Is it ever acceptable to run one or more additional CPCs to the middle
of a radial circuit, to restore the integrity of the earth until the
whole circuit can be replaced?

Friend asked me to check why she gets a "tingle" when touching both
her stainless steel kitchen sink and an adjacent metal electrical
appliance.

Inspection of her house - originally a small 2-up 2-down, extended
backwards and sideways about 15 years ago - revealed many bodges.
There is one lighting circuit, one radial to the boiler/CH controls
and just one ring main, all basically OK. There is also a fourth
circuit. This appears to have originally been a radial to a single
socket in the kitchen, or possibly to a small oven (it seems to be 4
or 6mm sq at the CU end). It appears to have been extended with the
house to serve 11 sockets (including washing machine, dishwasher,
microwave and an electric heater) as well as various spurs to lighting
circuits via FCUs. Very difficult to check the layout: most cabling is
buried in the concrete floor or behind three layers of tiling or
numerous fixed cabinets and half the sockets are now inaccessible
(you can plug things in but not remove the faceplate). Surprisingly
enough the 32A MCB never trips - seems the heavy power consumers are
never on together.

CU is old 4-way Wylex now fitted with MCBs; no RCD anywhere. No main
equipotential bonding of any sort in place.

What I think is the first socket on the radial reads 240v phase to
neutral and the CPC has continuity back to the main earthing point at
the CU. Others read between 115v and 175v phase-neutral with no load;
and their CPCs between about 50v and (at worst, near the sink) 115v to
the main earthing point (tested with a flying lead and multimeter). Or
in the latter case to the sink itself, hence the tingle.

Connections at all accessible points OK (for what it's worth bearing
in mind the circuit "design"). Haven't meggered anything yet - not
sure I've found all the parts of the installation - but hardly need to
to show there's a problem.

Temporarily bonding the sink to the CPC of the nearest socket solves
the "tingle" problem (of course) and doesn't trip the MCB but I don't
want to create a worse problem elsewhere eg in the bathroom (given the
lack of main bonding).

I can install main equipotential bonding reasonable easily and will do
so soon. But tracing and fixing the leakage to earth and broken CPC -
i.e. replacing the broken and overloaded radial with the new ring it
needs - will be disruptive and time-consuming. I won't have time to do
it for ages. Friend (single mother, two kids, failing job) is smart
but short of cash. I know she won't call in professionals unless I
convince her her life is in danger: the problem has existed for at
least 13 years and hasn't killed her (yet). Nor, amazingly, do any of
the appliances on the affected circuit seem to have under-performed.
Until I can do the job properly - probably several months - I plan to:

(a) install main equipotential bonding to the gas and water services

and

(b) extend it directly to as many accessible CPC connections on the
affected circuit as necessary to restore proper earthing at all points
I can test.

Yes it's a temporary bodge and no substitute for ripping out and
replacing the dodgy circuit - not least because I find it hard to
believe that this 50-115v potential in the CPC is not coming from some
phase-to-earth fault somewhere (though as I say above, temp bonding
doesn't trip the MCB). But is there any reason why in the
circumstances I should not do it?

wrote:
Is it ever acceptable to run one or more additional CPCs to the middle
of a radial circuit, to restore the integrity of the earth until the
whole circuit can be replaced?

snip

Hopefully having taken the time to write this considered summary and
read it back, you will realise that there is only one solution.

That is to *immediately* disconnect the faulty circuit and replace it
(hopefully with an appropriate ring). If you can't replace it right
away, even extension leads to vital appliances would be preferable to
the existing situation in the very short term.

The fact that the dangerous situation has existed for some time will be
no consolation to you should a tragedy happen now that you have
uncovered it. Remember it will only take one failure on the unearthed
section for *all* the appliances on that section to potentially become
live - and there are signs that a latent fault is already present.

I feel for your dilemma, but I think in this situation safety must come
first.

David

Hopefully having taken the time to write this considered summary and
read it back, you will realise that there is only one solution.

That is to *immediately* disconnect the faulty circuit and replace it
(hopefully with an appropriate ring). If you can't replace it right
away, even extension leads to vital appliances would be preferable to
the existing situation in the very short term.

The fact that the dangerous situation has existed for some time will be
no consolation to you should a tragedy happen now that you have
uncovered it. Remember it will only take one failure on the unearthed
section for *all* the appliances on that section to potentially become
live - and there are signs that a latent fault is already present.

I feel for your dilemma, but I think in this situation safety must come
first.

David


David,

Thanks - you are right of course but reality is that either I install some
sort of fix which will improve safety and not make things worse, or nothing
at all will be done for possibly many months. Hence my question.

Thanks - you are right of course but reality is that either I install some
sort of fix which will improve safety and not make things worse, or nothing
at all will be done for possibly many months. Hence my question.

Well, my original advice stands, but if you intend to go for a "fix",
one way to approach this would be to turn the radial circuit into a
ring by connecting the far end of the radial back to the originating
MCB.

However, that in itself is not a solution, you must then ensure
continuity of the CPC throughout the newly-created ring by finding the
break and replacing that portion. And of course the whole ring must
comply with the regs.

You should also find and fix the earth leakage problem, install an RCD,
and install main equipotential bonding and supplementary bonding.

This type of approach could ultimately be more work than installing a
new circuit.
David

wrote:
Is it ever acceptable to run one or more additional CPCs to the middle
of a radial circuit, to restore the integrity of the earth until the
whole circuit can be replaced?

Yes, but... (read on).

[...] Surprisingly enough the 32A MCB never trips - seems the heavy
power consumers are never on together.

That's not surprising, it takes over 45 A to trip a 32 A MCB "quickly".

CU is old 4-way Wylex now fitted with MCBs; no RCD anywhere. No main
equipotential bonding of any sort in place.

If it's old enough to have no bonding then the Wylex CU will probably be
the type with a partly wooden frame. Put replacing that on your longer
term remedial actions list.

[...] Others read between 115v and 175v phase-neutral with no load;

This is odd, you haven't mentioned things downstream of this point not
working. What is the P-N voltage on-load? You have either loose
connections (immediate fire risk), or a dodgy meter, or you really meant
P-E perhaps?

and their CPCs between about 50v and (at worst, near the sink) 115v to
the main earthing point (tested with a flying lead and multimeter). Or
in the latter case to the sink itself, hence the tingle.

Is this wired in twin-and-earth? Have you checked for a broken or loose
CPC connection at the first and second points along the cct. Most often
such breaks will be visible at points of termination, not buried in
concrete. The evidence may be buried under the earth sleeving, so give
everything a good tug.

[...] (b) extend it directly to as many accessible CPC connections on
the affected circuit as necessary to restore proper earthing at all
points I can test.
[...]
But is there any reason why in the circumstances I should not do it?

You'll need to install an RCD at the origin of the circuit concerned.
On a circuit with no RCD the CPC must be run in the same wiring system
(i.e. same route) as the P & N conductors, or in the immediate proximity
[Reg. 544-01-01]. With an RCD in place this restriction is removed and
you can run the CPC wherever you like, within reason. A separate CPC
with no mechanical protection (i.e not in conduit or trunking) should be
at least 4 mm^2.

--
Andy

wrote:

What I think is the first socket on the radial reads 240v phase to
neutral and the CPC has continuity back to the main earthing point at
the CU. Others read between 115v and 175v phase-neutral with no load;

That does not really make sense - at that level you would not expect
appliances plugged into sockets there (or downstream) to perform correctly.

(If you are talking about phase to earth then that I could understand!)

and their CPCs between about 50v and (at worst, near the sink) 115v to
the main earthing point (tested with a flying lead and multimeter). Or
in the latter case to the sink itself, hence the tingle.

You could observe that with a disconnected and floating CPC. Mains RFI
filters on many appliances will tend to pull the CPC toward 115V if it
is not connected.

Connections at all accessible points OK (for what it's worth bearing
in mind the circuit "design"). Haven't meggered anything yet - not
sure I've found all the parts of the installation - but hardly need to
to show there's a problem.

As a temporary fix I would be inclinded to prove the first couple of
sockets are OK, and disconnect the rest. Use extension leads from the
good sockets in the mean time.



--
Cheers,

John.

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

"Andy Wade" wrote in message
...
wrote:
Is it ever acceptable to run one or more additional CPCs to the middle
of a radial circuit, to restore the integrity of the earth until the
whole circuit can be replaced?

Yes, but... (read on).

[...] Surprisingly enough the 32A MCB never trips - seems the heavy
power consumers are never on together.

That's not surprising, it takes over 45 A to trip a 32 A MCB "quickly".

CU is old 4-way Wylex now fitted with MCBs; no RCD anywhere. No main
equipotential bonding of any sort in place.

If it's old enough to have no bonding then the Wylex CU will probably be
the type with a partly wooden frame. Put replacing that on your longer
term remedial actions list.

[...] Others read between 115v and 175v phase-neutral with no load;

This is odd, you haven't mentioned things downstream of this point not
working. What is the P-N voltage on-load? You have either loose
connections (immediate fire risk), or a dodgy meter, or you really meant
P-E perhaps?

and their CPCs between about 50v and (at worst, near the sink) 115v to
the main earthing point (tested with a flying lead and multimeter). Or
in the latter case to the sink itself, hence the tingle.

Is this wired in twin-and-earth? Have you checked for a broken or loose
CPC connection at the first and second points along the cct. Most often
such breaks will be visible at points of termination, not buried in
concrete. The evidence may be buried under the earth sleeving, so give
everything a good tug.

[...] (b) extend it directly to as many accessible CPC connections on
the affected circuit as necessary to restore proper earthing at all
points I can test.
[...]
But is there any reason why in the circumstances I should not do it?

You'll need to install an RCD at the origin of the circuit concerned. On a
circuit with no RCD the CPC must be run in the same wiring system (i.e.
same route) as the P & N conductors, or in the immediate proximity [Reg.
544-01-01]. With an RCD in place this restriction is removed and you can
run the CPC wherever you like, within reason. A separate CPC with no
mechanical protection (i.e not in conduit or trunking) should be at least
4 mm^2.

--
Andy

Sorry yes, the measurements are P-E. Meter is recently calibrated so I think
OK. Cabling is T&E and I have checked all accessible runs and points of
termination (though many aren't accessible). Thanks for alerting me to that
reg - though I know the proper solution is a full new circuit.

"John Rumm" wrote in message
...
wrote:

What I think is the first socket on the radial reads 240v phase to
neutral and the CPC has continuity back to the main earthing point at
the CU. Others read between 115v and 175v phase-neutral with no load;

That does not really make sense - at that level you would not expect
appliances plugged into sockets there (or downstream) to perform
correctly.

(If you are talking about phase to earth then that I could understand!)

and their CPCs between about 50v and (at worst, near the sink) 115v to
the main earthing point (tested with a flying lead and multimeter). Or
in the latter case to the sink itself, hence the tingle.

You could observe that with a disconnected and floating CPC. Mains RFI
filters on many appliances will tend to pull the CPC toward 115V if it is
not connected.

Connections at all accessible points OK (for what it's worth bearing
in mind the circuit "design"). Haven't meggered anything yet - not
sure I've found all the parts of the installation - but hardly need to
to show there's a problem.

As a temporary fix I would be inclinded to prove the first couple of
sockets are OK, and disconnect the rest. Use extension leads from the good
sockets in the mean time.



--
Cheers,

John.


Thanks yes it's actually P-E as also pointed out by Andy. Helpful to know
that these readings could be found with a disconnected and floating CPC
without there necessarily being other problems present.

wrote in message
...
Until I can do the job properly - probably several months - I plan to:

(a) install main equipotential bonding to the gas and water services

and

(b) extend it directly to as many accessible CPC connections on the
affected circuit as necessary to restore proper earthing at all points
I can test.



Given the time and money constraints you pose I suggest a different focus
than the main bonding issue which is not really relevant to the problem.
You have a suspicion of phase to earth breakdown but I would suggest an
initial theory of only a break in the CPC. You should perform a fuller
survey of which accessible outlet has CPC continuity to which accessible
outlet. Continuity is a much better test that voltage which can be
misleading. Identify a section of the circuit which is sound and as you
suggested connect that back to the installation earth. Place all other
sockets out of use. It may even become clear where the break is.

Finally you say some outlets are accessible but the faceplate can't be
removed. Care to share the reason since its an issue an electrician would
need to address. In fact while not the "problem" its the fundamental issue.

Jim A

"Jim Alexander" wrote in message
...

wrote in message
...
Until I can do the job properly - probably several months - I plan to:

(a) install main equipotential bonding to the gas and water services

and

(b) extend it directly to as many accessible CPC connections on the
affected circuit as necessary to restore proper earthing at all points
I can test.



Given the time and money constraints you pose I suggest a different focus
than the main bonding issue which is not really relevant to the problem.
You have a suspicion of phase to earth breakdown but I would suggest an
initial theory of only a break in the CPC. You should perform a fuller
survey of which accessible outlet has CPC continuity to which accessible
outlet. Continuity is a much better test that voltage which can be
misleading. Identify a section of the circuit which is sound and as you
suggested connect that back to the installation earth. Place all other
sockets out of use. It may even become clear where the break is.

Finally you say some outlets are accessible but the faceplate can't be
removed. Care to share the reason since its an issue an electrician would
need to address. In fact while not the "problem" its the fundamental
issue.

Jim A


Thanks Jim. Main bonding is indeed not the key issue. Where socket
faceplates can't be removed, it seems to be because they were installed and
cabinets or other fitted furniture were then put in over them, leaving just
enough room (eg at the backs of cupboards) to squeeze a plug in but none to
remove faceplates or allow work on the cabling. Of course all this junk will
have to come out for a proper fix, however it's done.

wrote in message
...
Is it ever acceptable to run one or more additional CPCs [snip]


CPC's. ?

Circuit Protective Conductors
Combined Precision Components
Certificate of Professional Competance
Chemical Protective Clothing.
etc, etc.

Take your pick.

Roger R

Roger R wrote:

CPC's. ?

Circuit Protective Conductors
Combined Precision Components
Certificate of Professional Competance
Chemical Protective Clothing.
etc, etc.

alternatively apply common sense in selecting the one appropriate for
the given context ...

rrh wrote:

Thanks yes it's actually P-E as also pointed out by Andy. Helpful to know
that these readings could be found with a disconnected and floating CPC
without there necessarily being other problems present.

This is also particularly true when using a digital meter to make your
readings. These place very little load on the circuit under test
(usually a good thing), but it does mean that completely disconnected
wires can appear live just from the inductive coupling resulting from
their running in close proximity to wires which are live.

--
Cheers,

John.

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

rrh wrote:

Thanks Jim. Main bonding is indeed not the key issue. Where socket
faceplates can't be removed, it seems to be because they were installed and
cabinets or other fitted furniture were then put in over them, leaving just
enough room (eg at the backs of cupboards) to squeeze a plug in but none to
remove faceplates or allow work on the cabling. Of course all this junk will
have to come out for a proper fix, however it's done.

Sounds like a job for a Fein Multimaster - that will be able to chop out
the surrounding wood etc without risking damage to anything else.

--
Cheers,

John.

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

"Andy Burns" wrote in message
...
Roger R wrote:

CPC's. ?

Circuit Protective Conductors
Combined Precision Components
Certificate of Professional Competance
Chemical Protective Clothing.
etc, etc.

alternatively apply common sense in selecting the one appropriate for the
given context ...

The Original Poster was addressing those who would immediately know what he
meant, but I couldn't initially get it because two others in my list somehow
blocked out further thought. It would help ordinary readers like me if
acronyms were expanded on first use.

Roger R

"Roger R" wrote in message
...

"Andy Burns" wrote in message
...
Roger R wrote:

CPC's. ?

Circuit Protective Conductors
Combined Precision Components
Certificate of Professional Competance
Chemical Protective Clothing.
etc, etc.

alternatively apply common sense in selecting the one appropriate for the
given context ...

The Original Poster was addressing those who would immediately know what
he meant, but I couldn't initially get it because two others in my list
somehow blocked out further thought. It would help ordinary readers like
me if acronyms were expanded on first use.

Roger R

I apologise if I wasn't clear, but I doubt that anyone who did not
immediately know what I meant by CPC, CU, RCD and MCB in the given context
would have been able to offer me sound advice.

"rrh" wrote in message
.uk...

"Roger R" wrote in message
...

"Andy Burns" wrote in message
...
Roger R wrote:

CPC's. ?

Circuit Protective Conductors
Combined Precision Components
Certificate of Professional Competance
Chemical Protective Clothing.
etc, etc.

alternatively apply common sense in selecting the one appropriate for
the given context ...

The Original Poster was addressing those who would immediately know what
he meant, but I couldn't initially get it because two others in my list
somehow blocked out further thought. It would help ordinary readers
like me if acronyms were expanded on first use.

Roger R

I apologise if I wasn't clear, but I doubt that anyone who did not
immediately know what I meant by CPC, CU, RCD and MCB in the given context
would have been able to offer me sound advice.

LOL. Anyone bar an electrician then

Enjoy doing a partial rewire or installing a new circuit for free. That is
what friends are for is it not?

It looks like it will be just as difficult to bodge this one as rewire the
circuit. I hope s/he is a good friend and will repay the favour.

Adam

ARWadsworth wrote:

Enjoy doing a partial rewire or installing a new circuit for free. That
is what friends are for is it not?

Ditto broken PCs in my case, substitute day-job here ...

"ARWadsworth" wrote in message
.uk...

"rrh" wrote in message
.uk...

"Roger R" wrote in message
...

"Andy Burns" wrote in message
...
Roger R wrote:

CPC's. ?

Circuit Protective Conductors
Combined Precision Components
Certificate of Professional Competance
Chemical Protective Clothing.
etc, etc.

alternatively apply common sense in selecting the one appropriate for
the given context ...

The Original Poster was addressing those who would immediately know what
he meant, but I couldn't initially get it because two others in my list
somehow blocked out further thought. It would help ordinary readers
like me if acronyms were expanded on first use.

Roger R

I apologise if I wasn't clear, but I doubt that anyone who did not
immediately know what I meant by CPC, CU, RCD and MCB in the given
context would have been able to offer me sound advice.

LOL. Anyone bar an electrician then

Enjoy doing a partial rewire or installing a new circuit for free. That is
what friends are for is it not?

It looks like it will be just as difficult to bodge this one as rewire the
circuit. I hope s/he is a good friend and will repay the favour.

Adam

Indeed, that's what friends are for.

Her cooking is out of this world and that's the payback!