About 18 months or so a thread was posted and some emails swapped regarding
armoured cable for an outside project.

At that time the information given ( and a pointer to a good document) was
that it was no longer considered good wiring practise to rely solely on the
steel armour wires for a CPC (earth connection)

I therefore for my work used 3 core throughout ......... the armour wires
are connected to earth, but the earth conductor actually providing the CPC.

I have just been picked up on this and told that this is NOT correct and
that it is still fully permissible under the regs to rely solely on the
steel wires armours for CPC portion.

Anybody care to comment further on this.

The quote made was " .........In fact regulation 543-02-02 (v) explicitly
states that cable armouring may be used as a CPC. "

Is this a question of the Regs allowing something but good wiring practise
advise something else ?

It makes no difference to the job I did as the only issue is that it may be
'over engineered, but I would like to get to the bottom of this.


Rick

On Mon, 5 Jul 2004 20:27:08 +0000 (UTC), "Rick Hughes"
wrote:

About 18 months or so a thread was posted and some emails swapped regarding
armoured cable for an outside project.

At that time the information given ( and a pointer to a good document) was
that it was no longer considered good wiring practise to rely solely on the
steel armour wires for a CPC (earth connection)

I therefore for my work used 3 core throughout ......... the armour wires
are connected to earth, but the earth conductor actually providing the CPC.

I have just been picked up on this and told that this is NOT correct and
that it is still fully permissible under the regs to rely solely on the
steel wires armours for CPC portion.

Anybody care to comment further on this.

The quote made was " .........In fact regulation 543-02-02 (v) explicitly
states that cable armouring may be used as a CPC. "

The actual wording is:

"A protective conductor may consist of one or more of the following:

(i) A single core cable

(ii) a conductor in a cable

(iii) an insulated or base conductor in a common enclosure with
insulated live conductors

(iv) a fixed bare or insulated conductor

(v) a metal covering, for example, the sheath, screen or armouring of
a cable

(vi) a metal conduit or other enclosure or electrically continuous
support system for conductors

(vii) an extraneous-conductive-part complying with Regulation
543-02-06"



Is this a question of the Regs allowing something but good wiring practise
advise something else ?

The operative words appear to be *may* (not *must*) and *one or more*
not just *one*.

Given that situation, I don't see why what you have done should be
criticised.

The problem is that if somebody inspecting goes down the route of
"good practice" and this is at variance with a specific aspect of the
Standard, then it opens Pandora's box on what is allowed and what is
not, making it arbitrary, It may please some inspectors to have a
perceived sense of power (so to speak), but the "good practice" aspect
should be a fall back to situations that are not explicitly covered in
the standard.



It makes no difference to the job I did as the only issue is that it may be
'over engineered, but I would like to get to the bottom of this.


Not really because you can use one or more.

I have yet to find anything in BS7671 which treats something that is
over-engineered as non-compliant.

I would suggest asking whoever did the inspection to justify their
comment. If it is simply what NICEIC recommends or something like
that, it is comment only and does not carry the authority of the
standard.

One point is that if you used three core three phase cable and the
third conductor is yellow, then it should be fully sleeved in
green/yellow.




..andy

To email, substitute .nospam with .gl

"Rick Hughes" wrote in message
...
About 18 months or so a thread was posted and some emails swapped
regarding
armoured cable for an outside project.

At that time the information given ( and a pointer to a good document) was
that it was no longer considered good wiring practise to rely solely on
the
steel armour wires for a CPC (earth connection)

I therefore for my work used 3 core throughout ......... the armour wires
are connected to earth, but the earth conductor actually providing the
CPC.

I have just been picked up on this and told that this is NOT correct and
that it is still fully permissible under the regs to rely solely on the
steel wires armours for CPC portion.

Who is picking you up ? Electrical work is not yet in the building regs
(unless you are n Scotland) though I know a few BCOs have voiced opinions on
the right way to do this. Both ways of course !

I have just been picked up on this and told that this is NOT correct and
that it is still fully permissible under the regs to rely solely on the
steel wires armours for CPC portion.

I was under the impression that the problem when using the armour is being
able to ensure that the earth loop impedence is adequete and will remain so,
even when the steel corrodes at the terminals.

Christian.

On Mon, 05 Jul 2004 21:46:20 +0100, Andy Hall wrote:

On Mon, 5 Jul 2004 20:27:08 +0000 (UTC), "Rick Hughes"
wrote:

About 18 months or so a thread was posted and some emails swapped regarding
armoured cable for an outside project.

At that time the information given ( and a pointer to a good document) was
that it was no longer considered good wiring practise to rely solely on the
steel armour wires for a CPC (earth connection)

I therefore for my work used 3 core throughout ......... the armour wires
are connected to earth, but the earth conductor actually providing the CPC.

I have just been picked up on this and told that this is NOT correct and
that it is still fully permissible under the regs to rely solely on the
steel wires armours for CPC portion.

Anybody care to comment further on this.

The quote made was " .........In fact regulation 543-02-02 (v) explicitly
states that cable armouring may be used as a CPC. "

The actual wording is:

"A protective conductor may consist of one or more of the following:

(i) A single core cable

(ii) a conductor in a cable

(iii) an insulated or base conductor in a common enclosure with
insulated live conductors

(iv) a fixed bare or insulated conductor

(v) a metal covering, for example, the sheath, screen or armouring of
a cable

(vi) a metal conduit or other enclosure or electrically continuous
support system for conductors

(vii) an extraneous-conductive-part complying with Regulation
543-02-06"



Is this a question of the Regs allowing something but good wiring practise
advise something else ?

The operative words appear to be *may* (not *must*) and *one or more*
not just *one*.

Given that situation, I don't see why what you have done should be
criticised.

The problem is that if somebody inspecting goes down the route of
"good practice" and this is at variance with a specific aspect of the
Standard, then it opens Pandora's box on what is allowed and what is
not, making it arbitrary, It may please some inspectors to have a
perceived sense of power (so to speak), but the "good practice" aspect
should be a fall back to situations that are not explicitly covered in
the standard.



It makes no difference to the job I did as the only issue is that it may be
'over engineered, but I would like to get to the bottom of this.


Not really because you can use one or more.

I have yet to find anything in BS7671 which treats something that is
over-engineered as non-compliant.

I would suggest asking whoever did the inspection to justify their
comment. If it is simply what NICEIC recommends or something like
that, it is comment only and does not carry the authority of the
standard.

One point is that if you used three core three phase cable and the
third conductor is yellow, then it should be fully sleeved in
green/yellow.


When I was doing some industrial electircal work many years ago. A new
length of thick SWA was being installed. (It might have been around 200mm^2
x3). This had been made with several of the steel armour wires replaced
with copper to mke sure the CPC had at least 50% of the conductivity of
the core conductors.

I suspect therefore that manufacturers make sure that armourings are
always adequate for use as a CPC.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

When I was doing some industrial electircal work many years ago. A new
length of thick SWA was being installed. (It might have been around 200mm^2
x3). This had been made with several of the steel armour wires replaced
with copper to mke sure the CPC had at least 50% of the conductivity of
the core conductors.

I suspect therefore that manufacturers make sure that armourings are
always adequate for use as a CPC.

AS Christain has said, its the long term corrosion factor which is the
main worry and I would have thought steel and copper in intimate contact
would be a surefire winner on the corrosion front.

Dave
--

Some people use windows, others have a life.

On Tue, 06 Jul 2004 19:09:07 +0100, Dave Stanton
wrote:


When I was doing some industrial electircal work many years ago. A new
length of thick SWA was being installed. (It might have been around 200mm^2
x3). This had been made with several of the steel armour wires replaced
with copper to mke sure the CPC had at least 50% of the conductivity of
the core conductors.

I suspect therefore that manufacturers make sure that armourings are
always adequate for use as a CPC.

AS Christain has said, its the long term corrosion factor which is the
main worry and I would have thought steel and copper in intimate contact
would be a surefire winner on the corrosion front.

Dave

Don't forget that the terminating glands are normally brass, so you
don't have steel wires in contact with copper.

I was reterminating the house end of one of my outside supplies last
weekend - I needed to move it. The gland is fitted to an exterior
box and is exposed to the elements apart from a rubber johnny pulled
up over the cable and the gland. On disassembly there was no sign
of corrosion at all. The installation has been there for 20 years.




..andy

To email, substitute .nospam with .gl

AS Christain has said, its the long term corrosion factor which is the
main worry and I would have thought steel and copper in intimate contact
would be a surefire winner on the corrosion front.

Dave

Don't forget that the terminating glands are normally brass, so you
don't have steel wires in contact with copper.

I was reterminating the house end of one of my outside supplies last
weekend - I needed to move it. The gland is fitted to an exterior
box and is exposed to the elements apart from a rubber johnny pulled
up over the cable and the gland. On disassembly there was no sign
of corrosion at all. The installation has been there for 20 years.




.andy

Fair comment, but I was more concerned with the guys comments about copper
and steel strands forming the armour.

Cheers

Dave

On Tue, 06 Jul 2004 20:31:44 +0100, Dave Stanton
wrote:


AS Christain has said, its the long term corrosion factor which is the
main worry and I would have thought steel and copper in intimate contact
would be a surefire winner on the corrosion front.

Dave

Don't forget that the terminating glands are normally brass, so you
don't have steel wires in contact with copper.

I was reterminating the house end of one of my outside supplies last
weekend - I needed to move it. The gland is fitted to an exterior
box and is exposed to the elements apart from a rubber johnny pulled
up over the cable and the gland. On disassembly there was no sign
of corrosion at all. The installation has been there for 20 years.




.andy

Fair comment, but I was more concerned with the guys comments about copper
and steel strands forming the armour.

Cheers

Dave


OK, I see what you are saying.


..andy

To email, substitute .nospam with .gl

In article .uk,
"Ed Sirett" writes:
When I was doing some industrial electircal work many years ago. A new
length of thick SWA was being installed. (It might have been around 200mm^2
x3). This had been made with several of the steel armour wires replaced
with copper to mke sure the CPC had at least 50% of the conductivity of
the core conductors.

I have a piece of 11kV 150mm^2 aluminium cable. All the armour on that
is copper, possibly because it's a single conductor with unbalanced
current flow where magnetic armour could cause a problem.

--
Andrew Gabriel

On Tue, 06 Jul 2004 19:09:07 +0100, Dave Stanton wrote:


When I was doing some industrial electircal work many years ago. A new
length of thick SWA was being installed. (It might have been around 200mm^2
x3). This had been made with several of the steel armour wires replaced
with copper to mke sure the CPC had at least 50% of the conductivity of
the core conductors.

I suspect therefore that manufacturers make sure that armourings are
always adequate for use as a CPC.

AS Christain has said, its the long term corrosion factor which is the
main worry and I would have thought steel and copper in intimate contact
would be a surefire winner on the corrosion front.

The armourings were steeped in pitch possibly for this very reason.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html