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aus+uk / uk.d-i-y / Re: Electrical earthing question

SubjectAuthor
* Electrical earthing questionScott
+* Re: Electrical earthing questionFredxx
|+* Re: Electrical earthing questionBrian Gaff
||+- Re: Electrical earthing questionScott
||+* Re: Electrical earthing questionFredxx
|||`* Re: Electrical earthing questionTheo
||| +- Re: Electrical earthing questionnib
||| +* Re: Electrical earthing questionFredxx
||| |`- Re: Electrical earthing questionScott
||| `- Re: Electrical earthing questionAndy Burns
||`- Re: Electrical earthing questionAndy Burns
|`- Re: Electrical earthing questionScott
+* Re: Electrical earthing questionjon
|+* Re: Electrical earthing questionAlan Lee
||`- Re: Electrical earthing questionjon
|+* Re: Electrical earthing questionAndy Burns
||`* Re: Electrical earthing questionalan_m
|| `- Re: Electrical earthing questionJohn Rumm
|+- Re: Electrical earthing questioncharles
|+- Re: Electrical earthing questionBrian Gaff
|`- Re: Electrical earthing questionJohn Rumm
+* Re: Electrical earthing questionBrian
|`* Re: Electrical earthing questionJohn Rumm
| +- Re: Electrical earthing questionBrian
| `* Re: Electrical earthing questionVir Campestris
|  +* Re: Electrical earthing questionAndy Burns
|  |`* Re: Electrical earthing questionScott
|  | +* Re: Electrical earthing questionAndy Burns
|  | |`- Re: Electrical earthing questionScott
|  | `* Re: Electrical earthing questionJohn Rumm
|  |  +* Re: Electrical earthing questionScott
|  |  |`* Re: Electrical earthing questionJohn Rumm
|  |  | `* Re: Electrical earthing questionSH
|  |  |  +- Re: Electrical earthing questionThe Natural Philosopher
|  |  |  `- Re: Electrical earthing questionJohn Rumm
|  |  `* Re: Electrical earthing questiontony sayer
|  |   +* Re: Electrical earthing questionJohn Rumm
|  |   |`- Re: Electrical earthing questionThe Natural Philosopher
|  |   `- Re: Electrical earthing questionMark Carver
|  `* Re: Electrical earthing questionJohn Rumm
|   `- Re: Electrical earthing questionnib
`* Re: Electrical earthing questionMike Clarke
 `- Re: Electrical earthing questionScott

Pages:12
Re: Electrical earthing question

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From: newsgro...@gefion.myzen.co.uk (Scott)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Tue, 24 Oct 2023 18:16:21 +0100
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 by: Scott - Tue, 24 Oct 2023 17:16 UTC

On Tue, 24 Oct 2023 14:57:02 -0100, Mike Clarke
<jmc-et@milibyte.co.uk> wrote:

>On 22/10/2023 20:53, Scott wrote:
>> Can anyone tell me - what is the name of the fault condition where the
>> neutral stops working and the earth takes over as the return path and
>> there is then a problem because (a) the earth wire is thinner than the
>> neutral wire and (b) the electricity could make its way through the
>> gas meter and cause a fire? I read about it somewhere but I cannot
>> find it on a search.
>
>Diverted Neutral Current. This relates to a break in the neutral
>conductor of your incoming supply, not the neutral within your house.
>
>John Ward has a thorough explanation of the problem and its dangers at
>https://www.youtube.com/watch?v=0nEsrlLpOzs&pp=ygUJam9obiB3YXJk and
>https://www.youtube.com/watch?v=fen8ekrhlBI&pp=ygUJam9obiB3YXJk

Thanks. I shall watch with interest once I have watched the final
episode of Sex Education.

Re: Electrical earthing question

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From: vir.camp...@invalid.invalid (Vir Campestris)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Fri, 27 Oct 2023 10:57:07 +0100
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 by: Vir Campestris - Fri, 27 Oct 2023 09:57 UTC

On 23/10/2023 13:27, John Rumm wrote:
>
> One of the reasons for the "Multiple" in PME supplies. They are
> connected to (real) earth at many places along the route making a full
> disconnection of the PEN conductor from earth very unlikely.

Shouldn't a modern box have an RCD that trips when live and neutral
currents mismatch?

Andy

Re: Electrical earthing question

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From: use...@andyburns.uk (Andy Burns)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Fri, 27 Oct 2023 11:23:20 +0100
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 by: Andy Burns - Fri, 27 Oct 2023 10:23 UTC

Vir Campestris wrote:

> John Rumm wrote:
>
>> One of the reasons for the "Multiple" in PME supplies. They are
>> connected to (real) earth at many places along the route making a full
>> disconnection of the PEN conductor from earth very unlikely.
>
> Shouldn't a modern box have an RCD that trips when live and neutral
> currents mismatch?

RCDs (each device typically covering half the circuits from a consumer
unit) or RCBOs (one device per circuit from a consumer unit) only care
about mismatch on the circuits that are downstream of the device. With
a PEN fault is upstream of them on the supplier's side, hence not detected.

Re: Electrical earthing question

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From: see.my.s...@nowhere.null (John Rumm)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Fri, 27 Oct 2023 12:54:25 +0100
Organization: Internode Ltd
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 by: John Rumm - Fri, 27 Oct 2023 11:54 UTC

On 27/10/2023 10:57, Vir Campestris wrote:
> On 23/10/2023 13:27, John Rumm wrote:
>>
>> One of the reasons for the "Multiple" in PME supplies. They are
>> connected to (real) earth at many places along the route making a full
>> disconnection of the PEN conductor from earth very unlikely.
>
> Shouldn't a modern box have an RCD that trips when live and neutral
> currents mismatch?

More than likely yes... However if you have a PME / TN-C-S supply the
bond between earth and neutral in on the main cutout, before your CU.

So if the neutral current is displaced and flowing through the earth
instead, the RCD in the CU will still see that as in balance since the
current is not flowing in the installations earth - only the supply earth.

--
Cheers,

John.

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

Re: Electrical earthing question

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From: new...@ingram-bromley.co.uk (nib)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Fri, 27 Oct 2023 11:59:29 -0000 (UTC)
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 by: nib - Fri, 27 Oct 2023 11:59 UTC

On Fri, 27 Oct 2023 12:54:25 +0100, John Rumm wrote:

> On 27/10/2023 10:57, Vir Campestris wrote:
>> On 23/10/2023 13:27, John Rumm wrote:
>>>
>>> One of the reasons for the "Multiple" in PME supplies. They are
>>> connected to (real) earth at many places along the route making a full
>>> disconnection of the PEN conductor from earth very unlikely.
>>
>> Shouldn't a modern box have an RCD that trips when live and neutral
>> currents mismatch?
>
> More than likely yes... However if you have a PME / TN-C-S supply the
> bond between earth and neutral in on the main cutout, before your CU.
>
> So if the neutral current is displaced and flowing through the earth
> instead, the RCD in the CU will still see that as in balance since the
> current is not flowing in the installations earth - only the supply
> earth.

The PEN-fault detector in my EV charger connection I think just measures
live to local earth voltage, so will trip if enough current flows back to
the supply through earth rather than neutral to cause the local earth to
rise more than a few volts.

nib

Re: Electrical earthing question

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From: newsgro...@gefion.myzen.co.uk (Scott)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Fri, 27 Oct 2023 14:53:09 +0100
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 by: Scott - Fri, 27 Oct 2023 13:53 UTC

On Fri, 27 Oct 2023 11:23:20 +0100, Andy Burns <usenet@andyburns.uk>
wrote:

>Vir Campestris wrote:
>
>> John Rumm wrote:
>>
>>> One of the reasons for the "Multiple" in PME supplies. They are
>>> connected to (real) earth at many places along the route making a full
>>> disconnection of the PEN conductor from earth very unlikely.
>>
>> Shouldn't a modern box have an RCD that trips when live and neutral
>> currents mismatch?
>
>RCDs (each device typically covering half the circuits from a consumer
>unit) or RCBOs (one device per circuit from a consumer unit) only care
>about mismatch on the circuits that are downstream of the device. With
>a PEN fault is upstream of them on the supplier's side, hence not detected.

Forgive my ignorance on the subject, but if the current is going down
the brown wire then returning (or not) via the earth there must be a
huge mismatch between the brown and the blue, which I thought was what
an RCD detected?

Re: Electrical earthing question

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From: use...@andyburns.uk (Andy Burns)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Fri, 27 Oct 2023 15:32:57 +0100
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 by: Andy Burns - Fri, 27 Oct 2023 14:32 UTC

Scott wrote:

> Forgive my ignorance on the subject, but if the current is going down
> the brown wire then returning (or not) via the earth there must be a
> huge mismatch between the brown and the blue, which I thought was what
> an RCD detected?

The fault isn't within the house circuits, the live/neutral currents
there are balanced.

The problem (with a PEN fault) is that the neutral current having
arrived at the neutral bar in the consumer unit, then leaves over the
neutral meter tail, but "finds" it can't leave the house via the main
incoming neutral as there's a break somewhere externally.

However the neutral is joined to the earth in the supplier's cutout, so
it leaves via the earth, or anything metallic bonded to the main earth
terminal, possibly a neighbour's pipes ...

None of this "finding any way via earth" is visible to the RCDs/RCBOs.

Re: Electrical earthing question

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From: newsgro...@gefion.myzen.co.uk (Scott)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Fri, 27 Oct 2023 15:50:45 +0100
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 by: Scott - Fri, 27 Oct 2023 14:50 UTC

On Fri, 27 Oct 2023 15:32:57 +0100, Andy Burns <usenet@andyburns.uk>
wrote:

>Scott wrote:
>
>> Forgive my ignorance on the subject, but if the current is going down
>> the brown wire then returning (or not) via the earth there must be a
>> huge mismatch between the brown and the blue, which I thought was what
>> an RCD detected?
>
>The fault isn't within the house circuits, the live/neutral currents
>there are balanced.
>
>The problem (with a PEN fault) is that the neutral current having
>arrived at the neutral bar in the consumer unit, then leaves over the
>neutral meter tail, but "finds" it can't leave the house via the main
>incoming neutral as there's a break somewhere externally.
>
>However the neutral is joined to the earth in the supplier's cutout, so
>it leaves via the earth, or anything metallic bonded to the main earth
>terminal, possibly a neighbour's pipes ...
>
>None of this "finding any way via earth" is visible to the RCDs/RCBOs.

Thanks. I mostly get it now.

Re: Electrical earthing question

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From: see.my.s...@nowhere.null (John Rumm)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Sat, 28 Oct 2023 16:29:19 +0100
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 by: John Rumm - Sat, 28 Oct 2023 15:29 UTC

On 27/10/2023 14:53, Scott wrote:
> On Fri, 27 Oct 2023 11:23:20 +0100, Andy Burns <usenet@andyburns.uk>
> wrote:
>
>> Vir Campestris wrote:
>>
>>> John Rumm wrote:
>>>
>>>> One of the reasons for the "Multiple" in PME supplies. They are
>>>> connected to (real) earth at many places along the route making a full
>>>> disconnection of the PEN conductor from earth very unlikely.
>>>
>>> Shouldn't a modern box have an RCD that trips when live and neutral
>>> currents mismatch?
>>
>> RCDs (each device typically covering half the circuits from a consumer
>> unit) or RCBOs (one device per circuit from a consumer unit) only care
>> about mismatch on the circuits that are downstream of the device. With
>> a PEN fault is upstream of them on the supplier's side, hence not detected.
>
> Forgive my ignorance on the subject, but if the current is going down
> the brown wire then returning (or not) via the earth there must be a
> huge mismatch between the brown and the blue, which I thought was what
> an RCD detected?

It would - but that imbalance would have to be on the load side of the RCD.

So for example pick up the cut end of a mower flex and make accidental
contact with live. You get a shock since the current flows through you
to earth bypassing neutral. That means the RCD will see the imbalance
between current in live and neutral and trip.

In this case the property is supplied by a Protective Earth & Neutral
(PEN) conductor. At the main cutout (i.e. before your electric meter and
your consumer unit) it is split to provide a neutral connection and a
main earth connection.

That main earth connection will also be connected via your main
equipotential bonding to things like gas and water services.

Now someone goes and cuts the PEN conductor to your property. That would
mean you have no neutral or earth to your property - and might expect
everything to just stop working.

However because the PEN conductor is bonded to lots of other earthed
things at your cutout, there may still be an indirect path for the
neutral current connected to the CU. So as long as there is no earth
fault on one of its circuits, the RCD will see balanced current in the L
& N, and it is fat dumb and happy.

What it does not know, is that the neutral that is connected to the CU,
is no longer the intended one, but is now being made by your water and
gas mains. And probably the neutral connection to your neighbours, since
there is likely a conductive path between their Neutral / Main Earth
terminal to yours. (e.g. if you share a metal water pipe with a
neighbour, and you both have main bonding to that water pipe, then you
have a direct connection to their neutral).

--
Cheers,

John.

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

Re: Electrical earthing question

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From: newsgro...@gefion.myzen.co.uk (Scott)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Mon, 30 Oct 2023 16:13:24 +0000
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 by: Scott - Mon, 30 Oct 2023 16:13 UTC

On Sat, 28 Oct 2023 16:29:19 +0100, John Rumm
<see.my.signature@nowhere.null> wrote:
[snip]
>What it does not know, is that the neutral that is connected to the CU,
>is no longer the intended one, but is now being made by your water and
>gas mains. And probably the neutral connection to your neighbours, since
>there is likely a conductive path between their Neutral / Main Earth
>terminal to yours. (e.g. if you share a metal water pipe with a
>neighbour, and you both have main bonding to that water pipe, then you
>have a direct connection to their neutral).

Thanks for the clear explanation. Does it matter if the earth on the
ring main is connected to the kitchen sink or cold water pipe? Can the
returning current make its way back through (or past) the meter into
the 'inside' earth and into the kitchen sink? If the earth for the
water pipe is inadequate, can you then get an electric shock from the
cold tap?

Re: Electrical earthing question

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From: see.my.s...@nowhere.null (John Rumm)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Tue, 31 Oct 2023 01:26:43 +0000
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 by: John Rumm - Tue, 31 Oct 2023 01:26 UTC

On 30/10/2023 16:13, Scott wrote:
> On Sat, 28 Oct 2023 16:29:19 +0100, John Rumm
> <see.my.signature@nowhere.null> wrote:
> [snip]
>> What it does not know, is that the neutral that is connected to the CU,
>> is no longer the intended one, but is now being made by your water and
>> gas mains. And probably the neutral connection to your neighbours, since
>> there is likely a conductive path between their Neutral / Main Earth
>> terminal to yours. (e.g. if you share a metal water pipe with a
>> neighbour, and you both have main bonding to that water pipe, then you
>> have a direct connection to their neutral).
>
> Thanks for the clear explanation. Does it matter if the earth on the
> ring main is connected to the kitchen sink or cold water pipe?

No, that is fairly typical since the main water pipe will be connected
to the main EQ bond, and the kitchen sink probably has a connection to
that.

In normal circumstances the load will be between the L and N, and the
RCD will be happy. If there is a fault, and some current flows to earth
(and that does not matter if the it is the "proper" circuit earth, or
something that is bonded to the main earth terminal, or just some
independent local earth) the RCD would see an imbalance, and trip.

> Can the
> returning current make its way back through (or past) the meter into
> the 'inside' earth and into the kitchen sink?

This is the concern with loss of the PEN conductor. Your loads were
strung between L & N. If N is cut, in the worst case (where the N in the
property is left unconnected to anything or "floating"), its voltage
will rise to mains voltage. The appliances won't work - since the
floating N can't sink or source any current - but it would be a shock
risk if you could touch the earthed but now live thing, and an
independent actually earthed thing at the same time.

That is why you have EQ bonding to create an equipotential zone. By
joining all the things that could introduce a potential into the zone
together, you limit the voltage difference, and hence reduce the shock
risk. So in a case where the incoming cold water pipe is actually
plastic for its underground run, the only metal conductive bits might be
the pipes in your house, they would would also now rise to mains voltage.

However it would be the same mains voltage as that which your main earth
has risen. So you could safely lean against an earthed (but now live)
cooker, and touch the cold tap, since they would both be at the same
voltage and hence no current would flow through you.

Now in many cases those EQ bonds will not only create an equipotential
zone (i.e. what they are designed to do), they will also give you what
is called fortuitous earthing (and by extension an accidental neutral as
well since they are joined at the cutout).

How good that earthing will be can vary. If it were to just an earth
rod, it could be tens or hundreds of ohms. If it were to a incoming
metallic a cold water pipe or gas pipe, It might actually be a fairly
decent earth - although the resistance will vary with soil conditions
etc. In a town with close adjacent properties, then there is a fair
chance those EQ bonds could actually be a pretty solid connection to the
(still connected) PEN in the property next door (via your Neutral ->
Main EQ bond -> Water pipe -> Neighbours Main EQ bond -> Their Neutral).
This could even hide the fact that your PEN conductor was disconnected.
Obviously this is less than ideal - especially since the main EQ bonds
are unlikely to be more than 10mm^2, but your meter tails will often be
25mm^2. So under high load, that earth is going to get hot!

> If the earth for the
> water pipe is inadequate, can you then get an electric shock from the
> cold tap?

Only if it is not included in the bonding...

--
Cheers,

John.

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

Re: Electrical earthing question

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From: i.l...@spam.com (SH)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Tue, 31 Oct 2023 08:36:28 +0000
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 by: SH - Tue, 31 Oct 2023 08:36 UTC

On 31/10/2023 01:26, John Rumm wrote:
> On 30/10/2023 16:13, Scott wrote:
>> On Sat, 28 Oct 2023 16:29:19 +0100, John Rumm
>> <see.my.signature@nowhere.null> wrote:
>> [snip]
>>> What it does not know, is that the neutral that is connected to the CU,
>>> is no longer the intended one, but is now being made by your water and
>>> gas mains. And probably the neutral connection to your neighbours, since
>>> there is likely a conductive path between their Neutral / Main Earth
>>> terminal to yours. (e.g. if you share a metal water pipe with a
>>> neighbour, and you both have main bonding to that water pipe, then you
>>> have a direct connection to their neutral).
>>
>> Thanks for the clear explanation. Does it matter if the earth on the
>> ring main is connected to the kitchen sink or cold water pipe?
>
> No, that is fairly typical since the main water pipe will be connected
> to the main EQ bond, and the kitchen sink probably has a connection to
> that.
>

Its all very well bonding a metal water pipe such as after the house's
stop valve to earth,

for many years all hot, cold and heating pipes were done in copper.

There is now heavy use of PEX plastic pipe. given that plastic pipe
cannot be bonded to earth, shoulding the metal kitchen sinks and the
wall radiators be bonded to earth as they are common touch points for
humans?

Re: Electrical earthing question

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From: tnp...@invalid.invalid (The Natural Philosopher)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Tue, 31 Oct 2023 14:11:25 +0000
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 by: The Natural Philosop - Tue, 31 Oct 2023 14:11 UTC

On 31/10/2023 08:36, SH wrote:
> given that plastic pipe cannot be bonded to earth, should the
> metal kitchen sinks and the wall radiators be bonded to earth as they
> are common touch points for humans?

If they are not connected to any other metal object that might become
live, why bother?

>

--
Climate is what you expect but weather is what you get.
Mark Twain

Re: Electrical earthing question

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From: see.my.s...@nowhere.null (John Rumm)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Tue, 31 Oct 2023 18:30:13 +0000
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 by: John Rumm - Tue, 31 Oct 2023 18:30 UTC

On 31/10/2023 08:36, SH wrote:
> On 31/10/2023 01:26, John Rumm wrote:
>> On 30/10/2023 16:13, Scott wrote:
>>> On Sat, 28 Oct 2023 16:29:19 +0100, John Rumm
>>> <see.my.signature@nowhere.null> wrote:
>>> [snip]
>>>> What it does not know, is that the neutral that is connected to the CU,
>>>> is no longer the intended one, but is now being made by your water and
>>>> gas mains. And probably the neutral connection to your neighbours,
>>>> since
>>>> there is likely a conductive path between their Neutral / Main Earth
>>>> terminal to yours. (e.g. if you share a metal water pipe with a
>>>> neighbour, and you both have main bonding to that water pipe, then you
>>>> have a direct connection to their neutral).
>>>
>>> Thanks for the clear explanation. Does it matter if the earth on the
>>> ring main is connected to the kitchen sink or cold water pipe?
>>
>> No, that is fairly typical since the main water pipe will be connected
>> to the main EQ bond, and the kitchen sink probably has a connection to
>> that.
>>
>
> Its all very well bonding a metal water pipe such as after the house's
> stop valve to earth,
>
> for many years all hot, cold and heating pipes were done in copper.
>
> There is now heavy use of PEX plastic pipe. given that plastic pipe
> cannot be bonded to earth, shoulding the metal kitchen sinks and the
> wall radiators be bonded to earth as they are common touch points for
> humans?

No, not as a general rule. The question you need to ask, is is the thing
in question capable of introducing a potential into an equipotential zone...

So in the case of a house with TN-C-S earthing you consider the whole
thing as one EQ zone - so anything that comes in from outside like
services etc gets bonded.

The you move down to rooms - some of which may have supplementary
bonding[1] because they are considered to be high shock risk
environments (like bathrooms etc). So in a bathroom the metal pipes
coming into it (be they water, drainage, or CH), the earth wire of any
circuits that serve the room would get bonded because they could bring a
potential into the room. However something like a stand alone metal
bath, sink or a radiator with plastic plumbing would not need bonding
since it can't introduce a potential into the zone.

[1] Note that supplementary bonding does not require a connection back
to the main earth terminal - it just needs things to be connected
together. (you may get a connection back to the main earth by virtue of
a circuit earth, which will usually be included in the bonding)

--
Cheers,

John.

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

Re: Electrical earthing question

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From: ton...@bancom.co.uk (tony sayer)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Mon, 13 Nov 2023 17:21:13 +0000
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 by: tony sayer - Mon, 13 Nov 2023 17:21 UTC

In article <uhj9cg$2uce5$1@dont-email.me>, John Rumm <see.my.signature@n
owhere.null> scribeth thus
>On 27/10/2023 14:53, Scott wrote:
>> On Fri, 27 Oct 2023 11:23:20 +0100, Andy Burns <usenet@andyburns.uk>
>> wrote:
>>
>>> Vir Campestris wrote:
>>>
>>>> John Rumm wrote:
>>>>
>>>>> One of the reasons for the "Multiple" in PME supplies. They are
>>>>> connected to (real) earth at many places along the route making a full
>>>>> disconnection of the PEN conductor from earth very unlikely.
>>>>
>>>> Shouldn't a modern box have an RCD that trips when live and neutral
>>>> currents mismatch?
>>>
>>> RCDs (each device typically covering half the circuits from a consumer
>>> unit) or RCBOs (one device per circuit from a consumer unit) only care
>>> about mismatch on the circuits that are downstream of the device. With
>>> a PEN fault is upstream of them on the supplier's side, hence not detected.
>>
>> Forgive my ignorance on the subject, but if the current is going down
>> the brown wire then returning (or not) via the earth there must be a
>> huge mismatch between the brown and the blue, which I thought was what
>> an RCD detected?
>
>It would - but that imbalance would have to be on the load side of the RCD.
>
>So for example pick up the cut end of a mower flex and make accidental
>contact with live. You get a shock since the current flows through you
>to earth bypassing neutral. That means the RCD will see the imbalance
>between current in live and neutral and trip.
>
>In this case the property is supplied by a Protective Earth & Neutral
>(PEN) conductor. At the main cutout (i.e. before your electric meter and
>your consumer unit) it is split to provide a neutral connection and a
>main earth connection.
>
>That main earth connection will also be connected via your main
>equipotential bonding to things like gas and water services.
>
>Now someone goes and cuts the PEN conductor to your property. That would
>mean you have no neutral or earth to your property - and might expect
>everything to just stop working.
>
>However because the PEN conductor is bonded to lots of other earthed
>things at your cutout, there may still be an indirect path for the
>neutral current connected to the CU. So as long as there is no earth
>fault on one of its circuits, the RCD will see balanced current in the L
>& N, and it is fat dumb and happy.
>
>What it does not know, is that the neutral that is connected to the CU,
>is no longer the intended one, but is now being made by your water and
>gas mains. And probably the neutral connection to your neighbours, since
>there is likely a conductive path between their Neutral / Main Earth
>terminal to yours. (e.g. if you share a metal water pipe with a
>neighbour, and you both have main bonding to that water pipe, then you
>have a direct connection to their neutral).
>
>

Wot if your water main incomer and gas are plastic?...

--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

Re: Electrical earthing question

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From: see.my.s...@nowhere.null (John Rumm)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Wed, 15 Nov 2023 23:06:14 +0000
Organization: Internode Ltd
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 by: John Rumm - Wed, 15 Nov 2023 23:06 UTC

On 13/11/2023 17:21, tony sayer wrote:
> In article <uhj9cg$2uce5$1@dont-email.me>, John Rumm <see.my.signature@n
> owhere.null> scribeth thus
>> On 27/10/2023 14:53, Scott wrote:
>>> On Fri, 27 Oct 2023 11:23:20 +0100, Andy Burns <usenet@andyburns.uk>
>>> wrote:
>>>
>>>> Vir Campestris wrote:
>>>>
>>>>> John Rumm wrote:
>>>>>
>>>>>> One of the reasons for the "Multiple" in PME supplies. They are
>>>>>> connected to (real) earth at many places along the route making a full
>>>>>> disconnection of the PEN conductor from earth very unlikely.
>>>>>
>>>>> Shouldn't a modern box have an RCD that trips when live and neutral
>>>>> currents mismatch?
>>>>
>>>> RCDs (each device typically covering half the circuits from a consumer
>>>> unit) or RCBOs (one device per circuit from a consumer unit) only care
>>>> about mismatch on the circuits that are downstream of the device. With
>>>> a PEN fault is upstream of them on the supplier's side, hence not detected.
>>>
>>> Forgive my ignorance on the subject, but if the current is going down
>>> the brown wire then returning (or not) via the earth there must be a
>>> huge mismatch between the brown and the blue, which I thought was what
>>> an RCD detected?
>>
>> It would - but that imbalance would have to be on the load side of the RCD.
>>
>> So for example pick up the cut end of a mower flex and make accidental
>> contact with live. You get a shock since the current flows through you
>> to earth bypassing neutral. That means the RCD will see the imbalance
>> between current in live and neutral and trip.
>>
>> In this case the property is supplied by a Protective Earth & Neutral
>> (PEN) conductor. At the main cutout (i.e. before your electric meter and
>> your consumer unit) it is split to provide a neutral connection and a
>> main earth connection.
>>
>> That main earth connection will also be connected via your main
>> equipotential bonding to things like gas and water services.
>>
>> Now someone goes and cuts the PEN conductor to your property. That would
>> mean you have no neutral or earth to your property - and might expect
>> everything to just stop working.
>>
>> However because the PEN conductor is bonded to lots of other earthed
>> things at your cutout, there may still be an indirect path for the
>> neutral current connected to the CU. So as long as there is no earth
>> fault on one of its circuits, the RCD will see balanced current in the L
>> & N, and it is fat dumb and happy.
>>
>> What it does not know, is that the neutral that is connected to the CU,
>> is no longer the intended one, but is now being made by your water and
>> gas mains. And probably the neutral connection to your neighbours, since
>> there is likely a conductive path between their Neutral / Main Earth
>> terminal to yours. (e.g. if you share a metal water pipe with a
>> neighbour, and you both have main bonding to that water pipe, then you
>> have a direct connection to their neutral).
>>
>>
>
> Wot if your water main incomer and gas are plastic?...

The RCD would still not see the imbalance. Whether you would get the
appearance of a functioning neutral via an alternative path (through
earth, extraneous conductive parts included in the bonding etc will
depend on the circumstances, soil conditions, how far from neighbours etc).

If there is no earth spike, no earthed metal connected via main bonding
conductors, then you might get a truly disconnected and hence "floating"
neutral at the main cutout.

No circuit will function, but all the earthed metalwork in the house
will rise to mains potential. Hopefully you are in an equipotential zone
that means you can't touch anything at real earth, and you won't notice!

--
Cheers,

John.

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

Re: Electrical earthing question

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From: mar...@invalid.com (Mark Carver)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Sun, 19 Nov 2023 16:18:37 +0000
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 by: Mark Carver - Sun, 19 Nov 2023 16:18 UTC

On 13/11/2023 17:21, tony sayer wrote:

>
> Wot if your water main incomer and gas are plastic?...

That's what we have, house totally reconfigured, rebuilt, rewired,
re-plumbed. Apparently no bonding to pipework or metalwork is required
by the regs (Changed recently, in the 2010s ?)

The incoming DNO cable connects to the house Earth to incoming Neutral
at the DNO 100A fuse-point.

I can't see any evidence of a PME Earth cable on the pole that feeds us,
but other poles along the road do.

Re: Electrical earthing question

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From: tnp...@invalid.invalid (The Natural Philosopher)
Newsgroups: uk.d-i-y
Subject: Re: Electrical earthing question
Date: Thu, 23 Nov 2023 15:28:12 +0000
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 by: The Natural Philosop - Thu, 23 Nov 2023 15:28 UTC

On 23/11/2023 14:14, tony sayer wrote:
>>>>
>>>
>>> Wot if your water main incomer and gas are plastic?...
>>
>> The RCD would still not see the imbalance. Whether you would get the
>> appearance of a functioning neutral via an alternative path (through
>> earth, extraneous conductive parts included in the bonding etc will
>> depend on the circumstances, soil conditions, how far from neighbours etc).
>>
>> If there is no earth spike, no earthed metal connected via main bonding
>> conductors, then you might get a truly disconnected and hence "floating"
>> neutral at the main cutout.
>>
>> No circuit will function, but all the earthed metalwork in the house
>> will rise to mains potential. Hopefully you are in an equipotential zone
>> that means you can't touch anything at real earth, and you won't notice!
>>
>>
> All noted John but i rather doubt the mains incoming Neutral will go
> we're fed by what looks like a co-ax mains cable inner insulator and
> outer wire armouring least thats what it looked like what a digger went
> trough it when they had the road up!. So the suppliers earth and neutral
> are together unless it is a Two core armoured cable, anyone know
> different?..
>
Nope, it is armoured coaxial cable and the neutral will be pinned to
earth somewhere. I have this and I also pinned it to 1.5 meters of
buried copper pipe.
Belt and braces...

> cheers...

--
"A point of view can be a dangerous luxury when substituted for insight
and understanding".

Marshall McLuhan


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