Searching \ for '[OT] Earth Grounds--a parable for our times' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/timers.htm?key=time
Search entire site for: 'Earth Grounds--a parable for our times'.

Exact match. Not showing close matches.
PICList Thread
'[OT] Earth Grounds--a parable for our times'
1999\09\19@230315 by William K. Borsum

flavicon
face
Recent threads on connectors and soldering and such brought this to mind...
Heard this story from a Brit I know......

Seems a lady complained that her dog would bark hysterically for a minute
or so prior to her phone ringing.

Repairman showed up and found:

Telephone used an earth ground for the return current.
The earth ground was the usual metallic stake in the ground in the yard.
The ground was normally dry.
Her dog was chained to the ground post with a metal chain.
When the phone range, it would complete the circuit to ground (90 volts or
thereabouts ring voltage) via the dog
       Who of course resented this and barked
       And urinated on the ground post
which allowed a good ground to occur, and the phone would then ring
normally and the dog would go back to sleep.

The moral--
Quite often problems can be solved by pissing on them.

Enjoy

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<spam_OUTborsumTakeThisOuTspamdascor.com> & <http://www.dascor.com>

1999\09\19@232423 by Sean H. Breheny

face picon face
At 08:01 PM 9/19/99 -0700, you wrote:
>Recent threads on connectors and soldering and such brought this to mind...
>Heard this story from a Brit I know......
>

ROTFL!!

Speaking of ground rods: does anyone have a good explanation of why they
work? I have been trying to understand for the longest while how a 6' rod
stuck into the ground can provide a suitable return. Soil conductivity,from
what I could find on the web,doesn't get much better than 400
mS/meter.So,if my calculations are right, even placing a 1 meter sphere
totally under ground would still give you a resistance of about 1 ohm per
meter (distance between the two ground points that are involved in the
return path,assuming the other point was also a 1 meter sphere). So, if you
were,say, 1km from your substation,GND would give you 1 1kohm resistance,
still pretty high! Even if GND were as close as the nearest power
pole,we're still talking tens of ohms.

Sean


|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
.....shb7KILLspamspam@spam@cornell.edu ICQ #: 3329174

1999\09\20@005119 by Dennis Plunkett

flavicon
face
At 23:21 19/09/99 -0400, you wrote:
{Quote hidden}

If you look at the ground stake you will find that the resistnace created
is hemispherical is shape, thus a 6" stake provides you with a reference
point that is 6" deep and 12" in diameter. Conduction will vary appon
constuction of the surrounding area and other metalic objects in the
ground. You will find that taking an earth measurment, is actually like
taking a hemispherical sample.

The substation earth is very different in construction, you will find that
it will have a resistance of less than 0.01 ohms with respect to a remote
earth (Nominaly tested 100 meters away in more than one direction from the
source). You seem to be speaking of a reference earth, nominaly not ment to
carry current, just provide a dump point in case of a fault condition. The
single wire earth retun circuits are rare due to the climatic changes that
effect the earth point.

In the point of telephones it is different again. Anyone know why ring is
90VRMS? Well it is because of earth, the idea is that ring will always get
to the phone and provide an indication to the subscriber that a call is
emminent, even if the reistance is so high that off hook can not be detected.

Dennis

{Quote hidden}

1999\09\20@015130 by Sean H. Breheny

face picon face
Hi Dennis,

Thanks for the answer:

At 02:57 PM 9/20/99 +1000, you wrote:
>If you look at the ground stake you will find that the resistnace created
>is hemispherical is shape, thus a 6" stake provides you with a reference
>point that is 6" deep and 12" in diameter. Conduction will vary appon
>constuction of the surrounding area and other metalic objects in the
>ground. You will find that taking an earth measurment, is actually like
>taking a hemispherical sample.

I don't quite understand - How can resistance have shape? Do you mean that
is is equivalent to a 12 foot diameter conductive hemisphere? The way I did
my (rough) calculations was to assume that the ground path consisted of two
ground connections,which formed a lossy capacitor with the soil as the
(resistive) dielectric. By integrating the product of conductivity times E
field over a sphere surrounding one of the two ground points, I got the
total current that comes from it. The applied voltage divided by this
current gave me the resistance. I used a value of about 300 mS/meter for my
conductivity(I took this from a soil profile on a web page,it was the peak
conductivity value)

>
>The substation earth is very different in construction, you will find that
>it will have a resistance of less than 0.01 ohms with respect to a remote
>earth (Nominaly tested 100 meters away in more than one direction from the
>source). You seem to be speaking of a reference earth, nominaly not ment to
>carry current, just provide a dump point in case of a fault condition. The
>single wire earth retun circuits are rare due to the climatic changes that
>effect the earth point.

Are you saying that the resistance between ground points (rods or whatever
they are) is independent of the distance between them? If so, my concept of
the conductivity must be incorrect. In addition, it seems to me that the
resistance from ground point to ground point depends on the structure of
the grounds at BOTH locations. If one is a tiny rod,making the other huge
won't make all that much difference.

I was thinking of a typical 6' saftey grounding rod,yes. However, I think
my argument is still valid. The ground rod at my house is supposed to give
a good enough ground to trip a circuit breaker in the event that something
shorts to a grounded case,right? This would meant no higher than a 120/15 =
8 ohm total path resistance from it to the substation or other relevant
ground point.

>
>In the point of telephones it is different again. Anyone know why ring is
>90VRMS? Well it is because of earth, the idea is that ring will always get
>to the phone and provide an indication to the subscriber that a call is
>emminent, even if the reistance is so high that off hook can not be detected.

Yes,this makes a good deal of sense.

>
>Dennis
>

Sean

|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
.....shb7KILLspamspam.....cornell.edu ICQ #: 3329174

1999\09\20@162909 by Steve Thackery

flavicon
face
part 0 2599 bytes
> Are you saying that the resistance between ground points (rods or
> whatever
> they are) is independent of the distance between them? If so, my concept
> of
> the conductivity must be incorrect.

Strange though it may seem, it is almost true.  The biggest problem with a
buried earth is getting a high enough surface area in intimate contact
with the ground.  (Incidentally, the sphere is the worst possible shape
for this, of course).

Once you've got that sorted out, it is almost true to say that the
resistance between two such earths is independent of distance.  This is
because there are in infinite number of paths - electrically "in
parallel" - between the two points.  You need to think in 3D for this:
obviously there is a dead straight path between the two points, and it
will have a particular resistance.  But there are other paths "around"
this one, each increasingly more curved (and thus longer), spreading
further and further into the planet.  Theoretically, a tiny bit of your
current might flow via the earth's core on its way between the two earth
electrodes!

You will appreciate that all these paths are - in effect - resistors in
parallel, which greatly reduces the total resistance between the two
points.

> In addition, it seems to me that the
> resistance from ground point to ground point depends on the structure of
> the grounds at BOTH locations. If one is a tiny rod,making the other
huge
> won't make all that much difference.

Yes, that is basically true.  Just like a normal electric circuit, of
course.  If your current has to pass through a 100 ohm resistor and a 1
ohm resistor, most of the loss occurs in the 100 ohm resistor.  Reducing
the 1 ohm to half an ohm won't increase your current flow much at all.

By the way, there was a remarkable communications system used during WW1,
in which both the transmitter and receiver used two buried rods in the
ground, several feet apart.  The transmitter drove an alternating current
between its two buried rods, modulated with speech (I believe, or maybe it
was Morse tones).  The receiver could be a considerable distance away.
Its buried rods, being themselves several feet apart, "tapped" across one
of the infinite paths of resistance which the transmitter's current was
flowing through, and thus was able to detect a voltage drop across it.
Quite remarkable.  I've attached a simple diagram.

Steve

Steve Thackery
Suffolk, England.
Web Site: http://www.btinternet.com/~stevethack/



Attachment converted: wonderland:earth.gif (GIFf/JVWR) (0000C9B4)

1999\09\20@164331 by Cser Laszlo

flavicon
face
Hi,

I really laughed a lot, but thinking on a few questions came to my mind.

>Telephone used an earth ground for the return current.


How could this happen? Was one of the wires accidentally tied to the earth
ground?

>The earth ground was the usual metallic stake in the ground in the yard.
>The ground was normally dry.
>Her dog was chained to the ground post with a metal chain.
>When the phone range, it would complete the circuit to ground (90 volts or
>thereabouts ring voltage) via the dog


In the normal dry situation why did the circuit complete via the dog? Why
was the resistance between the dog's paw and the soil smaller than between
the stake and the soil?

Regards,

Laszlo Cser
EraseMEs7222csespam_OUTspamTakeThisOuTural2.hszk.bme.hu

Please answer in a private mail.

1999\09\20@173841 by Richard Prosser

flavicon
face
The positive side of the telephone supply is normally connected to a very
solid earth point.

Richard


{Quote hidden}

--------snip------

1999\09\20@192337 by paulb

flavicon
face
Cser Laszlo wrote:

>> Telephone used an earth ground for the return current.
> How could this happen?  Was one of the wires accidentally tied to the
> earth ground?

 This is a *very old* story.  You have to know that it was a rural
situation where "party lines" were used.  A party line has two (or
more!) subscribers on the one line!  One subscriber has bell connected
between one wire and ground, the other between the other wire and
ground, so there are in effect, two different bells.

 Party lines for more subscribers used "selective ring" (now available
for home businesses etc. - a resurgence!) where each was to respond to a
different ring sequence.

 "Duplex" circuits allowed a relay box at each of the 2 subscribers on
a party line to have privacy.  Not only did the bell return to ground,
but so did both line circuits in order to make the connection, after
which they looped normally.

 We had one of these when I was little, this was in Sydney, not rural.
You pressed a button on top of the phone to seize the line.  Boy, I *am*
old!

> In the normal dry situation why did the circuit complete via the dog?
> Why was the resistance between the dog's paw and the soil smaller than
> between the stake and the soil?

 Because the stake was next to the house, shaded from the rain!  (What
rain?)

> Please answer in a private mail.

 You're kidding!

 Sean has already been reminded to think in 3D resistance instead of
1D, so that's well covered.
--
 Cheers,
       Paul B.

1999\09\20@224047 by Dennis Plunkett

flavicon
face
At 09:21 21/09/99 +1000, you wrote:
>Cser Laszlo wrote:
>
>>> Telephone used an earth ground for the return current.
>> How could this happen?  Was one of the wires accidentally tied to the
>> earth ground?
>

Paul B wrote:
{Quote hidden}

This is what is known as a ground start circuit, often used in simple PABX
systems. I can take this one step furhter back in time to the original
requirement of an earth return.

Back when the volcanos where erupting and Tomas had just invented the
telephoneectic device wire was not common. Telephone companies in order to
save costs (Expensive to put in poles) for a single country subscriber
often used the top strand of the fence to provide the telephone connection
(Phone conversations did get a bit nasty after some rain), and to save a
bit more money and time only a single line was used and an earth return was
employed.

The loop to ground indicates that Paul was connected to a manual exchage
where a wink would be recevied, so Duplexor and privacy? Not when Mavius
was on the switch. Also this box isloated only the subscribers on the party
line from each other, not from the remote connection, are,the first
subscriber from the exchange was always in control of the call. Didn't work
too well when relationships where streched! <G>


Dennis

P.S.
Party lines are still in use today, and can still be found (Although most
have been replaced because of winging neibours and flying bricks (That's
another story))



{Quote hidden}

1999\09\21@005924 by paulb

flavicon
face
Dennis Plunkett wrote:

> The loop to ground indicates that Paul was connected to a manual
> exchage where a wink would be recevied, so Duplexor and privacy?

 Nope, gotcha there!  It was an automatic exchange.  There were
actually two types of relay set (called "Relay set, Duplex, type...") of
which one required the pushbutton and one did not.  I know, because
years later I studied (and IIRC, photocopied) the manuals for them in
the Tech library.

 The wiring in the exchange was dead easy, just two normal subscriber
line sets with some connections wired funny.  Each connected the loop
(was it "L") relay to one of the line wires, when this relay pulled in,
both line wires went through that particular set and the other was
busied.

 Absolutely nothing to do with manual exchanges.
--
 Cheers,
       Paul B.

1999\09\21@011008 by Graeme Smith

flavicon
face
GRAEME SMITH                         email: KILLspamgrysmithKILLspamspamfreenet.edmonton.ab.ca
YMCA Edmonton

Address has changed with little warning!
(I moved across the hall! :) )

Email will remain constant... at least for now.


On Sun, 19 Sep 1999, Sean H. Breheny wrote:

{Quote hidden}

Most grounds today, are taken, (at least in Canada) from the copper Water
pipes that feed the hotwater heater.

This creates a massive ground plane, in that the pipe, the water, and any
soil that comes in contact with the pipe, become the ground mass.

The, I think they recommend 30 ft long copper bar, used for grounding, is
only a second best bet. I think the idea here, is to burry the end so
deep, that it gets imersed in the ground water, which increases the ground
mass significantly. Remember the only reason for a ground to exist at all,
is to have a reference voltage against which to measure other voltages.
When we talk about the ground or earth connection we are really talking
about a connection to a source that is normalized to the ground, and
therefore has a voltage of 0 volts with respect to ground.

We use this for safety, under the mistaken assumption that any connection
that has a 0 volt value with respect to ground, will also have zero
current unless connected to a larger voltage differential source. This of
course begs the question of whether a 0 volt with respect to ground value,
at one end of a long wire is the same as a 0 volt with respect to ground
value at the other end of the wire. (Which is one reason why we use signal
grounds, that are not the same as chassis grounds.)

Anyway, the primary way that a GROUND or EARTH connection works, is to
provide as low as possible resistance to ambient voltage with respect to
the earth surface at the point of measurement. Whether we do this by
hooking up to a common water pipe, or by sinking a long copper connector
into the ground, doesn't really matter, except for the voltage
differential that MIGHT exist between the real ground, and the wire
because of the resistance.

                               GREY

1999\09\21@183131 by Dennis Plunkett

flavicon
face
At 14:49 21/09/99 +1000, you wrote:
{Quote hidden}

AH! You are not as old as I thought!

Next thing you know, you will be telling us about the K and L relay sets,
uniselectors, first selectors and goup selectors. Slug relays and magnetic
concerntating yokes, then he will go off into why it is called tip and ring
and wink systems!

Dennis

1999\09\21@191154 by paulb

flavicon
face
Dennis Plunkett wrote:

> AH! You are not as old as I thought!

 No, I'm not *that* old.

> Next thing you know, you will be telling us about the K and L relay
> sets, uniselectors, first selectors and goup selectors.  Slug relays
> and magnetic concerntating yokes,

 You mean the "3N" yokes?

> then he will go off into why it is called tip and ring and wink
> systems!

 <Sigh>  Ah, </Sigh> *that* was logic circuitry, that was....
--
 Cheers,
       Paul B.

1999\09\22@204030 by Russell McMahon

picon face
Oi!!!
What about line finders and their ilk , rotary exchanges - motor driven with
electromagnetic clutches from a row motor with shafts feeding mechanical
power to the 'switches".
An oil can a needed accessory. I have a few sample switches in my "museum"
collection. Still running here into the 1970's AFAIR. Some of first
shipments of parts from Britain were sunk by U-Boat and had to be re-sent
:-)

I oversaw cut-over of one small exchange long long long ago that still used
a drop shutter manual board.




RM


_______________________________________
What can one man do?  Help the hungry for free at
http://www.thehungersite.com/

>AH! You are not as old as I thought!
>
>Next thing you know, you will be telling us about the K and L relay sets,
>uniselectors, first selectors and goup selectors. Slug relays and magnetic
>concerntating yokes, then he will go off into why it is called tip and ring
>and wink systems!
>
>Dennis
>

1999\09\22@210853 by Dennis Plunkett

flavicon
face
At 23:54 22/09/99 +1200, you wrote:
>Oi!!!
>What about line finders and their ilk , rotary exchanges - motor driven with
>electromagnetic clutches from a row motor with shafts feeding mechanical
>power to the 'switches".
>An oil can a needed accessory. I have a few sample switches in my "museum"
>collection. Still running here into the 1970's AFAIR. Some of first
>shipments of parts from Britain were sunk by U-Boat and had to be re-sent
>:-)

Are you sure about that? 1906 vintage? Ah yes I forgot that New Zealand
didn't get electricity until the 40s <VBG>

Fisrt generation Strouger equipment eh, not bad (2nd generation was
electromechanical, and some what larger than Step X Step).
I have a list fo the subscribers connected to Austrailas first automatic
exchange in Gelong (Seems that the city people where not worthy <G>)
I also have a list of the first subscribers connected to the Post Master
Generals Melbourne exchage (All 100 odd)
Beleive it or not, but Telstra installed Step exchange equipment into the 80s!

<Simle>


Dennis

{Quote hidden}

1999\09\22@213624 by Dave VanHorn

flavicon
face
> An oil can a needed accessory. I have a few sample switches in my "museum"
> collection. Still running here into the 1970's AFAIR. Some of first
> shipments of parts from Britain were sunk by U-Boat and had to be re-sent
> :-)


I had a shipment of terminals shot down by russian fighters (Korean Air)
I went to that company from another, where my last act was to repair a
Strowger switch that had been sitting on the repair shelf longer than anyone
could remember.

More... (looser matching)
- Last day of these posts
- In 1999 , 2000 only
- Today
- New search...