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Default Earth wire from consumer unit.

I'm having central heating installed, 75% done.

Plumber tells me I need an earth wire from the consumer unit to the outside
gas meter.

This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.

mark


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Default Earth wire from consumer unit.

On Nov 5, 5:50 pm, "Mark" wrote:
I'm having central heating installed, 75% done.

Plumber tells me I need an earth wire from the consumer unit to the outside
gas meter.

This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.

mark


Is your plumber an electrician? Why is he even getting involved in
this?

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Default Earth wire from consumer unit.


"stevelup" wrote in message
ups.com...
On Nov 5, 5:50 pm, "Mark" wrote:
I'm having central heating installed, 75% done.

Plumber tells me I need an earth wire from the consumer unit to the
outside
gas meter.

This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.

mark


Is your plumber an electrician? Why is he even getting involved in
this?


He isn't. He's not getting involved as he's put it on to me. I was going to
route the cable then have an electrician do the connections but that's not
my question.



mark



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Default Earth wire from consumer unit.

In article ,
Mark wrote:
I'm having central heating installed, 75% done.


Plumber tells me I need an earth wire from the consumer unit to the
outside gas meter.


This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.


This cross bonding is concerned with the house pipework - not the supply.
And the house gas pipework is likely copper? I'm pretty certain if the gas
pipe is buried in concrete etc which makes it difficult to get to the
meter end, bonding to where it first surfaces inside the house will be ok.
However if it simply runs under floorboards where it's too much trouble to
lift them this approach doesn't comply.

--
*Xerox and Wurlitzer will merge to market reproductive organs.

Dave Plowman London SW
To e-mail, change noise into sound.
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Default Earth wire from consumer unit.


"Dave Plowman (News)" wrote in message
...
In article ,
Mark wrote:
I'm having central heating installed, 75% done.


Plumber tells me I need an earth wire from the consumer unit to the
outside gas meter.


This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.


This cross bonding is concerned with the house pipework - not the supply.
And the house gas pipework is likely copper? I'm pretty certain if the gas
pipe is buried in concrete etc which makes it difficult to get to the
meter end, bonding to where it first surfaces inside the house will be ok.
However if it simply runs under floorboards where it's too much trouble to
lift them this approach doesn't comply.


Thanks for replying.
The pipework is all copper. To get from the consumer unit to where the
copper gas pipe enters the house is quite long route and lots of t&g
floorboards to lift.
Does it need to be as near the meter or house entry as possible? I guess
what I'm trying to say is, can't it be connected to a copper pipe a bit more
convenient.

mark





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Default Earth wire from consumer unit.

On Nov 5, 6:36 pm, "Mark" wrote:
"stevelup" wrote in message

ups.com...



On Nov 5, 5:50 pm, "Mark" wrote:
I'm having central heating installed, 75% done.


Plumber tells me I need an earth wire from the consumer unit to the
outside
gas meter.


This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.


mark


Is your plumber an electrician? Why is he even getting involved in
this?


He isn't. He's not getting involved as he's put it on to me. I was going to
route the cable then have an electrician do the connections but that's not
my question.

mark


Sorry, you misunderstood me.

What I mean is - why has the issue even arisen? How does the plumber -
who is not an electrician - know there is something wrong with your
earth bonding?

Really all he needs to concern himself with is bonding all his
pipework together at the boiler end.

Has he explained why he thinks this extra work is necessary? You might
not even have an electricity supply which requires supplementary
bonding. How long has the current electrical installation been in
place?

Steve

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Default Earth wire from consumer unit.

stevelup wrote:
On Nov 5, 6:36 pm, "Mark" wrote:
"stevelup" wrote in message

ups.com...



On Nov 5, 5:50 pm, "Mark" wrote:
I'm having central heating installed, 75% done.
Plumber tells me I need an earth wire from the consumer unit to the
outside
gas meter.
This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.
mark
Is your plumber an electrician? Why is he even getting involved in
this?

He isn't. He's not getting involved as he's put it on to me. I was going to
route the cable then have an electrician do the connections but that's not
my question.

mark


Sorry, you misunderstood me.

What I mean is - why has the issue even arisen? How does the plumber -
who is not an electrician - know there is something wrong with your
earth bonding?


If there's no bonding there, then there *is* a potential issue - simple
as that.
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Default Earth wire from consumer unit.

On Nov 5, 9:54 pm, Lobster wrote:
stevelup wrote:
On Nov 5, 6:36 pm, "Mark" wrote:
"stevelup" wrote in message


roups.com...


On Nov 5, 5:50 pm, "Mark" wrote:
I'm having central heating installed, 75% done.
Plumber tells me I need an earth wire from the consumer unit to the
outside
gas meter.
This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.
mark
Is your plumber an electrician? Why is he even getting involved in
this?
He isn't. He's not getting involved as he's put it on to me. I was going to
route the cable then have an electrician do the connections but that's not
my question.


mark


Sorry, you misunderstood me.


What I mean is - why has the issue even arisen? How does the plumber -
who is not an electrician - know there is something wrong with your
earth bonding?


If there's no bonding there, then there *is* a potential issue - simple
as that.


Agreed but it is not forced to be the case - PME is not mandatory - it
depends on the type of incoming supply.

If there is no existing PME arrangement, then it is probable that it
is not needed.

Steve

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..

What I mean is - why has the issue even arisen? How does the plumber -
who is not an electrician - know there is something wrong with your
earth bonding?

Really all he needs to concern himself with is bonding all his
pipework together at the boiler end.

Has he explained why he thinks this extra work is necessary? You might
not even have an electricity supply which requires supplementary
bonding. How long has the current electrical installation been in
place?

Steve



Rewiring is recent.
Central heating is in progress.
Seems like the electrician forgot to put an earth into the consumer unit.
I just want it to end up safe and conforming.

mark


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Default Earth wire from consumer unit.


"stevelup" wrote in message
ups.com...
On Nov 5, 5:50 pm, "Mark" wrote:
I'm having central heating installed, 75% done.

Plumber tells me I need an earth wire from the consumer unit to the
outside
gas meter.

This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.

mark


Is your plumber an electrician? Why is he even getting involved in
this?


Any CORGI plumber worth his salt would check for main equipotential bonding
on the gas and advise the customer that it needs doing if it is not done.

Adam



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Any CORGI plumber worth his salt would check for main equipotential
bonding on the gas and advise the customer that it needs doing if it is
not done.




He is.
He has.
Hence my original question.

mark


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Default Earth wire from consumer unit.

Mark wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
Mark wrote:
I'm having central heating installed, 75% done.


Plumber tells me I need an earth wire from the consumer unit to the
outside gas meter.


This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.


This cross bonding is concerned with the house pipework - not the supply.
And the house gas pipework is likely copper? I'm pretty certain if the gas
pipe is buried in concrete etc which makes it difficult to get to the
meter end, bonding to where it first surfaces inside the house will be ok.
However if it simply runs under floorboards where it's too much trouble to
lift them this approach doesn't comply.


Thanks for replying.
The pipework is all copper. To get from the consumer unit to where the
copper gas pipe enters the house is quite long route and lots of t&g
floorboards to lift.
Does it need to be as near the meter or house entry as possible? I guess
what I'm trying to say is, can't it be connected to a copper pipe a bit more
convenient.

mark


I dont see how you expect folk to suggest how or where to route
the wire when we dont know the construction or layout of the place.
All that can be said is a few generalities, such as its often not
necessary to lift floorboards to route wires, and that wire can be
routed externally without it being too visible - but with no further
info, who knows what details are involved.


NT

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Default Earth wire from consumer unit.

stevelup wrote:

If there is no existing PME arrangement, then it is probable that it
is not needed.


This is nothing to do with PME. If the house has metallic gas pipeing
then this must be included in the main equipotential bonding. This is
irrespective of the type of earthing arrangement of the supply.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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Default Earth wire from consumer unit.

Mark wrote:
I'm having central heating installed, 75% done.

Plumber tells me I need an earth wire from the consumer unit to the outside
gas meter.

This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.


The requirement is that the house pipework is bonded on the consumers
side of the meter as soon as is practical after it enters the house.
Often this is actually implemented by effecting the bond in the external
meter box if you have one, however this is not actually the letter of
the requirement since it is not after entry as such.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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Default Earth wire from consumer unit.

Mark wrote:

Thanks for replying.
The pipework is all copper. To get from the consumer unit to where the
copper gas pipe enters the house is quite long route and lots of t&g
floorboards to lift.
Does it need to be as near the meter or house entry as possible? I guess
what I'm trying to say is, can't it be connected to a copper pipe a bit more
convenient.


In reality if all the pipe joints were soldered then that would achieve
the desired result in practical terms. However it may not pass
inspection since it is not to the letter of the regulation. There is
nothing to stop you routing the main bond by a indirect route if it
helps (i.e. outside and back in later, up into a first floor void etc).


--
Cheers,

John.

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


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Default Earth wire from consumer unit.


"Mark" wrote in message
...


Any CORGI plumber worth his salt would check for main equipotential
bonding on the gas and advise the customer that it needs doing if it is
not done.




He is.
He has.
Hence my original question.

mark


If the copper pipework runs outside the house from the gas meter and then
enters the house near the CU and has no branches from it before the point of
entry to the house then bond the copper pipework at the point of entry to
the building.

Adam

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"John Rumm" wrote in message
...
Mark wrote:
I'm having central heating installed, 75% done.

Plumber tells me I need an earth wire from the consumer unit to the
outside gas meter.

This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.


The requirement is that the house pipework is bonded on the consumers side
of the meter as soon as is practical after it enters the house. Often this
is actually implemented by effecting the bond in the external meter box if
you have one, however this is not actually the letter of the requirement
since it is not after entry as such.


Meter is in a semi-concealed box at side of house. A 28mm copper pipe runs
up the wall and across the bedroom floor then into a landing cupboard where
the boiler is housed.

I can join the earth cable to this copper pipe in the bedroom without too
much trouble. This will be my 'as soon as practical' solution. It was the
thought of having to route it across the bedroom and down the wall which
prompted my original question.

I'm doing this to conform to regs. I don't really understand why.

Thanks for all the responses.

mark


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Default Earth wire from consumer unit.

In article ,
Mark wrote:
Meter is in a semi-concealed box at side of house. A 28mm copper pipe
runs up the wall and across the bedroom floor then into a landing
cupboard where the boiler is housed.


I can join the earth cable to this copper pipe in the bedroom without
too much trouble. This will be my 'as soon as practical' solution. It
was the thought of having to route it across the bedroom and down the
wall which prompted my original question.


It really needs to go where the pipe comes into the house. Unless you can
prove it is a continuous length from there to where you propose fitting
it.

I'm doing this to conform to regs. I don't really understand why.


Well, consider the fact that the pipe from the street is plastic. A metal
one running through earth would provide an earth of sorts - but plastic
won't. The copper within the house is connected to what? A boiler, gas
fire, cooker etc all of may also be connected to electricity. If one of
those developed a fault it's conceivable the electricity could get to the
pipe. And make all the copper pipe 'live'. I know it's unlikely but
protective measures have to allow for every possibility.

Thanks for all the responses.


--
*The average person falls asleep in seven minutes *

Dave Plowman London SW
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Default Earth wire from consumer unit.


"Mark" wrote

I'm having central heating installed, 75% done.

Plumber tells me I need an earth wire from the consumer unit to the
outside gas meter.

This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.


My understanding was that the point of connection to piping should be
accessible so that the presence and security of a pipe clamp and cable could
be checked in future.
If this point would be under flooring at the point of entry into the house,
shouldn't the connection deliberately be made in a cupboard or other
downstream more accessible location anyway??

Phil


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On 5 Nov, 22:36, "ARWadsworth" wrote:
"stevelup" wrote in message

ups.com...

On Nov 5, 5:50 pm, "Mark" wrote:
I'm having central heating installed, 75% done.


Plumber tells me I need an earth wire from the consumer unit to the
outside
gas meter.


This is quite difficult to achieve without leaving lots of earth cable
visible. Are there alternative options for me? Also, as the incoming gas
supply is plastic I can't see the point.


mark


Is your plumber an electrician? Why is he even getting involved in
this?


Any CORGI plumber worth his salt would check for main equipotential bonding
on the gas and advise the customer that it needs doing if it is not done.

Adam


Mine ran a new pipe back to the meter cupboard. No problem so far,
except he removed the earth clamp attached to the old pipe, and left
it dangling.

Ben




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On Nov 5, 11:51 pm, John Rumm wrote:
stevelup wrote:
If there is no existing PME arrangement, then it is probable that it
is not needed.


This is nothing to do with PME. If the house has metallic gas pipeing
then this must be included in the main equipotential bonding. This is
irrespective of the type of earthing arrangement of the supply.


I understand - sorry.

Steve

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Dave Plowman (News) wrote:

Well, consider the fact that the pipe from the street is plastic. A metal
one running through earth would provide an earth of sorts - but plastic
won't.


Which means plastic is safer. If the gas pipe were metal, in contact
with earth, then it would constitute an "extraneous-conductive-part" in
the language of BS 7671 - i.e. it's capable of importing a potential
(voltage) which might be different to that of the house electrical
earthing. The extreme example of this is a house on a PME supply where
the supplier's neutral connection has broken and all the electrical
earths are live at 230 V relative to an unbonded service pipe which
remains at the real local ground potential. Hence the requirement for
*bonding* (not "earthing" or "earth bonding") all incoming services to
equalise their potentials. *Bonding* reduces the risk of dangerous
touch voltages appearing between different accessible bits of metal.

Now, plastic service pipes don't constitute extraneous-conductive-parts,
and nor does the metal installation pipework downstream, provided it
doesn't come into contact with the ground. Hence, if you read BS 7671
literally, there's no requirement to bond metal gas or water pipework
fed from plastic service pipes. However the IEE, in its practical
advice (e.g. the OSG), continues to recommend that metal installation
pipework is bonded, probably because of the risk of some ground contact
occurring - contact with damp walls or grounded structural metalwork and
that sort of thing. The upshot of this is that it will be very
difficult to convince anyone doing formal inspection and testing that no
bonding is necessary.

The copper within the house is connected to what? A boiler, gas
fire, cooker etc all of may also be connected to electricity. If one of
those developed a fault it's conceivable the electricity could get to the
pipe. And make all the copper pipe 'live'. I know it's unlikely but
protective measures have to allow for every possibility.


But the protective measure there is the *earthing* of the electrical
equipment concerned [1] which ensures that the supply is quickly cut off
(by fuse, MCB or RCD) when such a fault occurs. Note that earthing does
*not* prevent the metalwork becoming live - during the fault a
significant fraction of the mains voltage will be dropped across the
relevant circuit protective conductor (CPC) - it just ensures that it
won't stay live for very long.

It really is quite important to understand that earthing and bonding are
quite different things, even though the same piece of wire can sometimes
carry out both jobs. Talking about "earth bonding" is strongly
deprecated, even though the sort of bonding we're talking about here is
earth/ed/.


[1] Or the use of Class 2 equipment (sometimes incorrectly called
double-insulated).

--
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In article ,
Andy Wade wrote:
Well, consider the fact that the pipe from the street is plastic. A
metal one running through earth would provide an earth of sorts - but
plastic won't.


Which means plastic is safer.


Yes, have everything in the house made of plastic and the risk of
electrocution diminishes.

If the gas pipe were metal, in contact
with earth, then it would constitute an "extraneous-conductive-part" in
the language of BS 7671 - i.e. it's capable of importing a potential
(voltage) which might be different to that of the house electrical
earthing.


Round here many are still iron barrel from house to street main - they
simply pushed plastic through it when they changed. How it is sealed to
the iron barrel I have no idea - but there is electrical continuity across
the gas meter to the pipe which disappears to the street.


The extreme example of this is a house on a PME supply where
the supplier's neutral connection has broken and all the electrical
earths are live at 230 V relative to an unbonded service pipe which
remains at the real local ground potential. Hence the requirement for
*bonding* (not "earthing" or "earth bonding") all incoming services to
equalise their potentials. *Bonding* reduces the risk of dangerous
touch voltages appearing between different accessible bits of metal.


Think you're splitting hairs. Incoming services are bonded to the same
'earth'. Which may or may not be a true earth - whatever that is.

Now, plastic service pipes don't constitute extraneous-conductive-parts,
and nor does the metal installation pipework downstream, provided it
doesn't come into contact with the ground. Hence, if you read BS 7671
literally, there's no requirement to bond metal gas or water pipework
fed from plastic service pipes. However the IEE, in its practical
advice (e.g. the OSG), continues to recommend that metal installation
pipework is bonded, probably because of the risk of some ground contact
occurring - contact with damp walls or grounded structural metalwork and
that sort of thing. The upshot of this is that it will be very
difficult to convince anyone doing formal inspection and testing that no
bonding is necessary.


The copper within the house is connected to what? A boiler, gas fire,
cooker etc all of may also be connected to electricity. If one of
those developed a fault it's conceivable the electricity could get to
the pipe. And make all the copper pipe 'live'. I know it's unlikely
but protective measures have to allow for every possibility.


But the protective measure there is the *earthing* of the electrical
equipment concerned [1] which ensures that the supply is quickly cut off
(by fuse, MCB or RCD) when such a fault occurs.


So you're happy to hypothesise about the neutral failing in a PME
installation but not an appliance ground being faulty? I know which one I
reckon is more common.

Note that earthing does
*not* prevent the metalwork becoming live - during the fault a
significant fraction of the mains voltage will be dropped across the
relevant circuit protective conductor (CPC) - it just ensures that it
won't stay live for very long.


Please define 'live'?

It really is quite important to understand that earthing and bonding are
quite different things, even though the same piece of wire can sometimes
carry out both jobs. Talking about "earth bonding" is strongly
deprecated, even though the sort of bonding we're talking about here is
earth/ed/.


What most set out to do is confuse.

[1] Or the use of Class 2 equipment (sometimes incorrectly called
double-insulated).


More semantics.

--
*I love cats...they taste just like chicken.

Dave Plowman London SW
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In message , John Rumm
writes
There is nothing to stop you routing the main bond by a indirect route
if it helps (i.e. outside and back in later


that's two suggestions to route it outside I've read - is it really a
good idea to route a wire essential for safety via a place where it
could be interfered with?

--
So (must get this sig automated!)
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dave wrote:
On Mon, 5 Nov 2007 19:56:49 -0000, "Mark"
wrote:
Thanks for replying.
The pipework is all copper. To get from the consumer unit to where the
copper gas pipe enters the house is quite long route and lots of t&g
floorboards to lift.
Does it need to be as near the meter or house entry as possible? I guess
what I'm trying to say is, can't it be connected to a copper pipe a bit more
convenient.


OT but coincdentally, today I had a letter from the gas co. telling me
that they want to come and change my gas meter for a newer one in a
couple of weeks. Having read this thread I went and checked if the
existing meter has an earth bond anywhere - and yipeee (sarcastic) it
hasn't. Being pessimistic, does this mean the gas fitter could come
along and refuse to install the new meter (after disconnecting the old
one of course) because of this lack of an earth bond? The distance
from gas meter to CU and earthbond is about 3 feet!


Wouldn't this be one of those cases where there's no compulsion to
upgrade an existing installation to meet modern regs? Surely
cross-bonding of the incoming services to the main earth hasn't always
been compulsory (at least, not judging by the number of times I've had
to install it myself!)

David


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dave wrote:

OT but coincdentally, today I had a letter from the gas co. telling me
that they want to come and change my gas meter for a newer one in a
couple of weeks.


Watch the guy like a hawk, and make sure they don't leave leaks. I don't
know if the twit who changed my meter was a CORGI (looked more like a
quickly trained temp), but we had to call out Transco when we started
smelling something gassy soon after.

Secondly, they have to reignite the boiler after completing the work.
This is the point where he may shake his head (if qualified to do so),
mutter something about poor servicing and ventilation - and plant an
expensive for this time of year 'do not use' notice capping the pipe as
well.

Happened to me :-(

Can't you put them off until the spring?

--
Adrian C
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Default Earth wire from consumer unit.

Si wrote:
In message , John Rumm
writes
There is nothing to stop you routing the main bond by a indirect route
if it helps (i.e. outside and back in later


that's two suggestions to route it outside I've read - is it really a
good idea to route a wire essential for safety via a place where it
could be interfered with?


Well its a judgement call. If its a short distance in your own garden,
and especially if in conduit or trunking, then it seems pretty safe. If
it was on the front of a building that was faced directly onto a public
street, then the answer may well be different.

--
Cheers,

John.

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Default Earth wire from consumer unit.

Lobster wrote:

Wouldn't this be one of those cases where there's no compulsion to
upgrade an existing installation to meet modern regs?


There is no compulsion if you are not making changes. However, once you
make a change anywhere then you ought to do it.


--
Cheers,

John.

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Default Earth wire from consumer unit.

Si wrote:
In message , John Rumm
writes


There is nothing to stop you routing the main bond by a indirect route
if it helps (i.e. outside and back in later


that's two suggestions to route it outside I've read - is it really a
good idea to route a wire essential for safety via a place where it
could be interfered with?


Its not essential for safety, its a safety extra.


NT

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Default Earth wire from consumer unit.

Dave Plowman (News) wrote:
In article ,
Andy Wade wrote:

If the gas pipe were metal, in contact
with earth, then it would constitute an "extraneous-conductive-part" in
the language of BS 7671 - i.e. it's capable of importing a potential
(voltage) which might be different to that of the house electrical
earthing.


Round here many are still iron barrel from house to street main - they
simply pushed plastic through it when they changed. How it is sealed to
the iron barrel I have no idea - but there is electrical continuity across
the gas meter to the pipe which disappears to the street.


Although Transco often use insulating inserts on the supply side of the
meter, with the aim or preventing earth leakage and diverted neutral
currents flowing in their metal pipes. (See 4.2(iii) and 4.3 in the OSG.)

Think you're splitting hairs.


No, I think that understanding the conceptual difference between
earthing and bonding is key to understanding the subject. It's
unhelpful when people muddy the water by referring to bonding as
earthing or using woolly terms like "earth bonding." Think of earthing
as being active protection, while bonding is passive.

Incoming services are bonded to the same 'earth'.


True, and ...?

Which may or may not be a true earth - whatever that is.


.... you've just demonstrated the need to define an equipotential zone by
bonding, so that the local ground potential is made largely irrelevant.

So you're happy to hypothesise about the neutral failing in a PME
installation but not an appliance ground being faulty? I know which one I
reckon is more common.


That's unfair. The PME neutral failing brings immediate danger
(mitigated by the bonding) but the o/c CPC situation requires a second
fault (insulation failure) to develop before a dangerous situation
arises. And that's why ... EaWR ... preventative maintenance ... etc.

Note that earthing does *not* prevent the metalwork becoming live -
during the fault a significant fraction of the mains voltage will
be dropped across the relevant circuit protective conductor (CPC) -
it just ensures that it won't stay live for very long.


Please define 'live'?


In this context just "at a hazardous voltage" (wrt surroundings) will
do; above the ELV limit; 50 V AC.

In a circuit where the phase and CPC are the same size (and simplifying
by assuming that Ze Zs) then during an earth fault an
exposed-conductive-part may rise to half mains voltage until the
protective device operates. If the circuit's wired in T&E with a
reduced size CPC then the voltage is higher, being Uo * m/(1+m), where m
is the ratio of L&N size to CPC size. 4 mm^2 is the worst case with an
m of 2.67, giving a fault voltage of around 170 V.

More semantics.


Isn't accurate use of language important in all technical disciplines?
In the present field there's a well defined vocabulary and no excuse...

--
Andy
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