Question on grounding rods
 

When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?

Question on grounding rods
 

On Sat, 07 Jul 2007 15:31:51 -0400, "Rick (W-A-one-R-K-T)"
wrote:


When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?


Hi Rick,

Ground is notable for having complex answers to simple questions. One
very good resource is:

UNITED STATES DEPARTMENT OF AGRICULTURE
Rural Electrification Administration
REA BULLETIN 1751F-802
SUBJECT: Electrical Protection Grounding Fundamentals

Another resource can be found in:

DEEP EARTH GROUNDING vs SHALLOW EARTH GROUNDING
by
Martin D. Conroy and Paul G. Richard
Computer Power Corporation
Omaha, Nebraska

Both can be found somewhere on the Web. The first is a PDF, the
second is a web page. I don't know specific locations, but the
details above should be suitable to Google.

73's
Richard Clark, KB7QHC

Question on grounding rods
 

"Rick (W-A-one-R-K-T)" wrote in message
.. .

When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?



yes. first there is the electrical safety code that you must comply with
which i believe generally calls for 8' rods. 4' rods may not be below the
frost line in the winter so may not provide any useful grounding for part of
the year. shallow buried wire has the same problem.

on rf issues, lots of shallow buried radials can help reduce ground loss
under certain antennas... but these are not substitutes for good electrical
safety grounds.

Question on grounding rods
 

Rick (W-A-one-R-K-T) wrote:

When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?



The easy answer is "it depends".

Where I live, it is virtually impossible to get an 8 foot ground rod in
vertically, without first having someone core-drill the site. Living on
a volcano has it's problems, and one of them certainly is grounding.

Solid rock with perhaps a few feet of earth on top makes for tough
grounding situations. Here, most electrical services are grounded to
something called a "ufer" ground, which is about 20 feet of #6 copper
inside the perimeter foundation and clamped to at least two 20 foot
lengths of rebar, all of which is embedded in the concrete.... external
ground rods (if any) are typically pounded onto the ground at an angle,
so they can follow the interface of the lava and earth. If the
individual is making any pretense of having a vertical rod, they'll bend
it vertical just before it sticks up out of the earth.

Even at 4000 feet elevation, it is rare to see frost on the ground more
than once every 3 to 5 years, so getting a ground below the "frost line"
is easy. When I lived near sea level, I built a workshop of 32' x 52'
and put about a thousand feet of bare copper wire underneath the slab in
a gridded configuration, with all long runs brought to a single point
where the ham shack was to be. It worked great as RF ground and was
tied to the ufer as well, so everything was at the same potential.

Here, multiple short rods would be used (and accepted by the electrical
inspector) for the sercvice entrance ground, if he hadn't already
inspected the ufer ground prior to the concrete pour. (I know someone
that put in the required ufer and poured the slab without getting the
electrical inspection, and had to do just that, add several vertical
rods, all tied together to satisfy the inspector). I've heard rumor
that new code is minimum of 2 each 8 foot rods, but people here aren't
on the newest code level by a long shot.

Best thing is to make sure what local code is first, then go for
overkill if you are at all thinking it isn't enough, especially if you
are putting in a tower and/or worried about lightning.

RF ground is a whole different matter than safety or lightning
grounding, as you are likely aware already.

Question on grounding rods
 

Dave wrote:
"Rick (W-A-one-R-K-T)" wrote in message
.. .

When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?




yes. first there is the electrical safety code that you must comply with
which i believe generally calls for 8' rods. 4' rods may not be below the
frost line in the winter so may not provide any useful grounding for part of
the year. shallow buried wire has the same problem.

on rf issues, lots of shallow buried radials can help reduce ground loss
under certain antennas... but these are not substitutes for good electrical
safety grounds.


The NEC allows a wide variety of electrical safety grounds (and,
interestingly, a ground rod is not usually allowed as the only grounding
electrode). The old standby of "cold water pipe" is specifically not
allowed any more (too many places with plastic pipe from street to house).

The preferred ground in most jurisdictions is a concrete encased
grounding electrode (aka a Ufer Ground, after the inventor's name Herb
Ufer).. 20 ft of appropriate conductor encased in concrete.

As far as rods go, you can dig a trench and lay it sideways and meet the
code requirement. 2 rods 4 feet long might meet code (if all of the rod
is buried and they are far enough apart).


However, in addition to any regulatory requirements, there's a
difference between a "good ground" for
a) electrical safety
b) RF
c) lightning

A grounding system that's good for one isn't necessarily good for the
others.


There's a good writeup on grounds, with particular attention to
antennas, cable TV, telephone, etc. at Mike Holt's website (He's a
electrical code guru that does seminars, etc.)

http://www.mikeholt.com/ is the site, look for the "low voltage
handbook", which is a free download and has all the relevant code
sections explained, with diagrams, etc.

Question on grounding rods
 

Isn't concrete an insulator??

"The preferred ground in most jurisdictions is a concrete encased grounding
electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. "

What am I missing here?

"Jim Lux" wrote in message
...
Dave wrote:
"Rick (W-A-one-R-K-T)" wrote in message
.. .

When electrically grounding one's station, is there any particular
advantage of a single 8-foot ground rod over two 4-foot ground rods, or
an
8-foot length of heavy gauge wire buried 6-12 inches under the ground?




yes. first there is the electrical safety code that you must comply with
which i believe generally calls for 8' rods. 4' rods may not be below
the frost line in the winter so may not provide any useful grounding for
part of the year. shallow buried wire has the same problem.

on rf issues, lots of shallow buried radials can help reduce ground loss
under certain antennas... but these are not substitutes for good
electrical safety grounds.
The NEC allows a wide variety of electrical safety grounds (and,
interestingly, a ground rod is not usually allowed as the only grounding
electrode). The old standby of "cold water pipe" is specifically not
allowed any more (too many places with plastic pipe from street to house).

The preferred ground in most jurisdictions is a concrete encased grounding
electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. 20 ft
of appropriate conductor encased in concrete.

As far as rods go, you can dig a trench and lay it sideways and meet the
code requirement. 2 rods 4 feet long might meet code (if all of the rod
is buried and they are far enough apart).


However, in addition to any regulatory requirements, there's a difference
between a "good ground" for
a) electrical safety
b) RF
c) lightning

A grounding system that's good for one isn't necessarily good for the
others.


There's a good writeup on grounds, with particular attention to antennas,
cable TV, telephone, etc. at Mike Holt's website (He's a electrical code
guru that does seminars, etc.)

http://www.mikeholt.com/ is the site, look for the "low voltage handbook",
which is a free download and has all the relevant code sections explained,
with diagrams, etc.

Question on grounding rods
 

John Doe wrote:

Isn't concrete an insulator??

"The preferred ground in most jurisdictions is a concrete encased grounding
electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. "

What am I missing here?

That while dry concrete is a pretty good insulator it is hard to
find such just about anywhere other than Southern Arizona.

--
Jim Pennino

Remove .spam.sux to reply.

Question on grounding rods
 

John Doe wrote:
Isn't concrete an insulator??

"The preferred ground in most jurisdictions is a concrete encased grounding
electrode (aka a Ufer Ground, after the inventor's name Herb Ufer).. "

What am I missing here?

Concrete is a conductor, and generally a better conductor than the soil
around it (it's hygroscopic), so rather than the sort of iffy contact
between the rod and soil, you have a much larger contact area between 20
feet of wire and concrete, and an even larger contact surface area
between the concrete and the soil. Run some numbers, and it turns out
that capacitive coupling from concrete to soil is probably lower
impedance than resistance.


There ARE high resistivity concretes (used for things like supporting
rails on electric trains), but that's unusual.

There's lots and lots of field tests, lab work, and theoretical analysis
to back up the consistent good performance of Ufer grounds.

Question on grounding rods
 

Question on grounding rods
 

"Jim Lux" wrote in message
...
wrote:
John Doe wrote:


Isn't concrete an insulator??


"The preferred ground in most jurisdictions is a concrete encased
grounding electrode (aka a Ufer Ground, after the inventor's name Herb
Ufer).. "


What am I missing here?


That while dry concrete is a pretty good insulator it is hard to
find such just about anywhere other than Southern Arizona.

And even there, the concrete is probably damper and a better conductor
than the surrounding soil. Ufer's original work was developing grounding
techniques for ammo bunkers in desert areas, since the ground rods didn't
work.



I, too, am amazed - I though concrete, whilst it would be damp on the
outside underground bit, would be
substantially dry after setting, and a good insulator, being essentially
sand.. I guess its porous or microporous..

Nick

Question on grounding rods
 

"Nick" wrote in message
...

"Jim Lux" wrote in message
...
wrote:
John Doe wrote:


Isn't concrete an insulator??


"The preferred ground in most jurisdictions is a concrete encased
grounding electrode (aka a Ufer Ground, after the inventor's name Herb
Ufer).. "


What am I missing here?


That while dry concrete is a pretty good insulator it is hard to
find such just about anywhere other than Southern Arizona.

And even there, the concrete is probably damper and a better conductor
than the surrounding soil. Ufer's original work was developing
grounding
techniques for ammo bunkers in desert areas, since the ground rods
didn't
work.



I, too, am amazed - I though concrete, whilst it would be damp on the
outside underground bit, would be
substantially dry after setting, and a good insulator, being essentially
sand.. I guess its porous or microporous..

Nick


Concrete never truly sets. The chemical reactions continue for centuries.
Concrete structures put up 2000 years ago by the Romans are still perfectly
useable today and under the surface remain chemically active. Many Roman
structures such as the Colosseum and aquaducts would not have been possible
without concrete. Some of the techniques developed then are still in use in
building today such as making the higher levels of a structure using
lighter, smaller aggregate.

Embedding steel or copper rods in concrete will pretty much guarantee that
the metalwork will remain in contact with moisture and conductive salts for
as long as the structure holds together. The constant exposure to moisture
and corrosive salts is the main reason for failure of modern ferro-concrete
structures. Concrete will suck up whatever moisture is around, either from
the air or the soil and is always damp inside, hence the steel rusting out
unless protected by heavy galvanisation and sacrificial electrodes.

Even in the worst environments, a couple of 8 foot copper rods embeded in
concrete should give a DC or low frequency AC resistance/impedance of less
than 200 ohms. Of course you could always use a dipole and balun. :-)

Mike G0ULI

Question on grounding rods
 

"Mike Kaliski" wrote in message
...

"Nick" wrote in message
...

"Jim Lux" wrote in message
...
wrote:
John Doe wrote:


Isn't concrete an insulator??


"The preferred ground in most jurisdictions is a concrete encased
grounding electrode (aka a Ufer Ground, after the inventor's name Herb
Ufer).. "


What am I missing here?


That while dry concrete is a pretty good insulator it is hard to
find such just about anywhere other than Southern Arizona.

And even there, the concrete is probably damper and a better conductor
than the surrounding soil. Ufer's original work was developing
grounding
techniques for ammo bunkers in desert areas, since the ground rods
didn't
work.



I, too, am amazed - I though concrete, whilst it would be damp on the
outside underground bit, would be
substantially dry after setting, and a good insulator, being essentially
sand.. I guess its porous or microporous..

Nick


Concrete never truly sets. The chemical reactions continue for centuries.
Concrete structures put up 2000 years ago by the Romans are still
perfectly
useable today and under the surface remain chemically active. Many Roman
structures such as the Colosseum and aquaducts would not have been
possible
without concrete. Some of the techniques developed then are still in use
in
building today such as making the higher levels of a structure using
lighter, smaller aggregate.

Embedding steel or copper rods in concrete will pretty much guarantee that
the metalwork will remain in contact with moisture and conductive salts
for
as long as the structure holds together. The constant exposure to moisture
and corrosive salts is the main reason for failure of modern
ferro-concrete
structures. Concrete will suck up whatever moisture is around, either from
the air or the soil and is always damp inside, hence the steel rusting out
unless protected by heavy galvanisation and sacrificial electrodes.

Even in the worst environments, a couple of 8 foot copper rods embeded in
concrete should give a DC or low frequency AC resistance/impedance of less
than 200 ohms. Of course you could always use a dipole and balun. :-)

Mike G0ULI

So then, what is the reason that they drive a separate ground rod in when
they install a commercial tower whose legs are in concrete?

Howard W3CQH

Question on grounding rods
 

Concrete never truly sets. The chemical reactions continue for centuries.
Concrete structures put up 2000 years ago by the Romans are still perfectly
useable today and under the surface remain chemically active. Many Roman
structures such as the Colosseum and aquaducts would not have been possible
without concrete. Some of the techniques developed then are still in use in
building today such as making the higher levels of a structure using
lighter, smaller aggregate.

Embedding steel or copper rods in concrete will pretty much guarantee that
the metalwork will remain in contact with moisture and conductive salts for
as long as the structure holds together. The constant exposure to moisture
and corrosive salts is the main reason for failure of modern ferro-concrete
structures. Concrete will suck up whatever moisture is around, either from
the air or the soil and is always damp inside, hence the steel rusting out
unless protected by heavy galvanisation and sacrificial electrodes.

Even in the worst environments, a couple of 8 foot copper rods embeded in
concrete should give a DC or low frequency AC resistance/impedance of less
than 200 ohms. Of course you could always use a dipole and balun. :-)

Mike G0ULI

Then there is the matter of whether to extend the rebar into the soil
or totally encapsulate in a concrete base for a tower...

And the matter of applying a protective coating of paint to the rebar
to minimize corrosion...

I have a couple of clothes line poles that are in pretty good
condition above and below the ground line but rusted completely
through at the ground line!

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

Question on grounding rods
 

Howard, W3CQH wrote:
"So then, what is the reason they drive a separate ground rod in when
they install a commercial tower whose legs are in concrete?"

Working with electricity you soon learn you need a rubber mat or rubber
soled shoes to protect against electric shock from the mains when you
are on bare concrete. It is often damp directly on the earth. When
poured as a slab, concrete is placed on plastic as a vapor barrier to
keep wood flooring from warping.

A tower base after years is not completely set but still contains
moisture and is still hardening.

Tower bases are bypassed by ground cables outside the concrete block so
that the moisture inside does not turn to steam during a lightning
strike and blow the concrete asunder.

Best regards, Richard Harrison, KB5WZI

Question on grounding rods
 

John Doe wrote:


So then, what is the reason that they drive a separate ground rod in when
they install a commercial tower whose legs are in concrete?

Howard W3CQH



Tradition?
Maybe it's easier to just drive the rod and hook it up than to explain
the subtleties of grounding to the inspector?
The contractor owns stock in a ground rod manufacturing company?

Question on grounding rods
 

John Ferrell wrote:

Concrete never truly sets. The chemical reactions continue for centuries.
Concrete structures put up 2000 years ago by the Romans are still perfectly
useable today and under the surface remain chemically active. Many Roman
structures such as the Colosseum and aquaducts would not have been possible
without concrete. Some of the techniques developed then are still in use in
building today such as making the higher levels of a structure using
lighter, smaller aggregate.

Embedding steel or copper rods in concrete will pretty much guarantee that
the metalwork will remain in contact with moisture and conductive salts for
as long as the structure holds together. The constant exposure to moisture
and corrosive salts is the main reason for failure of modern ferro-concrete
structures. Concrete will suck up whatever moisture is around, either from
the air or the soil and is always damp inside, hence the steel rusting out
unless protected by heavy galvanisation and sacrificial electrodes.

Even in the worst environments, a couple of 8 foot copper rods embeded in
concrete should give a DC or low frequency AC resistance/impedance of less
than 200 ohms. Of course you could always use a dipole and balun. :-)

Mike G0ULI


Then there is the matter of whether to extend the rebar into the soil
or totally encapsulate in a concrete base for a tower...
Never have the rebar extend into the soil..

The rebar should always be entirely contained within the concrete.

If it's not, it provides a path for water to creep in between the rebar
and concrete, leading to corrosion of the rebar, spalling, etc.

Question on grounding rods
 

In article ,
"John Doe" wrote:



So then, what is the reason that they drive a separate ground rod in when
they install a commercial tower whose legs are in concrete?

Howard W3CQH



There is a GIANT difference between RF Grounding and Lightning
Protection. Don't even think of confussing the two....

Question on grounding rods
 

You wrote:

There is a GIANT difference between RF Grounding and Lightning
Protection. Don't even think of confussing the two....

And there's a third reason and set of requirements for grounding which
is different from both of those -- AC safety ground. Its requirements
are dictated by the NEC and local electrical codes, and it shouldn't be
confused with either of the other two.

Roy Lewallen, W7EL

Question on grounding rods
 

"John Doe" wrote in message
. ..

"Mike Kaliski" wrote in message
...

"Nick" wrote in message
...

"Jim Lux" wrote in message
...
wrote:
John Doe wrote:


Isn't concrete an insulator??


"The preferred ground in most jurisdictions is a concrete encased
grounding electrode (aka a Ufer Ground, after the inventor's name
Herb
Ufer).. "


What am I missing here?


That while dry concrete is a pretty good insulator it is hard to
find such just about anywhere other than Southern Arizona.

And even there, the concrete is probably damper and a better
conductor
than the surrounding soil. Ufer's original work was developing
grounding
techniques for ammo bunkers in desert areas, since the ground rods
didn't
work.



I, too, am amazed - I though concrete, whilst it would be damp on the
outside underground bit, would be
substantially dry after setting, and a good insulator, being
essentially
sand.. I guess its porous or microporous..

Nick


Concrete never truly sets. The chemical reactions continue for
centuries.
Concrete structures put up 2000 years ago by the Romans are still
perfectly
useable today and under the surface remain chemically active. Many Roman
structures such as the Colosseum and aquaducts would not have been
possible
without concrete. Some of the techniques developed then are still in use
in
building today such as making the higher levels of a structure using
lighter, smaller aggregate.

Embedding steel or copper rods in concrete will pretty much guarantee
that
the metalwork will remain in contact with moisture and conductive salts
for
as long as the structure holds together. The constant exposure to
moisture
and corrosive salts is the main reason for failure of modern
ferro-concrete
structures. Concrete will suck up whatever moisture is around, either
from
the air or the soil and is always damp inside, hence the steel rusting
out
unless protected by heavy galvanisation and sacrificial electrodes.

Even in the worst environments, a couple of 8 foot copper rods embeded
in
concrete should give a DC or low frequency AC resistance/impedance of
less
than 200 ohms. Of course you could always use a dipole and balun. :-)

Mike G0ULI

So then, what is the reason that they drive a separate ground rod in when
they install a commercial tower whose legs are in concrete?

Howard W3CQH


Howard

It is necessary to provide a consistent earthing connection. The tower may
develop galvanic resistance at joints due to corrosion, or sections of the
tower may be insulated to prevent parasitic resonances at certain
frequencies, or any one of a hundred other 'faults'. With a single earthing
point, it is easier to monitor any deterioration in the system and achieve
specific design criteria with a known resistance which is unlikely to change
a great deal.

Mike G0ULI

Question on grounding rods
 

On Wed, 11 Jul 2007 11:35:11 -0700, Roy Lewallen wrote:


And there's a third reason and set of requirements for grounding which
is different from both of those -- AC safety ground. Its requirements
are dictated by the NEC and local electrical codes, and it shouldn't be
confused with either of the other two.

Is there such a thing as a ground that is good for both AC safety ground
and lightning protection ... or, both of those plus RF ground?

Question on grounding rods
 

Rick (W-A-one-R-K-T) wrote:
On Wed, 11 Jul 2007 11:35:11 -0700, Roy Lewallen wrote:


And there's a third reason and set of requirements for grounding which
is different from both of those -- AC safety ground. Its requirements
are dictated by the NEC and local electrical codes, and it shouldn't be
confused with either of the other two.

Is there such a thing as a ground that is good for both AC safety ground
and lightning protection ... or, both of those plus RF ground?

Sure. One way to do it is to make a proper AC safety ground, a good
lightning ground, and an effective RF ground, then bond them all
together (provided it's permitted by code).

Roy Lewallen, W7EL

Question on grounding rods
 

Roy Lewallen wrote in
:

Rick (W-A-one-R-K-T) wrote:
On Wed, 11 Jul 2007 11:35:11 -0700, Roy Lewallen wrote:


And there's a third reason and set of requirements for grounding
which is different from both of those -- AC safety ground. Its
requirements are dictated by the NEC and local electrical codes, and
it shouldn't be confused with either of the other two.

Is there such a thing as a ground that is good for both AC safety
ground and lightning protection ... or, both of those plus RF ground?

Sure. One way to do it is to make a proper AC safety ground, a good
lightning ground, and an effective RF ground, then bond them all
together (provided it's permitted by code).

Roy,

Isn't equipotential bonding part of making three independent earth
systems work compatibly with each other, to be a single system that is
effective for each of the purposes?

Owen

Roy Lewallen, W7EL

Question on grounding rods
 

"Owen Duffy" wrote in message
...
Roy Lewallen wrote in
:

Rick (W-A-one-R-K-T) wrote:
On Wed, 11 Jul 2007 11:35:11 -0700, Roy Lewallen wrote:


And there's a third reason and set of requirements for grounding
which is different from both of those -- AC safety ground. Its
requirements are dictated by the NEC and local electrical codes, and
it shouldn't be confused with either of the other two.

Is there such a thing as a ground that is good for both AC safety
ground and lightning protection ... or, both of those plus RF ground?

Sure. One way to do it is to make a proper AC safety ground, a good
lightning ground, and an effective RF ground, then bond them all
together (provided it's permitted by code).

Roy,

Isn't equipotential bonding part of making three independent earth
systems work compatibly with each other, to be a single system that is
effective for each of the purposes?

Owen

Roy Lewallen, W7EL


Owen

Equipotential bonding is the process whereby all exposed conductive parts
are connected together so that they are all at the same (usually earth)
potential. Cross connecting three independent earthing systems could well be
used to ensure that a system as a whole was properly grounded for power,
lightning and RF. However, you have to bear in mind that for some power
purposes, a high ohmic value is required in the earth circuit to prevent
lethal current flowing in event of a fault. Under these circumstances it
would be wrong to cross connect all the earths together. It is important to
study the design criteria for the power circuits and protection devices
before making any changes to an existing installation.

Mike G0ULI

Question on grounding rods
 

"Mike Kaliski" wrote in
:

Owen

Equipotential bonding is the process whereby all exposed conductive
parts are connected together so that they are all at the same (usually
earth) potential. Cross connecting three independent earthing systems

The problem is that in the event of a lightning strike, nothing is at earth
potential!

Owen

Question on grounding rods
 

"Owen Duffy" wrote in message
...
"Mike Kaliski" wrote in
:

Owen

Equipotential bonding is the process whereby all exposed conductive
parts are connected together so that they are all at the same (usually
earth) potential. Cross connecting three independent earthing systems

The problem is that in the event of a lightning strike, nothing is at
earth
potential!

Owen

and a corrolary of this: there is no such thing as an 'rf ground'.

Question on grounding rods
 

On Fri, 13 Jul 2007 11:03:23 GMT, "Dave" wrote:

The problem is that in the event of a lightning strike, nothing is at
earth
potential!

and a corrolary of this: there is no such thing as an 'rf ground'.

Two of the oddest statements (barring Gaussian arrays) that have ever
come down the pike.

1. WHAT problem?
2. no such THING?

1. Where are you standing where there is no earth potential in
relation to lightning's potential? Ground may elevate locally in
potential due to current and resistance at the strike point, but if
you are standing there (sans obvious catastrophic effects); your
potential rises in like manner and the sense of ground is preserved.
This is the entire point of a grounding system of equipotential
connections.

2. RF ground is deliberately constructed by the same motivations, at
a higher frequency. Given that lightning's RF pulse consists of a
prominant 1 µS event, its RF content is very similar to one of
thousands of AM systems that have grounds designed to exhibit a very
low loss. Excluding the catastrophic event, RF ground systems are
designed for other frequencies conforming to the identical
motivations.

73's
Richard Clark, KB7QHC

Question on grounding rods
 

Dave wrote:
"and a corrolary of this (----in the event of a lightning strike,
nothing is at earth potential):
there is no such thing as an "rf ground"."

I`ve worked at a number of broadcast stations, none of which suffered an
iota of lightning damage, though often removed from the air
automatically for an instant by a lightning instigated overload. I`m
convinced the (120) radials around each tower in their antenna arrays
diverted lightning strikes to earth and the strike energy never entered
the transmitter building.

Brown, Lewis, and Epstein showed that earth radials can lower the
resistance of the RF ground connection to the vanishing point (lower
than the earth`s resistance in many cases, think parallel paths).
Resistance is low for lower frequencies and DC too. Skin effect goes
down with frequency and resonance in radials is eliminated by ground
loss.

Best regards, Richard Harrison, KB5WZI

Question on grounding rods
 

"Richard Harrison" wrote in message
...
Dave wrote:
"and a corrolary of this (----in the event of a lightning strike,
nothing is at earth potential):
there is no such thing as an "rf ground"."

I`ve worked at a number of broadcast stations, none of which suffered an
iota of lightning damage, though often removed from the air
automatically for an instant by a lightning instigated overload. I`m
convinced the (120) radials around each tower in their antenna arrays
diverted lightning strikes to earth and the strike energy never entered
the transmitter building.

Brown, Lewis, and Epstein showed that earth radials can lower the
resistance of the RF ground connection to the vanishing point (lower
than the earth`s resistance in many cases, think parallel paths).
Resistance is low for lower frequencies and DC too. Skin effect goes
down with frequency and resonance in radials is eliminated by ground
loss.

Best regards, Richard Harrison, KB5WZI

when everything is properly bonded together the voltage of all the pieces
stays the same... everything may be 10's or 100's of kv above the infinitely
distant ground, but if they are all within a few volts of each other then
you'll never know it. where people get into trouble is they don't provide
for equalizing the local 'ground' voltage with the connections to the
outside world... i.e. you have to have a method to equalize those 10's of
kv's between ground and the power and phone lines coming into your house.
if you don't provide a low impedance path then your equipment will make one
for you, usually by releasing the blue smoke.