We have a TT supply at our house, i.e. the overall protection is a
100mA Time Delayed RCD and we have local earth rods.

Is there a "main earth bond" in such a system? If so where is it?
I'm concerned only because if there is a "main earth bond" then should
it be some proportion of the meter tail size (even on a TT system)?

--
Chris Green

Is there a "main earth bond" in such a system? If so where is it?
I'm concerned only because if there is a "main earth bond" then should
it be some proportion of the meter tail size (even on a TT system)?

TT doesn't need the large earth conductor sizes that TN-C-S (PME) requires,
as the RCD ensures that any earth current flow is short lived and requires
only 100mA to trip, so earth loop impedence is not particularly relevent
(within reason).

However, it is a VERY good idea to install the TN-C-S recommended sizes, as
it will enable you to upgrade to TN-C-S when it becomes available in your
area.

Christian.

TT doesn't need the large earth conductor sizes that TN-C-S (PME)
requires,

P.S. The On Site Guide has the required dimensions for TT (which vary
depending on whether mechanical protection is available). But, as I said, if
this is a new install, use the TN-C-S sizes.

Christian.

Christian McArdle wrote:
TT doesn't need the large earth conductor sizes that TN-C-S (PME)
requires,

P.S. The On Site Guide has the required dimensions for TT (which vary
depending on whether mechanical protection is available). But, as I said, if
this is a new install, use the TN-C-S sizes.

It's not a new install. I have the OSG too, I should have looked in
there, thanks!

--
Chris Green

"Christian McArdle" wrote in message
. net...
Is there a "main earth bond" in such a system? If so where is it?
I'm concerned only because if there is a "main earth bond" then should
it be some proportion of the meter tail size (even on a TT system)?

TT doesn't need the large earth conductor sizes that TN-C-S (PME)
requires,
as the RCD ensures that any earth current flow is short lived and requires
only 100mA to trip, so earth loop impedence is not particularly relevent
(within reason).

However, it is a VERY good idea to install the TN-C-S recommended sizes,
as
it will enable you to upgrade to TN-C-S when it becomes available in your
area.

Why do you see PME as an improvement ? Where we are the PME earth is so
far above real earth you daren't trust it and have to convert back.

In article ,
"G&M" writes:

"Christian McArdle" wrote in message
. net...
Is there a "main earth bond" in such a system? If so where is it?
I'm concerned only because if there is a "main earth bond" then should
it be some proportion of the meter tail size (even on a TT system)?

TT doesn't need the large earth conductor sizes that TN-C-S (PME)
requires,
as the RCD ensures that any earth current flow is short lived and requires
only 100mA to trip, so earth loop impedence is not particularly relevent
(within reason).

However, it is a VERY good idea to install the TN-C-S recommended sizes,
as
it will enable you to upgrade to TN-C-S when it becomes available in your
area.

Why do you see PME as an improvement ?

You can design for improved circuit protection without either
having the whole house on one or two RCDs, or having to use lots
of RCBOs.

Where we are the PME earth is so
far above real earth you daren't trust it and have to convert back.

What sort of voltage difference are you talking about?
The supplier is required to ground the PEN (Protective earth and
neutral) conductor within some fairly short distance from your
house (like 60m, but can't recall for sure). Any significant
PEN to ground voltage would indicate a supply fault.

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...

Where we are the PME earth is so
far above real earth you daren't trust it and have to convert back.

What sort of voltage difference are you talking about?
The supplier is required to ground the PEN (Protective earth and
neutral) conductor within some fairly short distance from your
house (like 60m, but can't recall for sure). Any significant
PEN to ground voltage would indicate a supply fault.

It is(was) about 45 volts, varying throughout the day. The earth is at
least half a mile away, I can see it dangling down the side of the pole
which feeds another farm first. Problem is when the last farm (of five) on
the chain runs a heavy load the earth really moves.

A while back we had a small water leak from the bottom of our hot water tank
which sits just above a stone floor. Shouldn't have been a problem to fix
but one couldn't touch it without getting a small shock due to the wet floor
and of course there is no 'off' switch for ground so we had to wait for the
whole thing to drain into the ground before we could deal with the leak.

Went off PME big time then and installed my own earth rods.

In article ,
"G&M" writes:

"Andrew Gabriel" wrote in message
...

Where we are the PME earth is so
far above real earth you daren't trust it and have to convert back.

What sort of voltage difference are you talking about?
The supplier is required to ground the PEN (Protective earth and
neutral) conductor within some fairly short distance from your
house (like 60m, but can't recall for sure). Any significant
PEN to ground voltage would indicate a supply fault.

It is(was) about 45 volts, varying throughout the day. The earth is at
least half a mile away, I can see it dangling down the side of the pole
which feeds another farm first. Problem is when the last farm (of five) on
the chain runs a heavy load the earth really moves.

There should be one where your service line joins the distributing
main. The 45 volts would also point to a fault. However, you can't
be losing 45 volts (and probably the same again from the phase
conductor) as you'd be pretty screwed if you only had 150V supply.
If it's just 45 Volts loss in the neutral and not the phase condutor,
that could point to a bad connection in the PEN which is very bad news.
If the 45 volts difference is being yanked towards a different phase
than yours, then the your mains voltage would be -cos(120º) x 45 =
23 volts higher than it should be, which should also be noticable.

You should report this as a fault to your distributor.
There's not enough info to tell what's wrong here -- it would be
interesting to know the three voltages L-N, L-real ground, N-real
ground, but don't try measuring these unless you are compitent at
working with mains voltages.

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...
In article ,
"G&M" writes:

"Andrew Gabriel" wrote in message
...

Where we are the PME earth is so
far above real earth you daren't trust it and have to convert back.

What sort of voltage difference are you talking about?
The supplier is required to ground the PEN (Protective earth and
neutral) conductor within some fairly short distance from your
house (like 60m, but can't recall for sure). Any significant
PEN to ground voltage would indicate a supply fault.

It is(was) about 45 volts, varying throughout the day. The earth is at
least half a mile away, I can see it dangling down the side of the pole
which feeds another farm first. Problem is when the last farm (of five)
on
the chain runs a heavy load the earth really moves.

There should be one where your service line joins the distributing
main. The 45 volts would also point to a fault. However, you can't
be losing 45 volts (and probably the same again from the phase
conductor) as you'd be pretty screwed if you only had 150V supply.
If it's just 45 Volts loss in the neutral and not the phase condutor,
that could point to a bad connection in the PEN which is very bad news.
If the 45 volts difference is being yanked towards a different phase
than yours, then the your mains voltage would be -cos(120º) x 45 =
23 volts higher than it should be, which should also be noticable.

You should report this as a fault to your distributor.
There's not enough info to tell what's wrong here -- it would be
interesting to know the three voltages L-N, L-real ground, N-real
ground, but don't try measuring these unless you are compitent at
working with mains voltages.


L-N is 251 volts. Drops slightly when the end farm is on load but not much.
L-N at the first farm is over the 253 volt limit but they don't want to
complain. L-N at the end farm can go as low as about 210 volts on load I
gather but they have been told tough.

N-real ground is typically 45 volts. It varies from 40 volts upwards but I
have never seen more than 50 volts. Do you think this still indicates a
problem at the PEN which as I say is about 3/4 mile away ?

Problem is the Peak Park Authority won't allow any more cables in the Park
and those we are using aren't really up to the task. Ideally the farms need
splitting into two groups with a separate transformer for each, and I am
sure United Utilities would do this if they were allowed. Remember the
prime goal of the Peak Park Authority is to turn the whole national park
into an unihabited tourist attraction.

Ideally the farms need splitting into two groups with a separate
transformer for each, and I am sure United Utilities would do this
if they were allowed.

Farms (particularly livestock) shouldn`t be provided with a PME earth
under the supply regs. Its down to the individual farmers to provide
their own earthing arrangements. There *may* be some latitude where only
crops are grown.

I know of a case where a horse was killed by a fault on the wiring to a
stable because the owners didn`t have a proper earth.

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"Colin Wilson" wrote in message
t...
Ideally the farms need splitting into two groups with a separate
transformer for each, and I am sure United Utilities would do this
if they were allowed.

Farms (particularly livestock) shouldn`t be provided with a PME earth
under the supply regs. Its down to the individual farmers to provide
their own earthing arrangements. There *may* be some latitude where only
crops are grown.

Interesting. But we definitely have a utility installed PME system from
many years ago complete with pure green earth wire into the neutral
connection. I'll check with the other farms tomorrow.

Does this apply to those buildings on the supply chain that are not farm
buildings ? Ours is a farmhouse with separate supply to the barns.

In article ,
"G&M" writes:
You should report this as a fault to your distributor.
There's not enough info to tell what's wrong here -- it would be
interesting to know the three voltages L-N, L-real ground, N-real
ground, but don't try measuring these unless you are compitent at
working with mains voltages.

L-N is 251 volts. Drops slightly when the end farm is on load but not much.
L-N at the first farm is over the 253 volt limit but they don't want to
complain. L-N at the end farm can go as low as about 210 volts on load I
gather but they have been told tough.

N-real ground is typically 45 volts. It varies from 40 volts upwards but I
have never seen more than 50 volts. Do you think this still indicates a
problem at the PEN which as I say is about 3/4 mile away ?

You only reported 2 of the 3 measurements.

--
Andrew Gabriel

"Andrew Gabriel" wrote in message
...
In article ,
"G&M" writes:
You should report this as a fault to your distributor.
There's not enough info to tell what's wrong here -- it would be
interesting to know the three voltages L-N, L-real ground, N-real
ground, but don't try measuring these unless you are compitent at
working with mains voltages.

L-N is 251 volts. Drops slightly when the end farm is on load but not
much.
L-N at the first farm is over the 253 volt limit but they don't want to
complain. L-N at the end farm can go as low as about 210 volts on load
I
gather but they have been told tough.

N-real ground is typically 45 volts. It varies from 40 volts upwards
but I
have never seen more than 50 volts. Do you think this still indicates a
problem at the PEN which as I say is about 3/4 mile away ?

You only reported 2 of the 3 measurements.

That's because I installed a local earth and didn't take that measurement
before I did it.
I'll try at my neighbour's place this week.



--
Andrew Gabriel

Farms (particularly livestock) shouldn`t be provided with a PME earth
under the supply regs. Its down to the individual farmers to provide
their own earthing arrangements. There *may* be some latitude where only
crops are grown.
Interesting. But we definitely have a utility installed PME system from
many years ago complete with pure green earth wire into the neutral
connection. I'll check with the other farms tomorrow.

I think I was drunk when I first posted the reply :-}

I don`t think they`re allowed to provide an earth by any means to a farm,
particularly with livestock - not just a PME :-}

ISTR any services from a stretch of overhead line that may serve a farm
with livestock along its length aren`t supposed to be provided with an
earth as it can change the line characteristics.

Some lines that have been refurbished may have an earth facility
available, but shouldn`t be used if livestock etc etc.

Earthing never was my strong point :-}

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"Colin Wilson" wrote in message
t...
Farms (particularly livestock) shouldn`t be provided with a PME earth
under the supply regs. Its down to the individual farmers to provide
their own earthing arrangements. There *may* be some latitude where
only
crops are grown.
Interesting. But we definitely have a utility installed PME system from
many years ago complete with pure green earth wire into the neutral
connection. I'll check with the other farms tomorrow.

I think I was drunk when I first posted the reply :-}

I don`t think they`re allowed to provide an earth by any means to a farm,
particularly with livestock - not just a PME :-}

ISTR any services from a stretch of overhead line that may serve a farm
with livestock along its length aren`t supposed to be provided with an
earth as it can change the line characteristics.

Some lines that have been refurbished may have an earth facility
available, but shouldn`t be used if livestock etc etc.


As this line hasn't been refurbished in the last thirty to forty years as
far as I can tell I'm now a bit concerned as to how well the other
farmhouses are earthed, if at all. As mentioned elsewhere I'll go test
them.

BTW, why does livestock make the difference ? Can't see how our sheep or
next farm's cows are going to reach any of the supply lines.

On Mon, 06 Sep 2004 20:38:40 +0100, G&M wrote:

BTW, why does livestock make the difference ? Can't see how our sheep or
next farm's cows are going to reach any of the supply lines.

The only thing I've ever seen is being careful about the siting of earth
rods if livestock are around.

A hefty fault current through an earth rod can create a significant
potential gradient radially in the locality. Couple that with nice wet
earth and grass and Miss Lamb will be meeting Mr Mintsauce quite soon.

In which case I would have thought it was better that the earth came via
the supply???

Timbo

--
Tim Southerwood
Website: http://www.dionic.net/
email: (remove DIESPAMDIE. to get address)

BTW, why does livestock make the difference ? Can't see how our sheep or
next farm's cows are going to reach any of the supply lines.

Can`t find anything more specific than this at present, and its not
particularly readable in my copied and pasted from page 20 of this pdf
file :-} :

http://www.dti.gov.uk/electricity-re...ns/gfesqcr.pdf

---
Distributors must not offer connections to earthing terminals from PME
networks for consumers=3F installations in caravans or boats. The
particular risk at these installations arises from the possibility of the
supply neutral conductor becoming disconnected from earth, possibly
causing the metalwork in the caravan or boat to rise to live potential
(assuming that the caravan or boat does not benefit from an independent
connection with earth).
Persons entering or exiting the caravan or boat would then be at risk of
electric shock.
There is a small inherent risk of danger to consumers (resulting from the
possible disconnection of the supply neutral conductor under fault
conditions) with all PME networks (see comments for regulation 7(1)),
however it is DTI=3Fs view that the risks are acceptable provided that:
(i) distributors comply with the requirements for multiple earthing
(regulation 9(2)) and take precautions to ensure continuity of the
supply neutral conductor (regulation 7(1)); and,
(ii) consumers comply with the equipotential bonding requirements of
BS7671 Requirements for Electrical Installations. Distributors
should note that at the time of connection they should be satisfied
that consumers=3F installations comply with BS7671 (see regulation 25
Connections to installations or to other networks).
Special consideration should be given to the earthing and protection
arrangements for certain installations where reliance on the connection
of the consumer=3Fs protective conductor with the distributor=3Fs combined
neutral and protective conductor could result in more significant risks.
For example, installations where it may prove difficult to attach and
maintain all the necessary equipotential bonding connections (e.g. farms
or building sites), installations at certain wet environments (e.g.
swimming pools and petrol filling stations) and certain installations
outside the equipotential zone of buildings (e.g. certain types of street
furniture). Further advice may be sought from the Health and Safety
Executive or the Institution of Electrical Engineers.
---

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"Colin Wilson" wrote in message
t...
There is a small inherent risk of danger to consumers (resulting from the
possible disconnection of the supply neutral conductor under fault
conditions) with all PME networks (see comments for regulation 7(1)),
however it is DTI=3Fs view that the risks are acceptable provided that:
(i) distributors comply with the requirements for multiple earthing
(regulation 9(2))

Oh ho-ho. There's a single thick wire running down the pole bolted to what
I assume (hope) is a buried metal thingy.

and take precautions to ensure continuity of the supply neutral conductor
(regulation 7(1));

Well if it breaks (as it does on a regular basis) it pulls the line wire
inside it down as well so I suppose that's safe-ish.

Oh ho-ho. There's a single thick wire running down the pole bolted to what
I assume (hope) is a buried metal thingy.

I don`t know the full circumstances of the dead horse incident, suffice
to say when electrocuted to death, they apparently get a h*rd-on.

I believe the vet was less than impressed too, receiving a shock while
trying to attend to it (already dead though) :-}

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In article ,
"G&M" writes:

"Andrew Gabriel" wrote in message
...
In article ,
"G&M" writes:
You should report this as a fault to your distributor.
There's not enough info to tell what's wrong here -- it would be
interesting to know the three voltages L-N, L-real ground, N-real
ground, but don't try measuring these unless you are compitent at
working with mains voltages.

L-N is 251 volts. Drops slightly when the end farm is on load but not
much.
L-N at the first farm is over the 253 volt limit but they don't want to
complain. L-N at the end farm can go as low as about 210 volts on load
I
gather but they have been told tough.

N-real ground is typically 45 volts. It varies from 40 volts upwards
but I
have never seen more than 50 volts. Do you think this still indicates a
problem at the PEN which as I say is about 3/4 mile away ?

You only reported 2 of the 3 measurements.

That's because I installed a local earth and didn't take that measurement
before I did it.
I'll try at my neighbour's place this week.

You need to measure all 3 at the same time (i.e not two yesterday
in one house and the third in a different house). The measurement
is against a local earth anyway, not the supplier's.

--
Andrew Gabriel