I think I have read enough posts to have this one worked out, please
can somebody confirm. There is a desprate shortage of local sparkies
round my way, the nerrerst is an hours drive away - my first plan, of
employing one as a consultant is not working too well. My father in
law was qualifed till he retired, a few weeks before Part - P arrived,
so he will help out, I just have to make sure I do the new bit
correct. This mainly seems to be restrictions on where I can run the
cables - and new colours.

For where to run my wires,

They can be 50mm below the surface, in which case I can put them where
I like. Each room (except one, see below) will have at least one studd
wall, 100mm thick. This means I will need to put them in the
insulation layers, do I have to do anything special for this ?

In the other walls I can run the cables vertically from a "device", or
horrizontally between 2 devices in the plasterwork, which some plastic
protection - is this correct ?

I intend to do each room, with a seperate run to/from the fuse box,
and two rings in the kitchen, one normal, one economey 7.

If this is OK, then my plans are fine, as I intend to finish a room in
turn, rather than first fix the whole house, then 2nd fix the whole
house. This is mainly because I am living in the house, and if I do a
room in turn I can keep living in it.

For my main room, I will have no studd walls, and no clear 100mm space
at the top, as that space if full of ceiling beams, and its too little
anyway. The plan is to put a wooden "trench" into the floor
insulation, and put the wires in this. I would then seal the top with
steel plate, which would be earth bonded. Is this OK ? I'd run the
"trench" round all the walls, and run the cables up to the devices.

Final problem, where can I put junction boxes ?

Can they go into the studd walls ?

I can live without them in the floor.

Thanks
Rick

Rick wrote:

For where to run my wires,

They can be 50mm below the surface, in which case I can put them where
I like. Each room (except one, see below) will have at least one studd
wall, 100mm thick. This means I will need to put them in the
insulation layers, do I have to do anything special for this ?

You do need to ensure that cables don't become totally surrounded by
insulation (unless you've done custom circuit designs taking that into
account). If using the usual cable sizes you have two options: cables
can either be clipped along the studs or run in PVC conduit fixed to the
studs. For these methods and T&E cable the current ratings in columns A
& B of the following table apply:

Size Ratings in amps (ambient temperature 30 deg.C
mm^2 A B C conductor temperature 70 deg.C)
---- ---- -- --
1 11.5 12 16
1.5 14.5 15 20
2.5 20 21* 27
4 26 27 37
6 32 35 47
10 44 47 64
16 57 63 85

Key to columns:
A - in conduit in insulated wall (ref. method 6)
B - directly in insulated wall (ref. method 15)
C - clipped direct (ref. method 1)


In the other walls I can run the cables vertically from a "device", or
horrizontally between 2 devices in the plasterwork, which some plastic
protection - is this correct ?

Yes, and no protection is required for cables in these zones. For more
detail (illustrated) see http://www.niceic.org.uk/downloads/C5-43.pdf.

I intend to do each room, with a seperate run to/from the fuse box,

If you mean having a separate power (sockets) circuit for each room,
each with its own MCB, then yes, that's OK. If we're talking about
normal sized rooms then you could use 20 A radial circuits rather than
rings.

and two rings in the kitchen, one normal, one economey 7.

You mean one ring on a time-switched supply? That would be unusual, but
I suppose you could. I take it you're using storage heaters too
(otherwise the DNO or metering company wouldn't normally give you a
switched supply).

For my main room, I will have no studd walls, and no clear 100mm space
at the top, as that space if full of ceiling beams, and its too little
anyway. The plan is to put a wooden "trench" into the floor
insulation, and put the wires in this. I would then seal the top with
steel plate, which would be earth bonded. Is this OK ? I'd run the
"trench" round all the walls, and run the cables up to the devices.

I think that could be made to work, or you could use a proprietary floor
trunking system. Isn't there a floor void or roof space above where you
could run the cables and drop down to each point though?

Final problem, where can I put junction boxes ?

You shouldn't need any if wiring anew from scratch. Make all your
branches and spurs at wiring accessories, then the accessibility
requirement is met.

Can they go into the studd walls ?

Not normal screw terminal ones, if they're going to be plasterboarded
over. Crimped or soldered joints in a suitable enclosure are needed for
that.

HTH
--
Andy

Rick wrote:

They can be 50mm below the surface, in which case I can put them where
I like. Each room (except one, see below) will have at least one studd
wall, 100mm thick. This means I will need to put them in the
insulation layers, do I have to do anything special for this ?

I take it that when you say 100mm thick, that is the thickness of the
studding? (i.e. with plasterboard and skim it is more like 125mm).

If it genuinely 100mm thick then you may have problems achieving the
required depth from *both* sides.

In the other walls I can run the cables vertically from a "device", or
horrizontally between 2 devices in the plasterwork, which some plastic
protection - is this correct ?

Yup, but you don't need the protection (although oval conduit is handy
for allowing wires to be replaced later). Remember also you can use the
150mm zone beside each corner, and down from the ceiling.


--
Cheers,

John.

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

On Mon, 10 Oct 2005 01:32:50 +0100, Andy Wade
wrote:

Rick wrote:

For where to run my wires,

They can be 50mm below the surface, in which case I can put them where
I like. Each room (except one, see below) will have at least one studd
wall, 100mm thick. This means I will need to put them in the
insulation layers, do I have to do anything special for this ?

You do need to ensure that cables don't become totally surrounded by
insulation (unless you've done custom circuit designs taking that into
account). If using the usual cable sizes you have two options: cables
can either be clipped along the studs or run in PVC conduit fixed to the
studs. For these methods and T&E cable the current ratings in columns A
& B of the following table apply:

Size Ratings in amps (ambient temperature 30 deg.C
mm^2 A B C conductor temperature 70 deg.C)
---- ---- -- --
1 11.5 12 16
1.5 14.5 15 20
2.5 20 21* 27
4 26 27 37
6 32 35 47
10 44 47 64
16 57 63 85

Key to columns:
A - in conduit in insulated wall (ref. method 6)
B - directly in insulated wall (ref. method 15)
C - clipped direct (ref. method 1)


In the other walls I can run the cables vertically from a "device", or
horrizontally between 2 devices in the plasterwork, which some plastic
protection - is this correct ?

Yes, and no protection is required for cables in these zones. For more
detail (illustrated) see http://www.niceic.org.uk/downloads/C5-43.pdf.

I intend to do each room, with a seperate run to/from the fuse box,

If you mean having a separate power (sockets) circuit for each room,
each with its own MCB, then yes, that's OK. If we're talking about
normal sized rooms then you could use 20 A radial circuits rather than
rings.

and two rings in the kitchen, one normal, one economey 7.

You mean one ring on a time-switched supply? That would be unusual, but
I suppose you could. I take it you're using storage heaters too
(otherwise the DNO or metering company wouldn't normally give you a
switched supply).

For my main room, I will have no studd walls, and no clear 100mm space
at the top, as that space if full of ceiling beams, and its too little
anyway. The plan is to put a wooden "trench" into the floor
insulation, and put the wires in this. I would then seal the top with
steel plate, which would be earth bonded. Is this OK ? I'd run the
"trench" round all the walls, and run the cables up to the devices.

I think that could be made to work, or you could use a proprietary floor
trunking system. Isn't there a floor void or roof space above where you
could run the cables and drop down to each point though?

Final problem, where can I put junction boxes ?

You shouldn't need any if wiring anew from scratch. Make all your
branches and spurs at wiring accessories, then the accessibility
requirement is met.

Can they go into the studd walls ?

Not normal screw terminal ones, if they're going to be plasterboarded
over. Crimped or soldered joints in a suitable enclosure are needed for
that.

HTH

Andy

Do you have a link on custom cable sizes, where the cables are totally
in the insulation, or can I simply use 2.5mm cable, and reduce the MCB
size. If I have a ring for each room, this would be fine by me, most
rooms will be bedrooms, studies, only the kitchen has lots of power
requirment.

Thanks
Rick

Rick wrote:

Do you have a link on custom cable sizes, where the cables are totally
in the insulation,

That really is a non-preferred way of doing it. The cable rating should
be taken as being half the clipped-direct rating. For a ring, where you
need 20 A as-installed rating, you'd need 40 A clipped-direct rating,
which would mean having to use 6 mm^2 cable. Since the terminal
capacity of most BS 1363 accessories is 10 mm^2 you have an immediate
problem in that it would be difficult to fit the two ring cables in the
terminal, let alone any spurs. IOW forget it.

or can I simply use 2.5mm cable, and reduce the MCB
size. If I have a ring for each room, this would be fine by me, most
rooms will be bedrooms, studies, only the kitchen has lots of power
requirment.

I'd advise strongly against such a non-standard design approach for
power circuits. There may be circumstances where you can get away with
cables totally embedded in insulation, e.g. parts of lighting circuits,
but you still need to be careful - e.g. you may need 2.5 mm^2 cable on a
10 A lighting circuit and could run into problems with terminal sizes again.

--
Andy

On Mon, 10 Oct 2005 23:40:35 +0100, Andy Wade
wrote:

Rick wrote:

Do you have a link on custom cable sizes, where the cables are totally
in the insulation,

That really is a non-preferred way of doing it. The cable rating should
be taken as being half the clipped-direct rating. For a ring, where you
need 20 A as-installed rating, you'd need 40 A clipped-direct rating,
which would mean having to use 6 mm^2 cable. Since the terminal
capacity of most BS 1363 accessories is 10 mm^2 you have an immediate
problem in that it would be difficult to fit the two ring cables in the
terminal, let alone any spurs. IOW forget it.

or can I simply use 2.5mm cable, and reduce the MCB
size. If I have a ring for each room, this would be fine by me, most
rooms will be bedrooms, studies, only the kitchen has lots of power
requirment.

I'd advise strongly against such a non-standard design approach for
power circuits. There may be circumstances where you can get away with
cables totally embedded in insulation, e.g. parts of lighting circuits,
but you still need to be careful - e.g. you may need 2.5 mm^2 cable on a
10 A lighting circuit and could run into problems with terminal sizes again.

Thanks Andy, I read some stuff, and was comming to the conclusion that
I need to think again, for the reason that I don't like working with
the thick cables, I never thought of the problems of getting the
cables into the connectors, I guess I'd have found that out too late
:-(

I will now look at trying to use the allowed zones, I guess a box of
chalk is about to be used, by me drawing all the cables onto the
walls. I'll run them between the insulation and the plasterboard.

I now see one reason Drivel insulates the outside of his house, I just
ordered another lorry full of the stuff.

Thanks
Rick

"Andy Wade" wrote in message
...
Rick wrote:

Do you have a link on custom cable sizes, where the cables are
totally
in the insulation,

That really is a non-preferred way of doing it. The cable rating
should
be taken as being half the clipped-direct rating. For a ring,
where you
need 20 A as-installed rating, you'd need 40 A clipped-direct
rating,
which would mean having to use 6 mm^2 cable.

Hi Andy,

This document I came across the other day would (if I'm reading it
correctly) seem to disagree.

http://www.iee.org/Publish/WireRegs/Amd1andRC.pdf

Regards

Jim

Jim Ingram wrote:

This document I came across the other day would (if I'm reading it
correctly) seem to disagree.

http://www.iee.org/Publish/WireRegs/Amd1andRC.pdf

Sorry, what does it disagree with? It's not concerned with cables
totally surrounded in thermal insulation at all, so far as I can see.

--
Andy

"Andy Wade" wrote in message
...
Jim Ingram wrote:

This document I came across the other day would (if I'm reading
it
correctly) seem to disagree.

http://www.iee.org/Publish/WireRegs/Amd1andRC.pdf

Sorry, what does it disagree with? It's not concerned with cables
totally surrounded in thermal insulation at all, so far as I can
see.

The whole of the first two paragraphs??

"Consultants raised concerns that ring circuits protected by 32 amp
circuit breakers and
wired in 2.5 mm2 twin with earth cable installed in conduit in a
thermally insulated
wall might not meet the specific requirements of BS 7671 : 2001. The
old Regulation
433-02-04 required that the
"minimum current carrying capacity Iz of the cable be not less than
0.67 x the
rated current setting In of the protective device".


For 32 amp devices this would require a cable rating of 21.44 amps.
Table 4D2A in
Appendix 4 reference method 4 (enclosed in an insulated wall etc)
provides a rating
of 18.5 amps.



Now, as contractors will know, this practice has been carried out for
some time and if
allowance is made for ambient temperature and the close protection
provided by
circuit breakers problems would not be anticipated. However, the
issue would not go
way so the National Committee responsible for BS 7671 looked into the
matter. The
Electrical Research Association were asked to measure the rating of
the standard UK
flat twin with earth insulated and sheathed cables. The cable ratings
given in BS 7671
were not derived from the direct measurement of this particular type
of cable. The
rating tables in the International and Cenelec and British Standard
(7671) are based on
typical type tests, and in the case of table 4D2A, on round cables.
The results of the
ERA's work are published in a new table 4D5A. The rating of 2.5 mm2
flat twin with
earth enclosed in conduit in an insulated wall (now installation
method 6) was found
to be 20 amps. The rating when installed directly into insulated wall
(now installation
method 15) is 21 amps."

It then goes on to say "After some debate the National Committee,
being keen to maintain the use of the UK
ring circuit, amended the basic requirement for the rating of the
current carrying
capacity of the cable to be no less than 20 amps."



Perhaps I'm simply confused by the terminology. If so what is the
difference between being enclosed in a thermaly insulated wall and
cables being surrounded by thermal insulation (I believe the original
post related to walls as opposed to insulation in ceilings which
might well be a different).

Jim

Jim Ingram wrote:

The whole of the first two paragraphs??
[Big snip]
Perhaps I'm simply confused by the terminology.

'Fraid so.

If so what is the difference between being enclosed in a thermaly
insulated wall and cables being surrounded by thermal insulation (I
believe the original post related to walls as opposed to insulation
in ceilings which might well be a different).

It's what I pointed out at the start. The table I posted is basically
Table 4D5A. It deals with two cable installation methods "installed
directly in an insulated wall" (Method 15) and "enclosed in conduit in
an insulated wall" (Method 6). In both cases one side of the cable or
its conduit is not covered in thermal insulation, but is against
studwork, allowing heat to escape. Wood has a thermal conductivity
about four times higher than most insulation materials.

Where a cable is completely surrounded by insulation on all sides (and
for a significant length) is a completely different situation. There's
far more resistance to getting the heat out and, for any given current,
the cable will run much hotter. The current rating is half the Method 1
(clipped direct) rating, pushing up the cable size required to an
impractical extent in some cases, as I tried to explain.

--
Andy

"Andy Wade" wrote in message
...
Jim Ingram wrote:

The whole of the first two paragraphs??
[Big snip]
Perhaps I'm simply confused by the terminology.

'Fraid so.



Thanks Andy. Your original explanation was fine. I should have read
your first post more carefully.

Jim