"Rick (W-A-one-R-K-T)" wrote in
news
On Sun, 15 Jul 2007 17:23:13 +0000, Walter Maxwell wrote:

This topic has aroused my curiosity. As a grounding device, why would a
solid rod be better than a hollow pipe, except for the current carrying
capability?

Good afternoon, Walt.

The thing is, the current carrying capability for transient events like
lightning strikes should be about the same for the same diameter pipe or
rod, since most of the current is carried in skin effect anyway.

I think that is flawed thinking.

A lighning down conductor needs to carry something like 20kA for 100ms, so
it needs to be substantial enough that it doesn't melt and remains in place
to protect against the next strike.

Owen

I doubt that there would be any real difference to start with. The pipes
are thin enough they would be hard to drive in the ground and after a while
they would rust out sooner.
==================================================
Copper ....rusting ? ........... must be veeeery acidic soil
.....perhaps in the backyard of a chemical plant ?


Frank GM0CSZ / KN6WH

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

How about a 10-foot length of copper water pipe, connected to a garden
hose with an adapter fitting (as simple as a short length of another
garden hose, clamped to the pipe with radiator hose clamps). Run water
down the pipe and stick the pipe in the ground, pulling it up and pushing
it down so that the water helps drill the hole in a manner just like you
described. Keep it up until it has gone in as far as it will go, then (if
it hasn't gone in the whole 10 feet) cut it off and solder a copper cap on
the end.

You end up with a hollow pipe in the ground instead of a solid steel rod,
but everything I read about lightning strikes says that the vast majority
of the current flows in skin effect anyway.


Copper clad steel rods are made precisely because the copper cladding on the
outside skin is what conducts the current anyhow. So it makes no difference
whether you utilize copper pipe or copper clad steek rods. To drive copper
pipe down I use a length of about 1 foot of aluminum tubing connected to a
garden hose (tubing fits in garden hose and is clamped tightly, Aluminum
tubing slides into copper pipe. The rubber hose goes up against the copper
tubing rather tightly to make a quasi seal, it'll be enough although some
little bit of spray from backpressure will come out. Turn on the faucet and
the copper pipe will very quickly begin to drive itself into the ground.
Enough slurried wet soil mix will compact around the pipe to make a good
earth ground contact but I usually let the hose saturate the ground area
around it for about a half hour after so the voids fill in.

Bill KC9CS
http://home1.gte.net/res0958z/

On Jul 15, 1:47 pm, Owen Duffy wrote:


I think that is flawed thinking.

Dunno.. Not if the ground connection itself is good enough..

A lighning down conductor needs to carry something like 20kA for 100ms, so
it needs to be substantial enough that it doesn't melt and remains in place
to protect against the next strike.

A #10 wire can handle that job if the ground connection is up to par.
Course, most real down conductor will be flat copper strap.
The rod or tube in the ground is not the down conductor per say,
although I guess you could consider it the end of it..
As far as DC contact with earth, it's possible the tubing could be
slightly better, as it's got surface both on the outside, and the
inside..
But I imagine RF flowing along tubing would mostly flow on the
outside,
rather than inside. But maybe a bit of both.. Not sure..
Copper tubing itself can easily handle any lightning strike. Way
overkill actually. If you had a well grounded copper tube lightning
rod, and it was struck, all you would see on the tip would be a tiny
arc spot, which might even be unnoticable unless you were looking
for it. Even a lowly #10 wire will barely raise temp when struck as
long as the connection to ground is real good. Of course, if it isn't,
it may well vaporize into blobs of metal..
MK

If you already have the copper pipe and you can get it in the ground I
doubt you will ever notice the difference.

I live on red clay in the Piedmont region of North Carolina. There are
times when I could push three feet of #3 rebar in the ground with one
hand. At this time of year I doubt I could drive it more than about 6
inches!

Two years ago I had a pro install lightning rods. They added two
galvanized 1/2 inch ground rods at diagonal corners of the house. They
then tied one of these to the power ground. They also tied one corner
to my tower with a massive clamp. A whole house surge protector was
installed at the power panel. I have since added a vertical antenna
(28 feet) with 35 radials 70 feet long.

I have not had a lightning strike since they did the install. I think
the charge bleeds off before it builds up to a serious level.

Before the install I was averaging about $500 a year in VCRs, TV sets,
Stereos, etc. The best advice I can offer is to use conventional
materials available in your area, meet code and keep your insurance
company satisfied.

BTW, I still unplug antennas and rotors when not in use!

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

I have used hollow copper pipe for years.

I have one 10 foot copper clad steel ground rod which I used to drive the
pilot hole into the ground, then hauled it out using a car jack. I then put
a copper pipe in the hole. The copper pipe has 1/4 inch holes drilled
along its length for the bottom three feet.

I used 3 pipes and the copper clad rod as a system of four tied together
with #2 copper which is soldered to all four pipes.

At first the copper pipes are loosely set into the hole left by the
steel rod, but after a while the ground settles and they are firmly
implanted.

Every year I take a mixture of water and epsom salts and pour it
down the hollow pipes. I cannot see what is happening under the
ground, but I consider my ground system to be as good as can be
hoped for.

I have run a couple marconi's without radials using the system
and found their performance 'pleasing'. One was an 80m folded
marconi -- about 50 ft of it vertical, and the rest folded back
at about 45 degrees. It was a great performer and a chum of mine
to whom I gave the design has worked all continents and most
countries on it. The ground, of course, is the secret.

The system has been in place for 24 years. four years ago I jacked
one of the pipes out just to see about all these rumors of corrosion
but it was fully intact. I steel-wooled it, then put it back in and
resoldered it to the system.

The pipe was cheaper than the ground rod although that was quite a
while back. I say go for it!


Irv VE6BP

Owen Duffy wrote:
"Rick (W-A-one-R-K-T)" wrote in
news

On Sun, 15 Jul 2007 17:23:13 +0000, Walter Maxwell wrote:


This topic has aroused my curiosity. As a grounding device, why would a
solid rod be better than a hollow pipe, except for the current carrying
capability?

Good afternoon, Walt.

The thing is, the current carrying capability for transient events like
lightning strikes should be about the same for the same diameter pipe or
rod, since most of the current is carried in skin effect anyway.


I think that is flawed thinking.

A lighning down conductor needs to carry something like 20kA for 100ms, so
it needs to be substantial enough that it doesn't melt and remains in place
to protect against the next strike.

Owen

The fusing/melting current for 1/2" copper pipe is probably well above
20kA, even for 100ms pulses. A more interesting potential failure mode
might be from the mechanical forces due to the magnetic field. (see,
e.g., quarter shrinking or can-crushing)

Jim Lux wrote in
:

Owen Duffy wrote:
"Rick (W-A-one-R-K-T)" wrote in
news

On Sun, 15 Jul 2007 17:23:13 +0000, Walter Maxwell wrote:


This topic has aroused my curiosity. As a grounding device, why
would a solid rod be better than a hollow pipe, except for the
current carrying capability?

Good afternoon, Walt.

The thing is, the current carrying capability for transient events
like lightning strikes should be about the same for the same diameter
pipe or rod, since most of the current is carried in skin effect
anyway.


I think that is flawed thinking.

A lighning down conductor needs to carry something like 20kA for
100ms, so it needs to be substantial enough that it doesn't melt and
remains in place to protect against the next strike.

Owen

The fusing/melting current for 1/2" copper pipe is probably well above
20kA, even for 100ms pulses. A more interesting potential failure mode
might be from the mechanical forces due to the magnetic field. (see,
e.g., quarter shrinking or can-crushing)


Hi Jim,

I note the "probably" in your comment, and the "dunno" in N5MK's
response.

The uncertainty in my statement is over the exact lightning scenario,
they vary, and the circuit response (ie current waveshape, amplitude,
duration, ringing etc) depend on the specific excitation and circuit
elements (parameters of the down conductor, nature of the earth system,
ground, environment etc).

As far as supposition as to the fusing current for conductors, that is
determinable for a given scenario. I have at hand the Protective Earthing
Code of Practice published by the Electricity Authority of NSW June 1975
and it shows that a 35mm^2 copper conductor has a fault current withstand
of 20kA for 100ms. (I have considered implementing the underlying
formulas in an online calculator.)

N5MK stated "A #10 wire can handle that job". If he is talking copper, I
understand that #10 means 2.5mm diameter, or ~5mm^2, or less than 15% of
the recommended conductor csa for the stated scenario. I am not familiar
with your water pipe sizes. If it were, say, a half inch diameter #19, it
has a CSA of around 35mm^2, so the #10 wire should melt before the pipe
electrode, thus protecting the pipe electrode from failure. Yes,
mechanical forces are also relevant to lightning conductors, but my
comment was about the fusing current.

In this part of the world there is an Australian Standard (AS1768)
relating to lightning protection, there may be a similar standard or
"code" in other jurisdictions, and they would not be a bad place to start
in understanding lightning protection and designing a protection scheme.

Another source of information is to walk around a mobile phone base
station and look at the earthing system from the outside. It is even more
enlightning (no pun) to look inside. These things withstand lightning
events quite well. Are they over engineered? Probably not, they do suffer
damage from time to time.

It is my view that there is a significant risk that an inadequate
lightning protection scheme may be much worse than doing nothing.

Owen

Owen

The fusing/melting current for 1/2" copper pipe is probably well above
20kA, even for 100ms pulses. A more interesting potential failure mode
might be from the mechanical forces due to the magnetic field. (see,
e.g., quarter shrinking or can-crushing)



Hi Jim,

I note the "probably" in your comment, and the "dunno" in N5MK's
response.
That's because I was lazy and didn't want to actually compute it. I've
put multi tens of kA pulses through 1/4" copper pipe, but they're not
100ms long.



The uncertainty in my statement is over the exact lightning scenario,
they vary, and the circuit response (ie current waveshape, amplitude,
duration, ringing etc) depend on the specific excitation and circuit
elements (parameters of the down conductor, nature of the earth system,
ground, environment etc).

One could certainly use the standard double exponential approximations..
either a 2/50 waveform for a strike or the longer surge impulse (I can't
remember the exact rise/fall times for the surge..)



As far as supposition as to the fusing current for conductors, that is
determinable for a given scenario. I have at hand the Protective Earthing
Code of Practice published by the Electricity Authority of NSW June 1975
and it shows that a 35mm^2 copper conductor has a fault current withstand
of 20kA for 100ms. (I have considered implementing the underlying
formulas in an online calculator.)

Preece or Onderdonk?
(http://home.earthlink.net/~jimlux/hv/fuses.htm

N5MK stated "A #10 wire can handle that job". If he is talking copper, I
understand that #10 means 2.5mm diameter, or ~5mm^2, or less than 15% of
the recommended conductor csa for the stated scenario.


Preece equation gives fusing current for AWG10 (2.5mm diameter, as you
say) as 316 amps, but that's sort of for a steady state.

Onderdonk's equation, plugging in 100 ms for the melt time, gives 4.7kA,
which I can believe. I've blown up a lot of AWG10 wire with those sorts
of currents in a quarter shrinker. Partly melting, partly mechanical
stresses in that application.

The purpose of the National Electrical Code (National, here, referring
chauvinistically to the U.S.) required AWG 6 (diam 0.15 inches, 3.8 mm)
bonding wire for grounds is NOT to carry the lightning current (which it
wouldn't, in most cases) but to carry fault currents from things like
shorts from line to grounding conductor, which are usually in the
hundreds of amps range. Say an energized power line falls down and hits
the antenna. You want the antenna's grounding conductor to carry the
likely fault current and not go open, and carry enough current to trip
any overcurrent protective devices.

Lightning protection is usually things like 2/0 (0.364 inch diameter,
9.25 mm), which has a fusing current (viz Onderdonk) of 65kA.

I am not familiar
with your water pipe sizes. If it were, say, a half inch diameter #19, it
has a CSA of around 35mm^2, so the #10 wire should melt before the pipe
electrode, thus protecting the pipe electrode from failure. Yes,
mechanical forces are also relevant to lightning conductors, but my
comment was about the fusing current.

35 mm^2 would have a fusing current of around 30-35 kA.

1/2" Copper pipe is 0.625" od and 0.545" id (very close to 1mm wall)
so, has about 47 mm^2 area.


In this part of the world there is an Australian Standard (AS1768)
relating to lightning protection, there may be a similar standard or
"code" in other jurisdictions, and they would not be a bad place to start
in understanding lightning protection and designing a protection scheme.

Another source of information is to walk around a mobile phone base
station and look at the earthing system from the outside. It is even more
enlightning (no pun) to look inside. These things withstand lightning
events quite well. Are they over engineered? Probably not, they do suffer
damage from time to time.

It is my view that there is a significant risk that an inadequate
lightning protection scheme may be much worse than doing nothing.

I would agree..



Owen

On Mon, 16 Jul 2007 21:26:16 +0000, Owen Duffy wrote:

It is my view that there is a significant risk that an inadequate
lightning protection scheme may be much worse than doing nothing.

Owen, certainly optimal is better than sub-optimal, but I don't understand
why sub-optimal can be worse than nothing at all. So far you have been
exceedingly helpful and I have learned a lot. Can you explain why
something isn't necessarily better, and in fact can be much worse, than
nothing?