Dear group,

The only formal training my limited attention span permitted was in
electronics and not electrical installation. I also work as a technician on
a site with all cables accessible and understand the difficulty of
predicting future needs.

This explains my instinct to wire my house in an unconventional way avoiding
cutting joists and running cables under the floor or buried in plaster.

My plan is to use vertical and horizontal cable ducts around the stairwell
at the centre of my house in addition to the already useful duct formed by
the gap between the first and second first upper floor joists which runs the
whole length of the house and which will also carry gas and water pipes.

In the absence of or high price of trunking that is easy on the eye, and
given that PVC trunking is permitted, I wonder if there would be any
objection to my using bespoke MDF service ducts.

I have done a fair bit of Googling on the subject but to no avail.

thanks ...

Jeremy

On Tue, 1 Feb 2005 05:53:15 UTC, "brugnospamsia"
wrote:

This explains my instinct to wire my house in an unconventional way avoiding
cutting joists and running cables under the floor or buried in plaster.

My plan is to use vertical and horizontal cable ducts around the stairwell
at the centre of my house in addition to the already useful duct formed by
the gap between the first and second first upper floor joists which runs the
whole length of the house and which will also carry gas and water pipes.

Ducts presumably count as trunking, so the cables will have to be
derated as per the regs. So you'll need better than 2.5mm2 for a final
ring circuit, for example, unless protected at (say) 20A.
--
Bob Eager
begin a new life...dump Windows!

On Tue, 01 Feb 2005 05:53:15 +0000, brugnospamsia wrote:

Dear group,

The only formal training my limited attention span permitted was in
electronics and not electrical installation. I also work as a technician on
a site with all cables accessible and understand the difficulty of
predicting future needs.

This explains my instinct to wire my house in an unconventional way avoiding
cutting joists and running cables under the floor or buried in plaster.

My plan is to use vertical and horizontal cable ducts around the stairwell
at the centre of my house in addition to the already useful duct formed by
the gap between the first and second first upper floor joists which runs the
whole length of the house and which will also carry gas and water pipes.

In the absence of or high price of trunking that is easy on the eye, and
given that PVC trunking is permitted, I wonder if there would be any
objection to my using bespoke MDF service ducts.

I have done a fair bit of Googling on the subject but to no avail.

thanks ...

Jeremy

Don't forget to apply any required grouping correction per the regs too if
there's more than one cable in there too.

I can't honestly advise on the pro's and cons of MDF for this. The only
question I would ask myself (and which I can't answer without checking) is
would MDF constitutes a greater fire or fume risk if one of the cables got
excessively hot due to a fault?

I suspect it doesn't matter as cables are routinely clipped to joists etc, but it's
worth thinking about.

HTH

Timbo

On Tue, 01 Feb 2005 10:41:54 +0000, Tim wrote:

On Tue, 01 Feb 2005 05:53:15 +0000, brugnospamsia wrote:

Dear group,

The only formal training my limited attention span permitted was in
electronics and not electrical installation. I also work as a technician on
a site with all cables accessible and understand the difficulty of
predicting future needs.

This explains my instinct to wire my house in an unconventional way avoiding
cutting joists and running cables under the floor or buried in plaster.

My plan is to use vertical and horizontal cable ducts around the stairwell
at the centre of my house in addition to the already useful duct formed by
the gap between the first and second first upper floor joists which runs the
whole length of the house and which will also carry gas and water pipes.

In the absence of or high price of trunking that is easy on the eye, and
given that PVC trunking is permitted, I wonder if there would be any
objection to my using bespoke MDF service ducts.

I have done a fair bit of Googling on the subject but to no avail.

thanks ...

Jeremy

Don't forget to apply any required grouping correction per the regs too if
there's more than one cable in there too.


I should have said *as well* as any derating due to enclosure as Bob
mentioned, I meant to reply to his reply.

Butterfingers me...

Timbo

"Bob Eager" wrote in message
...
On Tue, 1 Feb 2005 05:53:15 UTC, "brugnospamsia"
wrote:

This explains my instinct to wire my house in an unconventional way
avoiding
cutting joists and running cables under the floor or buried in plaster.

My plan is to use vertical and horizontal cable ducts around the
stairwell
at the centre of my house in addition to the already useful duct formed
by
the gap between the first and second first upper floor joists which runs
the
whole length of the house and which will also carry gas and water pipes.

Ducts presumably count as trunking, so the cables will have to be
derated as per the regs. So you'll need better than 2.5mm2 for a final
ring circuit, for example, unless protected at (say) 20A.
--

oh bum !

mind you at the moment I have a single ring for the whole house with an
immersion heater on it fused at 30 amps .....

Anyone know where I can get the asbestos substitute board I once saw them
use in my building and whether it's horribly expensive ?

Jeremy

The board you describe is called superboard available from Jewsons, a 8x4
sheet around £80,most likely available from all other merchants as well

brugnospamsia wrote:

"Bob Eager" wrote in message
...
Ducts presumably count as trunking, so the cables will have to be
derated as per the regs. So you'll need better than 2.5mm2 for a final
ring circuit, for example, unless protected at (say) 20A.

oh bum !

That's wrong though. The cable for a 32A ring only has to achieve 20A
in-situ rating, which a single 2.5 T&E cable in conduit, trunking or
duct easily does. You'd only have to go up to 4mm^2 if dictated by the
application of grouping factors with cables of other relevant circuits,
or unusually high ambient temperature.

Anyone know where I can get the asbestos substitute board I once saw them
use in my building and whether it's horribly expensive ?

Masterboard, from any builders' merchant?

--
Andy

On Wed, 2 Feb 2005 00:56:11 UTC, Andy Wade
wrote:

"Bob Eager" wrote in message
...
Ducts presumably count as trunking, so the cables will have to be
derated as per the regs. So you'll need better than 2.5mm2 for a final
ring circuit, for example, unless protected at (say) 20A.

oh bum !

That's wrong though. The cable for a 32A ring only has to achieve 20A
in-situ rating, which a single 2.5 T&E cable in conduit, trunking or
duct easily does. You'd only have to go up to 4mm^2 if dictated by the
application of grouping factors with cables of other relevant circuits,
or unusually high ambient temperature.

I was assuming that there would be grouping if he was making ducts -
perhaps there isn't...!

--
Bob Eager
begin a new life...dump Windows!

"Bob Eager" wrote in message
...
On Wed, 2 Feb 2005 00:56:11 UTC, Andy Wade
wrote:

"Bob Eager" wrote in message
...
Ducts presumably count as trunking, so the cables will have to be
derated as per the regs. So you'll need better than 2.5mm2 for a final
ring circuit, for example, unless protected at (say) 20A.

oh bum !

That's wrong though. The cable for a 32A ring only has to achieve 20A
in-situ rating, which a single 2.5 T&E cable in conduit, trunking or
duct easily does. You'd only have to go up to 4mm^2 if dictated by the
application of grouping factors with cables of other relevant circuits,
or unusually high ambient temperature.

I was assuming that there would be grouping if he was making ducts -
perhaps there isn't...!


thinking about it, the cable density is very low. The only problem I can see
is that the wide vertical duct will carry central heating pipes too - but
I'll insulate and keep them seperate. In essence my proposal isn't much
different from running cables behind drylining.

Is it possible to obtain meter tails longer than 1 metre ?

I would like to move my CU ...

thanks...

Jeremy

On Wed, 02 Feb 2005 15:37:40 +0000, brugnospamsia wrote:

Is it possible to obtain meter tails longer than 1 metre ?

I would like to move my CU ...


Believe so, as I heard of much longer runs. It's worth getting
professional advice if you're going to go more than about 2m away.
Something I read recently suggested 2m might require a fused isolator on
your side of the meter. I'm thinking of doing the same thing. The
electricity supply company might be able to advise.

Cheers

Timbo

"Tim S" wrote in message
news
On Wed, 02 Feb 2005 15:37:40 +0000, brugnospamsia wrote:

Is it possible to obtain meter tails longer than 1 metre ?

I would like to move my CU ...


Believe so, as I heard of much longer runs. It's worth getting
professional advice if you're going to go more than about 2m away.
Something I read recently suggested 2m might require a fused isolator on
your side of the meter. I'm thinking of doing the same thing. The
electricity supply company might be able to advise.

I wish they'd put my meter outside for free instead of pestering me to have
it changed :-(

Si is it permissible to use wood as trunking? I'm thinking here of
tweaked skirting board primarily.

NT

Tim S wrote:
On Wed, 02 Feb 2005 15:37:40 +0000, brugnospamsia wrote:

Is it possible to obtain meter tails longer than 1 metre ?

Pretty-well any electrical wholesaler will sell you any length of 25mm^2
6181Y cable you like by the metre - limited only by the reel length!

Believe so, as I heard of much longer runs. It's worth getting
professional advice if you're going to go more than about 2m away.
Something I read recently suggested 2m might require a fused isolator on
your side of the meter. I'm thinking of doing the same thing. The
electricity supply company might be able to advise.

That's essentially correct. The maximum length of meter tails is
limited to either two or three metres, depending on who your supply
distribution network operator is. This is because they will not allow
their main fuse to be used to protect your wiring, other than over the
short length of the tails.

If you want to move your consumer unit some distance away from the meter
you need to install a 100A DP switch-fuse (assuming a normal
single-phase domestic supply) within the 2m or 3m tails-reach limit of
the meter. You can then run a distribution circuit of any length you
like (in principle) to the CU - which should now strictly speaking be
called a distribution board. Or you can feed multiple distribution
circuits and boards using a suitably designed 'main switchboard' scheme
by the meter.

The distribution circuit(s) will need to be properly designed to comply
with all the relevant requirements of BS 7671: cable size/rating,
voltage drop, earth fault loop impedance and so on. There are several
valid choices for the type of cable that could be used - 'meter tail
cable' (6181Y), conduit cable (6491X) in conduit or trunking, steel wire
armoured (SWA), or mineral insulated (MICC) are probably the main ones.

A Google search will reveal lots of previous threads on this subject,
but because of the need for proper design input I don't suggest tackling
this as DIY unless you really know what you're doing.

--
Andy

"Andy Wade" wrote in message
...
Tim S wrote:
On Wed, 02 Feb 2005 15:37:40 +0000, brugnospamsia wrote:

Is it possible to obtain meter tails longer than 1 metre ?

Pretty-well any electrical wholesaler will sell you any length of 25mm^2
6181Y cable you like by the metre - limited only by the reel length!

Believe so, as I heard of much longer runs. It's worth getting
professional advice if you're going to go more than about 2m away.
Something I read recently suggested 2m might require a fused isolator
on
your side of the meter. I'm thinking of doing the same thing. The
electricity supply company might be able to advise.

That's essentially correct. The maximum length of meter tails is
limited to either two or three metres, depending on who your supply
distribution network operator is. This is because they will not allow
their main fuse to be used to protect your wiring, other than over the
short length of the tails.

If you want to move your consumer unit some distance away from the meter
you need to install a 100A DP switch-fuse (assuming a normal
single-phase domestic supply) within the 2m or 3m tails-reach limit of
the meter. You can then run a distribution circuit of any length you
like (in principle) to the CU - which should now strictly speaking be
called a distribution board. Or you can feed multiple distribution
circuits and boards using a suitably designed 'main switchboard' scheme
by the meter.

The distribution circuit(s) will need to be properly designed to comply
with all the relevant requirements of BS 7671: cable size/rating,
voltage drop, earth fault loop impedance and so on. There are several
valid choices for the type of cable that could be used - 'meter tail
cable' (6181Y), conduit cable (6491X) in conduit or trunking, steel wire
armoured (SWA), or mineral insulated (MICC) are probably the main ones.

This is all entirely correct. The new protected cable is often referred to
as a "sub-main". Don't forget you may need to run a new earth cable as well,
of suitable size. I have done it myself DIY.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Bob Mannix wrote:

This is all entirely correct. The new protected cable is often referred to
as a "sub-main".

In common parlance it is indeed, but if you look at the definitions in
BS 7671 'sub-main' specifically refers to the case of a distribution
circuit that feeds a separate building or installation.

--
Andy