Protecting CU tails - possibly one for ARW
 

I need to install a second CU on the opposite side of an inner (cavity)
wall to the side that has the: meter, isolator switch, Henley block and
existing CU. Once the new CU is in place I'll be transferring several
circuits to it and the old one will just be for the garage and
outbuildings. Currently the walls are bare block but will either be
plastered or dry lined later.
The question is how to protect the tails between the Henley block and
the new CU, and how to mount the CU. The distance will be about 3m.

The current plan is to sleeve the hole in the wall with waste pipe and
to either use metal trunking or wooden boxing on the walls to protect
the tails and provide access when the walls are plastered. Above the CU
I plan to provide a boxed-in area (with a removable lid) for the cable
drops.

I presume a flush-mounted CU is the way to go, but I'm open to other
suggestions. Are any particular types recommended? I'll probably have a
mix of RCBOs, MCBs and RCD ... I'd like to go all RCBO but the cost is
very high.

Protecting CU tails - possibly one for ARW
 

On 16/08/2018 16:38, wrote:
I need to install a second CU on the opposite side of an inner (cavity)
wall to the side that has the: meter, isolator switch, Henley block and
existing CU. Once the new CU is in place I'll be transferring several
circuits to it and the old one will just be for the garage and
outbuildings. Currently the walls are bare block but will either be
plastered or dry lined later.
The question is how to protect the tails between the Henley block and
the new CU, and how to mount the CU. The distance will be about 3m.

The current plan is to sleeve the hole in the wall with waste pipe and
to either use metal trunking or wooden boxing on the walls to protect
the tails and provide access when the walls are plastered. Above the CU
I plan to provide a boxed-in area (with a removable lid) for the cable
drops.

If the tails will be covered in, then they need to meet the requirements
for protection of concealed cables. i.e. buried deeper than 50mm or
protected by earthed metal enclosure, or have RCD protection with a =
30mA trip. Since the RCD protection for the whole CU is non compliant or
desirable, the the earthed metallic protection of some kind would be the
way to go. In this case I would just use a large metal galvanised
trunking.

I presume a flush-mounted CU is the way to go, but I'm open to other
suggestions. Are any particular types recommended? I'll probably have a
mix of RCBOs, MCBs and RCD ... I'd like to go all RCBO but the cost is
very high.

RCBOs are not that expensive now, so worth looking at. You could surface
mount the CU on the finished wall but allow cable entry from the rear.
That looks neater and there are no worries about adequately sealing
access to the CU via the knock-outs at the top.


--
Cheers,

John.

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

Protecting CU tails - possibly one for ARW
 

You need to provide mechanical and/or electrical protection to the meter tails.


I did this by using 3mm thick stainless steel as (a) stainless steel blunts most drill bits apart from cobalt ones and (b) does not corrode when plastered over.

I also attached a 10mm earth wire to the stainless steel sheet and connected it to the met ( main earth terminal)

As for rcbos, I got these for ten quid each plus vat so filling a cu with rcbos is not really a bank breaker.

Protecting CU tails - possibly one for ARW
 

Screwfix are selling BG RCBOs for £11.99 at the moment and BG main switch only CU with 10 spare ways is only £32.

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 00:37, John Rumm wrote:
On 16/08/2018 16:38, wrote:
I need to install a second CU on the opposite side of an inner
(cavity) wall to the side that has the: meter, isolator switch, Henley
block and existing CU. Once the new CU is in place I'll be
transferring several circuits to it and the old one will just be for
the garage and outbuildings. Currently the walls are bare block but
will either be plastered or dry lined later.
The question is how to protect the tails between the Henley block and
the new CU, and how to mount the CU. The distance will be about 3m.

The current plan is to sleeve the hole in the wall with waste pipe and
to either use metal trunking or wooden boxing on the walls to protect
the tails and provide access when the walls are plastered. Above the
CU I plan to provide a boxed-in area (with a removable lid) for the
cable drops.

If the tails will be covered in, then they need to meet the requirements
for protection of concealed cables. i.e. buried deeper than 50mm or
protected by earthed metal enclosure, or have RCD protection with a =
30mA trip. Since the RCD protection for the whole CU is non compliant or
desirable, the the earthed metallic protection of some kind would be the
way to go. In this case I would just use a large metal galvanised trunking.

SWA is perhaps an alternative. Given the bending radius I might go for 2
x 10mm^2 in parallel, which if clipped direct will be more that the
company fuse.

The alternative is 3mm of steel for mechanical protection if the cable
is hidden under plaster etc.

Protecting CU tails - possibly one for ARW
 

On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go for 2
x 10mm^2 in parallel, which if clipped direct will be more that the
company fuse.

There are issues with paralleling conductors and it's not standard practise.

The alternative is 3mm of steel for mechanical protection if the cable
is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy flexi
conduit (Kopex is very heavy duty, although plastic, it will survive
some quite ferocious beating - does not count as mechanical protection
for burying though).

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 00:37, John Rumm wrote:
On 16/08/2018 16:38, wrote:
I need to install a second CU on the opposite side of an inner
(cavity) wall to the side that has the: meter, isolator switch, Henley
block and existing CU. Once the new CU is in place I'll be
transferring several circuits to it and the old one will just be for
the garage and outbuildings. Currently the walls are bare block but
will either be plastered or dry lined later.
The question is how to protect the tails between the Henley block and
the new CU, and how to mount the CU. The distance will be about 3m.

The current plan is to sleeve the hole in the wall with waste pipe and
to either use metal trunking or wooden boxing on the walls to protect
the tails and provide access when the walls are plastered. Above the
CU I plan to provide a boxed-in area (with a removable lid) for the
cable drops.

If the tails will be covered in, then they need to meet the requirements
for protection of concealed cables. i.e. buried deeper than 50mm or
protected by earthed metal enclosure, or have RCD protection with a =
30mA trip. Since the RCD protection for the whole CU is non compliant or
desirable, the the earthed metallic protection of some kind would be the
way to go. In this case I would just use a large metal galvanised trunking.
For some reason I was thinking that I might need access to the tails,
but I was being dumb. My only concern about burying steel trunking is
that the smallest regular rectangular stuff I can find is quite big and
fairly easy to drill through, and the round conduit for 2 tails would be
too large (or would need individual conduits). Is suitable rectangular
trunking available? (Mr Google has not been helpful)

I presume a flush-mounted CU is the way to go, but I'm open to other
suggestions. Are any particular types recommended? I'll probably have
a mix of RCBOs, MCBs and RCD ... I'd like to go all RCBO but the cost
is very high.

RCBOs are not that expensive now, so worth looking at.
There will be 10-18 circuits (depending on whether/how I group them) so
RCBO cost is not insignificant.

You could surface
mount the CU on the finished wall but allow cable entry from the rear.
That looks neater and there are no worries about adequately sealing
access to the CU via the knock-outs at the top.
It's going to be quite a while until the rest of the room is ready for
plastering so surface mount is not an option ... hmmm, unless I mount it
on a temporary backing until the plastering is done (I hadn't thought of
that until now).

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 07:10, wrote:
You need to provide mechanical and/or electrical protection to the meter tails.


I did this by using 3mm thick stainless steel as (a) stainless steel blunts most drill bits apart from cobalt ones and (b) does not corrode when plastered over.

I also attached a 10mm earth wire to the stainless steel sheet and connected it to the met ( main earth terminal)

As for rcbos, I got these for ten quid each plus vat so filling a cu with rcbos is not really a bank breaker.


I understand about the need for protection, but this must be a common
problem so I'm surprised that I can't find suitable "off the peg" trunking.

What make were the RCBOs? I'll need between 10 and 18

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 09:20, wrote:
Screwfix are selling BG RCBOs for £11.99 at the moment and BG main switch only CU with 10 spare ways is only £32.

I was going to steer clear of BG because a few people have said they've
had problems with reliability. 10 ways is unlikely to be enough.

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go for
2 x 10mm^2 in parallel, which if clipped direct will be more that the
company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the cable
is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy flexi
conduit (Kopex is very heavy duty, although plastic, it will survive
some quite ferocious beating - does not count as mechanical protection
for burying though).

I'm surprised that I can't find some suitable rectangular steel trunking
- my google-fu must be weak today.

Protecting CU tails - possibly one for ARW
 

On Friday, 17 August 2018 13:41:47 UTC+1, wrote:
RCBOs are not that expensive now, so worth looking at.
There will be 10-18 circuits (depending on whether/how I group them) so
RCBO cost is not insignificant.

Put the lights on RCBOs (most disruption if they fail) and the cooker and immersion heater on RCBOs (most likely to have an element fail), and the rest can share a couple of RCDs.

Owain

Protecting CU tails - possibly one for ARW
 

On 17/08/18 13:41, wrote:

(or would need individual conduits).

No - can't do that if using metal conduit - eddy currents from
unbalanced conductors cause heating. All current carrying conductors on
a circuit must pass through the same metal conduit or trunking or hole
in a metal box (unless you cut a slot between 2 adjacent holes)

Protecting CU tails - possibly one for ARW
 

On 17/08/18 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go
for 2 x 10mm^2 in parallel, which if clipped direct will be more that
the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as mechanical
protection for burying though).

I'm surprised that I can't find some suitable rectangular steel trunking
- my google-fu must be weak today.


Do you need metal trunking? Surface mounting not an option?

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 16:09, Tim Watts wrote:
On 17/08/18 13:41, wrote:

(or would need individual conduits).

No - can't do that if using metal conduit - eddy currents from
unbalanced conductors cause heating. All current carrying conductors on
a circuit must pass through the same metal conduit or trunking or hole
in a metal box (unless you cut a slot between 2 adjacent holes)

I used to be involved with EMC so was very familiar with Mssrs. Lenz,
Faraday et al but I hadn't considered that there would be a practical
problem with conduit heating at the currents and distances involved. I
don't plan to use individual conduits, but it would be interesting to
understand more - any references to the problem?

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 15:24, wrote:
On Friday, 17 August 2018 13:41:47 UTC+1, wrote:
RCBOs are not that expensive now, so worth looking at.
There will be 10-18 circuits (depending on whether/how I group them) so
RCBO cost is not insignificant.

Put the lights on RCBOs (most disruption if they fail) and the cooker and immersion heater on RCBOs (most likely to have an element fail), and the rest can share a couple of RCDs.

Owain

That's more or less what I'd planned, but with the fridge and freezer
also on an RCBO.

Protecting CU tails - possibly one for ARW
 

Denmans do a nice looking curve consumer unit that has a door which covers the main switch and all the rcbos.



I have the cur-m18 version and this just has the main switch and room for up to 18 rcbos. I now have 16 rcbos in it with room for two more.....

Protecting CU tails - possibly one for ARW
 

Tim Watts wrote:

can't do that if using metal conduit - eddy currents from unbalanced
conductors cause heating. All current carrying conductors on a circuit
must pass through the same metal conduit or trunking or hole in a metal box

17th ed 521.5.1 does say that, I seem to remember some discussion of the
fancy insulated grommets with individual entries for tails within a
larger knockout? e.g.

https://tlc-direct.co.uk/Products/WKTKS32.html

Are they standard with new all-metal consumer units?

But Mr Flameport showed it didn't make a lot of odds to use two knock-outs

https://youtu.be/hg5eZkq2KgE

Protecting CU tails - possibly one for ARW
 

What problem?. Google for the John Ward eddy current video.

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go
for 2 x 10mm^2 in parallel, which if clipped direct will be more that
the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as mechanical
protection for burying though).

I'm surprised that I can't find some suitable rectangular steel trunking
- my google-fu must be weak today.

https://www.tlc-direct.co.uk/Main_In...ng_Galv_Index/


--
Cheers,

John.

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

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 17:55, wrote:
On 17/08/2018 16:09, Tim Watts wrote:
On 17/08/18 13:41, wrote:

(or would need individual conduits).

No - can't do that if using metal conduit - eddy currents from
unbalanced conductors cause heating. All current carrying conductors
on a circuit must pass through the same metal conduit or trunking or
hole in a metal box (unless you cut a slot between 2 adjacent holes)

I used to be involved with EMC so was very familiar with Mssrs. Lenz,
Faraday et al but I hadn't considered that there would be a practical
problem with conduit heating at the currents and distances involved. I
don't plan to use individual conduits, but it would be interesting to
understand more - any references to the problem?

Probably not an issue with domestic kit and the typical currents
involved. May prove relevant on industrial installs.

You may find this interesting:

https://www.youtube.com/watch?v=hg5eZkq2KgE



--
Cheers,

John.

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

Protecting CU tails - possibly one for ARW
 

On 18/08/2018 06:23, John Rumm wrote:
On 17/08/2018 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go
for 2 x 10mm^2 in parallel, which if clipped direct will be more
that the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as mechanical
protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.

https://www.tlc-direct.co.uk/Main_In...ng_Galv_Index/


Thanks, but I'd found that. 2"x2" seems rather excessive for a couple of
25mm2 tails, and it's too deep to be plastered over. I'm surprised that
it's so hard to find trunking that enables tails to be buried.

Protecting CU tails - possibly one for ARW
 

On 18/08/2018 06:28, John Rumm wrote:
On 17/08/2018 17:55, wrote:
On 17/08/2018 16:09, Tim Watts wrote:
On 17/08/18 13:41, wrote:

(or would need individual conduits).

No - can't do that if using metal conduit - eddy currents from
unbalanced conductors cause heating. All current carrying conductors
on a circuit must pass through the same metal conduit or trunking or
hole in a metal box (unless you cut a slot between 2 adjacent holes)

I used to be involved with EMC so was very familiar with Mssrs. Lenz,
Faraday et al but I hadn't considered that there would be a practical
problem with conduit heating at the currents and distances involved. I
don't plan to use individual conduits, but it would be interesting to
understand more - any references to the problem?

Probably not an issue with domestic kit and the typical currents
involved. May prove relevant on industrial installs.

You may find this interesting:

https://www.youtube.com/watch?v=hg5eZkq2KgE



Thanks, that's interesting and about what I'd expect. That's why I was
surprised that someone said it was a real world problem for a domestic
installation.
In case anyone wants to know (which I doubt): the magnetic field from a
single conductor decays linearly with distance, that from a pair with
equal and opposite currents decays as the separation divided by the
square of distance, and that from a coil decays as the cube of distance.
Turning these theoretical gems into something to predict actual heating
effect is beyond my current intellectual abilities, although I did once
have cause to use Maxwell's equations to solve a real-world problem ...
a long time ago!

Protecting CU tails - possibly one for ARW
 

On 17/08/2018 16:10, Tim Watts wrote:
On 17/08/18 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go
for 2 x 10mm^2 in parallel, which if clipped direct will be more
that the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as mechanical
protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.


Do you need metal trunking? Surface mounting not an option?
Surface mount is possible, but not preferred.

I think I've just come up with an alternative. If the tails take a
slightly longer route they can go via the roof space and drop down from
the ceiling with all the other cables. At a guess the run would be about
3.5m and it would be visible (up from the Henley block), in steel
conduit (across the top of the joists), and in the accessible boxed-in
area for the cable drop to the CU.

Protecting CU tails - possibly one for ARW
 

On 18/08/2018 16:11, wrote:
On 18/08/2018 06:23, John Rumm wrote:
On 17/08/2018 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go
for 2 x 10mm^2 in parallel, which if clipped direct will be more
that the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as mechanical
protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.

https://www.tlc-direct.co.uk/Main_In...ng_Galv_Index/


Thanks, but I'd found that. 2"x2" seems rather excessive for a couple of
25mm2 tails, and it's too deep to be plastered over. I'm surprised that
it's so hard to find trunking that enables tails to be buried.

What about steel capping (which you would need to earth)?:

https://www.tlc-direct.co.uk/Products/SC2.html



--
Cheers,

John.

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

Protecting CU tails - possibly one for ARW
 

If your meter rails exceed 3 metres you well need to put in oa switch-fuse...... at the beginning of the meter tail run.....

Protecting CU tails - possibly one for ARW
 

On 18/08/2018 20:16, wrote:
On 17/08/2018 16:10, Tim Watts wrote:
On 17/08/18 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go
for 2 x 10mm^2 in parallel, which if clipped direct will be more
that the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as mechanical
protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.


Do you need metal trunking? Surface mounting not an option?
Surface mount is possible, but not preferred.

I think I've just come up with an alternative. If the tails take a
slightly longer route they can go via the roof space and drop down from
the ceiling with all the other cables. At a guess the run would be about
3.5m and it would be visible (up from the Henley block), in steel
conduit (across the top of the joists), and in the accessible boxed-in
area for the cable drop to the CU.

We use steel conduit for tails behind the plaster. Is there any reason
you cannot just enter into the rear of the CU from the garage side?


--
Adam

Protecting CU tails - possibly one for ARW
 

On 19/08/2018 03:59, John Rumm wrote:
On 18/08/2018 16:11, wrote:
On 18/08/2018 06:23, John Rumm wrote:
On 17/08/2018 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go
for 2 x 10mm^2 in parallel, which if clipped direct will be more
that the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as mechanical
protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.

https://www.tlc-direct.co.uk/Main_In...ng_Galv_Index/


Thanks, but I'd found that. 2"x2" seems rather excessive for a couple
of 25mm2 tails, and it's too deep to be plastered over. I'm surprised
that it's so hard to find trunking that enables tails to be buried.

What about steel capping (which you would need to earth)?:

https://www.tlc-direct.co.uk/Products/SC2.html


That would not be compliant.


--
Adam

Protecting CU tails - possibly one for ARW
 

On 19/08/2018 07:31, wrote:
If your meter rails exceed 3 metres you well need to put in oa switch-fuse...... at the beginning of the meter tail run.....

Yes, I could do it with a sub-main but the only reasons to limit the
length can be impedance and risk of physical damage. The extra impedance
of 0.5m of 25mm2 copper is not going to have an appreciable effect on
the time it takes the service fuse to rupture if there's a fault, and I
can mitigate the damage risk by having the whole run protected.

AIUI DNOs used to spec a recommended max tail length but not all now do,
and I don't believe the regs spec a max length. I accept that 3m is
often quoted as a maximum (sometimes 2m or 6m too); where did you find a
3m limit documented?

Protecting CU tails - possibly one for ARW
 

On 19/08/2018 08:48, ARW wrote:
On 18/08/2018 20:16, wrote:
On 17/08/2018 16:10, Tim Watts wrote:
On 17/08/18 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go
for 2 x 10mm^2 in parallel, which if clipped direct will be more
that the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as mechanical
protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.


Do you need metal trunking? Surface mounting not an option?
Surface mount is possible, but not preferred.

I think I've just come up with an alternative. If the tails take a
slightly longer route they can go via the roof space and drop down
from the ceiling with all the other cables. At a guess the run would
be about 3.5m and it would be visible (up from the Henley block), in
steel conduit (across the top of the joists), and in the accessible
boxed-in area for the cable drop to the CU.

We use steel conduit for tails behind the plaster. Is there any reason
you cannot just enter into the rear of the CU from the garage side?


Unfortunately I need to put the CU on a wall that's at right angles to
the garage wall.

Protecting CU tails - possibly one for ARW
 

On 19/08/2018 03:59, John Rumm wrote:
On 18/08/2018 16:11, wrote:
On 18/08/2018 06:23, John Rumm wrote:
On 17/08/2018 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might go
for 2 x 10mm^2 in parallel, which if clipped direct will be more
that the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as mechanical
protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.

https://www.tlc-direct.co.uk/Main_In...ng_Galv_Index/


Thanks, but I'd found that. 2"x2" seems rather excessive for a couple
of 25mm2 tails, and it's too deep to be plastered over. I'm surprised
that it's so hard to find trunking that enables tails to be buried.

What about steel capping (which you would need to earth)?:

https://www.tlc-direct.co.uk/Products/SC2.html

The tails are about 13mm diameter and the capping is only 6mm high, plus
it's very easy to drill through (also, I hate trying to fix the stuff!)

Protecting CU tails - possibly one for ARW
 

On 19/08/2018 08:49, ARW wrote:
On 19/08/2018 03:59, John Rumm wrote:
On 18/08/2018 16:11, wrote:
On 18/08/2018 06:23, John Rumm wrote:
On 17/08/2018 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might
go for 2 x 10mm^2 in parallel, which if clipped direct will be
more that the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as
mechanical protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.

https://www.tlc-direct.co.uk/Main_In...ng_Galv_Index/


Thanks, but I'd found that. 2"x2" seems rather excessive for a couple
of 25mm2 tails, and it's too deep to be plastered over. I'm surprised
that it's so hard to find trunking that enables tails to be buried.

What about steel capping (which you would need to earth)?:

https://www.tlc-direct.co.uk/Products/SC2.html


That would not be compliant.

Agreed, it offers relatively little mechanical protection, but in
reality no worse than many of the so called earth shield cables.


--
Cheers,

John.

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

Protecting CU tails - possibly one for ARW
 

On 19/08/2018 10:51, wrote:
On 19/08/2018 07:31, wrote:
If your meter rails exceed 3 metres you well need to put in oa
switch-fuse...... at the beginning of the meter tail run.....

Yes, I could do it with a sub-main but the only reasons to limit the
length can be impedance and risk of physical damage. The extra impedance
of 0.5m of 25mm2 copper is not going to have an appreciable effect on
the time it takes the service fuse to rupture if there's a fault, and I
can mitigate the damage risk by having the whole run protected.

AIUI DNOs used to spec a recommended max tail length but not all now do,
and I don't believe the regs spec a max length. I accept that 3m is
often quoted as a maximum (sometimes 2m or 6m too); where did you find a
3m limit documented?
It just generally seems to be the norm.

eg

https://www.northernpowergrid.com/as...cument/539.pdf

--
Adam

Protecting CU tails - possibly one for ARW
 

On 19/08/2018 10:52, wrote:
On 19/08/2018 08:48, ARW wrote:
On 18/08/2018 20:16, wrote:
On 17/08/2018 16:10, Tim Watts wrote:
On 17/08/18 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might
go for 2 x 10mm^2 in parallel, which if clipped direct will be
more that the company fuse.

There are issues with paralleling conductors and it's not standard
practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or bendy
flexi conduit (Kopex is very heavy duty, although plastic, it will
survive some quite ferocious beating - does not count as
mechanical protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.


Do you need metal trunking? Surface mounting not an option?
Surface mount is possible, but not preferred.

I think I've just come up with an alternative. If the tails take a
slightly longer route they can go via the roof space and drop down
from the ceiling with all the other cables. At a guess the run would
be about 3.5m and it would be visible (up from the Henley block), in
steel conduit (across the top of the joists), and in the accessible
boxed-in area for the cable drop to the CU.

We use steel conduit for tails behind the plaster. Is there any reason
you cannot just enter into the rear of the CU from the garage side?


Unfortunately I need to put the CU on a wall that's at right angles to
the garage wall.

Sorry for the delay in replying.

As I said we use non touching 25mm galv conduit in such cases (L&N in
different conduits) OR go deeper than 50mm.

--
Adam

Protecting CU tails - possibly one for ARW
 

On 24/08/2018 18:51, ARW wrote:
On 19/08/2018 10:51, wrote:
On 19/08/2018 07:31, wrote:
If your meter rails exceed 3 metres you well need to put in oa
switch-fuse...... at the beginning of the meter tail run.....

Yes, I could do it with a sub-main but the only reasons to limit the
length can be impedance and risk of physical damage. The extra
impedance of 0.5m of 25mm2 copper is not going to have an appreciable
effect on the time it takes the service fuse to rupture if there's a
fault, and I can mitigate the damage risk by having the whole run
protected.

AIUI DNOs used to spec a recommended max tail length but not all now
do, and I don't believe the regs spec a max length. I accept that 3m
is often quoted as a maximum (sometimes 2m or 6m too); where did you
find a 3m limit documented?
It just generally seems to be the norm.

eg

https://www.northernpowergrid.com/as...cument/539.pdf


Thanks for the link, but they say "If the length is more than 3 metres,
you should ... as specified in the current IEE Wiring Regulations" ...
and AFAICS 3m *isn't* specified in the regs.

Protecting CU tails - possibly one for ARW
 

On 24/08/2018 18:53, ARW wrote:
On 19/08/2018 10:52, wrote:
On 19/08/2018 08:48, ARW wrote:
On 18/08/2018 20:16, wrote:
On 17/08/2018 16:10, Tim Watts wrote:
On 17/08/18 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might
go for 2 x 10mm^2 in parallel, which if clipped direct will be
more that the company fuse.

There are issues with paralleling conductors and it's not
standard practise.

The alternative is 3mm of steel for mechanical protection if the
cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or
bendy flexi conduit (Kopex is very heavy duty, although plastic,
it will survive some quite ferocious beating - does not count as
mechanical protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.


Do you need metal trunking? Surface mounting not an option?
Surface mount is possible, but not preferred.

I think I've just come up with an alternative. If the tails take a
slightly longer route they can go via the roof space and drop down
from the ceiling with all the other cables. At a guess the run would
be about 3.5m and it would be visible (up from the Henley block), in
steel conduit (across the top of the joists), and in the accessible
boxed-in area for the cable drop to the CU.

We use steel conduit for tails behind the plaster. Is there any
reason you cannot just enter into the rear of the CU from the garage
side?


Unfortunately I need to put the CU on a wall that's at right angles to
the garage wall.

Sorry for the delay in replying.

As I said we use non touching 25mm galv conduit in such cases (L&N in
different conduits) OR go deeper than 50mm.

No need to apologise, I'm very grateful for all and any info from people
who know what they're talking about.

Protecting CU tails - possibly one for ARW
 

On 24/08/2018 19:30, wrote:
On 24/08/2018 18:53, ARW wrote:
On 19/08/2018 10:52, wrote:
On 19/08/2018 08:48, ARW wrote:
On 18/08/2018 20:16, wrote:
On 17/08/2018 16:10, Tim Watts wrote:
On 17/08/18 13:53, wrote:
On 17/08/2018 12:39, Tim Watts wrote:
On 17/08/18 11:25, Fredxx wrote:

SWA is perhaps an alternative. Given the bending radius I might
go for 2 x 10mm^2 in parallel, which if clipped direct will be
more that the company fuse.

There are issues with paralleling conductors and it's not
standard practise.

The alternative is 3mm of steel for mechanical protection if
the cable is hidden under plaster etc.

I'd just surface run it in nice looking trunking (D-Line) or
bendy flexi conduit (Kopex is very heavy duty, although plastic,
it will survive some quite ferocious beating - does not count as
mechanical protection for burying though).

I'm surprised that I can't find some suitable rectangular steel
trunking - my google-fu must be weak today.


Do you need metal trunking? Surface mounting not an option?
Surface mount is possible, but not preferred.

I think I've just come up with an alternative. If the tails take a
slightly longer route they can go via the roof space and drop down
from the ceiling with all the other cables. At a guess the run
would be about 3.5m and it would be visible (up from the Henley
block), in steel conduit (across the top of the joists), and in the
accessible boxed-in area for the cable drop to the CU.

We use steel conduit for tails behind the plaster. Is there any
reason you cannot just enter into the rear of the CU from the garage
side?


Unfortunately I need to put the CU on a wall that's at right angles
to the garage wall.

Sorry for the delay in replying.

As I said we use non touching 25mm galv conduit in such cases (L&N in
different conduits) OR go deeper than 50mm.

No need to apologise, I'm very grateful for all and any info from people
who know what they're talking about.

It was a NICEIC inspector that passed this as acceptable on a first fix
inspection on a new build.

The non touching bit, I suppose, is there as it "stops" these pesky eddy
currents.

I might have some photos of that installation.




--
Adam

Protecting CU tails - possibly one for ARW
 

On 24/08/2018 19:28, wrote:
On 24/08/2018 18:51, ARW wrote:
On 19/08/2018 10:51, wrote:
On 19/08/2018 07:31, wrote:
If your meter rails exceed 3 metres you well need to put in oa
switch-fuse...... at the beginning of the meter tail run.....

Yes, I could do it with a sub-main but the only reasons to limit the
length can be impedance and risk of physical damage. The extra
impedance of 0.5m of 25mm2 copper is not going to have an appreciable
effect on the time it takes the service fuse to rupture if there's a
fault, and I can mitigate the damage risk by having the whole run
protected.

AIUI DNOs used to spec a recommended max tail length but not all now
do, and I don't believe the regs spec a max length. I accept that 3m
is often quoted as a maximum (sometimes 2m or 6m too); where did you
find a 3m limit documented?
It just generally seems to be the norm.

eg

https://www.northernpowergrid.com/as...cument/539.pdf


Thanks for the link, but they say "If the length is more than 3 metres,
you should ... as specified in the current IEE Wiring Regulations" ...
and AFAICS 3m *isn't* specified in the regs.

FWIW I read that[1] to mean the *protective device* is to be as
specified in the regs. not that the regs. set the 3m limit.

AIUI the 3m comes from guidance (on the ESQC?) rather than the wiring
regs. IIRC you can challenge their decision. If still not satisfied
you can refer their refusal to connect you to the Secretary of State
who'll then appoint an independent expert to decide the point. But you
may not get a connection in the meantime ;)


[1] in full for ease of reference "If the length is more than 3 metres,
you should install an additional protective device at the nearest
point to the supply inside the customers premises, as specified in the
current IEE Wiring Regulations"

--
Robin
reply-to address is (intended to be) valid

Protecting CU tails - possibly one for ARW
 

On Friday, 24 August 2018 19:28:30 UTC+1, wrote:
Thanks for the link, but they say "If the length is more than 3 metres,
you should ... as specified in the current IEE Wiring Regulations" ...

There are no current IEE Wiring Regulations*, so no requirement to do as specified :-)

Owain

They're now IET Regulations.

Protecting CU tails - possibly one for ARW
 

On 24/08/2018 22:47, wrote:
On Friday, 24 August 2018 19:28:30 UTC+1, wrote:
Thanks for the link, but they say "If the length is more than 3 metres,
you should ... as specified in the current IEE Wiring Regulations" ...

There are no current IEE Wiring Regulations*, so no requirement to do as specified :-)

Owain

They're now IET Regulations.

As an FIET I should have spotted that ;-)

Protecting CU tails - possibly one for ARW
 

On Fri, 24 Aug 2018 18:53:52 +0100, ARW wrote:

Unfortunately I need to put the CU on a wall that's at right angles to
the garage wall.

Sorry for the delay in replying.

As I said we use non touching 25mm galv conduit in such cases (L&N in
different conduits) OR go deeper than 50mm.

Going deeper than 50mm isn't an option here on internal walls - OK to do
from one side but then less than 50mm from the other! I tend to use
mini-trunking, especially as the walls are hollow 'brittle biscuit'
(whatever that's called).
--
Peter.
The gods will stay away
whilst religions hold sway