Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

On 13/11/2018 17:22, Pat Pending wrote:
Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Max 200 and ideally less than 100 ohms.

More earth rods and/or longer earth rods if you are able to drive them
into the soil.

This time of the year its wet and more imperative to aim for 100 ohms
for times when the ground is dry.

On 13/11/2018 18:36, Fredxx wrote:
On 13/11/2018 17:22, Pat Pending wrote:
Just put an electricity supply in to a shed at the bottom of the
garden - 4mm armoured cable to a separate CU in the shed. We have TT
earthing, so didn't use the cable earth and put in a 5/8" x 1m earth
rod outside. Measured the earth loop impedance, and I have 320 ohms -
far too high isn't it? Any suggestions?

Max 200 and ideally less than 100 ohms.

More earth rods and/or longer earth rods if you are able to drive them
into the soil.

This time of the year its wet and more imperative to aim for 100 ohms
for times when the ground is dry.

+1

I did a site supply this the summer. Just at the end of the 4 weeks
without rain. Could we hell get the Ze below 220 ohms. Last week I added
an extra 110V supply and it had ****ed it down all week. Now down to 30
ohms and the apprentice lost a work boot in the mud.

--
Adam

Seriously though, I am not really following the logic of the earthing
regimes. They are now so muddled that really any earth is better than no
Earth,
Brian

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

Blind user, so no pictures please
Note this Signature is meaningless.!
"Fredxx" wrote in message
news
On 13/11/2018 17:22, Pat Pending wrote:
Just put an electricity supply in to a shed at the bottom of the garden -
4mm armoured cable to a separate CU in the shed. We have TT earthing, so
didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Max 200 and ideally less than 100 ohms.

More earth rods and/or longer earth rods if you are able to drive them
into the soil.

This time of the year its wet and more imperative to aim for 100 ohms for
times when the ground is dry.

ARW wrote:
On 13/11/2018 18:36, Fredxx wrote:
On 13/11/2018 17:22, Pat Pending wrote:
Just put an electricity supply in to a shed at the bottom of the
garden - 4mm armoured cable to a separate CU in the shed. We have TT
earthing, so didn't use the cable earth and put in a 5/8" x 1m earth
rod outside. Measured the earth loop impedance, and I have 320 ohms -
far too high isn't it? Any suggestions?

Max 200 and ideally less than 100 ohms.

More earth rods and/or longer earth rods if you are able to drive them
into the soil.

This time of the year its wet and more imperative to aim for 100 ohms
for times when the ground is dry.

+1

I did a site supply this the summer. Just at the end of the 4 weeks
without rain. Could we hell get the Ze below 220 ohms. Last week I added
an extra 110V supply and it had ****ed it down all week. Now down to 30
ohms and the apprentice lost a work boot in the mud.

Is it permissible to bond the local earth to neutral in this situation?

Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable? By all means use the new stake in
parallel. An RCD at on or another end of the cable is probably needed
either way.

--

Roger Hayter

On 13/11/18 19:11, Bob Minchin wrote:

Is it permissible to bond the local earth to neutral in this situation?
No. That would give you a TN-C system and that is not allowed in
domestic settings.

--
Email does not work

On 13/11/2018 19:11, Bob Minchin wrote:
ARW wrote:
On 13/11/2018 18:36, Fredxx wrote:
On 13/11/2018 17:22, Pat Pending wrote:
Just put an electricity supply in to a shed at the bottom of the
garden - 4mm armoured cable to a separate CU in the shed. We have TT
earthing, so didn't use the cable earth and put in a 5/8" x 1m earth
rod outside. Measured the earth loop impedance, and I have 320 ohms -
far too high isn't it? Any suggestions?

Max 200 and ideally less than 100 ohms.

More earth rods and/or longer earth rods if you are able to drive them
into the soil.

This time of the year its wet and more imperative to aim for 100 ohms
for times when the ground is dry.

+1

I did a site supply this the summer. Just at the end of the 4 weeks
without rain. Could we hell get the Ze below 220 ohms. Last week I added
an extra 110V supply and it had ****ed it down all week. Now down to 30
ohms and the apprentice lost a work boot in the mud.

Is it permissible to bond the local earth to neutral in this situation?

No.

I actually had a very nice TNC-S supply to work with. Exporting the
earth was forbidden.

--
Adam

On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable? By all means use the new stake in
parallel. An RCD at on or another end of the cable is probably needed
either way.


What you suggest sounds logical, but I was told not to use the house
earth but disconnect it and put in a separate TT system. Not sure why,
what do the experts think?

Pat Pending wrote:

On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable? By all means use the new stake in
parallel. An RCD at on or another end of the cable is probably needed
either way.


What you suggest sounds logical, but I was told not to use the house
earth but disconnect it and put in a separate TT system. Not sure why,
what do the experts think?

I was aware of the advice for that advice for the TN-C-S system if there
was likely to be extraneous earthed conductors in or near the
outbuilding. But I can't see why that should apply to a TT system.
Though I would also like to hear from the experts on this.


--

Roger Hayter

On 13/11/2018 17:22, Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Its higher than ideal certainly, although will still pass enough fault
current to trip a 30mA RCD in most circumstances.

To get a lower Ze, you will need either/or longer earth rod / additional
earth roods spaced away from the first one. Most rods can be coupled to
additional ones to increase the length.


--
Cheers,

John.

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

On 13/11/2018 21:09, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable?Â*Â* By all means use the new stake in
parallel.Â* An RCD at on or another end of the cable is probably needed
either way.


What you suggest sounds logical, but I was told not to use the house
earth but disconnect it and put in a separate TT system. Not sure why,
what do the experts think?

You would want to avoid exporting the the house earth in some cases...

With TN-C-S systems, while you can legitimately add an earth electrode
of your own to it (it just becomes another of the "multiple" earths of a
PME system), exporting the earth also means you have to extend the
equipotential zone to the outbuilding. Depending on what it is and the
nature of its construction that may not be practical; e.g. a greenhouse
with easy access to an independent earth, or you may not have enough
cross section of copper available in the sub main to have it function as
a main bonding conductor.

With TN-S you won't want to join the exported earth to the TT system
since there may be significant distance between your earth spike and
that of the substation, and so there could exist a difference in the
local potentials, giving rise to higher than expected protective
conductor currents. (also in the event of a fault in the suppliers
earth, you might find your spike and the sheath of your supply cable now
becomes the main earth for the neighbourhood!)

With TT you could join them, although its still wise to aim for a system
that can function within sensible parameters without the Ze reduction
you get from the "other" bits of the system.

--
Cheers,

John.

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

On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable? By all means use the new stake in
parallel. An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in circuit.
This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high, I decided to fit an
extra earth rod. The rod I fitted was 4 feet not one metre, so obviously
by fitting another one it would go down 8 feet. In the end I couldn't
get the last foot down so I sawed it off leaving 7 feet in the ground.
The reading was now 212 ohms - with the house earth disconnected again.
Better, but still not good enough - and I can't think why it remains so
high. Anyway, I then reconnected the house earth and got a reading of 59
ohms. I think I'll leave it at that - especially as it's improved the
ELI throughout the property!

Still baffled about the high reading though.

On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable?Â*Â* By all means use the new stake in
parallel.Â* An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in circuit.
This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high, I decided to fit an
extra earth rod. The rod I fitted was 4 feet not one metre, so obviously
by fitting another one it would go down 8 feet. In the end I couldn't
get the last foot down so I sawed it off leaving 7 feet in the ground.
The reading was now 212 ohms - with the house earth disconnected again.
Better, but still not good enough - and I can't think why it remains so
high. Anyway, I then reconnected the house earth and got a reading of 59
ohms. I think I'll leave it at that - especially as it's improved the
ELI throughout the property!

Still baffled about the high reading though.

What kind of soil do you have? Stony, or sandy soils can be difficult to
get a low reading in. As can anywhere that is very dry.

Clay is usually fairly easy. (our TT earth is around 7 ohms)



--
Cheers,

John.

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

On Friday, 16 November 2018 17:48:51 UTC, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable? By all means use the new stake in
parallel. An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in circuit.
This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high, I decided to fit an
extra earth rod. The rod I fitted was 4 feet not one metre, so obviously
by fitting another one it would go down 8 feet. In the end I couldn't
get the last foot down so I sawed it off leaving 7 feet in the ground.
The reading was now 212 ohms - with the house earth disconnected again.
Better, but still not good enough - and I can't think why it remains so
high. Anyway, I then reconnected the house earth and got a reading of 59
ohms. I think I'll leave it at that - especially as it's improved the
ELI throughout the property!

Still baffled about the high reading though.

Due to low Summer rainfall, the subsoil is still very dry this year.
Unless you are in a valley bottom, this may be your problem.

When I was in the electricity board decades ago, we used to bury a lump of cast iron in a bed of coke dust for substation earths.

On 17/11/2018 00:51, John Rumm wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable?Â*Â* By all means use the new stake in
parallel.Â* An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high, I decided to fit an
extra earth rod. The rod I fitted was 4 feet not one metre, so
obviously by fitting another one it would go down 8 feet. In the end I
couldn't get the last foot down so I sawed it off leaving 7 feet in
the ground. The reading was now 212 ohms - with the house earth
disconnected again. Better, but still not good enough - and I can't
think why it remains so high. Anyway, I then reconnected the house
earth and got a reading of 59 ohms. I think I'll leave it at that -
especially as it's improved the ELI throughout the property!

Still baffled about the high reading though.

What kind of soil do you have? Stony, or sandy soils can be difficult to
get a low reading in. As can anywhere that is very dry.

Clay is usually fairly easy. (our TT earth is around 7 ohms)




Our soil is quite stony, and consequently well drained, so that's
probably the reason.

On 17/11/2018 06:38, harry wrote:
On Friday, 16 November 2018 17:48:51 UTC, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable? By all means use the new stake in
parallel. An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in circuit.
This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high, I decided to fit an
extra earth rod. The rod I fitted was 4 feet not one metre, so obviously
by fitting another one it would go down 8 feet. In the end I couldn't
get the last foot down so I sawed it off leaving 7 feet in the ground.
The reading was now 212 ohms - with the house earth disconnected again.
Better, but still not good enough - and I can't think why it remains so
high. Anyway, I then reconnected the house earth and got a reading of 59
ohms. I think I'll leave it at that - especially as it's improved the
ELI throughout the property!

Still baffled about the high reading though.

Due to low Summer rainfall, the subsoil is still very dry this year.
Unless you are in a valley bottom, this may be your problem.

You're probably right, and our soil is well drained. Overall, I'm happy
with the situation now so, as I said, I'll leave it at that.

On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable?Â*Â* By all means use the new stake in
parallel.Â* An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in circuit.
This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources such as
copper/lead water pipes, or did you test the house earth rod on it's own.


--
Adam

On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the garden
- 4mm armoured cable to a separate CU in the shed. We have TT earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the house
TT earth to the shed via the cable?Â*Â* By all means use the new stake in
parallel.Â* An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources such as
copper/lead water pipes, or did you test the house earth rod on it's own.




No, I didn't test the earth rod on its own. As I said in my first post I
don't have the tester to do that. The house doesn't have gas and the
water pipes - coming into the house at any rate - are plastic so I am
assuming that there are no parallel paths to earth and that the readings
I get at a socket are fairly accurate.

On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the
garden
- 4mm armoured cable to a separate CU in the shed. We have TT
earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod
outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the
house
TT earth to the shed via the cable?Â*Â* By all means use the new stake in
parallel.Â* An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources such
as copper/lead water pipes, or did you test the house earth rod on
it's own.




No, I didn't test the earth rod on its own. As I said in my first post I
don't have the tester to do that. The house doesn't have gas and the
water pipes - coming into the house at any rate - are plastic so I am
assuming that there are no parallel paths to earth and that the readings
I get at a socket are fairly accurate.

I take it you are testing with a plug in earth loop tester?

If so you can always temporarily disconnect any equipotential bonding
wires at the main earthing terminal while doing the test if needs be for
more accurate results.

If you wanted to test the rod in isolation, there is a method for doing
so without any special test gear described he

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





--
Cheers,

John.

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

On 19/11/2018 10:40, John Rumm wrote:
On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the
garden
- 4mm armoured cable to a separate CU in the shed. We have TT
earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod
outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the
house
TT earth to the shed via the cable?Â*Â* By all means use the new
stake in
parallel.Â* An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources such
as copper/lead water pipes, or did you test the house earth rod on
it's own.




No, I didn't test the earth rod on its own. As I said in my first post
I don't have the tester to do that. The house doesn't have gas and the
water pipes - coming into the house at any rate - are plastic so I am
assuming that there are no parallel paths to earth and that the
readings I get at a socket are fairly accurate.

I take it you are testing with a plug in earth loop tester?

If so you can always temporarily disconnect any equipotential bonding
wires at the main earthing terminal while doing the test if needs be for
more accurate results.

If you wanted to test the rod in isolation, there is a method for doing
so without any special test gear described he

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

OOI, is there any reason I can't use the neutral incomer as an
alternative to "Supplier's main earthing terminal"?

If there is a small residual voltage on the neutral, swapping the
transformer phase and taking the average of two measurements would help
but should be a fraction of 24V.

On 19/11/2018 10:40, John Rumm wrote:
On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the
garden
- 4mm armoured cable to a separate CU in the shed. We have TT
earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod
outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the
house
TT earth to the shed via the cable?Â*Â* By all means use the new
stake in
parallel.Â* An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources such
as copper/lead water pipes, or did you test the house earth rod on
it's own.




No, I didn't test the earth rod on its own. As I said in my first post
I don't have the tester to do that. The house doesn't have gas and the
water pipes - coming into the house at any rate - are plastic so I am
assuming that there are no parallel paths to earth and that the
readings I get at a socket are fairly accurate.

I take it you are testing with a plug in earth loop tester?

Yes, that's correct.


If so you can always temporarily disconnect any equipotential bonding
wires at the main earthing terminal while doing the test if needs be for
more accurate results.

If you wanted to test the rod in isolation, there is a method for doing
so without any special test gear described he

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



I might try that, I think I have a 24v transformer somewhere.

However, what do you think about this idea for getting a more accurate
Ze measurement? My loop tester has an iec connector for a mains input -
a type I have plenty of - and no other leads. I get a spare lead and
chop the plug off, strip the insulation back and fit a crop clip to the
earth lead and a probe to the live lead.

With the supply turned off at the CU and the earth input disconnected I
then connect the croc clip to the (disconnected) earth and the probe to
the input side of the main switch. Would this give me a true Ze reading,
or is my thinking incorrect (would I need to connect the neutral as well?)?

On 19/11/2018 11:34, Fredxx wrote:
On 19/11/2018 10:40, John Rumm wrote:
On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the
garden
- 4mm armoured cable to a separate CU in the shed. We have TT
earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod
outside.
Measured the earth loop impedance, and I have 320 ohms - far too
high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the
house
TT earth to the shed via the cable?Â*Â* By all means use the new
stake in
parallel.Â* An RCD at on or another end of the cable is probably
needed
either way.


Update on this shed ELI problem. Following the suggestion here I
did export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources such
as copper/lead water pipes, or did you test the house earth rod on
it's own.




No, I didn't test the earth rod on its own. As I said in my first
post I don't have the tester to do that. The house doesn't have gas
and the water pipes - coming into the house at any rate - are plastic
so I am assuming that there are no parallel paths to earth and that
the readings I get at a socket are fairly accurate.

I take it you are testing with a plug in earth loop tester?

If so you can always temporarily disconnect any equipotential bonding
wires at the main earthing terminal while doing the test if needs be
for more accurate results.

If you wanted to test the rod in isolation, there is a method for
doing so without any special test gear described he

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


OOI, is there any reason I can't use the neutral incomer as an
alternative to "Supplier's main earthing terminal"?

I would not fancy it ;-) Remember neutral is a "live" wire - it could be
several volts[1] away from local earth, and can supply reasonably
significant current in some circumstances.

If there is a small residual voltage on the neutral, swapping the
transformer phase and taking the average of two measurements would help
but should be a fraction of 24V.

[1] Or possibly more depending on the load being applied to it locally
(by yours and neighbouring properties), and distance from the substation
etc.


--
Cheers,

John.

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

On 19/11/2018 12:37, Pat Pending wrote:
On 19/11/2018 10:40, John Rumm wrote:
On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the
garden
- 4mm armoured cable to a separate CU in the shed. We have TT
earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod
outside.
Measured the earth loop impedance, and I have 320 ohms - far too
high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the
house
TT earth to the shed via the cable?Â*Â* By all means use the new
stake in
parallel.Â* An RCD at on or another end of the cable is probably
needed
either way.


Update on this shed ELI problem. Following the suggestion here I
did export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources such
as copper/lead water pipes, or did you test the house earth rod on
it's own.




No, I didn't test the earth rod on its own. As I said in my first
post I don't have the tester to do that. The house doesn't have gas
and the water pipes - coming into the house at any rate - are plastic
so I am assuming that there are no parallel paths to earth and that
the readings I get at a socket are fairly accurate.

I take it you are testing with a plug in earth loop tester?

Yes, that's correct.


If so you can always temporarily disconnect any equipotential bonding
wires at the main earthing terminal while doing the test if needs be
for more accurate results.

If you wanted to test the rod in isolation, there is a method for
doing so without any special test gear described he

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



I might try that, I think I have a 24v transformer somewhere.

However, what do you think about this idea for getting a more accurate
Ze measurement? My loop tester has an iec connector for a mains input -
a type I have plenty of - and no other leads. I get a spare lead and
chop the plug off, strip the insulation back and fit a crop clip to the
earth lead and a probe to the live lead.

With the supply turned off at the CU and the earth input disconnected I
then connect the croc clip to the (disconnected) earth and the probe to
the input side of the main switch. Would this give me a true Ze reading,
or is my thinking incorrect (would I need to connect the neutral as well?)?

If its anything like my old Megga LT5, then I think it uses the neutral
to power itself since it has no battery. However in principle, you could
lash up something to allow it to be powered, and also have a wandering
earth lead for connection to your electrode.


--
Cheers,

John.

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

On 19/11/2018 17:31, John Rumm wrote:
On 19/11/2018 12:37, Pat Pending wrote:
On 19/11/2018 10:40, John Rumm wrote:
On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the
garden
- 4mm armoured cable to a separate CU in the shed. We have TT
earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod
outside.
Measured the earth loop impedance, and I have 320 ohms - far too
high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect
the house
TT earth to the shed via the cable?Â*Â* By all means use the new
stake in
parallel.Â* An RCD at on or another end of the cable is probably
needed
either way.


Update on this shed ELI problem. Following the suggestion here I
did export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources
such as copper/lead water pipes, or did you test the house earth
rod on it's own.




No, I didn't test the earth rod on its own. As I said in my first
post I don't have the tester to do that. The house doesn't have gas
and the water pipes - coming into the house at any rate - are
plastic so I am assuming that there are no parallel paths to earth
and that the readings I get at a socket are fairly accurate.

I take it you are testing with a plug in earth loop tester?

Yes, that's correct.


If so you can always temporarily disconnect any equipotential bonding
wires at the main earthing terminal while doing the test if needs be
for more accurate results.

If you wanted to test the rod in isolation, there is a method for
doing so without any special test gear described he

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



I might try that, I think I have a 24v transformer somewhere.

However, what do you think about this idea for getting a more accurate
Ze measurement? My loop tester has an iec connector for a mains input
- a type I have plenty of - and no other leads. I get a spare lead and
chop the plug off, strip the insulation back and fit a crop clip to
the earth lead and a probe to the live lead.

With the supply turned off at the CU and the earth input disconnected
I then connect the croc clip to the (disconnected) earth and the probe
to the input side of the main switch. Would this give me a true Ze
reading, or is my thinking incorrect (would I need to connect the
neutral as well?)?

If its anything like my old Megga LT5, then I think it uses the neutral
to power itself since it has no battery. However in principle, you could
lash up something to allow it to be powered, and also have a wandering
earth lead for connection to your electrode.



That's what I'll do, I think, connect live and neutral to the input side
of the (switched off) main switch and connect the earth lead to the
disconnected external earth lead. That should give me a more accurate Ze.

On 19/11/2018 17:22, John Rumm wrote:
On 19/11/2018 11:34, Fredxx wrote:
On 19/11/2018 10:40, John Rumm wrote:
On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the
garden
- 4mm armoured cable to a separate CU in the shed. We have TT
earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod
outside.
Measured the earth loop impedance, and I have 320 ohms - far too
high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect
the house
TT earth to the shed via the cable?Â*Â* By all means use the new
stake in
parallel.Â* An RCD at on or another end of the cable is probably
needed
either way.


Update on this shed ELI problem. Following the suggestion here I
did export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources
such as copper/lead water pipes, or did you test the house earth
rod on it's own.




No, I didn't test the earth rod on its own. As I said in my first
post I don't have the tester to do that. The house doesn't have gas
and the water pipes - coming into the house at any rate - are
plastic so I am assuming that there are no parallel paths to earth
and that the readings I get at a socket are fairly accurate.

I take it you are testing with a plug in earth loop tester?

If so you can always temporarily disconnect any equipotential bonding
wires at the main earthing terminal while doing the test if needs be
for more accurate results.

If you wanted to test the rod in isolation, there is a method for
doing so without any special test gear described he

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



OOI, is there any reason I can't use the neutral incomer as an
alternative to "Supplier's main earthing terminal"?

I would not fancy it ;-) Remember neutral is a "live" wire - it could be
several volts[1] away from local earth, and can supply reasonably
significant current in some circumstances.

Several is less than 24V. I am aware that neutral is now considered
'live' so best to take care.

If there is a small residual voltage on the neutral, swapping the
transformer phase and taking the average of two measurements would
help but should be a fraction of 24V.

[1] Or possibly more depending on the load being applied to it locally
(by yours and neighbouring properties), and distance from the substation
etc.

Which should be taken into account if averaging in-phase power and
reverse phase currents.

The resistance ought to be a fraction of the local earth-spike
resistance. Either way it gives a worst case scenario of true live
conductor to local earth resistance and prospective earth fault current.

Or am I wrong?

On 20/11/2018 02:10, Fredxx wrote:
On 19/11/2018 17:22, John Rumm wrote:
On 19/11/2018 11:34, Fredxx wrote:
On 19/11/2018 10:40, John Rumm wrote:
On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of
the garden
- 4mm armoured cable to a separate CU in the shed. We have TT
earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod
outside.
Measured the earth loop impedance, and I have 320 ohms - far
too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect
the house
TT earth to the shed via the cable?Â*Â* By all means use the new
stake in
parallel.Â* An RCD at on or another end of the cable is probably
needed
either way.


Update on this shed ELI problem. Following the suggestion here I
did export the house earth as well as leaving the new earth rod
in circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources
such as copper/lead water pipes, or did you test the house earth
rod on it's own.




No, I didn't test the earth rod on its own. As I said in my first
post I don't have the tester to do that. The house doesn't have gas
and the water pipes - coming into the house at any rate - are
plastic so I am assuming that there are no parallel paths to earth
and that the readings I get at a socket are fairly accurate.

I take it you are testing with a plug in earth loop tester?

If so you can always temporarily disconnect any equipotential
bonding wires at the main earthing terminal while doing the test if
needs be for more accurate results.

If you wanted to test the rod in isolation, there is a method for
doing so without any special test gear described he

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




OOI, is there any reason I can't use the neutral incomer as an
alternative to "Supplier's main earthing terminal"?

I would not fancy it ;-) Remember neutral is a "live" wire - it could
be several volts[1] away from local earth, and can supply reasonably
significant current in some circumstances.

Several is less than 24V. I am aware that neutral is now considered
'live' so best to take care.

If there is a small residual voltage on the neutral, swapping the
transformer phase and taking the average of two measurements would
help but should be a fraction of 24V.

[1] Or possibly more depending on the load being applied to it locally
(by yours and neighbouring properties), and distance from the
substation etc.

Which should be taken into account if averaging in-phase power and
reverse phase currents.

The resistance ought to be a fraction of the local earth-spike
resistance. Either way it gives a worst case scenario of true live
conductor to local earth resistance and prospective earth fault current.

Or am I wrong?

No, you will get a reading...

All in all though it seems like more hassle than using a bit of pipe
stuck in the ground though!


--
Cheers,

John.

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

On 19/11/2018 08:50, Pat Pending wrote:
On 18/11/2018 19:45, ARW wrote:
On 16/11/2018 17:48, Pat Pending wrote:
On 13/11/2018 19:17, Roger Hayter wrote:
Pat Pending wrote:

Just put an electricity supply in to a shed at the bottom of the
garden
- 4mm armoured cable to a separate CU in the shed. We have TT
earthing,
so didn't use the cable earth and put in a 5/8" x 1m earth rod
outside.
Measured the earth loop impedance, and I have 320 ohms - far too high
isn't it? Any suggestions?

Pardon my ignorance, but is there any reason you can't connect the
house
TT earth to the shed via the cable?Â*Â* By all means use the new stake in
parallel.Â* An RCD at on or another end of the cable is probably needed
either way.


Update on this shed ELI problem. Following the suggestion here I did
export the house earth as well as leaving the new earth rod in
circuit. This reduced the reading to 109 ohms.

Still wondering why the shed TT earth was so high,

I wonder? Does the house earth benefit from other earth sources such
as copper/lead water pipes, or did you test the house earth rod on
it's own.




No, I didn't test the earth rod on its own. As I said in my first post I
don't have the tester to do that.

I missed that bit of info.


--
Adam