Hi

I think that the regs indicate the cables in walls need to be protected against physical damage
(e.g. hammering nails into the wall). I think that unless the cable is over 50mm deep in the
wall or within 150mm of the edge of the wall that mechanical protection is needed. Fair enough.

But in my house, re-wired in 1982, all the cables in the walls are less than 50mm deep and in
plastic oval conduit. If I'm extending the wiring, can I legitimately carry on with this
scheme, or need I install metal shielding?


Regards
John

On Thu, 28 Aug 2003 21:39:12 +0100, "Me"
wrote:

Hi

I think that the regs indicate the cables in walls need to be protected against physical damage
(e.g. hammering nails into the wall). I think that unless the cable is over 50mm deep in the
wall or within 150mm of the edge of the wall that mechanical protection is needed. Fair enough.

But in my house, re-wired in 1982, all the cables in the walls are less than 50mm deep and in
plastic oval conduit. If I'm extending the wiring, can I legitimately carry on with this
scheme, or need I install metal shielding?


Regards
John


The Wiring Regulations do allow you to run cables concealed without
either the 50mm depth or steel protection either vertically or
horizontally from wiring accessories - i.e. light switches and power
sockets etc.

You only need the depth or protection if you want to run them at an
angle or in other places - e.g. if you went horizontally from a switch
and then up without there being a wiring accessory at the point where
the cable changes direction.

There are also bands at the corners of walls as you say. To be
precise they are 150mm wide in corners (along each wall) and 150mm
from the top of a wall. The band at skirting board level for 150mm
is not a permitted zone from this perspective.


..andy

To email, substitute .nospam with .gl

On Thu, 28 Aug 2003 21:48:21 +0100, Andy Hall wrote:

The Wiring Regulations do allow you to run cables concealed without
either the 50mm depth or steel protection either vertically or
horizontally from wiring accessories - i.e. light switches and power
sockets etc.

You only need the depth or protection if you want to run them at an
angle or in other places - e.g. if you went horizontally from a
switch and then up without there being a wiring accessory at the
point where the cable changes direction.

Not quite. You don't need an accessory at the point of direction
change provided that that point is at the intersection of
vertical/horizontal lines from accessories.

eg fixed pitch font


-----A-----+-----


-----+-----B-----


You can cable between A and B via either route through the + points.

--
Cheers
Dave. pam is missing e-mail

On Thu, 28 Aug 2003 22:44:52 +0100 (BST), "Dave Liquorice"
wrote:

On Thu, 28 Aug 2003 21:48:21 +0100, Andy Hall wrote:

The Wiring Regulations do allow you to run cables concealed without
either the 50mm depth or steel protection either vertically or
horizontally from wiring accessories - i.e. light switches and power
sockets etc.

You only need the depth or protection if you want to run them at an
angle or in other places - e.g. if you went horizontally from a
switch and then up without there being a wiring accessory at the
point where the cable changes direction.

Not quite. You don't need an accessory at the point of direction
change provided that that point is at the intersection of
vertical/horizontal lines from accessories.

eg fixed pitch font


-----A-----+-----


-----+-----B-----


You can cable between A and B via either route through the + points.

Are you sure?

The OSG and Whitfield illustrate and seem to say that a direction
change without an accessory can only happen if the point of direction
change is within one of the corner or top of wall 150mm bands; not
even where a cable goes down vertically from an accessory to the
floor.



..andy

To email, substitute .nospam with .gl

Andy Hall wrote in message
...

Are you sure?

The OSG and Whitfield illustrate and seem to say that a direction
change without an accessory can only happen if the point of
direction change is within one of the corner or top of wall 150mm
bands; not even where a cable goes down vertically from an accessory
to the floor.

BS 7671 itself says: "Where the cable is connected to a point, accessory or
switchgear on the wall or partition, the cable may be installed outside
these zones[*] /only in a straight run/ either horizontally or vertically to
the point accessory or switchgear. [My emphasis]
[*] Meaning the zones within 150 mm of corners or the top of the wall.

That does seem to exclude Dave's interpretation, since that would require
two straight runs. Whether or not this is what the original authors
intended is a moot point. If you regard horizontal and vertical strips
running the full width and height of the wall from every accessory as 'no
go' zones for inserting fixings, then Dave's interpretation introduces no
further risk of damaging a cable.

BTW - to the OP - these requirements were introduced in the 1987 amendment
to the 15th edition and were effective from 12th June '87. Therefore your
house, rewired in '82, may not comply.

--
Andy

thanks, folks!

In article ,
Me wrote:
But in my house, re-wired in 1982, all the cables in the walls are less
than 50mm deep and in plastic oval conduit

I don't think plastic conduit would offer any protection from nails -
especially fine sharp ones like for picture hanging.

--
*Gaffer tape - The Force, light and dark sides - holds the universe together*

Dave Plowman London SW 12
RIP Acorn

On Fri, 29 Aug 2003 09:37:09 +0100, Andy Wade wrote:

BS 7671 itself says: "Where the cable is connected to a point,
accessory or switchgear on the wall or partition, the cable may be
installed outside these zones[*] /only in a straight run/ either
horizontally or vertically to the point accessory or switchgear. [My
emphasis]

[*] Meaning the zones within 150 mm of corners or the top of the
wall.

That does seem to exclude Dave's interpretation, since that would
require two straight runs.

It does indeed.

If you regard horizontal and vertical strips running the full width
and height of the wall from every accessory as 'no go' zones for
inserting fixings,

Which, IMHO, you have to do as you have no idea from looking at an
accessory which of the four possible directions are in use for buried
cables. OK you can take the accessory off and assume(*) that any sides
that don't have a cable leaving them are safe. If you do that with my
interpretation you are still "safe" though.

(*) As we all know "assume" makes an ASS out of U and ME.

--
Cheers
Dave. pam is missing e-mail