Hello,

What is the best way to chase walls for cabling? I read the wiki FAQ
and it talks about making two lines with an angle grinder and then a
bolster chisel to knock out the bit between. That's what I have been
doing. I am using a 115mm angle grinder which is cutting about an inch
into the wall. That's as far as it will go. It's cutting about 10mm of
plaster and 15mm of breeze block. Is that deep enough or do I need to
use a chisel to go deeper?

The angle grinder is making some nice deep lines, but I am not getting
a clean cut of the gap between the lines. The breeze block is very
rough. What is the best way to get a smooth finish? Do I need to
sharpen the chisel? Could it be blunt?

What is the best thing to drop the cable in? Wickes & Screwfix sell
some channeling, which is a bit like a gutter. The problems I see with
this a
1. plaster could get round the back and onto the cables or block the
channel
2. the wire could scrape against the rough surface of the wall

Wickes also sell the same in metal. I guess the metal offers more
protection against drilling/nailing through the cable but does it have
to be earthed? If it became live I cans see that could be very
dangerous.

I see the wiki uses proper conduit, which would avoid both of my
problems above, but if it is 20mm in diameter, it would only be 5mm
beneath the surface. Would that be deep enough? How do you hold it in
place whilst the plaster sets around it?

Thanks,
Sam.

"Sam" wrote in message
...
Hello,

What is the best way to chase walls for cabling? I read the wiki FAQ
and it talks about making two lines with an angle grinder and then a
bolster chisel to knock out the bit between. That's what I have been
doing. I am using a 115mm angle grinder which is cutting about an inch
into the wall. That's as far as it will go. It's cutting about 10mm of
plaster and 15mm of breeze block. Is that deep enough or do I need to
use a chisel to go deeper?

The angle grinder is making some nice deep lines, but I am not getting
a clean cut of the gap between the lines. The breeze block is very
rough. What is the best way to get a smooth finish? Do I need to
sharpen the chisel? Could it be blunt?

What is the best thing to drop the cable in? Wickes & Screwfix sell
some channeling, which is a bit like a gutter. The problems I see with
this a
1. plaster could get round the back and onto the cables or block the
channel
2. the wire could scrape against the rough surface of the wall

Wickes also sell the same in metal. I guess the metal offers more
protection against drilling/nailing through the cable but does it have
to be earthed? If it became live I cans see that could be very
dangerous.

I see the wiki uses proper conduit, which would avoid both of my
problems above, but if it is 20mm in diameter, it would only be 5mm
beneath the surface. Would that be deep enough? How do you hold it in
place whilst the plaster sets around it?

Thanks,
Sam.

Buy a sall cheap circular saw and change the blade for a masonry one you can
then set the depth what you like and at the same tie have a flat edge to
glide up the wall and also connect a hoover to it.. ;-)

Sam wrote:

What is the best way to chase walls for cabling? I read the wiki FAQ
and it talks about making two lines with an angle grinder and then a
bolster chisel to knock out the bit between. That's what I have been

It works, but only if you like dust!

One of the proper wall chasing machines that uses two angle grinder
blades and has a housing to control the dust is better.

doing. I am using a 115mm angle grinder which is cutting about an inch
into the wall. That's as far as it will go. It's cutting about 10mm of
plaster and 15mm of breeze block. Is that deep enough or do I need to
use a chisel to go deeper?

Plenty deep enough. If you use oval conduit for the cables you only 10mm
of depth or so for the conduit.

The angle grinder is making some nice deep lines, but I am not getting
a clean cut of the gap between the lines. The breeze block is very
rough. What is the best way to get a smooth finish? Do I need to
sharpen the chisel? Could it be blunt?

You don't really need a smooth finish - as long as the trunking can sit
in the chase deep enough to get covered up later, you should be ok.


What is the best thing to drop the cable in? Wickes & Screwfix sell
some channeling, which is a bit like a gutter. The problems I see with
this a
1. plaster could get round the back and onto the cables or block the
channel
2. the wire could scrape against the rough surface of the wall

This is capping - only really any use for protecting cables prior to
plastering. Not much use for your application.

Wickes also sell the same in metal. I guess the metal offers more
protection against drilling/nailing through the cable but does it have
to be earthed? If it became live I cans see that could be very
dangerous.

The thin metal stuff offers little more protection against nailing etc
than the plastic. The main benefit is that it stays where you bend it a
little better.

I see the wiki uses proper conduit, which would avoid both of my

What this one?:

http://wiki.diyfaq.org.uk/index.php?title=Wall_chaser

problems above, but if it is 20mm in diameter, it would only be 5mm
beneath the surface. Would that be deep enough? How do you hold it in
place whilst the plaster sets around it?

If you use the oval 22mm conduit:

http://www.tlc-direct.co.uk/Products/MTOV20.html

the depth is only 11mm

You can hold it in place with a blob of bonding plaster or gripfil etc.
Even just a couple of large head clout nails.



--
Cheers,

John.

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

"Sam" wrote in message
...
Hello,

What is the best way to chase walls for cabling? I read the wiki FAQ
and it talks about making two lines with an angle grinder and then a
bolster chisel to knock out the bit between. That's what I have been
doing. I am using a 115mm angle grinder which is cutting about an inch
into the wall. That's as far as it will go. It's cutting about 10mm of
plaster and 15mm of breeze block. Is that deep enough or do I need to
use a chisel to go deeper?

The angle grinder is making some nice deep lines, but I am not getting
a clean cut of the gap between the lines. The breeze block is very
rough. What is the best way to get a smooth finish? Do I need to
sharpen the chisel? Could it be blunt?

What is the best thing to drop the cable in? Wickes & Screwfix sell
some channeling, which is a bit like a gutter. The problems I see with
this a
1. plaster could get round the back and onto the cables or block the
channel
2. the wire could scrape against the rough surface of the wall

Wickes also sell the same in metal. I guess the metal offers more
protection against drilling/nailing through the cable but does it have
to be earthed? If it became live I cans see that could be very
dangerous.

I see the wiki uses proper conduit, which would avoid both of my
problems above, but if it is 20mm in diameter, it would only be 5mm
beneath the surface. Would that be deep enough? How do you hold it in
place whilst the plaster sets around it?

I just used normal trunking and screwed it into the chased wall. Inserted
the cables and then clipped the lid onto the trunking. This was firm enough
to plaster over.

Steven.

On Mon, 18 Aug 2008 23:26:04 +0100, "Steven Campbell"
wrote:

I just used normal trunking and screwed it into the chased wall. Inserted
the cables and then clipped the lid onto the trunking. This was firm enough
to plaster over.

That's fine as long as you remember that the cable is effectively
buried. Right angle bends in trunking will make it virtually
impossible to 'cut and draw' to replace a cable.

--
Frank Erskine

Thanks. I have returned the channeling and have exchanged it for the
oval conduit. How does this affect the rating of the T&E?

I looked at the URL you gave for the wiki and that's not the page I
found. I must have found a different DIY site (via google).

I read some old posts about the Aldi wall chaser. Now that people have
had time to play with them, what were your experiences?

Sam wrote:

Thanks. I have returned the channeling and have exchanged it for the
oval conduit. How does this affect the rating of the T&E?

It reduces it a little, but not much. Column C is the normal figure for
"clipped direct" or a cable buried directly in plaster. Using conduit
results in de-rating to the figures shown in column A. So 2.5mm T&E
drops from 27A to 23A

http://wiki.diyfaq.org.uk/index.php?title=Cables#T.26E

I looked at the URL you gave for the wiki and that's not the page I
found. I must have found a different DIY site (via google).

Thought that may be the case since our one probably answered your
question! ;-)

I read some old posts about the Aldi wall chaser. Now that people have
had time to play with them, what were your experiences?

Not tried the aldi one. I have a Sparky one, which is ok, and does a
good job of eliminating the dust. Has slightly awkward handling though.

--
Cheers,

John.

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

wrote:
On 19 Aug,
John Rumm wrote:

It reduces it a little, but not much. Column C is the normal figure for
"clipped direct" or a cable buried directly in plaster. Using conduit
results in de-rating to the figures shown in column A. So 2.5mm T&E
drops from 27A to 23A

And then you stick two cables in and it drops to 19.5, just below what is
necessary for a ring.

Two smaller conduits solve that problem, and are often easier to thread
anyway.

--
Cheers,

John.

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

On Wed, 20 Aug 2008 02:55:39 +0100, John Rumm
wrote:

Two smaller conduits solve that problem, and are often easier to thread
anyway.

Thanks for the link to the table. Where do you get the figure for
running two or more cables in the same conduit? I was going to run two
separate conduits anyway; partly because I hadn't seen wide conduit in
the shops and partly because like you, I think it would be easier to
push two wires down two separate conduits anyway. Do the regs. say
that the two conduits must be a certain distance apart? Do I have to
chase two separate channels or can I place them together in one wide
channel (the latter would be less work!)

One final question: our house does not have a hall, so you have to
walk from the stairs through the lounge through the dining room to the
kitchen. There are is one light switch at the stair end of the lounge
and one at the kitchen end of the dining room but nothing in between.
I would like to fit two-way switches between the lounge and dining
room. These would be either side of the same (breeze block) wall. I am
concerned if I chased a channel on either side of the wall, I would
effectively be removing twice the depth and would this weaken the
wall? Even if I offset the two channels, I wonder whether the effect
might be the same because they were so close? Is it that you are
allowed to remove one third the depth safely?

I wondered whether I should chase one channel on one side of the wall
to carry both wires and then drill a hole through the wall to take the
second wire to the other switch. Is this acceptable?

Thanks,
Sam.

Sam wrote:

Two smaller conduits solve that problem, and are often easier to thread
anyway.

Thanks for the link to the table. Where do you get the figure for
running two or more cables in the same conduit? I was going to run two

The On Site Guide has some info.

Drop me an email, I can send you some tables.

separate conduits anyway; partly because I hadn't seen wide conduit in
the shops and partly because like you, I think it would be easier to
push two wires down two separate conduits anyway. Do the regs. say
that the two conduits must be a certain distance apart? Do I have to
chase two separate channels or can I place them together in one wide
channel (the latter would be less work!)

One wide chase is ok IIUC.

One final question: our house does not have a hall, so you have to
walk from the stairs through the lounge through the dining room to the
kitchen. There are is one light switch at the stair end of the lounge
and one at the kitchen end of the dining room but nothing in between.
I would like to fit two-way switches between the lounge and dining
room. These would be either side of the same (breeze block) wall. I am
concerned if I chased a channel on either side of the wall, I would
effectively be removing twice the depth and would this weaken the
wall? Even if I offset the two channels, I wonder whether the effect
might be the same because they were so close? Is it that you are
allowed to remove one third the depth safely?

If you want switches on both sides of a wall, then chase one side only,
and run all the wires in that chase. Then drill though at the relevant
point for the other switch. (placing the switches slight offset from
each other)

I wondered whether I should chase one channel on one side of the wall
to carry both wires and then drill a hole through the wall to take the
second wire to the other switch. Is this acceptable?

;-) Should have read to the end of your post before writing the above!

--
Cheers,

John.

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

On Wed, 20 Aug 2008 02:55:39 +0100, John Rumm
wrote:

wrote:
On 19 Aug,
John Rumm wrote:

It reduces it a little, but not much. Column C is the normal figure for
"clipped direct" or a cable buried directly in plaster. Using conduit
results in de-rating to the figures shown in column A. So 2.5mm T&E
drops from 27A to 23A

And then you stick two cables in and it drops to 19.5, just below what is
necessary for a ring.

Two smaller conduits solve that problem, and are often easier to thread
anyway.


I wonder if you can help me? I have a socket that is halfway up the
wall and I would like to lower it to a more sensible level. The wires
to this socket are run in the metal capping you describe. I am
concerned because both wires are run together and having read the
above post it sounds as though the cables are rated at 19.5A "below
what is necessary for a ring".

When I lower the socket would it be a good idea to remove the capping
and replace it with two conduits? If this one socket is like this, I
suppose the rest of the house is. Should I be alarmed?

When you say the cable rating drops from 27A to 19A, does this mean
the rating of the whole ring drops, or just that section?

Thanks,
Stephen.

On Sat, 23 Aug 2008 00:22:21 +0100, John Rumm
wrote:

If you want switches on both sides of a wall, then chase one side only,
and run all the wires in that chase. Then drill though at the relevant
point for the other switch. (placing the switches slight offset from
each other)


Probably too late for the OP but if you just removed the plaster,
would this give you enough room to run capping on either side of the
wall without chasing?

The problem would be that if the light switches were back to back, you
would not be able to screw through the back of the box without hitting
the other! I don't know how you could get round this without making
one switch noticeably higher/lower/further from the door than the
other.

In article ,
Stephen writes:

I wonder if you can help me? I have a socket that is halfway up the
wall and I would like to lower it to a more sensible level. The wires
to this socket are run in the metal capping you describe. I am
concerned because both wires are run together and having read the
above post it sounds as though the cables are rated at 19.5A "below
what is necessary for a ring".

You're worrying too much. Rings are always installed as yours is.

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

Stephen wrote:

I wonder if you can help me? I have a socket that is halfway up the
wall and I would like to lower it to a more sensible level. The wires
to this socket are run in the metal capping you describe. I am
concerned because both wires are run together and having read the
above post it sounds as though the cables are rated at 19.5A "below
what is necessary for a ring".

Not sure that is correct anyway...

From the on site guide - 16th edition:

"7.2.1 Grouping of Cables
(i) In domestic premises, except for heating cables, the Table 4B1
conventional circuit design permits any number of
single-layer circuits when the spacing between
adjacent surfaces of the cables exceeds one cable
diameter, and, for other than semi-enclosed fuses,
(BS 3036) up to 5 touching, single-layer, circuits, when
clipped to a non-metallic surface (Installation Method 1)"

also, metal capping buried in plaster is treated as reference method C
in the 17th edition (i.e. clipped direct - as above). Hence the
installation method has no addition de-rating to impart.

In fact there are a couple of notes in the 17th edition that also
mention that mechanical protection over a cable buried in plaster (i.e.
capping) may in fact increase it current carrying capacity (for cables
with conductors of CSA = 16mm^2)

So, in summary, nothing to worry about.


--
Cheers,

John.

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

Hello again,

I have another wall chasing problem; this time plumbing rather than
electrical.

I have taken the skirting board off to decorate and noticed that in
places I can just see the top of copper pipe shining above the
concrete floor. The radiator pipes go into the concrete floor and run
along three of the four walls in the room. This means that they must
be running back and forth the length and width of the house. I am
concerned that these unlagged pipes must be losing a lot of heat into
the concrete floor.

Since we are decorating, I wondered about re-doing the plumbing at the
same time. The only way I can see would be to drop pipes from
upstairs. I was thinking of boxing these in a corner of the room but
SWMBO would like them chased into the walls so there is no boxing. The
problem is I would like to lag the pipes, and even with the "economy"
lagging, the diameter is 45mm, which I think is too much to remove
from a wall. What do you think? Should I insist on the box work?

I would also have to put drains on the low points of any pipe drop but
I would like to use chrome pipe where it will be visible; does anyone
know of any chrome plated drain cocks?

Thanks,
Stephen.

Stephen wrote:

upstairs. I was thinking of boxing these in a corner of the room but
SWMBO would like them chased into the walls so there is no boxing. The
problem is I would like to lag the pipes, and even with the "economy"
lagging, the diameter is 45mm, which I think is too much to remove
from a wall. What do you think? Should I insist on the box work?

Depends on the wall... on a wall made from 4" block or brick with
plaster over, you would not be cutting that far into the blocks. Stud
walls you could obviously run in the void. Also less of a problem on non
load bearing walls.

I would also have to put drains on the low points of any pipe drop but
I would like to use chrome pipe where it will be visible; does anyone
know of any chrome plated drain cocks?

You can get chrome rad vales with built in drain points, failing that
use a service valve tee'd off from the pipe.

--
Cheers,

John.

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

Stephen wrote:
On Fri, 05 Sep 2008 01:30:27 +0100, wrote:

I think he was confused by my post referring to running together enclosed in
conduit rather than under capping.

Sorry I joined the thread late and must have misread it; you are right
I thought capping = conduit. I am reassured that everything is ok.

I note that John said:

metal capping buried in plaster is treated as reference method C

What is the situation with plastic capping? Is that treated any
different?

In reality no. (Although it won't have any benefit from the point of
view of heat dissipation in the way that metal might.

I haven't got an on-site guide to check because I am waiting for the
17th edition version to be in print; it seems silly to get what will
soon be obsolete if a new version is due any day.

Supposedly release on the first of this month, but my Amazon order is
still waiting so it seems. (there are PDF versions of the 16th floating
about!)


--
Cheers,

John.

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

On Sat, 06 Sep 2008 05:40:19 +0100, John Rumm
wrote:


Depends on the wall... on a wall made from 4" block or brick with
plaster over, you would not be cutting that far into the blocks. Stud
walls you could obviously run in the void. Also less of a problem on non
load bearing walls.

I'm afraid they are not stud walls, unfortunately. The problem is that
I don't know what is under the plaster. I think the door frame is
about 9 cm wide, so I guess it's a 9 cm block, and I know from having
lifted floor boards that the joists start over it, so it is bearing
the upstairs floor on it.

You can get chrome rad vales with built in drain points

I have seen these but they would drain to the bottom of the radiator
rather than the bottom of the pipe run, wouldn't they? I don't know
whether this would be a major problem? I think I might be better
tee-ing off the pipe.

Thanks,
Stephen.

Stephen wrote:
On Sat, 06 Sep 2008 05:40:19 +0100, John Rumm
wrote:

Depends on the wall... on a wall made from 4" block or brick with
plaster over, you would not be cutting that far into the blocks. Stud
walls you could obviously run in the void. Also less of a problem on non
load bearing walls.

I'm afraid they are not stud walls, unfortunately. The problem is that
I don't know what is under the plaster. I think the door frame is
about 9 cm wide, so I guess it's a 9 cm block, and I know from having
lifted floor boards that the joists start over it, so it is bearing
the upstairs floor on it.

A "normal" block wall is about 4" (10cm) plus at least half inch of
plaster either side. Yours may be a thinner block I suppose.

You can get chrome rad vales with built in drain points

I have seen these but they would drain to the bottom of the radiator
rather than the bottom of the pipe run, wouldn't they? I don't know

Yup. Depending on how the pipe runs that may or may not matter. (in fact
even if the pipe has a little water left in it, it does not usually matter.

whether this would be a major problem? I think I might be better
tee-ing off the pipe.

In the past, I have tee'd off, into a service valve, then straight
through the wall into the gully the other side (obviously choosing the
tee position to match the gully rather than the other way around!)

--
Cheers,

John.

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

On Sat, 06 Sep 2008 23:57:42 +0100, John Rumm
wrote:

A "normal" block wall is about 4" (10cm) plus at least half inch of
plaster either side. Yours may be a thinner block I suppose.

There's about 10mm on the side I have "investigated", so possibly you
are right: about half an inch each side. I shall have to measure the
width across the door frame again.

I did wonder about chasing the external wall. This is thicker but of
course some of it's depth is cavity. Are both sides of a cavity wall
load bearing? I would think the outside bears the weight of all the
bricks above and that the inside bears the weight of the joists? I
presume joists do not cross the cavity? Wouldn't that defeat the point
of the cavity?

Depending on how the pipe runs that may or may not matter. (in fact
even if the pipe has a little water left in it, it does not usually matter.

In which case a lockshield with drain would be the easiest way to go.
Would it matter there was only a drain on one side of the radiator
though? Would I need a drain on the TRV side too?

In the past, I have tee'd off, into a service valve, then straight
through the wall into the gully the other side

I had not realised you were taking the tee outside; what a good idea
(where possible).

Regarding chasing for electrics, which is what the thread was about
before I hijacked it, when fixing oval conduit does it matter if you
use solvent adhesive? I use the cheap Tool station glue screws. I
wasn't sure if I had to use the solvent free version or whether the
solvent version would damage the plastic? I think the solvent version
sets faster so would be preferable if it is compatible with the
conduit plastic?

Thanks,
Stephen.

Stephen wrote:

I did wonder about chasing the external wall. This is thicker but of
course some of it's depth is cavity. Are both sides of a cavity wall
load bearing? I would think the outside bears the weight of all the

potentially... the inner leaf will carry the joists, and quite possibly
the roof load as well.

bricks above and that the inside bears the weight of the joists? I
presume joists do not cross the cavity? Wouldn't that defeat the point
of the cavity?

In modern places the joists do not piece either leaf of the wall - they
terminate in joist hangers that are either bolted to, or more commonly,
built into a mortar line the wall.

Depending on how the pipe runs that may or may not matter. (in fact
even if the pipe has a little water left in it, it does not usually matter.

In which case a lockshield with drain would be the easiest way to go.
Would it matter there was only a drain on one side of the radiator
though? Would I need a drain on the TRV side too?

One side is fine. That will let you drain the pipe and the rad. You can
then remove the rad a drain the other leg of pipe if you want straight
from the TRV.

In the past, I have tee'd off, into a service valve, then straight
through the wall into the gully the other side

I had not realised you were taking the tee outside; what a good idea
(where possible).

Not an idea I take credit for - remember seeing someone doing it on TV
many years ago (may have been a tomorrow's world special on houses of
the future), but it works well. Just a quick turn with a screw driver
lets you drain down without any mess and no titting about with hose
pipes or leaky drain valves etc.

Regarding chasing for electrics, which is what the thread was about
before I hijacked it, when fixing oval conduit does it matter if you
use solvent adhesive? I use the cheap Tool station glue screws. I
wasn't sure if I had to use the solvent free version or whether the
solvent version would damage the plastic? I think the solvent version
sets faster so would be preferable if it is compatible with the
conduit plastic?

This is just for getting the conduit to stay put in the chase I presume?
Yup any glue is fine, as would be a couple of large head clout nails
(for the avoidance of doubt, knocked in beside the conduit with the head
holding it it place - not driven through it! ;-))




--
Cheers,

John.

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