since it
will ensure better distribution of current in the two legs of the ring

You would think so, wouldn't you - this is what was at the back of my
mind. But if you think about it, it makes little difference, the
current will still be balanced from the spur take-off.

--
Nigel M

On Mon, 23 Jan 2006 17:24:47 +0000,it is alleged that David Hansen
spake thusly in uk.d-i-y:


1) conductors in parallel are not appreciated by the IEE. Since you
do not appear to understand why, I suggest that you find out.

Ring final circuit? I can't see an electrical difference between what
is being suggested and what the IEE keep promoting.


--
You cannot shake hands with a clenched fist.
- Indira Gandhi

Nigel Molesworth wrote:

On Mon, 23 Jan 2006 16:21:31 +0000, Andy Wade wrote:

Inserting the new socket into the ring is the better option, since it
will ensure better distribution of current in the two legs of the ring

You would think so, wouldn't you - this is what was at the back of my
mind. But if you think about it, it makes little difference, the
current will still be balanced from the spur take-off.

Yes, OK, it depends on the cable lengths involved. If the length of the
spur is very short it makes almost no difference.

--
Andy

David Hansen wrote:

There is something in the front of my mind that says you need to
learn rather more about electric wiring before doing any more work
yourself.

So stop willy waving and start teaching then... much better use of
bandwidth!


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Nigel Molesworth wrote:

You would think so, wouldn't you - this is what was at the back of my
mind. But if you think about it, it makes little difference, the
current will still be balanced from the spur take-off.

It depends on where in the ring the spur is. If it is near one end then
the majority of the current flow will be taken by one leg.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Mon, 23 Jan 2006 17:49:45 +0000 someone who may be Nigel
Molesworth wrote this:-

3) if the existing cable is incapable of meeting the duty cycle the
next size up should be used.

This is what I had in mind, 4mm or 6mm.

Only in this posting. In previous postings you were proposing using
two 2.5mm conductors in parallel.

I don't see why you find it necessary to insult me, what purpose does
it serve?

I have yet to insult you and see no reason to do so in the future. I
have pointed out that the questions you have asked imply a rather
lower level of knowledge than you appear to think you have.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Mon, 23 Jan 2006 21:17:14 GMT someone who may be Chip
wrote this:-

Ring final circuit?

That is a particular case of conductors in parallel which has been
thought through and, provided it is tested properly, provides an
appropriate balance between risk and cost.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Tue, 24 Jan 2006 00:34:13 +0000 someone who may be John Rumm
wrote this:-

So stop willy waving

Not something I am doing.

and start teaching then

The questions I have asked and the points I have raised should
promote learning. That is a very good way of using bandwidth.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

"David Hansen" wrote in message
...
On Mon, 23 Jan 2006 17:49:45 +0000 someone who may be Nigel
Molesworth wrote this:-

3) if the existing cable is incapable of meeting the duty cycle the
next size up should be used.

This is what I had in mind, 4mm or 6mm.

Only in this posting. In previous postings you were proposing using
two 2.5mm conductors in parallel.

I don't see why you find it necessary to insult me, what purpose does
it serve?

I have yet to insult you and see no reason to do so in the future. I
have pointed out that the questions you have asked imply a rather
lower level of knowledge than you appear to think you have.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Perhaps you're unaware of what can be construed as an insult.

I have always assumed that 2.5mm wiring would be OK for a double socket as
long as the wiring isn't embedded in insulation. However by saying he is
wrong without giving the reason why is not helpful to the OP nor the group.

No I'm not trying to be insulting but trying to be helpful so that your
replies are seen as a positive contribution in the OP's and group's eyes.

David Hansen wrote:

1) conductors in parallel are not appreciated by the IEE.

That's not true. BS 7671 has some specific requirements for conductors
in parallel, from which the 'classic ring' is exempted.

In summary, the requirements are these (my précis):

473-01-06: where protected by a single device there shall be no branch
circuits, switches or isolators in any of the individual
parallel paths;

473-01-07: where protected by a single device and current sharing is
equal, the value of Iz for the purposes of overload current
protection (reg. 433-02-xx) is the sum of the individual
Iz's. (Iz is the as-installed current rating, and current
sharing is deemed satisfied if 523-02-01 is satisfied.)

473-01-08: where currents are unequal, the design current and overload
protection of each conductor shall be considered
individually;

473-02-05: if a single device is used for s/c fault current protection
it must be effective for a fault at any position on one of
the parallel cables (and various alternative methods are
given if this can't be achieved);

533-02-01: measures shall be taken to ensure equal current sharing, the
requirement being satisfied if the cables are of the same
material, construction and CSA, and approximately the same
length with no branch circuits (and special precautions for
cables greater than 50/70 mm^2).

It is quite obvious that paralleling-up two ~equal lengths of 2.5 T&E
for the purpose being discussed does not violate any of these rules.

--
Andy

On Tue, 24 Jan 2006 06:57:14 +0000,it is alleged that David Hansen
spake thusly in uk.d-i-y:

On Mon, 23 Jan 2006 21:17:14 GMT someone who may be Chip
wrote this:-

Ring final circuit?

That is a particular case of conductors in parallel which has been
thought through and, provided it is tested properly, provides an
appropriate balance between risk and cost.

True, I was playing devil's advocate.g

This thread has however got me thinking. What the OP is proposing is
certainly extremely unconventional, almost like a ring with 'joined
bits', intersecting rings, etc.

But... the lengths paralleled would be almost identical in length,
thus the usual reasons for not using the arrangement would not apply.

Personally, like many others in this thread, I'd say 2.5 can handle it
unless buried in insulation, but would doubling the cables be *wrong*?

I don't see that it would in this instance.

--
You cannot shake hands with a clenched fist.
- Indira Gandhi

On Tue, 24 Jan 2006 09:54:36 +0000 someone who may be Andy Wade
wrote this:-

1) conductors in parallel are not appreciated by the IEE.

BS 7671 has some specific requirements for conductors
in parallel, from which the 'classic ring' is exempted.

Precisely.

It is quite obvious that paralleling-up two ~equal lengths of 2.5 T&E
for the purpose being discussed does not violate any of these rules.

I quite agree. However, the question was, is it a bad idea? My
answer is, yes it is for a bad idea for the five reasons I gave.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Tue, 24 Jan 2006 10:28:58 GMT someone who may be Chip
wrote this:-

Personally, like many others in this thread, I'd say 2.5 can handle it
unless buried in insulation, but would doubling the cables be *wrong*?

The question I answered was whether it would be a bad idea? My
answer to this question is, yes.

The Wiring Regulations are, rightly, not as prescriptive as some
would like and some think they are, but do make the point that
departures from them need to be justified and recorded by someone
who knows what they are doing.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Tue, 24 Jan 2006 09:30:26 -0000 someone who may be "Fred"
wrote this:-

Perhaps you're unaware of what can be construed as an insult.

Almost anything can be construed as an insult.

However by saying he is
wrong without giving the reason why is not helpful to the OP nor the group.

There are three things to consider:

1) some people ask genuine questions, others do not. Failing to
reply to questions/points about duty cycle, how the connections are
to be made and so on, then suddenly changing from two 2.5mm
conductors in parallel to single 4mm or 6mm conductors, allows
people to draw their own conclusions about this.

2) a little knowledge is often a dangerous thing.

3) if a question is genuine, spoon-feeding does is not helpful for
individuals or groups. What is helpful is learning how to learn. The
questions I have asked in this thread are an example of one way to
encourage learning.



--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Tue, 24 Jan 2006 11:49:56 +0000, David Hansen wrote:

then suddenly changing from two 2.5mm
conductors in parallel to single 4mm or 6mm conductors

Would you like to explain the difference, electrically?

--
Nigel M

John Rumm wrote:

Nigel Molesworth wrote:

You would think so, wouldn't you - this is what was at the back of my
mind. But if you think about it, it makes little difference, the
current will still be balanced from the spur take-off.

It depends on where in the ring the spur is. If it is near one end then
the majority of the current flow will be taken by one leg.


Surely no more so than if it is added to the ring at that point?

Either way, to come back to the op's question, I concur with Andy Wade.
Just change it to a double and stick with the 2.5 T+E (E&OE) Maybe
also check the connections at the other end are nice and tight.

On Tue, 24 Jan 2006 10:28:58 GMT, Chip wrote:

But... the lengths paralleled would be almost identical in length,
thus the usual reasons for not using the arrangement would not apply.

My apologies.

I should have said, and this is very relevant, the distance is about 1
metre! I just want to take the socket below the work top.

In the circumstances, I thought that doubled 2.5mm T&E would be OK,
but obviously 4mm or 6mm would be neater.

I take David's point about a "little knowledge", but I asked the
question originally because I was aware that it was unconventional.



--
Nigel M

On Tue, 24 Jan 2006 12:28:45 +0000 someone who may be Nigel
Molesworth wrote this:-

In the circumstances, I thought that doubled 2.5mm T&E would be OK,
but obviously 4mm or 6mm would be neater.

The existing cable may well be fine. However, only one of us can see
where and how it is installed, you. Only you can say about ambient
temperature, insulation, duty cycle and so on.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Tue, 24 Jan 2006 14:19:13 +0000, David Hansen wrote:

The existing cable may well be fine. However, only one of us can see
where and how it is installed, you. Only you can say about ambient
temperature, insulation, duty cycle and so on.

It's in an insulated timber partition. I don't know about the duty
cycle, but SWMBO is *supposed* to try to use the WMC and TD at
different times at night, during the Economy 7 periods.

Having looked further, I've now realised that I can't put the socket
where I wanted to anyway; I need to use timeswitches which would foul
the bottom of the basin.

I think my best bet is to use the existing single spur with a 2-outlet
socket plugged in via a flex, and mount this where the timeswitches
are accessible. If the 13A fuse blows, it means I need a re-think.

--
Nigel M

Following through this thread, I was wondering why no one had thrown up
the part pee bogy. Having seen a mention of a 'basin' I'm even more
surprised this hasn't been mentioned. I'm prepared to be educated but
isn't his just what part pee proscribes as the modification is taking
place in a kitchen or equivalent area ?

Rob

wrote in message
oups.com...
Following through this thread, I was wondering why no one had thrown up
the part pee bogy. Having seen a mention of a 'basin' I'm even more
surprised this hasn't been mentioned. I'm prepared to be educated but
isn't his just what part pee proscribes as the modification is taking
place in a kitchen or equivalent area ?

Rob


Isn't he just replacing a socket with a "near" equivalent? Saves using a 2
into 1 adapter.

wrote in message
oups.com...
Following through this thread, I was wondering why no one had thrown up
the part pee bogy. Having seen a mention of a 'basin' I'm even more
surprised this hasn't been mentioned. I'm prepared to be educated but
isn't his just what part pee proscribes as the modification is taking
place in a kitchen or equivalent area ?

Rob


Utility rooms are Part P exempt.

Adam

On Tue, 24 Jan 2006 18:36:09 GMT, ARWadsworth wrote:

Utility rooms are Part P exempt.

As are kitchens, if you have a large stock of red and black cable ;-)

--
Nigel M

"Nigel Molesworth" wrote in message
...
On Tue, 24 Jan 2006 18:36:09 GMT, ARWadsworth wrote:

Utility rooms are Part P exempt.

As are kitchens, if you have a large stock of red and black cable ;-)

--
Nigel M

Will it not self destruct in April?

Adaml

Andy Wade wrote:

It is quite obvious that paralleling-up two ~equal lengths of 2.5 T&E
for the purpose being discussed does not violate any of these rules.

And in some circumstances would actually have the advantage that 2 x
2.5mm^2 would have a lower earth fault loop impedance than a single
4mm^2 as a result of the greater total CPC CSA.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Owain wrote:

indeed I wouldn't recommend most plug-in timeswitches for sustained 13A
loads.

Emphatically seconded. Also the idea of using a flex and extension
socket will lead to grief. Feeding both appliances through a single 13
A fused plug really isn't on at all.

--
Andy

On Tue, 24 Jan 2006 19:40:50 +0000, Owain wrote:

You can use wired-in timeswitches anywhere on the (spur) circuit.

I started a new thread on this very topic.

Do you know where I can get an independent two-channel timer with 13A
contacts, preferably (although not essentially) the same shape as a
double 13A socket?

--
Nigel M

On Tue, 24 Jan 2006 16:32:25 +0000 someone who may be Nigel
Molesworth wrote this:-

It's in an insulated timber partition.

Does the cable have thermal insulation on both sides? Does the ring
main cable pass through similar insulation?

I don't know about the duty cycle,

I wish more washing machines and driers had lights to indicate when
the heating element is on. However, I suspect that you will find my
guesses are reasonably close to how your machines work.

I need to use timeswitches which would foul
the bottom of the basin.

I take it that the machines do not have built in timers and that
their leads are not long enough to reach a high level socket (or
this would not be approved by the boss).

This is what I would do for the situation as currently outlined:

1) fit two switched fused connection units in the ring main (these
are often cheaper than the alternatives). These could be flush
mounted in a metal box that can take two single accessories. If you
want them surface mounted then MK make a suitable box that their
accessories fit nicely. These would be at high level. If the
existing socket is not used a lot I might replace it with these,
otherwise I would put the new bits near the socket to make it easier
to modify the ring main.

2) run a cable from each connection unit to a time clock. These
would be at a suitable location depending on your needs. Time clocks
that fit on a single box are available. They are more expensive than
the plug in sort, but better made. If mounted together on a box that
takes two single accessories, make sure that the time clocks don't
have a bottom plate that makes them a little wider than a single
accessory (some do, some don't).

3) run a cable from each time clock to an unswitched socket in a
suitable place to plug the appliance in.

4) test and energise.

5) mark the sockets, time clocks and connection units so it is clear
that they are not normal sockets.

The size of the cable from the connection unit will depend on the
precise installation details. 1.5mm will probably be fine, but only
you know the kitchen.

If the cables are to be buried then beware of the acceptable zones
for wiring and what one does if the cables are not in these zones.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

On Wed, 25 Jan 2006 10:42:49 +0000, David Hansen wrote:

1) fit two switched fused connection units in the ring main

2) run a cable from each connection unit to a time clock. ...
Time clocks that fit on a single box are available.

I had come to the same conclusion as you, but I was going to use
plug-in timers, then go *into" a connection unit to get back to cable.

Reason for this strange arrangement is that I can't find any
non-mechanical fixed timers that switch 13A. Any suggestions?

--
Nigel M

On Wed, 25 Jan 2006 14:14:34 +0000 someone who may be Nigel
Molesworth wrote this:-

Reason for this strange arrangement is that I can't find any
non-mechanical fixed timers that switch 13A. Any suggestions?

The timers I have seen for fixed wiring have all been mechanical,
but I have not seen that many and the last new one I saw was a year
or two ago. I would suggest the makers of central heating
controllers might make other types of time clock.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54