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.