ring main woes

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Fred

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Feb 18, 2008, 9:10:56 AM2/18/08
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Hello,

Is there a rule that you should re-wire a house every x years, and if
so, what is x?

The wiring in our house is, I presume, the original from the 1970s.
Rather than run T&E to the lamps, the builders/electrician has used
conduit cable. The electrician that visited told us he hadn't seen
anything like it, though he was younger than the house!

The problem is that in the 1970s we didn't have pcs, dvds, etc and all
the sockets were put onto one 32A ring main. To be fair that's not a
problem under normal use but other houses we have lived in have had
two ring mains; usually one for upstairs and one for downstairs or one
for front and one for back of the house.

Recently I was working on the CH during a cold spell, so we had a
couple of fan heaters on. The problem was that a couple of 3kW fan
heaters and a kettle, left little room for anything else, so the mcb
tripped once or twice.

The CH is up and running now, so hopefully we will not need the fan
heaters for a while, but it would be nice to divide the ring main into
two. I think it would be useful to divide the ring logically, e.g. all
upstairs on one; all downstairs on another (incidentally they did this
with the lights, so why no the sockets?). I don't suppose this is
possible? I suppose the ring main lies between the up and downstairs
floors and drops down into the ground floor rooms and up to the
upstairs alternately? Would I have to settle for a front of house/back
of house divide?

Is it just a matter of disconnecting one end of the ring and then
disconnecting at different sockets to see which are powered or is
there any easier way to trace the ring main?

Once it is split in half, is it just a matter of adding a new T&E tail
to each half, back to the CU to convert the two radials into two
rings?

Thanks.

The Natural Philosopher

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Feb 18, 2008, 10:29:59 AM2/18/08
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Fred wrote:
> Hello,
>
> Is there a rule that you should re-wire a house every x years, and if
> so, what is x?
>
Around 60 for a total rewire, and 30 for a damn good check.

> The wiring in our house is, I presume, the original from the 1970s.
> Rather than run T&E to the lamps, the builders/electrician has used
> conduit cable. The electrician that visited told us he hadn't seen
> anything like it, though he was younger than the house!
>
> The problem is that in the 1970s we didn't have pcs, dvds, etc and all
> the sockets were put onto one 32A ring main. To be fair that's not a
> problem under normal use but other houses we have lived in have had
> two ring mains; usually one for upstairs and one for downstairs or one
> for front and one for back of the house.
>
> Recently I was working on the CH during a cold spell, so we had a
> couple of fan heaters on. The problem was that a couple of 3kW fan
> heaters and a kettle, left little room for anything else, so the mcb
> tripped once or twice.
>
> The CH is up and running now, so hopefully we will not need the fan
> heaters for a while, but it would be nice to divide the ring main into
> two. I think it would be useful to divide the ring logically, e.g. all
> upstairs on one; all downstairs on another (incidentally they did this
> with the lights, so why no the sockets?). I don't suppose this is
> possible?

Anything is possible, bu the time taken to work out how to do it may
exceed the time to lay a complete pair of rings.


> I suppose the ring main lies between the up and downstairs
> floors and drops down into the ground floor rooms and up to the
> upstairs alternately? Would I have to settle for a front of house/back
> of house divide?
>

Not necessarily, but it does get tricky..

> Is it just a matter of disconnecting one end of the ring and then
> disconnecting at different sockets to see which are powered or is
> there any easier way to trace the ring main?
>
> Once it is split in half, is it just a matter of adding a new T&E tail
> to each half, back to the CU to convert the two radials into two
> rings?

Essentially yes but really, by the time you have done all that its
easier to hoick up all the floorboards ad do it all over again.

I would strongly recommend a bit of bullet biting, a new consumer unit,
and a totally modern installation: If some of the original cable can be
used regard that as a bonus.

Just don't expect it.


>
> Thanks.

David Hansen

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Feb 18, 2008, 11:07:00 AM2/18/08
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On Mon, 18 Feb 2008 14:10:56 GMT someone who may be Fred
<fr...@neitherhere.northere> wrote this:-

>The wiring in our house is, I presume, the original from the 1970s.
>Rather than run T&E to the lamps, the builders/electrician has used
>conduit cable. The electrician that visited told us he hadn't seen
>anything like it, though he was younger than the house!

Not much of an electrician if he can't cope with conduit.

>it would be nice to divide the ring main into
>two. I think it would be useful to divide the ring logically, e.g. all
>upstairs on one; all downstairs on another

It would be nice.

>(incidentally they did this with the lights, so why no the sockets?).

They were economising.

>I don't suppose this is possible?

Most things are possible. However, in extending conduit one either
needs to use conduit, or measure and calculate carefully whether
some other sort of cabling system like twin & earth can be added to
the system safely. There are a number of pitfalls in this to do with
fault currents and ensuring a proper earth connection everywhere.

Unless you have the skills to slowly DIY all this the cheapest
option will be to get someone else to install two new ring mains.

It would also be worth testing the existing system to check on
disconnection times. Sometimes conduit can rust to the extent that
it goes high impedance.

--
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

John

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Feb 18, 2008, 11:20:13 AM2/18/08
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"David Hansen" <SENDdavi...@spidacom.co.uk> wrote in message
news:2qajr394oh6j11vga...@4ax.com...

I think you mean that the house is wired in "single" cables (as would be
used in conduit). You do not imply that conduit is used.

I did a lighting circuit like that in the '60's - but the wire was double
insulated and at the time suitable for burying in plaster. Is yours double
insulated singles?

A cable of 3 strands of 0.029" was used. The red and blacks had an outer
grey sheath.


Fred

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Feb 18, 2008, 12:54:46 PM2/18/08
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On Mon, 18 Feb 2008 16:20:13 GMT, "John"
<john.plan...@ntlworld.com> wrote:

>I think you mean that the house is wired in "single" cables (as would be
>used in conduit). You do not imply that conduit is used.
>
>I did a lighting circuit like that in the '60's - but the wire was double
>insulated and at the time suitable for burying in plaster. Is yours double
>insulated singles?
>
>A cable of 3 strands of 0.029" was used. The red and blacks had an outer
>grey sheath.


I'm sorry if I have used the wrong term. I think the other poster
thought conduit had been used as an earth? That's not the case. I
didn't know that was allowed. The ring main for the sockets is (as far
as I have seen) wired in T&E.

I think I have confused the issue by saying that the lighting circuit,
but only the lighting circuit, is wired in what I thought was called
"conduit cable"; you are right that what I meant by this is that a
double sleeved black neutral wire runs to each light and a double
sleeved red (or rather two of them) run to and from the switches.

As it happens the inner and outer sheaths are the same colour.

Fred

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Feb 18, 2008, 12:57:07 PM2/18/08
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On Mon, 18 Feb 2008 15:29:59 +0000, The Natural Philosopher <a@b.c>
wrote:

>Essentially yes but really, by the time you have done all that its
>easier to hoick up all the floorboards ad do it all over again.
>
>I would strongly recommend a bit of bullet biting, a new consumer unit,
>and a totally modern installation: If some of the original cable can be
>used regard that as a bonus.


Thanks. The CU looks relatively modern (mcbs rather than fuses); it's
a shame they didn't modernise everything else at the same time!

The problem with a re-wire is that it requires lifting all the carpets
and a lot of floorboards so it becomes a big job. That would not be so
bad because carpets and boards can be re-laid but my worry is getting
the wires down the walls. No doubt they are plastered in and will
require half my walls to be demolished too!

Fred

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Feb 18, 2008, 3:53:56 PM2/18/08
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On Mon, 18 Feb 2008 15:29:59 +0000, The Natural Philosopher <a@b.c>
wrote:

>> Is there a rule that you should re-wire a house every x years, and if


>> so, what is x?
>>
>Around 60 for a total rewire, and 30 for a damn good check.

I have been thinking about this some more. The house was built in the
70's, so we are at the "damn good check" distance. What is involved in
a damn good check? Like the other poster said, if you have to lift
everything to go looking, I suppose you may as well replace everything
at the same time?

John

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Feb 18, 2008, 6:19:01 PM2/18/08
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> As it happens the inner and outer sheaths are the same colour.

So it is wired in Twin Sheathed Single Cables.
What do the experts make of that? I guess it is ok?


meow...@care2.com

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Feb 19, 2008, 6:19:42 AM2/19/08
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John wrote:

I'd say that was a trivial issue. If there's no earth wire, thats
less
than ideal, and its best not to use any metal light or switch
fittings.
Once its buried in plaster its no more or less drillable than T&E,
and the risk of cable drilling is tiny anwyay.


NT

meow...@care2.com

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Feb 19, 2008, 6:33:01 AM2/19/08
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Fred wrote:

> Hello,
>
> Is there a rule that you should re-wire a house every x years, and if
> so, what is x?

No. Once you get as far back as the 60s then the need to rewire
becomes high. And if the 60s wire is rubber insulated, fairly certain.

> The wiring in our house is, I presume, the original from the 1970s.
> Rather than run T&E to the lamps, the builders/electrician has used
> conduit cable.

singles

The problem you describe sounds trivial, and the solution you
propose sounds far more inconvenient. So it doesnt make a lot of
sense really.

If you want to split the ring, yes as you say 2x T&E runs back to
the CU. You dont know how the existing wiring is routed so you
wont get a halfway split, unless by chance, and it doesnt matter
anyway. Just pick the furthest point from the CU to split it to
maximise the amount of socket distribution.

But really I cant see any point in it.

70s installs are normally ungenerous but adequate capacity-wise,
imperfect but pretty good safety wise, totally inadequate in terms
of number of sockets, and quite often have been subject to various
inexpert bits of rewiring that need sorting out safely.

So with such an installation if you dont know its history an
inspection should pick up any issues that need sorting - but bear
in mind it will also pick up issues that don't. There is no practical
or legal reason such installs would need to meet the regs for a
new install, but any spark touting for business will pretend it must.

Re socket provision, lots more sockets can be added to an
existing ring without causing a problem. More sockets doesnt
change system capacity.


NT

Andy Wade

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Feb 19, 2008, 5:22:22 PM2/19/08
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Fred wrote:

> Is there a rule that you should re-wire a house every x years, and if
> so, what is x?

There are no hard and fast rules. The design life of PVC cable running
continuously at its full rated load is 25 years, but of course the
actual loading pattern of house wiring usually comes nowhere near that,
making cable life effectively indefinite (apart from specific issues
such as cables affected by the 'green goo problem').

It's recommended that a formal 'periodic inspection report' (PIR) is
commissioned every 10 years, although this is seldom observed in
practice in owner-occupied premises. The purpose of a PIR is to assess
whether an electrical installation remains safe for continued service.
A PIR consists of a thorough visual inspection of the installation
together with relevant testing - insulation resistance, earth fault loop
impedance, RCD operation, etc. The report follows a standardised format
and includes schedules of inspections and of test results, the later
identifying all the final circuits. Issues identified are 'coded' for
severity: code 1 = immediate danger, 2 = requires improvement, 3 =
requires further investigation and 4 = not compliant with current regs
but not necessarily dangerous. Assessment is always to the current
version of the regs, so older installations will always throw up a
number of code 4s, and possibly the worse code 1s and 2s. Effective
PIR-ing needs a knowledgeable electrician, preferably one holding the
C&G 2391 qualification.

> The CH is up and running now, so hopefully we will not need the fan
> heaters for a while, but it would be nice to divide the ring main into
> two.

You have to ask yourself whether it's worth the bother, if/when use of
electric heating will be pretty rare. If it won't be rare you could
consider adding one or two dedicated radial heating circuits instead.

> I think it would be useful to divide the ring logically, e.g. all
> upstairs on one; all downstairs on another (incidentally they did this
> with the lights, so why no the sockets?).

It happens naturally for lighting circuits which tend to have one 'tail'
for each floor.

> I suppose the ring main lies between the up and downstairs
> floors and drops down into the ground floor rooms and up to the
> upstairs alternately?

If your house has a suspended timber ground floor you'll probably find
that one end of the ring goes under the ground floor floorboards, loops
round all the ground floor sockets and then rises somewhere for a
similar loop upstairs. If that's the case then cut the rising section
and join on two new ends.

> Is it just a matter of disconnecting one end of the ring and then
> disconnecting at different sockets to see which are powered or is
> there any easier way to trace the ring main?

You'll probably need to use a mixture of visual inspection, selective
disconnection and continuity testing to work it out.

> Once it is split in half, is it just a matter of adding a new T&E tail
> to each half, back to the CU to convert the two radials into two
> rings?

Essentially yes, although, since you are modifying circuit(s) it will
need to comply with current regs, including 30 mA RCD protection
(sockets likely to be used for portable equipment outdoors) and the
adequacy of the underlying earthing an bonding.

--
Andy

Andrew Gabriel

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Feb 19, 2008, 6:13:59 PM2/19/08
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In article <fu3jr3p5dh0d9fc45...@4ax.com>,

Fred <fr...@neitherhere.northere> writes:
> Hello,
>
> Is there a rule that you should re-wire a house every x years, and if
> so, what is x?

If it's rubber, should have been done ~30 years ago.
If it's PVC, then even the earliest PVC installations
should still have sound cable unless it's got hot, and
should remain good for decades yet. IEE estimates 1000
year live of the PVC in ideal conditions, dropping to
21 years for a cable operating continuously at max
rated temperature of 70C. Some wiring schemes such as
conduit can suffer high earth impedance after a long
time.

Wiring accessories (switches, sockets, fuse box, etc)
will not generally last as long as the wiring and should
be checked periodically -- life will depend on usage and
original quality. Fortunately, they are much easier to replace
than the wiring. Also check for terminal screw tightness,
as poor contacts there can lead to heating and damage to
accessories and cable (and worse).

Standards and expectations change over the years.
A 50 year old PVC installation could still be in perfect
order, but would be lacking the number of sockets expected
today, and below current earthing standards. That doesn't
necessarily mean a rewire is required, but poorly done
piecemeal expansion of an original installation is a common
cuase of an installation having become an unrepairable mess.

My parents installation was one for earliest PVC ones in
the 1950s. The original accessories are all MK, except the
fusebox which was Wylex. I found the fusebox was in need
of replacing 10 years ago during an inspection -- the
contacts on the ring circuit fuse holder were getting too
hot and caused insulation to go brittle. I replaced the
fusebox as part of rewiring/refitting the kitchen and
bringing service bonding up to spec. I can only think of
one of the MK accessories which has failed -- a light switch.
About half of them have been replaced during room redecorations
over the 50 years, but none had anything wrong with them.
A few of the terminal screws have been retightened.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Frank Erskine

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Feb 19, 2008, 6:39:21 PM2/19/08
to
On Tue, 19 Feb 2008 22:22:22 +0000, Andy Wade
<spamb...@maxwell.myzen.co.uk> wrote:

>The design life of PVC cable running continuously at its full rated load is 25 years,

That's interesting - have you got a reference for that? Was it just a
'think of a number' when PVC cable was introduced? Clearly there are
different qualities of PVC (not only for cable insulation/sheathing).

Most of my wiring is (AFAIK) original, the house having been built
around 1973. The original stuff is stranded, so it's likely to be
7/0·029 for the sockets, although I've never measured it. Generally it
seems to be in good condition. Not that it runs anywhere near its full
rated load!

--
Frank Erskine

Andy Wade

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Feb 19, 2008, 8:52:04 PM2/19/08
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Frank Erskine wrote:
> On Tue, 19 Feb 2008 22:22:22 +0000, Andy Wade
> <spamb...@maxwell.myzen.co.uk> wrote:
>
>> The design life of PVC cable running continuously at its full rated load is 25 years,
>
> That's interesting - have you got a reference for that?

http://groups.google.com/group/uk.d-i-y/msg/5b3c4b11cc841eca?dmode=source
has more detail.

> Most of my wiring is (AFAIK) original, the house having been built
> around 1973. The original stuff is stranded, so it's likely to be
> 7/0·029 for the sockets, although I've never measured it.

Hmm, not so sure about 7/0.029 in 1973. Cable went metric around
1969-70, IIRC. 2.5 mm^2 was, and still is, available in stranded form
(7/0.67 mm IIRC). Generally 7/0.029 to BS 2004 will have tinned
conductors and metric to BS 6004 will be plain copper.

--
Andy

Terry Fields

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Feb 20, 2008, 3:09:34 AM2/20/08
to

Andy Wade wrote:

>The design life of PVC cable running
>continuously at its full rated load is 25 years, but of course the
>actual loading pattern of house wiring usually comes nowhere near that,
>making cable life effectively indefinite (apart from specific issues
>such as cables affected by the 'green goo problem').

Could you expand a little on the 'green goo' and why it's a problem?

TIA

Fred

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Feb 20, 2008, 3:55:32 AM2/20/08
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On Tue, 19 Feb 2008 22:22:22 +0000, Andy Wade
<spamb...@maxwell.myzen.co.uk> wrote:

>
>If your house has a suspended timber ground floor you'll probably find
>that one end of the ring goes under the ground floor floorboards, loops
>round all the ground floor sockets and then rises somewhere for a
>similar loop upstairs. If that's the case then cut the rising section
>and join on two new ends.

No, it's a concrete ground floor I'm afraid, so I think the cables
drop from above.

Andy Wade

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Feb 20, 2008, 4:31:23 AM2/20/08
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Terry Fields wrote:

> Could you expand a little on the 'green goo' and why it's a problem?

Quote from
http://www.voltimum.co.uk/consult.php?action=main&mode=consult&id=2861&universe=home
attributed to Dr. Jeremy Hodge of BASEC.

Green gunge / goo from older PVC cables
---------------------------------------
Green gunge (sometimes called green goo) is sometimes seen exuding from
the ends of some older PVC insulated and sheathed cable. This is seen
in some cables made in the 1960s and 1970s, but is not generally seen in
modern PVC cables.

Its origin is the plasticiser used to provide flexibility in the PVC
polymer compound. This is generally di-octyl phthalate, which over time
or with excessive heat has reacted with the copper conductors to produce
copper phthalate (hence the green colour) suspended in the liquid
plasticiser. The material is of health concern, so should be handled
with care – gloves should be used and waste disposed of properly.

Industry guidance is generally as follows, if green gunge is seen.
Although there does not appear to be a problem with the electrical
performance or safety of the cable itself, any exuded gunge should be
removed as it can cause corrosion or affect the action of switches and
terminations, potentially resulting in tracking / overheating. It can
also cause cosmetic problems such as staining. The affected circuits
should be rewired as soon as possible.

The original manufacturer of the cable should be contacted if there are
any additional questions.

</quote>

HTH
--
Andy

David Hansen

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Feb 20, 2008, 4:55:09 AM2/20/08
to
On Wed, 20 Feb 2008 08:55:32 GMT someone who may be Fred
<fr...@neitherhere.northere> wrote this:-

>No, it's a concrete ground floor I'm afraid, so I think the cables
>drop from above.

Separating the floors out is going to be complicated. Perhaps
something for a leisurely DIY task. It will be far more rapid to
install new cables from scratch.

However, there is no reason to separate floors in a domestic
building. It is only done that way for ease of wiring. It may be
more logical to separate circuits by the area they are in. For
example rooms on all floors in a particular corner of the house.
That may make the re-arrangement a lot easier, but it depends on how
it is currently wired. We don't know how the house is wired and have
no way of finding out. Only you can do that.

Terry Fields

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Feb 20, 2008, 5:15:25 AM2/20/08
to

Andy Wade wrote:

>Terry Fields wrote:
>
>> Could you expand a little on the 'green goo' and why it's a problem?
>
>Quote from
>http://www.voltimum.co.uk/consult.php?action=main&mode=consult&id=2861&universe=home
>attributed to Dr. Jeremy Hodge of BASEC.
>
>Green gunge / goo from older PVC cables

<snip>

Many thanks.

ac1951

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Feb 20, 2008, 5:29:10 AM2/20/08
to

When I used to do re-wires some years ago I preferred to use Double
insulated singles (with earth) for the lighting circuits. It made
life so simple, dropping a nuetral round all the lamp holders and also
allowed you to keep the colour coding right i.e. the return live from
the switch. (red instead of black when you use TW&E)
However, I don't see double insulted singles on sale today well not 1
or 1.5mm anyway.

Is that because it's not an approved way anymore ?
Are there circumstances where it should it be replaced. i.e If you
where, as the OP would like to do, spliting the light circuits into
two domains would the Part P inspector expect any "double insulated
singles" to be replaced with TW&E.

Roger

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Feb 20, 2008, 6:52:24 AM2/20/08
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The message <7nqnr3pp91hut9108...@4ax.com>
from Fred <fr...@neitherhere.northere> contains these words:

> >If your house has a suspended timber ground floor you'll probably find
> >that one end of the ring goes under the ground floor floorboards, loops
> >round all the ground floor sockets and then rises somewhere for a
> >similar loop upstairs. If that's the case then cut the rising section
> >and join on two new ends.

> No, it's a concrete ground floor I'm afraid, so I think the cables
> drop from above.

Like my house which once only had 3 circuits, lights, ring and cooker.
It now has 3 ring mains, North, South and kitchen and 2 lighting
circuits, downstairs and upstairs. As it happens the lighting circuits
were harder to separate, wired in part with double insulated singles but
via some very odd routes.

One of the other things I have done is to try and eliminate all the
diagonal wires that offend current regulations.

--
Roger Chapman

sm_jamieson

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Feb 20, 2008, 10:18:13 AM2/20/08
to

Taking neutrals round a different path to the lives is not
recommended, since it can cause problems for inductance loop hearing
aids used by deaf people. Not that they would normally be using that
mode in a house anyway - more often in churches, concert halls, banks
etc.
Not sure if the regs actually ban it though.
Simon.

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