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.