Got very useful input from here last week - thanks again.
My home electric circuits were tested as ok some weeks ago, including
adequate earthing, when a survey was done for a new combi boiler. When
they came to fit boiler, this was abandoned when initial tests showed
earthing inadequate - nearly 5 ohms instead og 1. In the interim new
street mains and house supply gas pipes were replaced with plastic and
one possibility is that my equipotential bonding to old iron gas pipes
was helping earth my system, instead of gas pipes being earthed to my
system.

Impedance of about 5 ohms was measured at earth connection on sockets.
Same was measured at what was supposed to be the actual main earth; an
earth wire from the consumer unit - what I call the fuse box!! - to an
ordinary earth clamp (http://www.ultimatehandyman.co.uk/
earth_clamp.htm) round the pipe containing the incoming mains
electricity supply. The theory, by both British Gas (boiler fitters)
and Scottish Power (DNO for my area) is that the earthing supplied by
this pipe is inadequate or has become compromised.

One electrician did try scraping the pipe a bit at this earth
connection to get a better connection, without success. However, I've
since noticed that what looks like copper is more like some ancient
gunge/paint/corrosion which I've scraped down to a shiny metal surface
and re-attached the earth.

I'd like to now measure the earthing impedance at this earth
connection down the pipe and, if possible, at the sockets. After
initial crude tests with 'socket and see', I think electricians
previously tested it with multimeter.
I know enough about volts amps and ohms to know what they are, but
don't usually touch electrics - but I do enough about electrics to
know what not to try!!

What I don't understand is how to find impedance down earth pipe and
at socket with a multimeter. I'm not measuring the resistance across
something but down something where I dont have access to the other
end. Do I attach attach one probe to something non-conductive and the
other to the pipe to get the resistance to leakage in one direction,
and how do I safely get a reading at socket (and no, I do know enough
not to poke into the live supply).

There is a delay in the DNO attending - I'd be interested to know
whether things are safer meantime and to what extent what one
electrician saw as the possible problem, might have been corrected.

Regards

Toom

In article
,
Toom Tabard wrote:
What I don't understand is how to find impedance down earth pipe and
at socket with a multimeter.

In practice, you can't. You need a proper tester which just looks a bit
like a multi-meter. It puts a very large load to earth on the circuit for
a fraction of a second and measures the current flow, and from that
calculates the impedance.
They are quite expensive devices and need regular calibration.

--
*What happens when none of your bees wax? *

Dave Plowman London SW
To e-mail, change noise into sound.

"Toom Tabard" wrote in message
...
Got very useful input from here last week - thanks again.
My home electric circuits were tested as ok some weeks ago, including
adequate earthing, when a survey was done for a new combi boiler. When
they came to fit boiler, this was abandoned when initial tests showed
earthing inadequate - nearly 5 ohms instead og 1. In the interim new
street mains and house supply gas pipes were replaced with plastic and
one possibility is that my equipotential bonding to old iron gas pipes
was helping earth my system, instead of gas pipes being earthed to my
system.

Impedance of about 5 ohms was measured at earth connection on sockets.
Same was measured at what was supposed to be the actual main earth; an
earth wire from the consumer unit - what I call the fuse box!! - to an
ordinary earth clamp (http://www.ultimatehandyman.co.uk/
earth_clamp.htm) round the pipe containing the incoming mains
electricity supply. The theory, by both British Gas (boiler fitters)
and Scottish Power (DNO for my area) is that the earthing supplied by
this pipe is inadequate or has become compromised.

One electrician did try scraping the pipe a bit at this earth
connection to get a better connection, without success. However, I've
since noticed that what looks like copper is more like some ancient
gunge/paint/corrosion which I've scraped down to a shiny metal surface
and re-attached the earth.

I'd like to now measure the earthing impedance at this earth
connection down the pipe and, if possible, at the sockets. After
initial crude tests with 'socket and see', I think electricians
previously tested it with multimeter.
I know enough about volts amps and ohms to know what they are, but
don't usually touch electrics - but I do enough about electrics to
know what not to try!!

What I don't understand is how to find impedance down earth pipe and
at socket with a multimeter. I'm not measuring the resistance across
something but down something where I dont have access to the other
end. Do I attach attach one probe to something non-conductive and the
other to the pipe to get the resistance to leakage in one direction,
and how do I safely get a reading at socket (and no, I do know enough
not to poke into the live supply).

There is a delay in the DNO attending - I'd be interested to know
whether things are safer meantime and to what extent what one
electrician saw as the possible problem, might have been corrected.

Regards

Toom


Put a photo up on photobucket so we can have a look.

--
Adam

"Dave Plowman (News)" wrote in message
...
In article
,
Toom Tabard wrote:
What I don't understand is how to find impedance down earth pipe and
at socket with a multimeter.

In practice, you can't. You need a proper tester which just looks a bit
like a multi-meter. It puts a very large load to earth on the circuit for
a fraction of a second and measures the current flow, and from that
calculates the impedance.
They are quite expensive devices and need regular calibration.


Wouldn't a 3 bar electric fire between live and earth do the job? Where you
measure the voltage (change) between earth and neutral?

Resistance = voltage / current through fire?

On 2 Sep, 16:32, Toom Tabard wrote:
Got very useful input from here last week - thanks again.
My home electric circuits were tested as ok some weeks ago, including
adequate earthing, when a survey was done for a new combi boiler. When
they came to fit boiler, this was abandoned when initial tests showed
earthing inadequate - nearly 5 ohms instead og 1. In the interim new
street mains and house supply gas pipes were replaced with plastic and
one possibility is that my equipotential bonding to old iron gas pipes
was helping earth my system, instead of gas pipes being earthed to my
system.

Impedance of about 5 ohms was measured at earth connection on sockets.
Same was measured at what was supposed to be the actual main earth; an
earth wire from the consumer unit - what I call the fuse box!! - to an
ordinary earth clamp (http://www.ultimatehandyman.co.uk/
earth_clamp.htm) round the pipe containing the incoming mains
electricity supply. The theory, by both British Gas (boiler fitters)
and Scottish Power (DNO for my area) is that the earthing supplied by
this pipe is inadequate or has become compromised.

One electrician did try scraping the pipe a bit at this earth
connection to get a better connection, without success. However, I've
since noticed that what looks like copper is more like some ancient
gunge/paint/corrosion which I've scraped down to a shiny metal surface
and re-attached the earth.

I'd like to now measure the earthing impedance at this earth
connection down the pipe and, if possible, at the sockets. After
initial crude tests with 'socket and see', I think electricians
previously tested it with multimeter.
I know enough about volts amps and ohms to know what they are, but
don't usually touch electrics - but I do enough about electrics to
know what not to try!!

What I don't understand is how to find impedance down earth pipe and
at socket with a multimeter. I'm not measuring the resistance across
something but down something where I dont have access to the other
end. Do I attach attach one probe to something non-conductive and the
other to the pipe to get the resistance to leakage in one direction,
and how do I safely get a reading at socket (and no, I do know enough
not to poke into the live supply).

There is a delay in the DNO attending - I'd be interested to know
whether things are safer meantime and to what extent what one
electrician saw as the possible problem, might have been corrected.

Regards

Toom

You probably need to get yourself a new earth spike or maybe more than
one.
If your house is built one sand or one high ground there is sometimes
a problem getting a good earth especially in dry weather. There's
usually no problem in clay soils. In a worst case scenario, you may
have to excavate a trench and lay copper tape in it, even import some
clay. I was traditional to cover the tape in charcoal/coke in the
past before burying(Conducts electrcity.)
Dunno if that's still done.
Soil in trench has to be well compacted and wetted down to ensure
intimate contact.
Lots of problems arose when gas and water pipes became plastic
instead of metal.
If you have metal gas or water pipes coming into the house, you can
get an indication of what's going on by measuring resistance between
them and your earth spike. (Before you connect it on to anything.) It
should be virtually zero.
This however is NOT a proper test but you can find out if your new
earth spike is likely to have a good effect or not.

On 2 Sep, 19:22, harry wrote:
On 2 Sep, 16:32, Toom Tabard wrote:





Got very useful input from here last week - thanks again.
My home electric circuits were tested as ok some weeks ago, including
adequate earthing, when a survey was done for a new combi boiler. When
they came to fit boiler, this was abandoned when initial tests showed
earthing inadequate - nearly 5 ohms instead og 1. In the interim new
street mains and house supply gas pipes were replaced with plastic and
one possibility is that my equipotential bonding to old iron gas pipes
was helping earth my system, instead of gas pipes being earthed to my
system.

Impedance of about 5 ohms was measured at earth connection on sockets.
Same was measured at what was supposed to be the actual main earth; an
earth wire from the consumer unit - what I call the fuse box!! - to an
ordinary earth clamp (http://www.ultimatehandyman.co.uk/
earth_clamp.htm) round the pipe containing the incoming mains
electricity supply. The theory, by both British Gas (boiler fitters)
and Scottish Power (DNO for my area) is that the earthing supplied by
this pipe is inadequate or has become compromised.

One electrician did try scraping the pipe a bit at this earth
connection to get a better connection, without success. However, I've
since noticed that what looks like copper is more like some ancient
gunge/paint/corrosion which I've scraped down to a shiny metal surface
and re-attached the earth.

I'd like to now measure the earthing impedance at this earth
connection down the pipe and, if possible, at the sockets. After
initial crude tests with 'socket and see', I think electricians
previously tested it with multimeter.
I know enough about volts amps and ohms to know what they are, but
don't usually touch electrics - but I do enough about electrics to
know what not to try!!

What I don't understand is how to find impedance down earth pipe and
at socket with a multimeter. I'm not measuring the resistance across
something but down something where I dont have access to the other
end. Do I attach attach one probe to something non-conductive and the
other to the pipe to get the resistance to leakage in one direction,
and how do I safely get a reading at socket (and no, I do know enough
not to poke into the live supply).

There is a delay in the DNO attending - I'd be interested to know
whether things are safer meantime and to what extent what one
electrician saw as the possible problem, might have been corrected.

Regards

Toom

You probably need to get yourself a new earth spike or maybe more than
one.
If your house is built one sand or one high ground there is sometimes
a problem getting a good earth especially in dry weather. *There's
usually no problem in clay soils. *In a worst case scenario, you may
have to excavate a trench and lay copper tape in it, even import some
clay. *I was traditional to cover the tape in charcoal/coke in the
past before burying(Conducts electrcity.)
Dunno if that's still done.
Soil in trench has to be well compacted and wetted down to ensure
intimate contact.
*Lots of problems arose when gas and water pipes became plastic
instead of metal.
If you have metal gas or water pipes coming into the house, you can
get an indication of what's going on by measuring resistance between
them and your earth spike. (Before you connect it on to anything.) It
should be virtually zero.
This however is NOT a proper test but you can find out if your new
earth spike is likely to have a good effect or not.- Hide quoted text -

- Show quoted text -

I'd say your assessment of the earth being supported by the old metal
underground pipes is correct. Forget all the above comments about
using ground spikes on their own and get a pro with an earth fault
loop impedance tester to check it correctly. Its very unlikely that an
earth spike or multiple earth spikes will be adequate to solve your
problem in most parts of the uk as you will typically have ground loop
resistances in excess of 15 ohms and maybe as high as the hundreds.
Unless the supply undertaking are willing to provide you with a low
impedance earth terminal you should change to a TT system with RCD
protection.

On 2 Sep, 20:44, John Rumm wrote:

Careful there - it sounds like the OP has what is intended to be a TN-S
supply where the earth is provided by the supplier. That last thing he
wants to do is start messing about providing his own earth connection
when that is the supplier's responsibility. It would also potentially
mean changing the whole installation to make it suitable for TT rather
than TN-S.


John,

Many thanks for your input - and thanks to all others for information
and comment.
My understanding is my present situation is an earthing through an
available pipe (the one containing the incoming supply), but that both
British Gas (boiler electrician) and DNO electrian are saying I need a
DNO-provided connection to the incoming cabling rather than being
earthed through the pipe. I assume that would then give me the TN-S
you refer to. They gave the impression it should be straightforward
and I just request it from DNO. My concerns are the vintage looks of
the DNO supply to the house and whether it's as straightforward as
that (much like the vintage gas supply pipes that have just been
replaced).

I take the point from others that an amateur can't easily accurately
measure the earth resistance at main connector or sockets. All the
cheap socket testers just seem to distinguish between some level of
earth and no earth and the more expensive (sok34) type only give three
levels of LCD display of qualitative earthing effectiveness.

I've contacted the DNO again to try and speed up the initial
assessment - I think they should be the first option. I'm in a
residential area of a large city but mainly older property (1930s)
and, understandably, the public supply water, gas and electricity
pipes/cables are/were somewhat elderly. I can't be the only one who
has needed new earthing and I'm hoping DNO provide a viable solution.
Otherwise, if I understand the electrician, I think some sort of front-
end RCD to the whole system was what he was suggesting as a possible
option.

Thanks again

Regards,

Toom

John Rumm wrote:

The way in which an earth loop impedance meter will test, is to apply a
known voltage to the earth, and measure the current that flows down it.
...
The theory:
...

Nice explanation. But for the process to work, there is an underlying
assumption that there is a practically zero ohm connection between N and E
somewhere out there (i.e. that N and E are well bonded together at the
substation or wherever the supply is coming from). That being the case,
why would it not suffice simply to measure the DC resistance between N
and E directly with an ordinary multimeter?

Another question is how nearly zero "practically zero" really is. Where
highish currents are involved, there will be a voltage drop in the mains
cable supplying the house, i.e. across the cable impedances Zl and Zn in
the diagram below.

Zl
L ----------------/\/\/\/\/\----------------- L

House N ----------------/\/\/\/\/\--------------+-- N Substation
Zn |
E ----/\/\/\/\--+ +--/\/\/\/\--+
Zeh | | Zes
| Zee |
+--/\/\/\/\--+

Zes is the earth impedance at the substation end which is presumed to be
of very high quality (of the order of milliohms I guess), and Zeh is the
earth impedance at the house end which is under test. Zee is the "real"
(non-cable) earth path impedance which is presumed (isn't it?) also to be
virtually zero.

Now when you connect your shunt in the first instance between L and N for
calibration purposes, and subsequently move it to between L and E, what
you are calculating from your measurements isn't Zeh, but it is the
amount by which Zeh+Zee+Zes exceeds Zn. Zee+Zes can be disregarded as
being of a lower order of magnitude, but I wouldn't expect Zn to be
small enough to ignore when we're expecting Zeh to be less than 0.3 ohm.

Is it normal practice to measure Zn (actually to measure Zl+Zn and to
assume Zn is half that) by measuring the voltage between L and N under
no-load and known high-load conditions, and to take this into account
when calculating Zeh?

On Fri, 03 Sep 2010 01:33:49 -0700, Toom Tabard wrote:

My understanding is my present situation is an earthing through an
available pipe (the one containing the incoming supply), but that both
British Gas (boiler electrician) and DNO electrian are saying I need a
DNO-provided connection to the incoming cabling rather than being
earthed through the pipe. I assume that would then give me the TN-S you
refer to. They gave the impression it should be straightforward and I
just request it from DNO. My concerns are the vintage looks of the DNO
supply to the house and whether it's as straightforward as that (much
like the vintage gas supply pipes that have just been replaced).

We have an incomer that dates back to the 1920s (still has a tag saying
"Herne Bay Electricity Supply Company". The conversion to TN-S took very
little time - minutes.

I take the point from others that an amateur can't easily accurately
measure the earth resistance at main connector or sockets. All the cheap
socket testers just seem to distinguish between some level of earth and
no earth and the more expensive (sok34) type only give three levels of
LCD display of qualitative earthing effectiveness.

That's right....and they don't do that under the same conditions, either.

Bear in mind that with TN-S you need to be careful with appliances used
outside the house - an RCD on them, at minimum, is a must - even if you
don't immediately have RCDs elsewhere.
--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

*lightning protection* - a w_tom conductor

On 02/09/2010 19:16, Fredxx wrote:
"Dave Plowman wrote in message
...
In article
,
Toom wrote:
What I don't understand is how to find impedance down earth pipe and
at socket with a multimeter.

In practice, you can't. You need a proper tester which just looks a bit
like a multi-meter. It puts a very large load to earth on the circuit for
a fraction of a second and measures the current flow, and from that
calculates the impedance.
They are quite expensive devices and need regular calibration.


Wouldn't a 3 bar electric fire between live and earth do the job? Where you
measure the voltage (change) between earth and neutral?

Resistance = voltage / current through fire?


That would work well, I think, in the absence of more sophisticated
equipment.

Many years ago I was having problems with hum in a particular piece of
equipment. The problem only occurred first thing in the morning, so I
swapped out the obvious part for further examination. When I'd done so,
every thing was perfect, as anticipated.

Until the following morning!

I missed that day's display but turned up bright and early the following
day to witness the problem at its most severe. It defied all logic and I
was desparate but luck was on my side. It was an office in old building
and the corner I was working in wasn't very well lit - it was mid winter
and natural light was virtually non-existent.

As I disconnected an earthed cable I saw a minute spark between the
connector and the earthed chassis. I plugged it back in again and,
almost immediately, I noticed the fault condition sharply reduce in
intensity - and realised that a girl was just returning to her desk
after turning down the fan heater they were using to supplement the
central heating ...

I immediately realised that earth and neutral must be reversed somewhere
along the line and connected a meter between the 'earthed' chassis and
the cable that I knew was most definitely earthed down in the basement.
Each kilowatt step on the fan heater produced a voltage drop of 500mV or
so and the hum was obviously being injected by the hefty AC current
passing through the screen of the cable.

I was deceived on my first visit, of course, because, by the time I'd
got the kit going again, the temperature had risen sufficiently for the
temporary fan heater to be switched off completely for the rest of the
day ...

--

Terry

On 3 Sep, 09:51, Bob Eager wrote:
On Fri, 03 Sep 2010 01:33:49 -0700, Toom Tabard wrote:
My understanding is my present situation is an earthing through an
available pipe (the one containing the incoming supply), but that both
British Gas (boiler electrician) and DNO electrian are saying I need a
DNO-provided connection to the incoming cabling rather than being
earthed through the pipe. I assume that would then give me the TN-S you
refer to. They gave the impression it should be straightforward and I
just request it from DNO. My concerns are the vintage looks of the DNO
supply to the house and whether it's as straightforward as that (much
like the vintage gas supply pipes that have just been replaced).

We have an incomer that dates back to the 1920s (still has a tag saying
"Herne Bay Electricity Supply Company". The conversion to TN-S took very
little time - minutes.


Thanks for that - gives me some hope that it's easy. DNO emergency
electrician didn't comment on obvious vintage and seemed to think it
would about an hour's work for their connections division. Suppose I'm
just a bit jaded after doing so much recent refurbishment of my 1930's
house, where you start something, and uncover another problem, and
when you start to fix that .... - the new McCarthy and Stone
retirement apartments across the road are almost starting to look like
an attractive option for me.

Toom

In article , John
Rumm writes

Not all multimeters take kindly to being placed across a live
circuit on their ohms range.

) I think we've all tried to measure the resistance of the mains in
an unguarded moment!

--
(\__/)
(='.'=)
(")_(")

In article ,
Mike Tomlinson wrote:
In article , John
Rumm writes

Not all multimeters take kindly to being placed across a live
circuit on their ohms range.

) I think we've all tried to measure the resistance of the mains in
an unguarded moment!

I had the magic smoke from a well used Maplin Gold DVM when measuring
mains voltage - and it was on the correct setting.

Investigation showed brass dust from the switch tracks has caused it to
flash over. Managed to fix it, though.

--
*Consciousness: That annoying time between naps.

Dave Plowman London SW
To e-mail, change noise into sound.

John Rumm wrote:
On 04/09/2010 05:17, Mike Tomlinson wrote:
In articleC9udna_20fKfpBzRnZ2dnUVZ8q2dnZ2d@brightvie w.co.uk, John
writes

Not all multimeters take kindly to being placed across a live
circuit on their ohms range.

o) I think we've all tried to measure the resistance of the mains
in an unguarded moment!

Yup, I still have most of the probe left to prove it ;-)

(amazingly the meter survived (an ICE Multitest 80), although that
ohms range was always a bit suspect after)

I like the fuse in my 17th edition tester.

--
Adam

On 4 Sep, 15:18, "ARWadsworth" wrote:

ohms range was always a bit suspect after)

I like the fuse in my 17th edition tester.

--
Adam

The definition of a semiconductor is an expensive fast acting device
to open circuit in time to protect a cheap fuse

cynic wrote:

The definition of a semiconductor is an expensive fast acting device
to open circuit in time to protect a cheap fuse

You want to see the price of the fast acting fuses recommended to
protect the solid state relays controlling dad's kiln, I think he has
given up on the fuses as the relays are cheaper to replace.

cynic wrote:
On 4 Sep, 15:18, "ARWadsworth" wrote:

ohms range was always a bit suspect after)
I like the fuse in my 17th edition tester.

--
Adam

The definition of a semiconductor is an expensive fast acting device
to open circuit in time to protect a cheap fuse

Not so expensive these days.


Compare the cost of a diode and a fuse..

On 4 Sep,
Andy Burns wrote:

You want to see the price of the fast acting fuses recommended to
protect the solid state relays controlling dad's kiln, I think he has
given up on the fuses as the relays are cheaper to replace.

I came across that in a 110 volt 3 phase to DC transformer many years ago.
The fast acting fuses were failing frequently costing about £3 to replace.
The diodes they were protecting were about 80p each.

After replacing the fuses with cheaper ones fast enough to protect for
overload, neither the fuses or the diodes failed.

--
B Thumbs
Change lycos to yahoo to reply

wrote:

Andy wrote:

You want to see the price of the fast acting fuses recommended to
protect the solid state relays controlling dad's kiln, I think he has
given up on the fuses as the relays are cheaper to replace.

I came across that in a 110 volt 3 phase to DC transformer many years ago.
The fast acting fuses were failing frequently costing about £3 to replace.

Just checked the emails and these were £13 each, with minimum quantity
of 10.

On Sat, 04 Sep 2010 17:10:33 +0100, Andy Burns
wrote:

cynic wrote:

The definition of a semiconductor is an expensive fast acting device
to open circuit in time to protect a cheap fuse

You want to see the price of the fast acting fuses recommended to
protect the solid state relays controlling dad's kiln, I think he has
given up on the fuses as the relays are cheaper to replace.

It's the same with a stage lighting dimmer pack we had at a local
theatre. However it was much quicker to replace the very fast-acting
fuse than the triac.

--
Frank Erskine

wrote:

I came across that in a 110 volt 3 phase to DC transformer many years ago.
The fast acting fuses were failing frequently costing about £3 to replace.
The diodes they were protecting were about 80p each.

After replacing the fuses with cheaper ones fast enough to protect for
overload, neither the fuses or the diodes failed.

On a rather larger scale, the substantial semiconductors used in
the Traction Convertor in APT-P had pretty large (1) and
expensive fuses which appeared to be blowing spuriously.

Upon opening them up for investigation, the internal structure
was of multiple parallel thin copper strips, with sections
punched out to create lots of necking points in series. Close
examination showed that the necking points which had shared the
arcing when it blew all had little blobs of fused sand (with
which the fuse cartridge was filled). However, there were also a
fair number of clean breaks, and it was eventually determined
that they were failing mechanically due to vibration, and thus as
the number of parallel paths reduced, the current capacity slowly
degraded.

(1) In the region of 1000 V, several hundred amps.

Chris
--
Chris J Dixon Nottingham UK


Have dancing shoes, will ceilidh.

On 3 Sep, 19:25, John Rumm wrote:
..........
Yup TT would be one option. Note also though that in many cases the
supplier can upgrade an installation to TN-C-S these days. Perhaps a
first step is finding out what earthing they think you have!


John, many thanks again for so much clear and useful info

Two weeks after their quick initial safety check, Scottish Power
project manager (seemed to be purely administrative) turned up at door
and simply looked at installation. Couldn't tell what they can do
because incoming cable is completely sheathed in pipe!! Situation is,
they'll send me a quote for what standard earthing will cost. I prepay
and send signed acceptance, then job goes into queue - so it could be
six weeks before they can tell me if they can do it in which case
they'll do it then!!!! No option for sending someone qualified and
equipped now. Seems another case where company procedures trounce
customer requirements. Meantime, I think I'd better enquire about
options in case I'm left high and dry. Before calling in commercial
contractors, I've been trying to find some local (Edinburgh)
independent electrical installation inspector or consultant to give
impartial advice for a fee, but can't locate even one.

Thanks for explaining what the options are and pointing to other info.

Regards

Norman