[No Name]

I watched the YouTube video by John Ward about EV chargers and earthing.

I saw a 2nd video by the same person in connection with earthing of
outbuildings.

See https://youtu.be/NvENsVUhDUs

I happen to have a 3 core 10mm2 SWA run between the house integral
garage and the metal wood shed and metal framed greenhouse.

This has yet to be connected up at both ends.

I was going to go down the TT earth rod route but John Ward in his video
is saying that you can export the earth from the house to the
outbuilding provided it is 10mm2 or higher.

He also seems to imply that exporting the earth is a better and safer
option than using an Earth rod.

Would Adam Wadsworth, John Rumm et. al. like to comment?

S.

[Theo[_3_]]

No Name wrote:
I happen to have a 3 core 10mm2 SWA run between the house integral
garage and the metal wood shed and metal framed greenhouse.

This has yet to be connected up at both ends.

I was going to go down the TT earth rod route but John Ward in his video
is saying that you can export the earth from the house to the
outbuilding provided it is 10mm2 or higher.

He also seems to imply that exporting the earth is a better and safer
option than using an Earth rod.

Would Adam Wadsworth, John Rumm et. al. like to comment?

IANA electrician but I think that makes sense.

Think about what happens if you short line to earth at the consumer unit.

What you want is for the fault current to blow the supply fuse - which might
be 100A (but need a higher current to blow rapidly). That depends on having
a low enough loop impedance from the transformer, through the live circuit,
to the short, then around the earth/neutral circuit[1] back to the
transformer, such that the current that can flow is enough to blow that fuse
in a short enough time. If your earth impedance is too high, the fuse won't
blow. On TN-S and TN-C-S loop impedance should be a fraction of an ohm.

Downstream of the CU the same applies, although there may be a low-rated MCB
in the circuit instead. So you might have say a 32A type B MCB, which is
rated to trip at 5*32A = 160A. You need a low enough earth impedance to
carry 160A. Going to 10mm2 will reduce the impedance and increase the fault
current, meaning the MCB is more likely to trip.

If you're on TT with earth rods the earth impedance depends on the state of
the ground, the weather etc, but can be tens of ohms. That means a very low
fault current (2A say) can flow that won't trip the MCB. This is why on a
TT system you'd need an RCD to actively detect that small fault current and
trip where the MCB won't notice.

So a 10mm2 earth conductor to the house is preferable to an earth rod, but
both are helped by having an RCD at the outbuilding end. An RCD can't be
the only means of protection, however, which is why the earthing matters.

I think.

Theo


[1] exact configuration depends on whether TN-S or TN-C-S

[John Rumm]

On 04/08/2020 10:59, No Name wrote:

I watched the YouTube video by John Ward about EV chargers and earthing.

I saw a 2nd video by the same person in connection with earthing of
outbuildings.

See https://youtu.be/NvENsVUhDUs

I happen to have a 3 core 10mm2 SWA run between the house integral
garage and the metal wood shed and metal framed greenhouse.

This has yet to be connected up at both ends.

I was going to go down the TT earth rod route but John Ward in his video
is saying that you can export the earth from the house to the
outbuilding provided it is 10mm2 or higher.

If you get into the situation of needing to export the house's
equipotential zone to the outbuilding (usually when you have TN-C-S
earthing in the house), then the earth connection needs to be large
enough to function as a main bonding conductor, hence the 10mm requirement.

He also seems to imply that exporting the earth is a better and safer
option than using an Earth rod.

Exported earth when appropriate is usually less costly and less complex.
There is also less need for ongoing routine testing. So its often a good
choice.

However there are cases where it can be a less ideal choice. JW covered
the case where it gets too expensive, but there is also the case of a
building like a greenhouse where it is in effect impossible to maintain
a proper equipotential zone, since there is ready access to a local
earth (i.e. you are likely standing on it!) that you can't bond to your
equipotential zone.

You then have the risk that under fault conditions the exported TN-C-S
earth could be exporting a dangerous potential to the greenhouse.

Would Adam Wadsworth, John Rumm et. al. like to comment?

I think the first question is what earthing system does your house have?

See:

http://wiki.diyfaq.org.uk/index.php/Earthing_Types

Then have a look at the relevant sections he

http://wiki.diyfaq.org.uk/index.php/...ricity_outside

As they cover these questions in some detail.


--
Cheers,

John.

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

[Adam Funk[_3_]]

On 2020-08-04, John Rumm wrote:

On 04/08/2020 10:59, No Name wrote:

I happen to have a 3 core 10mm2 SWA run between the house integral
garage and the metal wood shed and metal framed greenhouse.
....
However there are cases where it can be a less ideal choice. JW covered
the case where it gets too expensive, but there is also the case of a
building like a greenhouse where it is in effect impossible to maintain
a proper equipotential zone, since there is ready access to a local
earth (i.e. you are likely standing on it!) that you can't bond to your
equipotential zone.

Just curious: how does that compare with the local earth you can stand
on in a cellar with a bare dirt floor?

[No Name]

On 04/08/2020 12:02, John Rumm wrote:
On 04/08/2020 10:59, No Name wrote:

I watched the YouTube video by John Ward about EV chargers and earthing.

I saw a 2nd video by the same person in connection with earthing of
outbuildings.

See https://youtu.be/NvENsVUhDUs

I happen to have a 3 core 10mm2 SWA run between the house integral
garage and the metal wood shed and metal framed greenhouse.

This has yet to be connected up at both ends.

I was going to go down the TT earth rod route but John Ward in his
video is saying that you can export the earth from the house to the
outbuilding provided it is 10mm2 or higher.

If you get into the situation of needing to export the house's
equipotential zone to the outbuilding (usually when you have TN-C-S
earthing in the house), then the earth connection needs to be large
enough to function as a main bonding conductor, hence the 10mm requirement.

He also seems to imply that exporting the earth is a better and safer
option than using an Earth rod.

Exported earth when appropriate is usually less costly and less complex.
There is also less need for ongoing routine testing. So its often a good
choice.

However there are cases where it can be a less ideal choice. JW covered
the case where it gets too expensive, but there is also the case of a
building like a greenhouse where it is in effect impossible to maintain
a proper equipotential zone, since there is ready access to a local
earth (i.e. you are likely standing on it!) that you can't bond to your
equipotential zone.

You then have the risk that under fault conditions the exported TN-C-S
earth could be exporting a dangerous potential to the greenhouse.

Would Adam Wadsworth, John Rumm et. al. like to comment?

I think the first question is what earthing system does your house have?

See:

http://wiki.diyfaq.org.uk/index.php/Earthing_Types

Then have a look at the relevant sections he

http://wiki.diyfaq.org.uk/index.php/...ricity_outside

As they cover these questions in some detail.



My earthing system at the meter cupboard is a TN-C-S system.

the wood shed is made of corrugated metal panels and the greenhouse is
aluminium framework with glazing. So I would be looking to earth bond
these in any case.

I have already got both an earth rod, a reel of 10mm single core earth
wire and of course the already buried 3 core 10mm2 SWA cable. The length
of this SWA is 20m.

The plan was to connect this to a 32A MCB in the house consumer unit and
have all RCBO sub-consumer unit in the wood store to supply both the
wood store and adjacent greenhouse.

Both are sited on a 100 mm sub base of MoT1, 50 mm of sharp sand and 50
mm x 600 mm x 600 mm paving slabs.

(all my greenhouse plants are in pots and there is an automatic watering
system which is fed by 25 mm MDPE from the house so no metal pipe.

In that EV vehicle video, there was a discussion about putting in a
earth rod and connecting that to the MET.

If it is permitted, I have no personal objection to putting an earth rod
& exporting the MET earth for the eventuality that:

"that under fault conditions the exported TN-C-S earth could be
exporting a dangerous potential to the greenhouse."

putting an earth grid over 20 m2 of my garden does not appeal to me!

S.

[Dave Liquorice[_2_]]

On 04 Aug 2020 11:57:32 +0100 (BST), Theo wrote:

If you're on TT with earth rods the earth impedance depends on the state
of the ground, the weather etc, but can be tens of ohms. That means a
very low fault current (2A say) can flow that won't trip the MCB.

That doesn't parse very well in my mind. B-)

The relatively high earth loop impedance means that any fault current
is limited by that impedance. So if the earth loop impedance is 10
ohms the maximum earth fault current is 24(ish) amps. Which a 32 A
MCB isn't going to worry too much about...

This is why on a TT system you'd need an RCD to actively detect that
small fault current and trip where the MCB won't notice.

The RCD isn't detecting the fault current as such it's detecting an
imbalance in the currents flowing in the L & N wires through it. The
assumption is the imbalance current is going somewhere it shouldn't,
like directly to earth be that an exported one or earth rod or
through someone to earth.

So a 10mm2 earth conductor to the house is preferable to an earth rod,
but both are helped by having an RCD at the outbuilding end.

Isn't there some reg that says any socket likely to have an appliance
connected that is used outdoors needs to be RCD protected?

And of course there is the problem of the exported earth riseing
above real earth under fault condtions. That 160 A guaranteed 32 A
MCB trip current will produce 80 V across 0.5 ohms. That's enough for
"quite a tingle". OK 0.5 ohms equates to 250+ m of 10mm^2 (assuming
perfect connections) but you get the picture.

--
Cheers
Dave.

[John Rumm]

On 04/08/2020 12:56, Adam Funk wrote:
On 2020-08-04, John Rumm wrote:

On 04/08/2020 10:59, No Name wrote:

I happen to have a 3 core 10mm2 SWA run between the house integral
garage and the metal wood shed and metal framed greenhouse.
....
However there are cases where it can be a less ideal choice. JW covered
the case where it gets too expensive, but there is also the case of a
building like a greenhouse where it is in effect impossible to maintain
a proper equipotential zone, since there is ready access to a local
earth (i.e. you are likely standing on it!) that you can't bond to your
equipotential zone.

Just curious: how does that compare with the local earth you can stand
on in a cellar with a bare dirt floor?

Similar situation..., (although properties old enough for a bare earth
cellar floor did not likely have TN-C-S head ends either)


--
Cheers,

John.

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

[John Rumm]

On 04/08/2020 13:04, No Name wrote:
On 04/08/2020 12:02, John Rumm wrote:
On 04/08/2020 10:59, No Name wrote:

I watched the YouTube video by John Ward about EV chargers and earthing.

I saw a 2nd video by the same person in connection with earthing of
outbuildings.

See https://youtu.be/NvENsVUhDUs

I happen to have a 3 core 10mm2 SWA run between the house integral
garage and the metal wood shed and metal framed greenhouse.

This has yet to be connected up at both ends.

I was going to go down the TT earth rod route but John Ward in his
video is saying that you can export the earth from the house to the
outbuilding provided it is 10mm2 or higher.

If you get into the situation of needing to export the house's
equipotential zone to the outbuilding (usually when you have TN-C-S
earthing in the house), then the earth connection needs to be large
enough to function as a main bonding conductor, hence the 10mm
requirement.

He also seems to imply that exporting the earth is a better and safer
option than using an Earth rod.

Exported earth when appropriate is usually less costly and less
complex. There is also less need for ongoing routine testing. So its
often a good choice.

However there are cases where it can be a less ideal choice. JW
covered the case where it gets too expensive, but there is also the
case of a building like a greenhouse where it is in effect impossible
to maintain a proper equipotential zone, since there is ready access
to a local earth (i.e. you are likely standing on it!) that you can't
bond to your equipotential zone.

You then have the risk that under fault conditions the exported TN-C-S
earth could be exporting a dangerous potential to the greenhouse.

Would Adam Wadsworth, John Rumm et. al. like to comment?

I think the first question is what earthing system does your house have?

See:

http://wiki.diyfaq.org.uk/index.php/Earthing_Types

Then have a look at the relevant sections he

http://wiki.diyfaq.org.uk/index.php/...ricity_outside

As they cover these questions in some detail.



My earthing system at the meter cupboard is a TN-C-S system.

the wood shed is made of corrugated metal panels and the greenhouse is
aluminium framework with glazing. So I would be looking to earth bond
these in any case.
I have already got both an earth rod, a reel of 10mm single core earth
wire and of course the already buried 3 core 10mm2 SWA cable. The length
of this SWA is 20m.

The plan was to connect this to a 32A MCB in the house consumer unit and
have all RCBO sub-consumer unit in the wood store to supply both the
wood store and adjacent greenhouse.

With the house end on a non RCD protected feed?

(you don't want cascaded RCDs)

Both are sited on a 100 mm sub base of MoT1, 50 mm of sharp sand and 50
mm x 600 mm x 600 mm paving slabs.

So it sounds like with your greenhouse, you should be able to include
all its extraneous conductive parts into the bonding should you want.

There is a slight risk still from the frame of the greenhouse itself
though since someone standing outside of it, has access to an
independent earth and the exported TN-C-S earth which I presume is
accessible without the need of a tool.

(personally I would use the TN-C-S earth to protect the submain as far
as the greenhouse (and other metal buildings), but isolate it there and
make those TT).

(all my greenhouse plants are in pots and there is an automatic watering
system which is fed by 25 mm MDPE from the house so no metal pipe.

In that EV vehicle video, there was a discussion about putting in a
earth rod and connecting that to the MET.

If it is permitted, I have no personal objection to putting an earth rod
& exporting the MET earth for the eventuality that:

"that under fault conditions the exported TN-C-S earth could be
exporting a dangerous potential to the greenhouse."

putting an earth grid over 20 m2 of my garden does not appeal to me

If you add an earth rod to a PME earth, then it just becomes another of
the multiple earth connections.



--
Cheers,

John.

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

[Tricky Dicky[_4_]]

I was left a little bemused by the video in that it concluded there was no ideal solution to a TN-C-S setup except for the for the impractical 20m2 grid only a least bad setup namely to export the earth. I have an interest in this question as I am hoping to take delivery of a PHEV at the end of the month so an EV charger is on the agenda. The plan is to house the charger in the garage which at present is connected to the supply by 10mm2 T&E using the CPC as the exported earth inside the garage is a CU with an RCD for a main switch. The garage is not attached to the house but is only 1.2m away and the supply is run between buildings in a conduit attached to a beam above a gateway. It did not seem worthwhile using SWA and burying for such a small distance since the longest portion of the supply cable runs under the floor of the house to the CU.

I take it from the video that to have a charger I will now have to run a separate 10mm2 earth single back to the main CU. So what do I do in the garage leave the earthing arrangement for all the other circuits as is and use this 10mm2 bond exclusively for the charger or should I bond all the garage circuits to this earth?

I watched another video by an electrician fitting a charger to the outside wall of a house, he could easily have exported the earth with the CU mounted on the same wall as the charger with the supply passing from the CU outside through a wall perpendicular to the fixing wall. He bonded the SWA at the consumer end but not at the charger and used a separate earth rod for the charger which was some metres from the charger but did not look like 5m to me and was a matter of inches from the house wall. According to the JW video that was not the best solution. Confused yes I am!

Richard

[Andy Burns[_13_]]

Tricky Dicky wrote:

Confused yes I am!

Look at videos on the Zappi charger either by Artisan Electrics, or
eFixx, that doesn't need an earth rod (maybe it does still need 10mm
bonding? I don't know)


https://youtu.be/3-HEKqeSrwk?t=32
https://youtu.be/gwmiGf6tChE

[No Name]

On 04/08/2020 13:46, John Rumm wrote:
On 04/08/2020 13:04, No Name wrote:
On 04/08/2020 12:02, John Rumm wrote:
On 04/08/2020 10:59, No Name wrote:

I watched the YouTube video by John Ward about EV chargers and
earthing.

I saw a 2nd video by the same person in connection with earthing of
outbuildings.

See https://youtu.be/NvENsVUhDUs

I happen to have a 3 core 10mm2 SWA run between the house integral
garage and the metal wood shed and metal framed greenhouse.

This has yet to be connected up at both ends.

I was going to go down the TT earth rod route but John Ward in his
video is saying that you can export the earth from the house to the
outbuilding provided it is 10mm2 or higher.

If you get into the situation of needing to export the house's
equipotential zone to the outbuilding (usually when you have TN-C-S
earthing in the house), then the earth connection needs to be large
enough to function as a main bonding conductor, hence the 10mm
requirement.

He also seems to imply that exporting the earth is a better and
safer option than using an Earth rod.

Exported earth when appropriate is usually less costly and less
complex. There is also less need for ongoing routine testing. So its
often a good choice.

However there are cases where it can be a less ideal choice. JW
covered the case where it gets too expensive, but there is also the
case of a building like a greenhouse where it is in effect impossible
to maintain a proper equipotential zone, since there is ready access
to a local earth (i.e. you are likely standing on it!) that you can't
bond to your equipotential zone.

You then have the risk that under fault conditions the exported
TN-C-S earth could be exporting a dangerous potential to the greenhouse.

Would Adam Wadsworth, John Rumm et. al. like to comment?

I think the first question is what earthing system does your house have?

See:

http://wiki.diyfaq.org.uk/index.php/Earthing_Types

Then have a look at the relevant sections he

http://wiki.diyfaq.org.uk/index.php/...ricity_outside

As they cover these questions in some detail.



My earthing system at the meter cupboard is a TN-C-S system.

the wood shed is made of corrugated metal panels and the greenhouse is
aluminium framework with glazing. So I would be looking to earth bond
these in any case.
I have already got both an earth rod, a reel of 10mm single core earth
wire and of course the already buried 3 core 10mm2 SWA cable. The
length of this SWA is 20m.

The plan was to connect this to a 32A MCB in the house consumer unit
and have all RCBO sub-consumer unit in the wood store to supply both
the wood store and adjacent greenhouse.

With the house end on a non RCD protected feed?

(you don't want cascaded RCDs)


I plan to change the 32A RCBO in the main CU to a 32A MCB

As for the Sub CU, I am going to put in RCBOs with functional earth
which as I understand it gives a bit more protection against a missing
neutral or a missing earth?

Both are sited on a 100 mm sub base of MoT1, 50 mm of sharp sand and
50 mm x 600 mm x 600 mm paving slabs.

So it sounds like with your greenhouse, you should be able to include
all its extraneous conductive parts into the bonding should you want.

There is a slight risk still from the frame of the greenhouse itself
though since someone standing outside of it, has access to an
independent earth and the exported TN-C-S earth which I presume is
accessible without the need of a tool.


There is a concrete post and wood panel fence on two sides, then there
is 10m2 of slabbing on eon e side.

On the 4th side there is 90 mm wide slabbing before meeting the lawn.


(personally I would use the TN-C-S earth to protect the submain as far
as the greenhouse (and other metal buildings), but isolate it there and
make those TT).

As I understood from John Ward, the exported earth has a lower impedance
than an earth rod....

(all my greenhouse plants are in pots and there is an automatic
watering system which is fed by 25 mm MDPE from the house so no metal
pipe.

In that EV vehicle video, there was a discussion about putting in a
earth rod and connecting that to the MET.

If it is permitted, I have no personal objection to putting an earth
rod & exporting the MET earth for the eventuality that:

"that under fault conditions the exported TN-C-S earth could be
exporting a dangerous potential to the greenhouse."

putting an earth grid over 20 m2 of my garden does not appeal to me

If you add an earth rod to a PME earth, then it just becomes another of
the multiple earth connections.

I seem to recall reading somewhere ages ago that connecting a PME earth
and a TT earth together was not a good idea and that one should choose
between one or the other.

S.

[John Rumm]

On 04/08/2020 18:53, No Name wrote:
On 04/08/2020 13:46, John Rumm wrote:
On 04/08/2020 13:04, No Name wrote:
On 04/08/2020 12:02, John Rumm wrote:
On 04/08/2020 10:59, No Name wrote:

Would Adam Wadsworth, John Rumm et. al. like to comment?

I think the first question is what earthing system does your house
have?

See:

http://wiki.diyfaq.org.uk/index.php/Earthing_Types

Then have a look at the relevant sections he

http://wiki.diyfaq.org.uk/index.php/...ricity_outside

As they cover these questions in some detail.



My earthing system at the meter cupboard is a TN-C-S system.

the wood shed is made of corrugated metal panels and the greenhouse
is aluminium framework with glazing. So I would be looking to earth
bond these in any case.
I have already got both an earth rod, a reel of 10mm single core
earth wire and of course the already buried 3 core 10mm2 SWA cable.
The length of this SWA is 20m.

The plan was to connect this to a 32A MCB in the house consumer unit
and have all RCBO sub-consumer unit in the wood store to supply both
the wood store and adjacent greenhouse.

With the house end on a non RCD protected feed?

(you don't want cascaded RCDs)


I plan to change the 32A RCBO in the main CU to a 32A MCB

Yup that would be ok.

As for the Sub CU, I am going to put in RCBOs with functional earth
which as I understand it gives a bit more protection against a missing
neutral or a missing earth?

It does - it allows it to trip on more fault conditions than just a
straight current imbalance.

Both are sited on a 100 mm sub base of MoT1, 50 mm of sharp sand and
50 mm x 600 mm x 600 mm paving slabs.

So it sounds like with your greenhouse, you should be able to include
all its extraneous conductive parts into the bonding should you want.

There is a slight risk still from the frame of the greenhouse itself
though since someone standing outside of it, has access to an
independent earth and the exported TN-C-S earth which I presume is
accessible without the need of a tool.


There is a concrete post and wood panel fence on two sides, then there
is 10m2 of slabbing on eon e side.

On the 4th side there is 90 mm wide slabbing before meeting the lawn.

90mm (just under a brick's width)?

Either way, it sounds like your setup is somewhat more substantial than
many a greenhouse sat directly on damp soil. So the risk of having the
exposed PME earth is going to be vanishingly small (and in reality there
are plenty of exported PME earths in garden sockets up and down the land
that don't typically kill any one. (or at least not due to the earthing!))


(personally I would use the TN-C-S earth to protect the submain as far
as the greenhouse (and other metal buildings), but isolate it there
and make those TT).

As I understood from John Ward, the exported earth has a lower impedance
than an earth rod....

It does (usually), although with TT you rely on the RCDs to handle earth
faults, so you don't actually need a particularly low earth impedance
for the system to work.

(all my greenhouse plants are in pots and there is an automatic
watering system which is fed by 25 mm MDPE from the house so no metal
pipe.

In that EV vehicle video, there was a discussion about putting in a
earth rod and connecting that to the MET.

If it is permitted, I have no personal objection to putting an earth
rod & exporting the MET earth for the eventuality that:

"that under fault conditions the exported TN-C-S earth could be
exporting a dangerous potential to the greenhouse."

putting an earth grid over 20 m2 of my garden does not appeal to me

If you add an earth rod to a PME earth, then it just becomes another
of the multiple earth connections.

I seem to recall reading somewhere ages ago that connecting a PME earth
and a TT earth together was not a good idea and that one should choose
between one or the other.

Well PME has multiple earth connections all along the LV side of the
distribution network (its one of the ways they try to reduce the chances
of there ever being an interruption in the PME conductor). So adding
additional ones does not combine TT and PME - it just makes the PME
network slightly bigger.

(there is an argument that if your property did get a PEN disconnection
along with a lump of the neighbourhood, you may not want your earth
spike serving the whole neighbourhood!)



--
Cheers,

John.

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

[No Name]

On the 4th side there is 90 mm wide slabbing before meeting the lawn.

90mm (just under a brick's width)?

Oops... I meant 900 mm!

Either way, it sounds like your setup is somewhat more substantial than
many a greenhouse sat directly on damp soil. So the risk of having the
exposed PME earth is going to be vanishingly small (and in reality there
are plenty of exported PME earths in garden sockets up and down the land
that don't typically kill any one. (or at least not due to the earthing!))

That is a good point, I have on the external walls of the main house 7
separate external IP67 rated sockets.... 4 are singles and 3 are doubles.

I was careful to put the garden taps below the external sockets amd
these 7 sockets feed back to the garage to switched FCus which in turn
then connect to a ring main supplied by a 32A RCBO. The idea being two
fold, I could isolate faulty sockets and if a fault occurred, no other
internal electrics were affected.

(personally I would use the TN-C-S earth to protect the submain as
far as the greenhouse (and other metal buildings), but isolate it
there and make those TT).

As I understood from John Ward, the exported earth has a lower
impedance than an earth rod....

It does (usually), although with TT you rely on the RCDs to handle earth
faults, so you don't actually need a particularly low earth impedance
for the system to work.


(all my greenhouse plants are in pots and there is an automatic
watering system which is fed by 25 mm MDPE from the house so no
metal pipe.

In that EV vehicle video, there was a discussion about putting in a
earth rod and connecting that to the MET.

If it is permitted, I have no personal objection to putting an earth
rod & exporting the MET earth for the eventuality that:

"that under fault conditions the exported TN-C-S earth could be
exporting a dangerous potential to the greenhouse."

putting an earth grid over 20 m2 of my garden does not appeal to me

If you add an earth rod to a PME earth, then it just becomes another
of the multiple earth connections.

I seem to recall reading somewhere ages ago that connecting a PME
earth and a TT earth together was not a good idea and that one should
choose between one or the other.

Well PME has multiple earth connections all along the LV side of the
distribution network (its one of the ways they try to reduce the chances
of there ever being an interruption in the PME conductor). So adding
additional ones does not combine TT and PME - it just makes the PME
network slightly bigger.

(there is an argument that if your property did get a PEN disconnection
along with a lump of the neighbourhood, you may not want your earth
spike serving the whole neighbourhood!)

Which is what I was hopign a RCBO with a functional earth might help
with.... by tripping off in the case of a broken neutral/PEN