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Old March 16th 19, 12:07 AM posted to uk.d-i-y
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Posts: 302
Default EV charger earthing

I've only just spotted that EV chargers on TN-C-S systems are now
supposed to be earthed as TT systems, with their own earth rod. AFAIK
this wasn't the case in 2017 when I installed my (Rolec) charger, so the
CPC to the charger is connected to the earth bar in the CU which,
coincidentally, is also connected to an earth rod that's positioned
almost directly below the charger.
I don't see that there is a real-world risk from my current charger
earthing arrangement but I'm thinking through the options: leave it as
it is, or install a second earth rod (which would need to be very close
to the existing one). Any comments from the assembled jury?

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Old March 16th 19, 02:56 PM posted to uk.d-i-y
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Posts: 22,075
Default EV charger earthing

On 15/03/2019 23:07, wrote:
I've only just spotted that EV chargers on TN-C-S systems are now
supposed to be earthed as TT systems, with their own earth rod. AFAIK
this wasn't the case in 2017 when I installed my (Rolec) charger, so the
CPC to the charger is connected to the earth bar in the CU which,
coincidentally, is also connected to an earth rod that's positioned
almost directly below the charger.


They added a specific section (722) to the 18th edition:

This basically applies where the charging will take place outside,
rather than say in a garage.

Its pretty much the same rules as for any PME supply used outside of the
main equipotential zone, plus it also requires the use of (at least) a
type A RCD [1]


[1]
http://wiki.diyfaq.org.uk/index.php/...haracteristics

I don't see that there is a real-world risk from my current charger
earthing arrangement but I'm thinking through the options: leave it as
it is, or install a second earth rod (which would need to be very close
to the existing one). Any comments from the assembled jury?


Its unlikely to kill you, but there is the traditional danger associated
with PME systems, that could result in the CPC/PEN conductor voltage
rising to mains potential under some fault conditions (e.g. a
disconnection in the PEN conductor of the supply). This is potentially
dangerous if you are outside of the equipotential zone and have ready
access to a local earth.

So normally I would do it as a TT install with the submain protected by
the TN earth as far as the point of use, then it would be isolated at
that point, and the local earth used for the installation. Ideally
however the earth spike should be driven far enough away from the
existing one to not overlap resistance area.


--
Cheers,

John.

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


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Old March 16th 19, 04:19 PM posted to uk.d-i-y
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First recorded activity by DIYBanter: Dec 2017
Posts: 302
Default EV charger earthing

On 16/03/2019 13:56, John Rumm wrote:
On 15/03/2019 23:07, wrote:
I've only just spotted that EV chargers on TN-C-S systems are now
supposed to be earthed as TT systems, with their own earth rod. AFAIK
this wasn't the case in 2017 when I installed my (Rolec) charger, so
the CPC to the charger is connected to the earth bar in the CU which,
coincidentally, is also connected to an earth rod that's positioned
almost directly below the charger.


They added a specific section (722) to the 18th edition:

This basically applies where the charging will take place outside,
rather than say in a garage.

Its pretty much the same rules as for any PME supply used outside of the
main equipotential zone, plus it also requires the use of (at least) a
type A RCD [1]


[1]
http://wiki.diyfaq.org.uk/index.php/...haracteristics

I don't see that there is a real-world risk from my current charger
earthing arrangement but I'm thinking through the options: leave it as
it is, or install a second earth rod (which would need to be very
close to the existing one). Any comments from the assembled jury?


Its unlikely to kill you, but there is the traditional danger associated
with PME systems, that could result in the CPC/PEN conductor voltage
rising to mains potential under some fault conditions (e.g. a
disconnection in the PEN conductor of the supply). This is potentially
dangerous if you are outside of the equipotential zone and have ready
access to a local earth.

So normally I would do it as a TT install with the submain protected by
the TN earth as far as the point of use, then it would be isolated at
that point, and the local earth used for the installation. Ideally
however the earth spike should be driven far enough away from the
existing one to not overlap resistance area.


In my case the house is fed from an overhead line to the final pole and
then a short (new) underground run to the (attached) garage. It's marked
TN-C-S but there is also a connection to an earth rod that's just
outside the garage, so I don't see that a supply fault could cause a
safety issue. Have I missed something?
The furthest extremity of the car plus cable is about 8m from the
charger and existing earth rod. Any new rod that I added would need to
be within a metre of the existing rod and would still be the same
distance from the car extremity - I don't see that a new rod would
change the risk. I suppose I could reduce the small risk of a
disconnected cable by connecting the charger earth directly to the
existing rod rather than the CU earth bar (leaving the rod's connection
to the supply) but that hardly seems bothering with. Again, have I
missed something?
As always, I'm very grateful to be able to bounce these ideas around.
Thanks.
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Old March 16th 19, 05:07 PM posted to uk.d-i-y
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Posts: 8,227
Default EV charger earthing

On Friday, 15 March 2019 23:07:47 UTC, wrote:
I've only just spotted that EV chargers on TN-C-S systems are now
supposed to be earthed as TT systems, with their own earth rod. AFAIK
this wasn't the case in 2017 when I installed my (Rolec) charger, so the
CPC to the charger is connected to the earth bar in the CU which,
coincidentally, is also connected to an earth rod that's positioned
almost directly below the charger.
I don't see that there is a real-world risk from my current charger
earthing arrangement but I'm thinking through the options: leave it as
it is, or install a second earth rod (which would need to be very close
to the existing one). Any comments from the assembled jury?


They don't earth the frames of solar panels either.
You get a definite prickle if you touch one.
  #8   Report Post  
Old March 16th 19, 11:00 PM posted to uk.d-i-y
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First recorded activity by DIYBanter: Jul 2006
Posts: 22,075
Default EV charger earthing

On 16/03/2019 15:19, wrote:
On 16/03/2019 13:56, John Rumm wrote:
On 15/03/2019 23:07,
wrote:
I've only just spotted that EV chargers on TN-C-S systems are now
supposed to be earthed as TT systems, with their own earth rod. AFAIK
this wasn't the case in 2017 when I installed my (Rolec) charger, so
the CPC to the charger is connected to the earth bar in the CU which,
coincidentally, is also connected to an earth rod that's positioned
almost directly below the charger.


They added a specific section (722) to the 18th edition:

This basically applies where the charging will take place outside,
rather than say in a garage.

Its pretty much the same rules as for any PME supply used outside of
the main equipotential zone, plus it also requires the use of (at
least) a type A RCD [1]


[1]
http://wiki.diyfaq.org.uk/index.php/...haracteristics


I don't see that there is a real-world risk from my current charger
earthing arrangement but I'm thinking through the options: leave it
as it is, or install a second earth rod (which would need to be very
close to the existing one). Any comments from the assembled jury?


Its unlikely to kill you, but there is the traditional danger
associated with PME systems, that could result in the CPC/PEN
conductor voltage rising to mains potential under some fault
conditions (e.g. a disconnection in the PEN conductor of the supply).
This is potentially dangerous if you are outside of the equipotential
zone and have ready access to a local earth.

So normally I would do it as a TT install with the submain protected
by the TN earth as far as the point of use, then it would be isolated
at that point, and the local earth used for the installation. Ideally
however the earth spike should be driven far enough away from the
existing one to not overlap resistance area.


In my case the house is fed from an overhead line to the final pole and
then a short (new) underground run to the (attached) garage. It's marked
TN-C-S but there is also a connection to an earth rod that's just
outside the garage,


PME setups can have a local earth rod - it just becomes one of of the
"multiple" earths that the name suggests.

so I don't see that a supply fault could cause a
safety issue. Have I missed something?


The classic case would be loss of the Protective Earth and Neutral close
to your installation. That could leave a local combined earth and
neutral floating, and connected to line via all the loads in your
installation - hence the voltage would tend to rise toward line
potential, taking all the earthed metalwork in the installation with it.

In reality, the chances of this happening are very small since the
supply is earthed at multiple locations. Since you have an additional
earth rod, that will limit the voltage rise on the earth - but how much
will depend on the earth impedance via that rod. You may also get some
additional fortuitous earthing from your equipotential bonds to other
incoming services.

The furthest extremity of the car plus cable is about 8m from the
charger and existing earth rod. Any new rod that I added would need to
be within a metre of the existing rod and would still be the same
distance from the car extremity - I don't see that a new rod would
change the risk.


An additional rod can be at a distance from the point of use so long as
the connecting wire to it is adequately protected / of a suitable size.

The distance to the car does not make much difference AFAICS.

I suppose I could reduce the small risk of a
disconnected cable by connecting the charger earth directly to the
existing rod rather than the CU earth bar (leaving the rod's connection
to the supply) but that hardly seems bothering with. Again, have I
missed something?


You could disconnect the main CU from the earth rod altogether, and use
that just for the TT earth for the charger. That way if there ever was a
voltage rise issue, it would only affect the house and not the
independently earthed charger. If you add an additional rod, then it
needs to be far enough away from the existing that you don't end up in
effect joining them with a short distance of soil.

As always, I'm very grateful to be able to bounce these ideas around.
Thanks.


As I said earlier - in reality the risks are tiny, and you have RCD
protection for the charger anyway.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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Old Yesterday, 12:49 AM posted to uk.d-i-y
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First recorded activity by DIYBanter: Dec 2017
Posts: 302
Default EV charger earthing

On 16/03/2019 22:00, John Rumm wrote:
On 16/03/2019 15:19, wrote:
On 16/03/2019 13:56, John Rumm wrote:
On 15/03/2019 23:07,
wrote:
I've only just spotted that EV chargers on TN-C-S systems are now
supposed to be earthed as TT systems, with their own earth rod.
AFAIK this wasn't the case in 2017 when I installed my (Rolec)
charger, so the CPC to the charger is connected to the earth bar in
the CU which, coincidentally, is also connected to an earth rod
that's positioned almost directly below the charger.

They added a specific section (722) to the 18th edition:

This basically applies where the charging will take place outside,
rather than say in a garage.

Its pretty much the same rules as for any PME supply used outside of
the main equipotential zone, plus it also requires the use of (at
least) a type A RCD [1]


[1]
http://wiki.diyfaq.org.uk/index.php/...haracteristics


I don't see that there is a real-world risk from my current charger
earthing arrangement but I'm thinking through the options: leave it
as it is, or install a second earth rod (which would need to be very
close to the existing one). Any comments from the assembled jury?

Its unlikely to kill you, but there is the traditional danger
associated with PME systems, that could result in the CPC/PEN
conductor voltage rising to mains potential under some fault
conditions (e.g. a disconnection in the PEN conductor of the supply).
This is potentially dangerous if you are outside of the equipotential
zone and have ready access to a local earth.

So normally I would do it as a TT install with the submain protected
by the TN earth as far as the point of use, then it would be isolated
at that point, and the local earth used for the installation. Ideally
however the earth spike should be driven far enough away from the
existing one to not overlap resistance area.


In my case the house is fed from an overhead line to the final pole
and then a short (new) underground run to the (attached) garage. It's
marked TN-C-S but there is also a connection to an earth rod that's
just outside the garage,


PME setups can have a local earth rod - it just becomes one of of the
"multiple" earths that the name suggests.

so I don't see that a supply fault could cause a safety issue. Have I
missed something?


The classic case would be loss of the Protective Earth and Neutral close
to your installation. That could leave a local combined earth and
neutral floating, and connected to line via all the loads in your
installation - hence the voltage would tend to rise toward line
potential, taking all the earthed metalwork in the installation with it.

In reality, the chances of this happening are very small since the
supply is earthed at multiple locations. Since you have an additional
earth rod, that will limit the voltage rise on the earth - but how much
will depend on the earth impedance via that rod. You may also get some
additional fortuitous earthing from your equipotential bonds to other
incoming services.

The furthest extremity of the car plus cable is about 8m from the
charger and existing earth rod. Any new rod that I added would need to
be within a metre of the existing rod and would still be the same
distance from the car extremity - I don't see that a new rod would
change the risk.


An additional rod can be at a distance from the point of use so long as
the connecting wire to it is adequately protected / of a suitable size.

The distance to the car does not make much difference AFAICS.

I was thinking of the potential gradient to the earth rod.

I suppose I could reduce the small risk of a disconnected cable by
connecting the charger earth directly to the existing rod rather than
the CU earth bar (leaving the rod's connection to the supply) but that
hardly seems bothering with. Again, have I missed something?


You could disconnect the main CU from the earth rod altogether, and use
that just for the TT earth for the charger. That way if there ever was a
voltage rise issue, it would only affect the house and not the
independently earthed charger. If you add an additional rod, then it
needs to be far enough away from the existing that you don't end up in
effect joining them with a short distance of soil.

As always, I'm very grateful to be able to bounce these ideas around.
Thanks.


As I said earlier - in reality the risks are tiny, and you have RCD
protection for the charger anyway.

Yes. Unless someone comes up with something else to consider I think
I'll leave it as it is.
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Old Today, 09:19 AM posted to uk.d-i-y
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First recorded activity by DIYBanter: Jan 2015
Posts: 9,601
Default EV charger earthing

On Saturday, 16 March 2019 22:00:28 UTC, John Rumm wrote:
On 16/03/2019 15:19, wrote:
On 16/03/2019 13:56, John Rumm wrote:
On 15/03/2019 23:07,
wrote:
I've only just spotted that EV chargers on TN-C-S systems are now
supposed to be earthed as TT systems, with their own earth rod. AFAIK
this wasn't the case in 2017 when I installed my (Rolec) charger, so
the CPC to the charger is connected to the earth bar in the CU which,
coincidentally, is also connected to an earth rod that's positioned
almost directly below the charger.

They added a specific section (722) to the 18th edition:

This basically applies where the charging will take place outside,
rather than say in a garage.

Its pretty much the same rules as for any PME supply used outside of
the main equipotential zone, plus it also requires the use of (at
least) a type A RCD [1]


[1]
http://wiki.diyfaq.org.uk/index.php/...haracteristics


I don't see that there is a real-world risk from my current charger
earthing arrangement but I'm thinking through the options: leave it
as it is, or install a second earth rod (which would need to be very
close to the existing one). Any comments from the assembled jury?

Its unlikely to kill you, but there is the traditional danger
associated with PME systems, that could result in the CPC/PEN
conductor voltage rising to mains potential under some fault
conditions (e.g. a disconnection in the PEN conductor of the supply).
This is potentially dangerous if you are outside of the equipotential
zone and have ready access to a local earth.

So normally I would do it as a TT install with the submain protected
by the TN earth as far as the point of use, then it would be isolated
at that point, and the local earth used for the installation. Ideally
however the earth spike should be driven far enough away from the
existing one to not overlap resistance area.


In my case the house is fed from an overhead line to the final pole and
then a short (new) underground run to the (attached) garage. It's marked
TN-C-S but there is also a connection to an earth rod that's just
outside the garage,


PME setups can have a local earth rod - it just becomes one of of the
"multiple" earths that the name suggests.

so I don't see that a supply fault could cause a
safety issue. Have I missed something?


The classic case would be loss of the Protective Earth and Neutral close
to your installation. That could leave a local combined earth and
neutral floating, and connected to line via all the loads in your
installation - hence the voltage would tend to rise toward line
potential, taking all the earthed metalwork in the installation with it.

In reality, the chances of this happening are very small since the
supply is earthed at multiple locations. Since you have an additional
earth rod, that will limit the voltage rise on the earth - but how much
will depend on the earth impedance via that rod. You may also get some
additional fortuitous earthing from your equipotential bonds to other
incoming services.

The furthest extremity of the car plus cable is about 8m from the
charger and existing earth rod. Any new rod that I added would need to
be within a metre of the existing rod and would still be the same
distance from the car extremity - I don't see that a new rod would
change the risk.


An additional rod can be at a distance from the point of use so long as
the connecting wire to it is adequately protected / of a suitable size.

The distance to the car does not make much difference AFAICS.

I suppose I could reduce the small risk of a
disconnected cable by connecting the charger earth directly to the
existing rod rather than the CU earth bar (leaving the rod's connection
to the supply) but that hardly seems bothering with. Again, have I
missed something?


You could disconnect the main CU from the earth rod altogether, and use
that just for the TT earth for the charger. That way if there ever was a
voltage rise issue, it would only affect the house and not the
independently earthed charger. If you add an additional rod, then it
needs to be far enough away from the existing that you don't end up in
effect joining them with a short distance of soil.

As always, I'm very grateful to be able to bounce these ideas around.
Thanks.


As I said earlier - in reality the risks are tiny, and you have RCD
protection for the charger anyway.


I'd say the risk of dangerous CPC voltage rise on a TT setup is worse than PME, so you're better off keeping the rod as another PME element than using it just for the charger feed.


NT


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