On Thu, 09 Oct 2003 10:54:39 GMT, indago Gave
With the relatively short distance between a dog's paws, I hardly
think he'd notice any difference at all. Especially as the ground
became more and more conductive.
First of all, the technique you use for measuring the ground electrode
resistance is critical. This is because what you are measuring is the
effective resistance between the electrode under test and a theoretical
zero resistance earth reference at some distance from the electrode.
Reference electrode(s) installed at some distance (usually more than 100
feet, depending on local regulations )from the one under test are
Even if you position the reference electrode properly, an ohm meter may
give an erroneous reading because it uses too low a test current. Part
of the path under test is the contact between the ground electrode and
the soil. The interaction at this interface is rather complex, involving
some electrochemistry and as a result, may exhibit non-linear behavior
with respect to the current flow. A proper measurement method should
specify a minimum test current as well as the test electrode setup.
BEM=electrician? Never heard of it.
Why would an engineer have tools?
An IBEW wireman would never carry anothers tools.
But back too the point, is the only method of increasing a ground
fields conductivity achieved by pissing on it? Come on guys someone
knows the answer. I'll post the answer tomorrow if no one does.
Remove RATSandSCABS to reply
Impeach George Bush.
An ohmmeter of the normal type (i.e. a Fluke) is absolutely useless for
measuring grounding resistance.
There is a strong voltage related non-linearity as the low voltage of an
ohmmeter is simply not enough to break down contact resistance between the
rod and the soil or between soil particles. There has to be sufficient
potential applied to get an appreciable current flowing several ampers at
least. There are specific techniques used to measure ground resistance - the
recommended one is to pass current between a remote rod and the rod under
test and measure the voltage with respect to the rod under test at points in
between using a third rod as a probe. The voltage will reach a plateau
somewhere and this voltage and the current may be used to determine the
resistance (if no plateau then the remote rod is too close).
There are also special "meggers" designed for ground resistance
measurements. However with the above technique these are not needed.
remove the urine to answer
It's not often that I agree with you but you are absolutely right regarding
the higher voltage than that of a DVM.
By reading voltage on a shunt resistor - are you implying use of a third rod
as a probe?. If so - fine -otherwise, please clarify.
remove the urine to answer
The ONLY way too perform this operations is too measure the
conductivity! This is measured in siemens. The fluke multi megger
xj596 ought too do you the trick. Good luck and be careful.
Remove RATSandSCABS to reply
Impeach George Bush.
Standard techniques I'm familiar with are;
On new installations - increase the square surface area of the grounding
electrode material in contact with the earth, concrete encase the grounding
electrodes to increase the surface area in contact with the soil, Ufer
grounds in the bottom of concrete foundations, etc.
To increase conductivity of existing ground fields;
The addition of conductive, or moisture retentive minerals (bentonite is
one commonly used) to the sub-soil around the grounding electrode system,
grade the soil surface to provide natural pooling of surface water over the
ground field, or till and garden (flowers or otherwise) in the soil above
the ground field.
One of the most clever solutions to the problem of poor performing ground
fields, in a very dry, rocky, climate known for problematic ground
resistance, was the installation of large copper conductors buried in the
soil below septic drainfield trenches before the rock was added (moisture
frequently replenished :-] ).
Remove the two fish in Address to reply
On Fri, 10 Oct 2003 02:13:41 GMT, "Don Kelly" Gave
A DC power supply that is well regulated, and a DVM, and a 0.1 ohm
resistor. Pass a known voltage between two separated rods with the
resistor in series with the circuit. Read amperage across the
resistor in milliamps per millivolt. Calculate resistance of the
remaining segment of the circuit (the earth in question) with ohm's
law using the amperage reading and known input voltage in the
Subtract for the minuscule resistor drop if you really think it is
important. Don't forget to detach the system lead from the main
ground rod, if possible.
I'll add to that. Using DC current can give inaccurate readings due to the
chemical interaction that you referred to. Also, there are stray AC currents
in the test path. Earth resistance testers use AC current at a non-harmonic
frequency and filter out the unwanted currents.
The measurements are made with a kelvin setup, and proper placement of the
potential electrode is critical. A two-wire measurement with any type of
instrument is just not going to give the correct result.
Thank you. You are substituting a resistor and DVM for an ammeter, nothing
more. No problem there.
The problem is that you are measuring the effective series resistance
between the particular rods and cannot separate out the resistance to
ground of either rod. What is wanted is the resistance to "true ground" for
the rod under test.
One way to make this work is to use 3 well separated rods and measure the
resistance between pairs of rods, then use a delta-wye transformation to
determine the resistance to the "star point" which is assumed to be true
Another way is to measure current in a 2 rod system and measure the voltage
from the rod being tested and a third rod. move the third rod to various
points in between and determine where the rate of change of voltage is 0 or
near 0. (i.e. end effects at the rods are eliminated) This voltage and
the current will give the resistance to "true ground" and the method is, as
far as I recall, the method recommended in IEEE.
remove the urine to answer
Right on. In addition, the current distribution in the ground for AC (even
at 60Hz) is generally different from that for DC.
remove the urine to answer
Is that right? Could you please tell me how to measure antenna
impedance with an ohm meter? Reactance?
If you think that you can measure ground conductivity with a regular ohm
meter, you are far more deluded than I thought.
Why don't you offer up some kind of proof of this? Given your 40 years
in farming, pyro, physics, electrical engineering, and computers, when
did you have time? Hope I didn't leave out any of your "careers".
Oops, that's right, you're a hydrogen fusion expert too. Sorry, I
almost forgot about that.
Well they did Harry, now what have you to say? Oh that's right, nothing
as usual. Hit and run Harry strikes again. BTW, are you still telling
people to shut their computers down with the power switch, instead of
that proper shutdown "nonsense" that everyone else in the industry
On Sat, 11 Oct 2003 04:50:58 GMT, "Don Kelly" Gave
Yes, it allows one to determine any gradation in conductivity in the
top 8 feet of a large 3-d space. A wad of earth. hehe
You are correct. 100% Ufer slabs read pretty low back east.
Out here, in the dessert, pretty dry base.
Evidently you missed the fact that the question concerned ground
resistance, not impedance.
I'll assume that you grasp the distinction, between resistance,
impedance, and rectance. If not, I'll be happy to explain it to you.
Anthony, you can easily demonstrate that the ground resistance is
below some limiting value with an ohm meter, since electrode potential
and other electrolytic effects will act to drive the ohm measurement
to a higher than actual value. Also, since most VOMs have current
measuring capability, galvanic action, if present, is easily detected.
How. Want me to describe the installion and certification used in the
installation of ground systems for the a.m. radio station vertical
towers that I have installed? (Hint: These typically employ 120
quarter wave radials made of bare #12 or #10 wire radiating outward
over 360 degrees from the base of the tower. You certify their ground
resistance using an ohm meter, follow by masurment of their ground
impedance by typically employing a General Radio Model 916A r.f.
impedance bridge excited at the design frequency.)
Since you probably are unfamiliar with things like this, you may want
to read Edmund A. Laport's book: "Radio Antenna Engineering" published
some years ago by McGraw-Hill. It cover the constuction and
certification of grounding systems in detail.
Your no doubt equally unfamiliar with the class r.f. bridges. This
citation may help you familiarize yourself with these instruments, and
notably the General Radio 916A which for many year was a standard of
the industry before the "no operator skill required" computer based
bridges hit the market.
Well, even some of us poor, dumb, New Jersey farm kids are pretty
quick reads and learn fast. I earned by FCC First Class Radio
Operators license while in highschool (my ham ticket when I was 12 or
13), and had earned a B.S. in physics and an M.S. in electrical
engineering by 24. I worked as the chief engineer of WBUD (Trenton,
NJ), and as a staff engineer at WCAU and WFIL in Philadelphia which
paid for my professonal education.
What I had no time for was drinking, parties, sports, and chasing
You missed the fact the from 1972 to 1980 I worked as manager of
system engineering at General Railway Signal Company in Rochester, NY
where I managed the development and installation of the control
systems for both the Washington Metro and Atlanta transit systems
(WMATA and MARTA) while raising 3 children, but still managed to shoot
professional fireworks displays for relaxation and recreation.
Hardly an expert, but I did manage to earn a few bucks (and learn a
few things) as a COOP student working on the constructon of both the
Particle Accelerator and Stellerator project at Princeton's Forrestal
Not much, other than the fact is simply that likely less than 0.01% of
the existing ground systems have had such certification, nor in most
venues are they required to. The responders made some very good
points, but for the most part largely academic. Had you some actual
experience, you should realize that most ground systems are just one
or more copper rods coupled togeter and driven in the ground to the
point where they strike ledge and can't be driven any further.
Sometimes a superficial test will be conducted, but more often than
not the electrician or lineman driving the ground will declare that
based on his experience, "that's good enough for government work."
This is reality!
Anthony, now that you have shot your wad and I have responded, how
about telling newsgroup readers a bit about yourself, including both
your credentials, years of experience, and accomplishments that you
can at least take partial credit for?
My guess is that from the content of your posts, you earn your living
as a 3rd shift computer operator at some networking firm or ISP, you
lack a professional education and have no degrees in engineering or
science, and more than likely have only a limited level of expertise
in either programming or the design of computers (or for that matter
anything electronic), and you probably consider yourself to be some
sort of an expert hacker. On top of that, you have a serious
psychological problem with anyone who has achieved or accomplished
more than yourself, and have a difficult time dealing with it.
Prove me wrong. Tell the group about yourself.
It does quite a bit better than this as the voltage probe is carrying
negligable current The process looks for the "0" equipotential surface just
as one could probe the field between two charges
No more of a problem than in parts of Quebec where the lakes are more
conductive than the granite which is barely below the surface. Hence a power
station ground was made of a grid which was tossed into the forebay and
T-lines had continuous counterpoises as well as overhead ground wires.
remove the urine to answer -
Not at all. I was referring to your open ended statement about "25 Ohms
is 25 Ohms on any resistance measuring unit".
Perhaps not so well as thou, but I've tinkered.
I would accept that you could measure it with a large enough voltage
source and a current indicator, but not with "any" or even most VOM's.
If you're talking about a full fledged AM broadcast antenna, that wire
probably wouldn't last a year in the soil. You must be referring to
amateur radio type antennas for HF.
I've tuned a "few" antennas in my life Harry.
What a life.
I supose that's true if you include all residential ground rods, and I
do mean all.
This is precisely the kind of thing you said to me the first time we
conversed. I suspect that's why I hold you in such high esteem.
Never said that I did. But then I wasn't telling the OP how to
incorrectly check his grounding either. I find that if you don't know
the NEC inside out, it's probably not safe to be guessing about things
like power and grounding around here.
Oh I have a couple years worth of experience with computers and
electronics. ;-) Epert hacker though, that's pretty good Harry. I've
hacked a few things I guess, you must have done your homework before
Oh you've definitely got me pegged Harry, I didn't know that you were a
physchologist as well.
I doubt the group cares to hear me brag, it seems that few people here
do that. Besides, I could hardly put on a performance like you. You
already know my credentials as we've been thru this before when you were
bantering about something that you effectively know nothing of any
significant detail about. Let's see you pull something out of Google
demonstrating me espousing a false set of credentials.
On 11 Oct 2003 14:02:58 -0700, firstname.lastname@example.org (Harry Conover) Gave
"drive"??? Hahahhaahah... A higher value resistor passes LESS.
The simple fact is that it is not a straight line on the graph and
the current characteristics for the ground at the test potential a DVM
makes is not going to match what a 60 volt loop or 120 volt loop would
exhibit under observation. Ergo; you would get a non-calibrated