I am about to lay some 10mm2 CSA SWA from one end of the garden to the
other.

I need to decide whether to export the (Protective multiple earthed) CPC
from the garage via the SWA cable (where a supplementary CU is being
installed) or use an earth rod at the shed & greenhouse at the bottom of
the garden to form an independent earth.

Total seperation distance laterally is 13m but length of SWA cable is
nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1 phase
cable so I am forced to shove some brown, blue, Green& yellow PVC tape
on both ends of the SWA cable?

On 11/05/18 21:15, Stephen wrote:
I am about to lay some 10mm2 CSA SWA from one end of the garden to the
other.

I need to decide whether to export the (Protective multiple earthed) CPC
from the garage via the SWA cable (where a supplementary CU is being
installed) or use an earth rod at the shed & greenhouse at the bottom of
the garden to form an independent earth.

Total seperation distance laterally is 13m but length of SWA cable is
nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1 phase
cable so I am forced to shove some brown, blue, Green& yellow PVC tape
on both ends of the SWA cable?

You can if you try really hard, but to be honest, it's a good to have a
bit more CPC via a core as well as the armour - saves a lot of wibbling
trying to decide if the armour is sufficient to supply an earth for the
scenario concerned.

The main question I would ask:

Is there ready access to "local ground earth" in the location? You said
greenhouse, so that would be a yes. Even if it was a wooden affair, you
have open ground inside. More so if it has a metal frame and you bond
that (because you are mounting lights or sockets on it).

In the event of various conditions/faults on a PME (TN-C-S) supply, you
can get the supply earth going up to some potential above true earth -
which would mean a voltage between your imported earth and the likely
wet ground you are standing on. This is where the danger lies.

In this scenario, I would consider a local TT (earth rod) for safety,
obviously RCD on all circuits as per regs and do NOT connect the
incoming earth to the earth rod - separate it in a plastic enclosure
that terminates the SWA.

If your house supply is TN-S, it's less of an issue, but bear in mind
that TN-S is going our of fashion and the electricy co could convert you
to TN-C-S at any time.

Of course, you'll need to test your earth rod - and that's beyond me -
never worked with them...


In my scenario, my garden supply goes to a wooden shed with a wooden
floor, so no extraneous earths in there and very little risk even if the
house earth did rise to some voltage above local ground.

I'd have thought with the current state of electronics, it could be arranged
that the earth was mainly from the house and a circuit between the local
ground and the main earth could be monitored and the whole lot cut off if
the potential rose to outside tolerances.

In the murky past I've actually just bonded the incoming earth both to any
local mass and a ground rod, and nothing ever went bang or caught fire!
I can see however that there could be circumstances where a earth is
effectively from live to earth and it would be hoped that before the whole
lot failed or caught fire, the local fuse for that circuit be it breaker or
whatever would trip and isolate it all.
Of course there are other issues as has been mentioned before to do with
nasty noise on the mains etc, but that would probably only affect somebody
looking for electronically quiet supplies.

I do sometimes wonder as complexity goes up in this apparently simple
wiring, if we are not making things so awkward nobody will understand it and
just ignore it, which is also a danger.
Most folk around here I notice still just string some mains cable down
their fence and fit a 13 a socket in the shed.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Tim Watts" wrote in message
news
On 11/05/18 21:15, Stephen wrote:
I am about to lay some 10mm2 CSA SWA from one end of the garden to the
other.

I need to decide whether to export the (Protective multiple earthed) CPC
from the garage via the SWA cable (where a supplementary CU is being
installed) or use an earth rod at the shed & greenhouse at the bottom of
the garden to form an independent earth.

Total seperation distance laterally is 13m but length of SWA cable is
nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1 phase
cable so I am forced to shove some brown, blue, Green& yellow PVC tape on
both ends of the SWA cable?

You can if you try really hard, but to be honest, it's a good to have a
bit more CPC via a core as well as the armour - saves a lot of wibbling
trying to decide if the armour is sufficient to supply an earth for the
scenario concerned.

The main question I would ask:

Is there ready access to "local ground earth" in the location? You said
greenhouse, so that would be a yes. Even if it was a wooden affair, you
have open ground inside. More so if it has a metal frame and you bond that
(because you are mounting lights or sockets on it).

In the event of various conditions/faults on a PME (TN-C-S) supply, you
can get the supply earth going up to some potential above true earth -
which would mean a voltage between your imported earth and the likely wet
ground you are standing on. This is where the danger lies.

In this scenario, I would consider a local TT (earth rod) for safety,
obviously RCD on all circuits as per regs and do NOT connect the incoming
earth to the earth rod - separate it in a plastic enclosure that
terminates the SWA.

If your house supply is TN-S, it's less of an issue, but bear in mind that
TN-S is going our of fashion and the electricy co could convert you to
TN-C-S at any time.

Of course, you'll need to test your earth rod - and that's beyond me -
never worked with them...


In my scenario, my garden supply goes to a wooden shed with a wooden
floor, so no extraneous earths in there and very little risk even if the
house earth did rise to some voltage above local ground.

On 11/05/2018 21:27, Tim Watts wrote:
On 11/05/18 21:15, Stephen wrote:
I am about to lay some 10mm2 CSA SWA from one end of the garden to the
other.

I need to decide whether to export the (Protective multiple earthed)
CPC from the garage via the SWA cable (where a supplementary CU is
being installed) or use an earth rod at the shed & greenhouse at the
bottom of the garden to form an independent earth.

Total seperation distance laterally is 13m but length of SWA cable is
nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1 phase
cable so I am forced to shove some brown, blue, Green& yellow PVC tape
on both ends of the SWA cable?

You can if you try really hard, but to be honest, it's a good to have a
bit more CPC via a core as well as the armour - saves a lot of wibbling
trying to decide if the armour is sufficient to supply an earth for the
scenario concerned.

The main question I would ask:

Is there ready access to "local ground earth" in the location? You said
greenhouse, so that would be a yes. Even if it was a wooden affair, you
have open ground inside. More so if it has a metal frame and you bond
that (because you are mounting lights or sockets on it).

In the event of various conditions/faults on a PME (TN-C-S) supply, you
can get the supply earth going up to some potential above true earth -
which would mean a voltage between your imported earth and the likely
wet ground you are standing on. This is where the danger lies.

In this scenario, I would consider a local TT (earth rod) for safety,
obviously RCD on all circuits as per regs and do NOT connect the
incoming earth to the earth rod - separate it in a plastic enclosure
that terminates the SWA.

If your house supply is TN-S, it's less of an issue, but bear in mind
that TN-S is going our of fashion and the electricy co could convert you
to TN-C-S at any time.


The NICEIC are now saying that you should always treat TN-S as TN-C-S

--
Adam

On 12/05/2018 08:25, ARW wrote:
On 11/05/2018 21:27, Tim Watts wrote:
On 11/05/18 21:15, Stephen wrote:
I am about to lay some 10mm2 CSA SWA from one end of the garden to
the other.

I need to decide whether to export the (Protective multiple earthed)
CPC from the garage via the SWA cable (where a supplementary CU is
being installed) or use an earth rod at the shed & greenhouse at the
bottom of the garden to form an independent earth.

Total seperation distance laterally is 13m but length of SWA cable is
nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1 phase
cable so I am forced to shove some brown, blue, Green& yellow PVC
tape on both ends of the SWA cable?

You can if you try really hard, but to be honest, it's a good to have
a bit more CPC via a core as well as the armour - saves a lot of
wibbling trying to decide if the armour is sufficient to supply an
earth for the scenario concerned.

The main question I would ask:

Is there ready access to "local ground earth" in the location? You
said greenhouse, so that would be a yes. Even if it was a wooden
affair, you have open ground inside. More so if it has a metal frame
and you bond that (because you are mounting lights or sockets on it).

In the event of various conditions/faults on a PME (TN-C-S) supply,
you can get the supply earth going up to some potential above true
earth - which would mean a voltage between your imported earth and the
likely wet ground you are standing on. This is where the danger lies.

In this scenario, I would consider a local TT (earth rod) for safety,
obviously RCD on all circuits as per regs and do NOT connect the
incoming earth to the earth rod - separate it in a plastic enclosure
that terminates the SWA.

If your house supply is TN-S, it's less of an issue, but bear in mind
that TN-S is going our of fashion and the electricy co could convert
you to TN-C-S at any time.


The NICEIC are now saying that you should always treat TN-S as TN-C-S


So for clafication:

THe SWA cable has 3 equally sized conductors plus steel wire armour so I
can use one of these as a CPC.

My house has a PME supply supplied so the earth is supplied to me by the
electricity supplier. So there is no secondary earth provisioned within
the main house.

So which is better: should I then export this supplied earth to the
outside CU or provide my own local independent earth to the outbuildings?

The seperation distance laterally is 13m.

All of my current and new consumer units all or will use RCBOs.

The ones in the house are 30mA RCBOs. If I use a local independent earth
for the outbuildings, won't that mean I then have to consider using time
delayed or 100mA RCBOs to avoid nuisance trips?

In message , Brian Gaff
writes
Most folk around here I notice still just string some mains cable down
their fence and fit a 13 a socket in the shed.

I do agree with Brian. Rightly or wrongly, the percentage of people who
really know about this sort of thing must be minuscule, and that
includes those who know there is more to it than just running a length
of cable down the garden, even if they don't understand what really
needs doing.

SOP is a length of cable hopefully at least tacked to the fence, socket
on the shed end, job done.
--
Graeme

On 12/05/18 08:08, Brian Gaff wrote:
I'd have thought with the current state of electronics, it could be arranged
that the earth was mainly from the house and a circuit between the local
ground and the main earth could be monitored and the whole lot cut off if
the potential rose to outside tolerances.

Non starter - you are absolutely not allowed to have switching elements
in the protective conductor.


In the murky past I've actually just bonded the incoming earth both to any
local mass and a ground rod, and nothing ever went bang or caught fire!

You can do that (and may have to if you run a backup generator, and it
*might* be a feature of the upcoming 18th Edition of the Wiring Regs)

I can see however that there could be circumstances where a earth is
effectively from live to earth and it would be hoped that before the whole
lot failed or caught fire, the local fuse for that circuit be it breaker or
whatever would trip and isolate it all.

Againt, you're not allowed to put fuses in the CPC.

Of course there are other issues as has been mentioned before to do with
nasty noise on the mains etc, but that would probably only affect somebody
looking for electronically quiet supplies.

I do sometimes wonder as complexity goes up in this apparently simple
wiring, if we are not making things so awkward nobody will understand it and
just ignore it, which is also a danger.
Most folk around here I notice still just string some mains cable down
their fence and fit a 13 a socket in the shed.
Brian

On 12/05/18 08:25, ARW wrote:

The NICEIC are now saying that you should always treat TN-S as TN-C-S


Wise words, the way the suppliers are moving

On Saturday, 12 May 2018 08:08:29 UTC+1, Brian Gaff wrote:
I'd have thought with the current state of electronics, it could be arranged
that the earth was mainly from the house and a circuit between the local
ground and the main earth could be monitored and the whole lot cut off if
the potential rose to outside tolerances.

Earth monitoring/proving is widely used in certain areas eg

https://www.blakley.co.uk/protection...nuity-monitors

At 13 metres it's still within the guidelines for maximum length for using an extension lead which would export the earth anyway.

Owain

On 12/05/2018 09:09, Stephen wrote:
On 12/05/2018 08:25, ARW wrote:
On 11/05/2018 21:27, Tim Watts wrote:
On 11/05/18 21:15, Stephen wrote:
I am about to lay some 10mm2 CSA SWA from one end of the garden to
the other.

I need to decide whether to export the (Protective multiple earthed)
CPC from the garage via the SWA cable (where a supplementary CU is
being installed) or use an earth rod at the shed & greenhouse at the
bottom of the garden to form an independent earth.

Total seperation distance laterally is 13m but length of SWA cable
is nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1
phase cable so I am forced to shove some brown, blue, Green& yellow
PVC tape on both ends of the SWA cable?

You can if you try really hard, but to be honest, it's a good to have
a bit more CPC via a core as well as the armour - saves a lot of
wibbling trying to decide if the armour is sufficient to supply an
earth for the scenario concerned.

The main question I would ask:

Is there ready access to "local ground earth" in the location? You
said greenhouse, so that would be a yes. Even if it was a wooden
affair, you have open ground inside. More so if it has a metal frame
and you bond that (because you are mounting lights or sockets on it).

In the event of various conditions/faults on a PME (TN-C-S) supply,
you can get the supply earth going up to some potential above true
earth - which would mean a voltage between your imported earth and
the likely wet ground you are standing on. This is where the danger
lies.

In this scenario, I would consider a local TT (earth rod) for safety,
obviously RCD on all circuits as per regs and do NOT connect the
incoming earth to the earth rod - separate it in a plastic enclosure
that terminates the SWA.

If your house supply is TN-S, it's less of an issue, but bear in mind
that TN-S is going our of fashion and the electricy co could convert
you to TN-C-S at any time.


The NICEIC are now saying that you should always treat TN-S as TN-C-S


So for clafication:

THe SWA cable has 3 equally sized conductors plus steel wire armour so I
can use one of these as a CPC.

Yes.


My house has a PME supply supplied so the earth is supplied to me by the
electricity supplier. So there is no secondary earth provisioned within
the main house.

OK

So which is better: should I then export this supplied earth to the
outside CU or provide my own local independent earth to the outbuildings?
Is there power to the greenhouse or just the shed? I might be more
tempted to TT it if the greenhouse is getting power.

The seperation distance laterally is 13m.

All of my current and new consumer units all or will use RCBOs.

The ones in the house are 30mA RCBOs. If I use a local independent earth
for the outbuildings, won't that mean I then have to consider using time
delayed or 100mA RCBOs to avoid nuisance trips?


No. This would only apply if you had a TT supply to your house OR you
want to run RCDs in series. Normally with a PME supply you would use a
MCB at the head end and have the RCD protection down at the shed (SWA
does not need RCD protection).

--
Adam

On 12/05/2018 13:15, ARW wrote:
On 12/05/2018 09:09, Stephen wrote:
On 12/05/2018 08:25, ARW wrote:
On 11/05/2018 21:27, Tim Watts wrote:
On 11/05/18 21:15, Stephen wrote:
I am about to lay some 10mm2 CSA SWA from one end of the garden to
the other.

I need to decide whether to export the (Protective multiple
earthed) CPC from the garage via the SWA cable (where a
supplementary CU is being installed) or use an earth rod at the
shed & greenhouse at the bottom of the garden to form an
independent earth.

Total seperation distance laterally is 13m but length of SWA cable
is nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1
phase cable so I am forced to shove some brown, blue, Green& yellow
PVC tape on both ends of the SWA cable?

You can if you try really hard, but to be honest, it's a good to
have a bit more CPC via a core as well as the armour - saves a lot
of wibbling trying to decide if the armour is sufficient to supply
an earth for the scenario concerned.

The main question I would ask:

Is there ready access to "local ground earth" in the location? You
said greenhouse, so that would be a yes. Even if it was a wooden
affair, you have open ground inside. More so if it has a metal frame
and you bond that (because you are mounting lights or sockets on it).

In the event of various conditions/faults on a PME (TN-C-S) supply,
you can get the supply earth going up to some potential above true
earth - which would mean a voltage between your imported earth and
the likely wet ground you are standing on. This is where the danger
lies.

In this scenario, I would consider a local TT (earth rod) for
safety, obviously RCD on all circuits as per regs and do NOT connect
the incoming earth to the earth rod - separate it in a plastic
enclosure that terminates the SWA.

If your house supply is TN-S, it's less of an issue, but bear in
mind that TN-S is going our of fashion and the electricy co could
convert you to TN-C-S at any time.


The NICEIC are now saying that you should always treat TN-S as TN-C-S


So for clafication:

THe SWA cable has 3 equally sized conductors plus steel wire armour so
I can use one of these as a CPC.

Yes.


My house has a PME supply supplied so the earth is supplied to me by
the electricity supplier. So there is no secondary earth provisioned
within the main house.

OK

So which is better: should I then export this supplied earth to the
outside CU or provide my own local independent earth to the outbuildings?
Is there power to the greenhouse or just the shed? I might be more
tempted to TT it if the greenhouse is getting power.

The seperation distance laterally is 13m.

All of my current and new consumer units all or will use RCBOs.

The ones in the house are 30mA RCBOs. If I use a local independent
earth for the outbuildings, won't that mean I then have to consider
using time delayed or 100mA RCBOs to avoid nuisance trips?


No. This would only apply if you had a TT supply to your house OR you
want to run RCDs in series. Normally with a PME supply you would use a
MCB at the head end and have the RCD protection down at the shed (SWA
does not need RCD protection).

So two core SWA would be more than sufficient?

Perhaps a silly question, but what if the house was supplied TT?

What would you connect the armour to?
What would the Armour

On 12/05/2018 13:28, Fredxx wrote:
On 12/05/2018 13:15, ARW wrote:
On 12/05/2018 09:09, Stephen wrote:
On 12/05/2018 08:25, ARW wrote:
On 11/05/2018 21:27, Tim Watts wrote:
On 11/05/18 21:15, Stephen wrote:
I am about to lay some 10mm2 CSA SWA from one end of the garden to
the other.

I need to decide whether to export the (Protective multiple
earthed) CPC from the garage via the SWA cable (where a
supplementary CU is being installed) or use an earth rod at the
shed & greenhouse at the bottom of the garden to form an
independent earth.

Total seperation distance laterally is 13m but length of SWA cable
is nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1
phase cable so I am forced to shove some brown, blue, Green&
yellow PVC tape on both ends of the SWA cable?

You can if you try really hard, but to be honest, it's a good to
have a bit more CPC via a core as well as the armour - saves a lot
of wibbling trying to decide if the armour is sufficient to supply
an earth for the scenario concerned.

The main question I would ask:

Is there ready access to "local ground earth" in the location? You
said greenhouse, so that would be a yes. Even if it was a wooden
affair, you have open ground inside. More so if it has a metal
frame and you bond that (because you are mounting lights or sockets
on it).

In the event of various conditions/faults on a PME (TN-C-S) supply,
you can get the supply earth going up to some potential above true
earth - which would mean a voltage between your imported earth and
the likely wet ground you are standing on. This is where the danger
lies.

In this scenario, I would consider a local TT (earth rod) for
safety, obviously RCD on all circuits as per regs and do NOT
connect the incoming earth to the earth rod - separate it in a
plastic enclosure that terminates the SWA.

If your house supply is TN-S, it's less of an issue, but bear in
mind that TN-S is going our of fashion and the electricy co could
convert you to TN-C-S at any time.


The NICEIC are now saying that you should always treat TN-S as TN-C-S


So for clafication:

THe SWA cable has 3 equally sized conductors plus steel wire armour
so I can use one of these as a CPC.

Yes.


My house has a PME supply supplied so the earth is supplied to me by
the electricity supplier. So there is no secondary earth provisioned
within the main house.

OK

So which is better: should I then export this supplied earth to the
outside CU or provide my own local independent earth to the
outbuildings?
Is there power to the greenhouse or just the shed? I might be more
tempted to TT it if the greenhouse is getting power.

The seperation distance laterally is 13m.

All of my current and new consumer units all or will use RCBOs.

The ones in the house are 30mA RCBOs. If I use a local independent
earth for the outbuildings, won't that mean I then have to consider
using time delayed or 100mA RCBOs to avoid nuisance trips?


No. This would only apply if you had a TT supply to your house OR you
want to run RCDs in series. Normally with a PME supply you would use a
MCB at the head end and have the RCD protection down at the shed (SWA
does not need RCD protection).

So two core SWA would be more than sufficient?


It could be!

Perhaps a silly question, but what if the house was supplied TT?

What would you connect the armour to?
What would the Armour

If the house supply was TT then the SWA would need RCD protection.
Normally 100mA time delayed if feeding other RCDs or sockets.

--
Adam

On 12/05/2018 09:09, Stephen wrote:
On 12/05/2018 08:25, ARW wrote:
On 11/05/2018 21:27, Tim Watts wrote:
On 11/05/18 21:15, Stephen wrote:
I am about to lay some 10mm2 CSA SWA from one end of the garden to
the other.

I need to decide whether to export the (Protective multiple earthed)
CPC from the garage via the SWA cable (where a supplementary CU is
being installed) or use an earth rod at the shed & greenhouse at the
bottom of the garden to form an independent earth.

Total seperation distance laterally is 13m but length of SWA cable
is nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1
phase cable so I am forced to shove some brown, blue, Green& yellow
PVC tape on both ends of the SWA cable?

You can if you try really hard, but to be honest, it's a good to have
a bit more CPC via a core as well as the armour - saves a lot of
wibbling trying to decide if the armour is sufficient to supply an
earth for the scenario concerned.

The main question I would ask:

Is there ready access to "local ground earth" in the location? You
said greenhouse, so that would be a yes. Even if it was a wooden
affair, you have open ground inside. More so if it has a metal frame
and you bond that (because you are mounting lights or sockets on it).

In the event of various conditions/faults on a PME (TN-C-S) supply,
you can get the supply earth going up to some potential above true
earth - which would mean a voltage between your imported earth and
the likely wet ground you are standing on. This is where the danger
lies.

In this scenario, I would consider a local TT (earth rod) for safety,
obviously RCD on all circuits as per regs and do NOT connect the
incoming earth to the earth rod - separate it in a plastic enclosure
that terminates the SWA.

If your house supply is TN-S, it's less of an issue, but bear in mind
that TN-S is going our of fashion and the electricy co could convert
you to TN-C-S at any time.


The NICEIC are now saying that you should always treat TN-S as TN-C-S


So for clafication:

THe SWA cable has 3 equally sized conductors plus steel wire armour so I
can use one of these as a CPC.

If you want...

(places like TLC Direct (and most other wholesalers) will do two core
though if you want)

My house has a PME supply supplied so the earth is supplied to me by the
electricity supplier. So there is no secondary earth provisioned within
the main house.

So which is better: should I then export this supplied earth to the
outside CU or provide my own local independent earth to the outbuildings?

If one of those is a greenhouse, it can be near impossible to export
the PME equipotential zone into it, so TT would become a much better
option.

Have a look at:

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

and the following bit about exporting equipotential zones.

The seperation distance laterally is 13m.

All of my current and new consumer units all or will use RCBOs.

The ones in the house are 30mA RCBOs. If I use a local independent earth
for the outbuildings, won't that mean I then have to consider using time
delayed or 100mA RCBOs to avoid nuisance trips?

You can use a normal MCB for the submain feed rather than a RCBO. You
isolate the PME earth at the point it connects to the outbuilding CU. So
you have overload and fault protection for the SWA provided by the MCB.
Earth fault protection for the outbuilding is then provided by the local
RCD/RCBO.



--
Cheers,

John.

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

Brian Gaff wrote

I'd have thought with the current state of electronics, it could be
arranged that the earth was mainly from the house and a circuit between
the local ground and the main earth could be monitored and the whole lot
cut off if the potential rose to outside tolerances.

It obviously can be. And one kid here has just been
quite literally rendered blind and brain damaged when
that happened here just a couple of months ago now.
http://www.abc.net.au/news/2018-04-1...r-says/9654696

And google is now one hell of a resource. Got that as
the first hit with perth girl blind electrical fault abc

In the murky past I've actually just bonded the incoming earth both to
any local mass and a ground rod, and nothing ever went bang or caught
fire! I can see however that there could be circumstances where a earth is
effectively from live to earth and it would be hoped that before the
whole lot failed or caught fire, the local fuse for that circuit be it
breaker or whatever would trip and isolate it all.

Of course there are other issues as has been mentioned before to do with
nasty noise on the mains etc, but that would probably only affect somebody
looking for electronically quiet supplies.

I do sometimes wonder as complexity goes up in this apparently simple
wiring, if we are not making things so awkward nobody will understand it
and just ignore it, which is also a danger.

Wouldn’t be a problem if the system shuts
down when there is a problem with the earth.

Most folk around here I notice still just string some mains cable down
their fence and fit a 13 a socket in the shed.

When I was building the house, I ran the whole house,
including the storage hot water system, the wall oven,
microwave and cooktop from the builders temporary
supply and a jesus adapter until the electrical supply
authority eventually chucked a tantrum and made
me install what you lot call a CU.

"Tim Watts" wrote in message
news
On 11/05/18 21:15, Stephen wrote:
I am about to lay some 10mm2 CSA SWA from one end of the garden to the
other.

I need to decide whether to export the (Protective multiple earthed) CPC
from the garage via the SWA cable (where a supplementary CU is being
installed) or use an earth rod at the shed & greenhouse at the bottom of
the garden to form an independent earth.

Total seperation distance laterally is 13m but length of SWA cable is
nearer 20m.

And why is all SWA cable all 3 phase? I can't seem to get any 1 phase
cable so I am forced to shove some brown, blue, Green& yellow PVC tape
on both ends of the SWA cable?

You can if you try really hard, but to be honest, it's a good to have a
bit more CPC via a core as well as the armour - saves a lot of wibbling
trying to decide if the armour is sufficient to supply an earth for the
scenario concerned.

The main question I would ask:

Is there ready access to "local ground earth" in the location? You said
greenhouse, so that would be a yes. Even if it was a wooden affair, you
have open ground inside. More so if it has a metal frame and you bond
that (because you are mounting lights or sockets on it).

In the event of various conditions/faults on a PME (TN-C-S) supply, you
can get the supply earth going up to some potential above true earth -
which would mean a voltage between your imported earth and the likely wet
ground you are standing on. This is where the danger lies.

In this scenario, I would consider a local TT (earth rod) for safety,
obviously RCD on all circuits as per regs and do NOT connect the incoming
earth to the earth rod - separate it in a plastic enclosure that
terminates the SWA.

If your house supply is TN-S, it's less of an issue, but bear in mind
that TN-S is going our of fashion and the electricy co could convert you
to TN-C-S at any time.

Of course, you'll need to test your earth rod - and that's beyond me -
never worked with them...


In my scenario, my garden supply goes to a wooden shed with a wooden
floor, so no extraneous earths in there and very little risk even if the
house earth did rise to some voltage above local ground.

Tim Watts wrote
Brian Gaff wrote

I'd have thought with the current state of electronics, it could be
arranged that the earth was mainly from the house and a circuit between
the local ground and the main earth could be monitored and the whole lot
cut off if the potential rose to outside tolerances.

Non starter

Nope.

you are absolutely not allowed to have switching elements in the
protective conductor.

There wouldnt be any. The switching elements
are already in the mains and neutral, not the earth.

The entire house supply is shut down if the voltage between
the mains earth and the local ground gets too high.

In the murky past I've actually just bonded the incoming earth both to
any
local mass and a ground rod, and nothing ever went bang or caught fire!

You can do that (and may have to if you run a backup generator, and it
*might* be a feature of the upcoming 18th Edition of the Wiring Regs)

I can see however that there could be circumstances where a earth is
effectively from live to earth and it would be hoped that before the
whole lot failed or caught fire, the local fuse for that circuit be it
breaker or whatever would trip and isolate it all.

Againt, you're not allowed to put fuses in the CPC.

There is already a fuse in the incoming supply.

Of course there are other issues as has been mentioned before to do
with nasty noise on the mains etc, but that would probably only affect
somebody looking for electronically quiet supplies.

I do sometimes wonder as complexity goes up in this apparently simple
wiring, if we are not making things so awkward nobody will understand it
and just ignore it, which is also a danger.

Most folk around here I notice still just string some mains cable down
their fence and fit a 13 a socket in the shed.