Hi

I need to wire in my garden electrics with armour cable etc...
Can anyone advise on what MCB's and what size armour cable to use?

I have done a small diagram if it helps?
http://i5.tinypic.com/20iz8jn.gif

many thanks

"John" wrote in message
...
Hi

I need to wire in my garden electrics with armour cable etc...
Can anyone advise on what MCB's and what size armour cable to use?

I have done a small diagram if it helps?
http://i5.tinypic.com/20iz8jn.gif

many thanks

You need to tell us the cable lengths before an accurate answer can be told
:-)

"Sparks" wrote in message
...
"John" wrote in message
...
Hi

I need to wire in my garden electrics with armour cable etc...
Can anyone advise on what MCB's and what size armour cable to use?

I have done a small diagram if it helps?
http://i5.tinypic.com/20iz8jn.gif

many thanks

You need to tell us the cable lengths before an accurate answer can be
told :-)

House to Garage = 8m
Garage to Shed = 6m
Shed to Summerhouse = 5m

cheers
;-)

House to Garage = 8m
Garage to Shed = 6m
Shed to Summerhouse = 5m

There are lots of ways you could do this. I'd run 6mm 2 core SWA from the
house to the garage, with a 32A Type B MCB in the house.

At the garage, I'd have:
30mA RCD for the entire lot. Isolate the earth from the house. Do not
connect to the garage. Use an earth rod.
6A MCB for the lighting
16/20A MCB for the sockets (you can go up to 32A if you wish)
16A MCB for the shed/summer house

Then 3 core 2.5mm SWA, exporting the garage earth down one core, from there
to the shed and summer house. Run shed/summer house lighting from local 3A
FCUs if the fittings do not indicate compatibility with a 16A circuit.

Don't forget that you will need to notify the council and have the
installation tested.

Note that your proposed spotlights for your garage might not be a good idea.
Spotlights are appalling inefficient for space lighting and contribute
significantly to global warming.

Christian.

"Christian McArdle" wrote in message
...
House to Garage = 8m
Garage to Shed = 6m
Shed to Summerhouse = 5m

There are lots of ways you could do this. I'd run 6mm 2 core SWA from the
house to the garage, with a 32A Type B MCB in the house.

At the garage, I'd have:
30mA RCD for the entire lot. Isolate the earth from the house. Do not
connect to the garage. Use an earth rod.
6A MCB for the lighting
16/20A MCB for the sockets (you can go up to 32A if you wish)
16A MCB for the shed/summer house

Then 3 core 2.5mm SWA, exporting the garage earth down one core, from
there
to the shed and summer house. Run shed/summer house lighting from local 3A
FCUs if the fittings do not indicate compatibility with a 16A circuit.

Don't forget that you will need to notify the council and have the
installation tested.

Note that your proposed spotlights for your garage might not be a good
idea.
Spotlights are appalling inefficient for space lighting and contribute
significantly to global warming.

Christian.



Nice one Christian
cheers

Christian McArdle wrote:
House to Garage = 8m
Garage to Shed = 6m
Shed to Summerhouse = 5m


There are lots of ways you could do this. I'd run 6mm 2 core SWA from the
house to the garage, with a 32A Type B MCB in the house.

At the garage, I'd have:
30mA RCD for the entire lot. Isolate the earth from the house. Do not
connect to the garage. Use an earth rod.
6A MCB for the lighting
16/20A MCB for the sockets (you can go up to 32A if you wish)
16A MCB for the shed/summer house

Then 3 core 2.5mm SWA, exporting the garage earth down one core, from there
to the shed and summer house. Run shed/summer house lighting from local 3A
FCUs if the fittings do not indicate compatibility with a 16A circuit.

Don't forget that you will need to notify the council and have the
installation tested.

Note that your proposed spotlights for your garage might not be a good idea.
Spotlights are appalling inefficient for space lighting and contribute
significantly to global warming.

Christian.



Why the earth rod for shed? would you like to quote a reg to justify it
please.
My preferred way would be 5 way consumer unit in garage rcd sockets
where nessary, no rcd protection to server (to prevent nusicence
tripping) agree with all mcb/cable sizes but would put small 2way
"garage consumer units" with rcd main switch in shed and summer house

mitchd wrote:

Why the earth rod for shed? would you like to quote a reg to justify it
please.
My preferred way would be 5 way consumer unit in garage rcd sockets
where nessary, no rcd protection to server (to prevent nusicence
tripping) agree with all mcb/cable sizes but would put small 2way
"garage consumer units" with rcd main switch in shed and summer house

Not an engineer etc...

I doubt there is a specific reg that says "you must do TT etc". It's going
to be a matter of making the design compliant with several relevant regs.

If you are going to export the house earth then it must be safe to do so.

See here first for some excellent background info:

http://www.iee.org/Publish/WireRegs/...s_answered.pdf

If you have a TN-S (elec co supply earth as a separate core back to
substation) then many would agree that exporting to outbuildings is OK
over short distances, for some definition of short that I'm not prepared to
define...

PME supplies are dodgey as it's not impossible for the earth/neutral to fall
off upstream (esp. in rural locations) then your neutral AND your local
earth is now being pulled up towards phase by attached loads (yours or
neighbours'). In the case of a metal greenhouse with supply and earth
bonding, your frame is now at 240V and the ground is still earthed - so you
get the idea. And you don't bank entirely on the main RCD to get you out of
trouble...

TT - you have your own electrode with a relatively high impedance. Phase to
earth fault in the house will float this up (and thus your greenhouse frame
in the previous example) to potentially dangerous voltages relative to the
real earth. Wet grass, bare feet leaning on the greenhouse you would not
need full mains voltages to potentially kill you.

--

If you have doubts as to exporting the supply earth, then the only sensible
option left is a local TT earth at each location (shed/greenhouse/garage
etc). This must be a proper TT installation, required RCD and MUST be
tested to prove that it has suffiently low impedance. Potential for messing
it up exists, so the testing is exceedingly important (Whifield's
exposition on the wiring regs does detail a method involving multimeters
and a car battery, but may as well hire a suitable tester).

With the greenhouse example, a phase-earth fault in the house has no effect
providing you isolate the two earthing systems, and a local fault is
hopefully going to achieve a lower differential voltage betwen the ground
and the frame (because the earth rod is in the vincinity). It's deemed
acceptable because there's not a lot else you could do to better it.

The whole thing is a bit of a minefield and it's far less easy to just give
a prescription answer, compared to many other aspects of domestic wiring.

All of the above is an attempt to offer general explanation to your query,
do not take it as a recipe to implement a specific solution!!!

Cheers

Tim

Tim S wrote:
mitchd wrote:


Why the earth rod for shed? would you like to quote a reg to justify it
please.
My preferred way would be 5 way consumer unit in garage rcd sockets
where nessary, no rcd protection to server (to prevent nusicence
tripping) agree with all mcb/cable sizes but would put small 2way
"garage consumer units" with rcd main switch in shed and summer house


Not an engineer etc...

I doubt there is a specific reg that says "you must do TT etc". It's going
to be a matter of making the design compliant with several relevant regs.

If you are going to export the house earth then it must be safe to do so.

See here first for some excellent background info:

http://www.iee.org/Publish/WireRegs/...s_answered.pdf

If you have a TN-S (elec co supply earth as a separate core back to
substation) then many would agree that exporting to outbuildings is OK
over short distances, for some definition of short that I'm not prepared to
define...

PME supplies are dodgey as it's not impossible for the earth/neutral to fall
off upstream (esp. in rural locations) then your neutral AND your local
earth is now being pulled up towards phase by attached loads (yours or
neighbours'). In the case of a metal greenhouse with supply and earth
bonding, your frame is now at 240V and the ground is still earthed - so you
get the idea. And you don't bank entirely on the main RCD to get you out of
trouble...

TT - you have your own electrode with a relatively high impedance. Phase to
earth fault in the house will float this up (and thus your greenhouse frame
in the previous example) to potentially dangerous voltages relative to the
real earth. Wet grass, bare feet leaning on the greenhouse you would not
need full mains voltages to potentially kill you.

--

If you have doubts as to exporting the supply earth, then the only sensible
option left is a local TT earth at each location (shed/greenhouse/garage
etc). This must be a proper TT installation, required RCD and MUST be
tested to prove that it has suffiently low impedance. Potential for messing
it up exists, so the testing is exceedingly important (Whifield's
exposition on the wiring regs does detail a method involving multimeters
and a car battery, but may as well hire a suitable tester).

With the greenhouse example, a phase-earth fault in the house has no effect
providing you isolate the two earthing systems, and a local fault is
hopefully going to achieve a lower differential voltage betwen the ground
and the frame (because the earth rod is in the vincinity). It's deemed
acceptable because there's not a lot else you could do to better it.

The whole thing is a bit of a minefield and it's far less easy to just give
a prescription answer, compared to many other aspects of domestic wiring.

All of the above is an attempt to offer general explanation to your query,
do not take it as a recipe to implement a specific solution!!!

Cheers

Tim

Pause for thought indeed, been an electrician for nighon 30 years and
would not consider earth rod for outbuildings unless their was an
existing tt system, just as likely to loose your earth rod connection as
your main supply earth surly, how often should your earth rod be tested
3mts, 6mths a year? That just will not happen in a domestic house, As
long as rcd protection is used,imo using house earth is the safest way.

"mitchd" wrote in message
...
Tim S wrote:
mitchd wrote:


Why the earth rod for shed? would you like to quote a reg to justify it
please.
My preferred way would be 5 way consumer unit in garage rcd sockets
where nessary, no rcd protection to server (to prevent nusicence
tripping) agree with all mcb/cable sizes but would put small 2way
"garage consumer units" with rcd main switch in shed and summer house


Not an engineer etc...

I doubt there is a specific reg that says "you must do TT etc". It's
going
to be a matter of making the design compliant with several relevant regs.

If you are going to export the house earth then it must be safe to do so.

See here first for some excellent background info:

http://www.iee.org/Publish/WireRegs/...s_answered.pdf

If you have a TN-S (elec co supply earth as a separate core back to
substation) then many would agree that exporting to outbuildings is OK
over short distances, for some definition of short that I'm not prepared
to
define...

PME supplies are dodgey as it's not impossible for the earth/neutral to
fall
off upstream (esp. in rural locations) then your neutral AND your local
earth is now being pulled up towards phase by attached loads (yours or
neighbours'). In the case of a metal greenhouse with supply and earth
bonding, your frame is now at 240V and the ground is still earthed - so
you
get the idea. And you don't bank entirely on the main RCD to get you out
of
trouble...

TT - you have your own electrode with a relatively high impedance. Phase
to
earth fault in the house will float this up (and thus your greenhouse
frame
in the previous example) to potentially dangerous voltages relative to
the
real earth. Wet grass, bare feet leaning on the greenhouse you would not
need full mains voltages to potentially kill you.

--

If you have doubts as to exporting the supply earth, then the only
sensible
option left is a local TT earth at each location (shed/greenhouse/garage
etc). This must be a proper TT installation, required RCD and MUST be
tested to prove that it has suffiently low impedance. Potential for
messing
it up exists, so the testing is exceedingly important (Whifield's
exposition on the wiring regs does detail a method involving multimeters
and a car battery, but may as well hire a suitable tester).

With the greenhouse example, a phase-earth fault in the house has no
effect
providing you isolate the two earthing systems, and a local fault is
hopefully going to achieve a lower differential voltage betwen the ground
and the frame (because the earth rod is in the vincinity). It's deemed
acceptable because there's not a lot else you could do to better it.

The whole thing is a bit of a minefield and it's far less easy to just
give
a prescription answer, compared to many other aspects of domestic wiring.

All of the above is an attempt to offer general explanation to your
query,
do not take it as a recipe to implement a specific solution!!!

Cheers

Tim

Pause for thought indeed, been an electrician for nighon 30 years and
would not consider earth rod for outbuildings unless their was an existing
tt system, just as likely to loose your earth rod connection as your main
supply earth surly, how often should your earth rod be tested 3mts, 6mths
a year? That just will not happen in a domestic house, As long as rcd
protection is used,imo using house earth is the safest way.

The NICEIC did a crackng article a few months ago in Professional
Electrician and Installer magazine (the free one at the wholesalers) on how
the export an earth to outbuildings with a PME supply.

The main criteria was that the combined CPC and main bonding conductor for
the exported earth meets regs 547-02-01, 542-01-09, and 543-01-01.

Unfortunately the article was covering out buildings with extraneous
conducting parts and made no mention buildings without.

Adam

Pause for thought indeed, been an electrician for nighon 30 years and
would not consider earth rod for outbuildings unless their was an
existing tt system, just as likely to loose your earth rod connection as
your main supply earth surly, how often should your earth rod be tested
3mts, 6mths a year? That just will not happen in a domestic house, As
long as rcd protection is used,imo using house earth is the safest way.

...and of course think about what happens to the earth rod impedance when we get a long hot spell &
the ground dries out...

Mike Harrison wrote:


Pause for thought indeed, been an electrician for nighon 30 years and
would not consider earth rod for outbuildings unless their was an
existing tt system, just as likely to loose your earth rod connection as
your main supply earth surly, how often should your earth rod be tested
3mts, 6mths a year? That just will not happen in a domestic house, As
long as rcd protection is used,imo using house earth is the safest way.

..and of course think about what happens to the earth rod impedance when
we get a long hot spell & the ground dries out...

Yes indeed - I did say it was a minefield...

I've heard differing opinions from engineers too, each with a perfectly goog
sounding argument to back his theory up. I think this is one of those areas
where getting expert advice in a specific situation is most definitely a
good idea, even if it costs... Then I did say I wasn't an engineer.

If it were me, and I'd concluded I ought to TT each out-building,

I'd probably sink two of the longest rods I could physically
bash into the ground (at least 4 feet, preferably more) at diagonally
opposite corners of the building and bond the lot solid.

Then that's just me - "if in doubt, double it, if still not sure double it
again!"

Cheers

Tim

mitchd wrote:

Pause for thought indeed, been an electrician for nighon 30 years and
would not consider earth rod for outbuildings unless their was an
existing tt system, just as likely to loose your earth rod connection as
your main supply earth surly, how often should your earth rod be tested
3mts, 6mths a year? That just will not happen in a domestic house, As
long as rcd protection is used,imo using house earth is the safest way.

Hi

I won't argue with experience (especially as I have little, but just happen
to have read around the issue a bit)...

The only thing I would add is that at least a local rod (or rods) can be
maintained under reasonably controlled conditions and inspected/tested
regularly IMHO.

As to the likelihood of a PME supply failing wrongside - I don't know how
likely that is in reality, but it is outside of the householders control.

Perfectly valid point on (not) testing local TT.

Just out of interest, how far do you consider it reasonable to export a TN-S
earth - I'd be interested for when I have to do it?

Cheers

Tim

Mike Harrison wrote:


Pause for thought indeed, been an electrician for nighon 30 years and
would not consider earth rod for outbuildings unless their was an
existing tt system, just as likely to loose your earth rod connection as
your main supply earth surly, how often should your earth rod be tested
3mts, 6mths a year? That just will not happen in a domestic house, As
long as rcd protection is used,imo using house earth is the safest way.

..and of course think about what happens to the earth rod impedance when
we get a long hot spell & the ground dries out...

Deep enough rods hopefully and re-test if there's an element of doubt.

Cheers

Tim

Tim S wrote:
mitchd wrote:


Pause for thought indeed, been an electrician for nighon 30 years and
would not consider earth rod for outbuildings unless their was an
existing tt system, just as likely to loose your earth rod connection as
your main supply earth surly, how often should your earth rod be tested
3mts, 6mths a year? That just will not happen in a domestic house, As
long as rcd protection is used,imo using house earth is the safest way.


Hi

I won't argue with experience (especially as I have little, but just happen
to have read around the issue a bit)...

The only thing I would add is that at least a local rod (or rods) can be
maintained under reasonably controlled conditions and inspected/tested
regularly IMHO.

As to the likelihood of a PME supply failing wrongside - I don't know how
likely that is in reality, but it is outside of the householders control.

Perfectly valid point on (not) testing local TT.

Just out of interest, how far do you consider it reasonable to export a TN-S
earth - I'd be interested for when I have to do it?

Cheers

Tim

Hi don't think distance is relevant, a decent earth loop reading is the
thing i would look for.
and another thing......
if you decided to put in a new pme supply from local electricity
supplier to said garage there would be no need for an earth rod. My
point is all customers really on electricity supplier for an earth point
unless their a tt system.
I have had issues with tn-s supplies, first thing to check is earth loop
had quite a few with high readings, they were simply converted to
tnc-s by local electricity supplier, but the house had been without an
effective earth for who knows how long.

"mitchd" wrote in message
...
Tim S wrote:
mitchd wrote:

..

Just out of interest, how far do you consider it reasonable to export a
TN-S
earth - I'd be interested for when I have to do it?

Cheers

Tim

Hi don't think distance is relevant, a decent earth loop reading is the
thing i would look for.

Calculate the cable size needed needed using
http://www.tlc-direct.co.uk/Technica...ltageDrop.html
and table 54G of the 16th edition for the CPC if there is no main bonding
required in the outbuilding

and another thing......
if you decided to put in a new pme supply from local electricity supplier
to said garage there would be no need for an earth rod. My point is all
customers really on electricity supplier for an earth point unless their a
tt system.
I have had issues with tn-s supplies, first thing to check is earth loop
had quite a few with high readings, they were simply converted to tnc-s by
local electricity supplier, but the house had been without an effective
earth for who knows how long.

It is more likely that you will see a TT supply converted to a TN-C-S
without the main earth connection being made as the bonding on the
installation was not up to TN-C-S standards and so the installation is left
as a TT.

Adam

Mike Harrison wrote:

..and of course think about what happens to the earth rod impedance when we get a long hot spell &
the ground dries out...

Well it only needs to muster a feeble 8K ohms to be able to trip a 30mA
RCD.

The thing to bear in mind is that with a PME system and an exported
earth, there is the possibility that you will pass no leakage current in
the case of a disconnected CNE conductor to the property. That can leave
phase voltage on your exposed metalwork indefinately. Hence why
maintaining the equipotential zone in the outbuilding is important if
you are exporting the earth.

--
Cheers,

John.

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

John Rumm wrote:

Well it only needs to muster a feeble 8K ohms to be able to trip a 30mA
RCD.

Although the limit of 1667 ohms to comply with BS 7671 [413-02-20] is a
bit more relevant and ensures that the touch voltage won't exceed 50 V.
If the supply feeds a greenhouse then section 605 applies and the
limits become 25 V and 833 ohms [605-06-01].

If you achieve the OSG recommendation of 200 ohms in normal conditions
then I really don't think you'll need to worry too much about the ground
drying out or freezing in extreme weather, unless you're on very rocky
ground (literally).

If a 100 mA is involved the figures become 500 and 250 ohms, so the
margin is reduced somewhat. IME (which is limited to chalky and clayey
soils) you're unlikely to have any worries if an 8 ft earth rod is used.

The thing to bear in mind is that with a PME system and an exported
earth, there is the possibility that you will pass no leakage current in
the case of a disconnected CNE conductor to the property. That can leave
phase voltage on your exposed metalwork indefinately. Hence why
maintaining the equipotential zone in the outbuilding is important if
you are exporting the earth.

Absolutely. And where that's just not practical - the aluminium
greenhouse being the archetypal example - go for TT.

--
Andy

mitchd wrote:

Why the earth rod for shed? would you like to quote a reg to justify it
please.

I suggest the following are relevant:

130-02-02
131-01-01 (i)
541-01-01
541-01-02
542-01-09

--
Andy

Andy Wade wrote:
mitchd wrote:

Why the earth rod for shed? would you like to quote a reg to justify
it please.


I suggest the following are relevant:

130-02-02
131-01-01 (i)
541-01-01
541-01-02
542-01-09

would agree regs quoted are relevent, to every installation, just don't
see the relevance to an earth rod being required on an outbuilding
installation

mitchd wrote:

would agree regs quoted are relevent, to every installation, just don't
see the relevance to an earth rod being required on an outbuilding

131-01-01 (i) requires you to /design/ an installation to be safe. A
PME earth connection is potentially unsafe if it's exported outside the
equipotential zone and there is risk of simultaneous contact between
exposed-conductive-parts of the electrical installation and the general
mass of earth. These risks will arise if the DNO's combined neutral and
earth (CNE) supply conductor is broken, or if a phase-neutral or
phase-earth fault occurs elsewhere on the distribution network,
temporarily raising the PME 'earth' potential above ground, due to the
voltage drop along the CNE conductor. Such faults can take more than
0.4 s, and even more than 5 s to clear.

There's usually no difficulty if the outbuilding is dry. Any incoming
service pipes that constitute extraneous-conductive-parts can be
main-bonded to the incoming submain's earth in the usual way, creating
an equipotential zone. The earth conductor in the submain (usually the
SWA's armour) then functions as both a CPC and a main bonding conductor.
Because of the latter function the min. size for this 'earth' is 10
mm^2 copper, or 22.6 mm^2 steel armouring. This is met by 2-core SWA
(BS 5467) of size 6 mm^2 or larger.

So far, so good. But if the outbuilding is a garage with a damp floor,
or a greenhouse, the only way you could create a dependable
equipotential zone would be with a buried earth mat in the floor
structure, or in the soil - not very practical for existing structures.
Worse still is when the user uses an extension lead to use Class 1
equipment outdoors. The problem could be avoided by using only Class 2
equipment in the outbuilding, but that would preclude installing any
3-pin socket outlets, using metalclad accessories, which are usually
desirable on grounds of robustness.

The problem can be avoided by using TT earthing for the outbuilding - a
much safer arrangement all round, provided that the earth system and the
RCD(s) can be maintained. This is fairly standard practice, and has
been since use of PME became well-established during the 1970s.

The ESQC regulations legally forbid suppliers from providing PME earth
connections on supplies to caravans or boats. (Regulation 9 (4) "The
distributor shall not connect his combined neutral and protective
conductor to any metalwork in a caravan or boat.")

--
Andy

Andy Wade wrote:

If you achieve the OSG recommendation of 200 ohms in normal conditions
then I really don't think you'll need to worry too much about the ground
drying out or freezing in extreme weather, unless you're on very rocky
ground (literally).

If a 100 mA is involved the figures become 500 and 250 ohms, so the
margin is reduced somewhat. IME (which is limited to chalky and clayey
soils) you're unlikely to have any worries if an 8 ft earth rod is used.

From the measurements I have taken from my installation (heavy clay
soil) a 4' rod will give a resoanably consistent 11 - 13 ohms year round.


--
Cheers,

John.

/================================================== ===============\
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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

From the measurements I have taken from my installation (heavy clay
soil) a 4' rod will give a resoanably consistent 11 - 13 ohms year round.

I'd say that's exceptionally low for a single 4 ft. 50 - 100 ohms is
more common, so you've clearly got very good soil.

For my workshop & shed installations I've got two 8 footers in parallel
(one of them deliberately near a soakaway) and find a consistent 7.5 to
8 ohms.

--
Andy

"Andy Wade" wrote in message
...
John Rumm wrote:

From the measurements I have taken from my installation (heavy clay soil)
a 4' rod will give a resoanably consistent 11 - 13 ohms year round.

I'd say that's exceptionally low for a single 4 ft. 50 - 100 ohms is more
common, so you've clearly got very good soil.

For my workshop & shed installations I've got two 8 footers in parallel
(one of them deliberately near a soakaway) and find a consistent 7.5 to 8
ohms.
--
Andy

Sorry to butt-in here, but can you tell me how you measure earth rods?
What do you use to do the measuring, and what is the other test lead
connected to?

Ta :-)

Andy Wade wrote:

From the measurements I have taken from my installation (heavy clay
soil) a 4' rod will give a resoanably consistent 11 - 13 ohms year round.


I'd say that's exceptionally low for a single 4 ft. 50 - 100 ohms is
more common, so you've clearly got very good soil.

Yup, I was quite pleasently surprised. When we moved in the *only* earth
connection was to the gas supply (also about 12 ohms), so I was
wondering what reading I would get from a rod on its own without any
contribution from the gas and water bonds. After some experimentation it
seems that close to the house any length of rod that goes more than a
few inches into the ground gets you about 12 ohms.

My workshop earth was reading about 22 ohms (probably in dryer soil with
lots of tree roots about). So I added a second rod in parallel about 14'
away to that to get it down to the same as the house.

For my workshop & shed installations I've got two 8 footers in parallel
(one of them deliberately near a soakaway) and find a consistent 7.5 to
8 ohms.

What sort of earth connection would they have at a typical substation?

--
Cheers,

John.

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

Sparks wrote:

Sorry to butt-in here, but can you tell me how you measure earth rods?
What do you use to do the measuring, and what is the other test lead
connected to?

I usually use a Megger LT5 digital loop tester. It actually measures the
earth fault loop impedance for a whole circuit, so is not quite a true
reading of the electrode resistance in isolation, but does give a
reasonable indication. Obviously you need to disconnect the main
equipotential bonds when you take a reading so as not to include any
fortuitous lowering of impedance they may give you.

--
Cheers,

John.

/================================================== ===============\
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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
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On Sun, 23 Jul 2006 18:28:18 +0100, "Sparks"
had this to say:


Sorry to butt-in here, but can you tell me how you measure earth rods?
What do you use to do the measuring, and what is the other test lead
connected to?

http://www.ees-group.co.uk/downloads...g%20Manual.pdf

--
Frank Erskine

Sparks wrote:

Sorry to butt-in here, but can you tell me how you measure earth rods?
What do you use to do the measuring, and what is the other test lead
connected to?

a) with a proper earth electrode testing kit, or

b) with a loop-tester, as John Rumm has already said (and this method is
endorsed by the On-Site Guide), or

c) my DIY cheat's method, see
http://groups.google.com/group/uk.d-...e=source&hl=en

--
Andy

"Andy Wade" wrote in message
...
Sparks wrote:

Sorry to butt-in here, but can you tell me how you measure earth rods?
What do you use to do the measuring, and what is the other test lead
connected to?

a) with a proper earth electrode testing kit, or

b) with a loop-tester, as John Rumm has already said (and this method is
endorsed by the On-Site Guide), or

c) my DIY cheat's method, see
http://groups.google.com/group/uk.d-...e=source&hl=en


Thanks for that :-)

You say...
"connect one end of the secondary
via a suitable length of wire to the main earth terminal in the house
and connect the other end to your earth electrode via an ammeter."

Do I assume this would be done with the rod disconnected from this main
earth terminal?

If so, if this is a TT installation, and there is no other path to earth in
the house (plastic water pipes etc..) how will you get a reading?

If not, surely this is only testing the cable between the rod and the earth
terminal (and your test cable!), not the rod it self?

Sparks...

Re.
http://groups.google.com/group/uk.d-...e=source&hl=en

Sparks wrote:

You say...
"connect one end of the secondary
via a suitable length of wire to the main earth terminal in the house
and connect the other end to your earth electrode via an ammeter."

Do I assume this would be done with the rod disconnected from this main
earth terminal?

Yes, obviously - otherwise you'd have a short across the transformer
secondary.

If so, if this is a TT installation, and there is no other path to earth in
the house (plastic water pipes etc..) how will you get a reading?

Ah, yes, OK. There is an implicit assumption in that article that
you're wanting to test an earth rod for an outbuilding, etc., and the
house already has a functioning TN earth kindly provided by the DNO. If
you don't have the latter then there are probably two options:

(a) sink a third temporary electrode as far away as you can from the
other two and use that as the return connection for the test current.
You might have to increase the test voltage available to get enough test
current flowing (make sure to mask any residual voltage that might be
present between the rod under test and the reference electrode);

(b) resort to hairier methods such as using the mains neutral as the
test current return (it will be earthed somewhere), or obtain your test
current directly from the mains (phase) via a series resistance (such as
a couple of 1 kW fire elements in series) instead of using the
transformer. Clearly such methods have the potential to be dangerous,
so don't attempt them unless you have a clear understanding of what
you're doing and appreciate the dangers involved etc., etc.

If not, surely this is only testing the cable between the rod and the earth
terminal (and your test cable!), not the rod it self?

Well, quite.

--
Andy