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.

On 22/10/2023 22:53, 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 Currents?

On Sun, 22 Oct 2023 22:53:44 +0100, 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.

Never, ever bond an electrical earth to a gas pipe.

On 23/10/2023 05:20, jon wrote:
> On Sun, 22 Oct 2023 22:53:44 +0100, 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.
>
> Never, ever bond an electrical earth to a gas pipe.

That's total bollocks.
Bonding the gas is one of the principal things that must be done if the
incoming pipe is metal, or can give an earth potential.
The cable size is important, and must be 10mm CSA for most domestic
installations. An existing 6mm cable could be permissable under certain
conditions.

--
Remove the '+' and replace with 'plus' to reply by email

jon wrote:

> 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

"PEN fault" or "lost neutral"

>> 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?

There ought to be insulated washers on the pipes in and out of the gas meter

>> I read about it somewhere but I cannot find it on a search.
>
> Never, ever bond an electrical earth to a gas pipe.

^^^ Ignore that advice ^^^

Never use a gas pipe as an earth,
but always bond metal gas and water pipes to the main earth terminal!

A Scott <newsgroups@gefion.myzen.co.uk> 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.
>

I suspect you are referring to what is, generally known as, a PME fault -
although it generally relates to any ‘hazardous’ route to earth for the
fault current when the Neutral fails.

For example, if you have an outside tap which isn’t isolated and the copper
pipes are bounded to the Neutral to provide your local Earth ( a TN-C-S or
PME system) and there is a Neutral break, your pipes ‘rise’ to the Live
voltage.

Touch the outside tap and there is a current path via the earth ( the stuff
you are standing on) and the numerous PME points prior to the break.

The good news is, fatalities from such incidents are very rare. That said,
Neutral faults are less so.

In article <uh4s9m$2u4lj$1@dont-email.me>,
jon <jon@nospam.cn> wrote:
> On Sun, 22 Oct 2023 22:53:44 +0100, 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.

> Never, ever bond an electrical earth to a gas pipe.

Ours was bonded by the DNO.

--
from KT24 in Surrey, England - sent from my RISC OS 4té²
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On 23/10/2023 08:05, Andy Burns wrote:
>
> jon wrote:
>
>> 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
>
> "PEN fault" or "lost neutral"
>
>>> 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?
>
> There ought to be insulated washers on the pipes in and out of the gas
> meter
>
>>> I read about it somewhere but I cannot find it on a search.
>>
>> Never, ever bond an electrical earth to a gas pipe.
>
> ^^^ Ignore that advice ^^^
>
> Never use a gas pipe as an earth,
> but always bond metal gas and water pipes to the main earth terminal!
>

I believe that the gas bonding should also be within 600mm of the meter
outlet.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On Mon, 23 Oct 2023 06:55:52 +0100, Alan Lee wrote:

> On 23/10/2023 05:20, jon wrote:
>> On Sun, 22 Oct 2023 22:53:44 +0100, 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.
>>
>> Never, ever bond an electrical earth to a gas pipe.
>
> That's total bollocks.
> Bonding the gas is one of the principal things that must be done if the
> incoming pipe is metal, or can give an earth potential.
> The cable size is important, and must be 10mm CSA for most domestic
> installations. An existing 6mm cable could be permissable under certain
> conditions.

Industry sources say many reported appliance failures, which have led to
fires, were in fact a result of NCD. The fault can cause gas explosions,
according to Mackenzie. While the cause of the majority of gas explosions
are recorded as gas leaks, he noted that NCDs are so prevalent on gas
pipes that the gas industry attaches jump leads between gas pipes before
changing them, because they generate sparks.

In its written response, the government added that the Gas Safety
(Installation and Use) Regulations require additional electrical bonding
when cutting conducting gas pipes to minimise the risk to workers.

However, Mackenzie said these measures were not adequate and would not
mitigate the risks associated with the heightened levels of current that
can flow through gas pipes where NCD exists. He also pointed out that any
metallic piping could carry the current, including water and oil pipes,
which are not covered under these regulations.

It would be a pretty naff installation if it had live wires anywhere near
the gas in the meter.
Would this not be picked up by modern circuit breakers though?

The difficult part would be finding the break.
I'd imagine a double insulated device that had no earth, enough to not work
on part of the system where the neutral is disconnected.

Brian

--

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briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"Fredxx" <fredxx@spam.invalid> wrote in message
news:uh466f$2m54e$1@dont-email.me...
> On 22/10/2023 22:53, 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 Currents?

I'd assume that would be so obvious, it should not need saying.
Most smart gas meters I've seen of late are battery powered and use plastic
pipes.
Brian

--

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This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
briang1@blueyonder.co.uk
Blind user, so no pictures please
Note this Signature is meaningless.!
"jon" <jon@nospam.cn> wrote in message news:uh4s9m$2u4lj$1@dont-email.me...
> On Sun, 22 Oct 2023 22:53:44 +0100, 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.
>
> Never, ever bond an electrical earth to a gas pipe.

On Sun, 22 Oct 2023 23:02:56 +0100, Fredxx <fredxx@spam.invalid>
wrote:

>On 22/10/2023 22:53, 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 Currents?

Thanks - that is the term I was looking for.

On Mon, 23 Oct 2023 10:09:10 +0100, "Brian Gaff"
<brian1gaff@gmail.com> wrote:

>It would be a pretty naff installation if it had live wires anywhere near
>the gas in the meter.
> Would this not be picked up by modern circuit breakers though?
>
>The difficult part would be finding the break.
> I'd imagine a double insulated device that had no earth, enough to not work
>on part of the system where the neutral is disconnected.
>
Thanks, Brian. It's just I read about it somewhere in the media and I
wanted to know more about it. When I read it, I was as sceptical as
you are. To my mind, if I take away the neutral for the washing
machine there is no amount of AI that would allow it to substitute the
earth wire to allow it to continue with the spin cycle.

On 23/10/2023 10:09, Brian Gaff wrote:
> It would be a pretty naff installation if it had live wires anywhere near
> the gas in the meter.
> Would this not be picked up by modern circuit breakers though?
>
> The difficult part would be finding the break.
> I'd imagine a double insulated device that had no earth, enough to not work
> on part of the system where the neutral is disconnected.
>
> Brian

Neutral is not a 'live' wire. Earth and Neutral typically come into the
home as a single cable and only separated at the incomer.

The issue and I recommend doing some research of your own, is that when
a neutral on the incomer goes o/c, the neutral and earth are then
dependent on any local bonding, such as to a gas pipe. I recall a
description to a block of flats where the gas pipe was running hot,
because the gas pipe was supplying the neutral current into the block.

This is nothing about live wires, except that the Neutral/Earth
conductor, in a fault o/c condition, can creep towards Live depending on
bonding.

Fredxx <fredxx@spam.invalid> wrote:
> On 23/10/2023 10:09, Brian Gaff wrote:
> > It would be a pretty naff installation if it had live wires anywhere near
> > the gas in the meter.
> > Would this not be picked up by modern circuit breakers though?
> >
> > The difficult part would be finding the break. I'd imagine a double
> > insulated device that had no earth, enough to not work
> > on part of the system where the neutral is disconnected.
> >
> > Brian
>
> Neutral is not a 'live' wire. Earth and Neutral typically come into the
> home as a single cable and only separated at the incomer.
>
> The issue and I recommend doing some research of your own, is that when
> a neutral on the incomer goes o/c, the neutral and earth are then
> dependent on any local bonding, such as to a gas pipe. I recall a
> description to a block of flats where the gas pipe was running hot,
> because the gas pipe was supplying the neutral current into the block.
>
> This is nothing about live wires, except that the Neutral/Earth
> conductor, in a fault o/c condition, can creep towards Live depending on
> bonding.

AIUI the issue with a PEN fault is that a turned-on appliance causes the
neutral to go live. If you have, say, an incandescent light bulb that is
switched on, a loss of neutral will cause the current to drop to near-zero
(so it's not illuminated) but the resistance of the bulb is low so the
neutral wire is now at live potential. If the neutral is bonded to earth,
so is all your earthed exposed metalwork, and so your metalwork is now live.

It's only if there's another conductive path back to the neutral will enough
current flow to illuminate the bulb and drag down the neutral voltage to a
safe level. If the neutral is bonded to earth, that means the earth needs a
good enough conductive path back to the neutral bypassing the fault (via the
earth to next door's bonded neutral that is still functional, or an earth
path all the way back to the substation), then the neutral will be viable
and not at a dangerous voltage.

When installing an EV charger, you either have to provide it a separate
earth rod (not part of PME), or a device that shuts off the live if a PEN
fault is detected. There are noises about making such a PEN fault detector
part of a standard consumer unit - sounds like a good idea to me.

Theo

Brian Gaff wrote:

> The difficult part would be finding the break.

But it'll be out in the street, so supplier's responsibility.

On Mon, 23 Oct 2023 12:33:03 +0100, Theo wrote:

> Fredxx <fredxx@spam.invalid> wrote:
>> On 23/10/2023 10:09, Brian Gaff wrote:
>> > It would be a pretty naff installation if it had live wires anywhere
>> > near the gas in the meter.
>> > Would this not be picked up by modern circuit breakers though?
>> >
>> > The difficult part would be finding the break. I'd imagine a double
>> > insulated device that had no earth, enough to not work
>> > on part of the system where the neutral is disconnected.
>> >
>> > Brian
>>
>> Neutral is not a 'live' wire. Earth and Neutral typically come into the
>> home as a single cable and only separated at the incomer.
>>
>> The issue and I recommend doing some research of your own, is that when
>> a neutral on the incomer goes o/c, the neutral and earth are then
>> dependent on any local bonding, such as to a gas pipe. I recall a
>> description to a block of flats where the gas pipe was running hot,
>> because the gas pipe was supplying the neutral current into the block.
>>
>> This is nothing about live wires, except that the Neutral/Earth
>> conductor, in a fault o/c condition, can creep towards Live depending
>> on bonding.
>
> AIUI the issue with a PEN fault is that a turned-on appliance causes the
> neutral to go live. If you have, say, an incandescent light bulb that
> is switched on, a loss of neutral will cause the current to drop to
> near-zero (so it's not illuminated) but the resistance of the bulb is
> low so the neutral wire is now at live potential. If the neutral is
> bonded to earth, so is all your earthed exposed metalwork, and so your
> metalwork is now live.
>
> It's only if there's another conductive path back to the neutral will
> enough current flow to illuminate the bulb and drag down the neutral
> voltage to a safe level. If the neutral is bonded to earth, that means
> the earth needs a good enough conductive path back to the neutral
> bypassing the fault (via the earth to next door's bonded neutral that is
> still functional, or an earth path all the way back to the substation),
> then the neutral will be viable and not at a dangerous voltage.
>
> When installing an EV charger, you either have to provide it a separate
> earth rod (not part of PME), or a device that shuts off the live if a
> PEN fault is detected.

If it's like mine, then on a fault it disconnects all three: L, N and E
before the EV wall box.

nib

There are noises about making such a PEN fault
> detector part of a standard consumer unit - sounds like a good idea to
> me.
>
> Theo

On 23/10/2023 12:33, Theo wrote:
> Fredxx <fredxx@spam.invalid> wrote:
>> On 23/10/2023 10:09, Brian Gaff wrote:
>>> It would be a pretty naff installation if it had live wires anywhere near
>>> the gas in the meter.
>>> Would this not be picked up by modern circuit breakers though?
>>>
>>> The difficult part would be finding the break. I'd imagine a double
>>> insulated device that had no earth, enough to not work
>>> on part of the system where the neutral is disconnected.
>>>
>>> Brian
>>
>> Neutral is not a 'live' wire. Earth and Neutral typically come into the
>> home as a single cable and only separated at the incomer.
>>
>> The issue and I recommend doing some research of your own, is that when
>> a neutral on the incomer goes o/c, the neutral and earth are then
>> dependent on any local bonding, such as to a gas pipe. I recall a
>> description to a block of flats where the gas pipe was running hot,
>> because the gas pipe was supplying the neutral current into the block.
>>
>> This is nothing about live wires, except that the Neutral/Earth
>> conductor, in a fault o/c condition, can creep towards Live depending on
>> bonding.
>
> AIUI the issue with a PEN fault is that a turned-on appliance causes the
> neutral to go live. If you have, say, an incandescent light bulb that is
> switched on, a loss of neutral will cause the current to drop to near-zero
> (so it's not illuminated) but the resistance of the bulb is low so the
> neutral wire is now at live potential. If the neutral is bonded to earth,
> so is all your earthed exposed metalwork, and so your metalwork is now live.
>
> It's only if there's another conductive path back to the neutral will enough
> current flow to illuminate the bulb and drag down the neutral voltage to a
> safe level. If the neutral is bonded to earth, that means the earth needs a
> good enough conductive path back to the neutral bypassing the fault (via the
> earth to next door's bonded neutral that is still functional, or an earth
> path all the way back to the substation), then the neutral will be viable
> and not at a dangerous voltage.
>
> When installing an EV charger, you either have to provide it a separate
> earth rod (not part of PME), or a device that shuts off the live if a PEN
> fault is detected. There are noises about making such a PEN fault detector
> part of a standard consumer unit - sounds like a good idea to me.

In my experience my bonded earth was quite a low resistance and only by
putting a kettle on did the neutral rise by 80VAC or so. This affected 2
other neighbours, and given the location of the fault, would have meant
their mains voltage would have risen by sqrt(3) x 80V

There are rumours of an extra component in a consumer unit that measures
earth current to disconnect when there is a measurable flow. It's
closely reminiscent of an earth leakage breaker.

Theo wrote:

> When installing an EV charger, you either have to provide it a separate
> earth rod (not part of PME), or a device that shuts off the live

*and* earth

> if a PEN fault is detected.

On Mon, 23 Oct 2023 12:46:26 +0100, Fredxx <fredxx@spam.invalid>
wrote:

>On 23/10/2023 12:33, Theo wrote:
>> Fredxx <fredxx@spam.invalid> wrote:
>>> On 23/10/2023 10:09, Brian Gaff wrote:
>>>> It would be a pretty naff installation if it had live wires anywhere near
>>>> the gas in the meter.
>>>> Would this not be picked up by modern circuit breakers though?
>>>>
>>>> The difficult part would be finding the break. I'd imagine a double
>>>> insulated device that had no earth, enough to not work
>>>> on part of the system where the neutral is disconnected.
>>>>
>>>> Brian
>>>
>>> Neutral is not a 'live' wire. Earth and Neutral typically come into the
>>> home as a single cable and only separated at the incomer.
>>>
>>> The issue and I recommend doing some research of your own, is that when
>>> a neutral on the incomer goes o/c, the neutral and earth are then
>>> dependent on any local bonding, such as to a gas pipe. I recall a
>>> description to a block of flats where the gas pipe was running hot,
>>> because the gas pipe was supplying the neutral current into the block.
>>>
>>> This is nothing about live wires, except that the Neutral/Earth
>>> conductor, in a fault o/c condition, can creep towards Live depending on
>>> bonding.
>>
>> AIUI the issue with a PEN fault is that a turned-on appliance causes the
>> neutral to go live. If you have, say, an incandescent light bulb that is
>> switched on, a loss of neutral will cause the current to drop to near-zero
>> (so it's not illuminated) but the resistance of the bulb is low so the
>> neutral wire is now at live potential. If the neutral is bonded to earth,
>> so is all your earthed exposed metalwork, and so your metalwork is now live.
>>
>> It's only if there's another conductive path back to the neutral will enough
>> current flow to illuminate the bulb and drag down the neutral voltage to a
>> safe level. If the neutral is bonded to earth, that means the earth needs a
>> good enough conductive path back to the neutral bypassing the fault (via the
>> earth to next door's bonded neutral that is still functional, or an earth
>> path all the way back to the substation), then the neutral will be viable
>> and not at a dangerous voltage.
>>
>> When installing an EV charger, you either have to provide it a separate
>> earth rod (not part of PME), or a device that shuts off the live if a PEN
>> fault is detected. There are noises about making such a PEN fault detector
>> part of a standard consumer unit - sounds like a good idea to me.
>
>In my experience my bonded earth was quite a low resistance and only by
>putting a kettle on did the neutral rise by 80VAC or so. This affected 2
>other neighbours, and given the location of the fault, would have meant
>their mains voltage would have risen by sqrt(3) x 80V
>
>There are rumours of an extra component in a consumer unit that measures
>earth current to disconnect when there is a measurable flow. It's
>closely reminiscent of an earth leakage breaker.

Come to think of it, this was also mentioned in the original piece
that I had forgotten about. There *may* have been a suggestion of
mandating this in the future.

On 23/10/2023 05:20, jon wrote:
> On Sun, 22 Oct 2023 22:53:44 +0100, 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.
>
> Never, ever bond an electrical earth to a gas pipe.

Since it is a BS7671 requirement that main equipotential bonds be
present on all installations, that is not something you can avoid doing
generally.

--
Cheers,

John.

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

On 23/10/2023 08:07, Brian wrote:
> A Scott <newsgroups@gefion.myzen.co.uk> 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.
>>
>
> I suspect you are referring to what is, generally known as, a PME fault -
> although it generally relates to any ‘hazardous’ route to earth for the
> fault current when the Neutral fails.
>
> For example, if you have an outside tap which isn’t isolated and the copper
> pipes are bounded to the Neutral to provide your local Earth ( a TN-C-S or
> PME system) and there is a Neutral break, your pipes ‘rise’ to the Live
> voltage.
>
> Touch the outside tap and there is a current path via the earth ( the stuff
> you are standing on) and the numerous PME points prior to the break.
>
> The good news is, fatalities from such incidents are very rare. That said,
> Neutral faults are less so.

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.

--
Cheers,

John.

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

On 23/10/2023 09:03, alan_m wrote:
> On 23/10/2023 08:05, Andy Burns wrote:
>>
>> jon wrote:
>>
>>> 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
>>
>> "PEN fault" or "lost neutral"
>>
>>>> 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?
>>
>> There ought to be insulated washers on the pipes in and out of the gas
>> meter
>>
>>>> I read about it somewhere but I cannot find it on a search.
>>>
>>> Never, ever bond an electrical earth to a gas pipe.
>>
>> ^^^ Ignore that advice ^^^
>>
>> Never use a gas pipe as an earth,
>> but always bond metal gas and water pipes to the main earth terminal!
>>
>
> I believe that the gas bonding should also be within 600mm of the meter
> outlet.

Yup, that is correct for meters inside the building. If internal, then
the connection should be within 600mm of the union on the outlet of the
meter. If it is an external meter, then it should be within 600mm of the
point of entry into the building. These are qualifies with a "where
practical". The guidance also applies to isolation points and unions in
addition to meters (when say in large installation with one central
meter, but individual isolators into each dwelling)

544.1.2 applies.

--
Cheers,

John.

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

John Rumm <see.my.signature@nowhere.null> wrote:
> On 23/10/2023 08:07, Brian wrote:
>> A Scott <newsgroups@gefion.myzen.co.uk> 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.
>>>
>>
>> I suspect you are referring to what is, generally known as, a PME fault -
>> although it generally relates to any ‘hazardous’ route to earth for the
>> fault current when the Neutral fails.
>>
>> For example, if you have an outside tap which isn’t isolated and the copper
>> pipes are bounded to the Neutral to provide your local Earth ( a TN-C-S or
>> PME system) and there is a Neutral break, your pipes ‘rise’ to the Live
>> voltage.
>>
>> Touch the outside tap and there is a current path via the earth ( the stuff
>> you are standing on) and the numerous PME points prior to the break.
>>
>> The good news is, fatalities from such incidents are very rare. That said,
>> Neutral faults are less so.
>
> 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.
>

Absolutely.

That said, there was a time poorer quality cables were used and some cases
of corrosion have led to failures between the consumer a the ‘last’ bonding
point.

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

--
Mike Clarke