On Jul 19, 1:03*pm, Jim Higgins wrote:
On Mon, 19 Jul 2010 09:23:53 -0700, Jim Lux
wrote:

Tom Horne wrote:

Owen
The NEC only requires 5.261 (mm)2 for the protective down conductor
and 13.30 (mm)2 for the bonding conductor between electrodes. *Since
those sizes are at best a bad joke

Perhaps you could explain why you think it's a bad joke? *Do you think a
13 square mm conductor couldn't carry the strike current? (it can)

Or, perhaps, you're thinking that there are some other design criteria
that might push one towards a larger conductor (mechanical strength in
the face of icing and storms might be one).

Maybe E=IR has something to do with wanting a larger conductor. *The
voltage between the strike point and true ground is going to be the 20
- 100 kA of the strike times the resistance of the down conductor from
the strike point to true ground. *With a smaller conductor,
fewer/shorter ground rods, or other conditions that raise the
resistance of the path to ground that voltage will be higher and if
high enough the strike will seek additional paths to ground by arcing
to nearby objects closer to ground potential.

That's why I tie everything together. In my case, the ground rods
are minimal.. Just a few copper tubes pounded into the ground
around the base of the mast. None are too deep. But I consider
the ground adequate for the purpose, and it seems to be, being
as I've taken strikes on that mast with no damage to anything.
But I tie that ground into the electrical ground, and also the
plumbing, which I clamp to just a few feet away from the base
of the mast. If all grounds are at the same appx potential, and
the connection to ground is up to par as far as resistance, you
shouldn't see flashing over to other objects. I've never had that
problem here so far. In fact, the connection to ground seems
good enough that strikes to that mast are fairly silent and
only make an electrical arc sound which sounds like throwing
a light bulb onto the ground.
On the other hand, a strike to a poorly grounded object with
high resistance is hugely loud.. Say when it strikes the tree
in the front yard.. It's like a 12 gauge going off. And this
sound is separate from the sonic boom of the strike as
it travels through the air. The sonic boom will come from
overhead and is not local like the actual strike noise at the
object being struck.

The NEC only requires 5.261 (mm)2 for the protective down conductor
and 13.30 (mm)2 for the bonding conductor between electrodes. Since
those sizes are at best a bad joke I was hoping to elicit best
practice advise on what size the conductors should actually be as well
as advise on how to accomplish the bonding of the interior single
point grounding buss bar to the exterior grounding conductors and
Grounding Electrode System.
--

In what way is #6 a "bad joke?"

Do you expect it to vaporize and set your roof on fire?

"John Gilmer" wrote in
net:

Do you expect it to vaporize and set your roof on fire?

Well, engineering of lightning protection is about design of a protection
system that will, amongst other things, survive most events so as to
continue to provide protection, and to minimise incidental damage.

So, yes, down conductors adequately sized to manage the risk of the
conductor "vapourising" is part of the scope, and physical design to
minimise the risk of side flash causing damage is also part of the scope.

It is interesting, no confusing, that you have two guides that give such
different guidance. In Australia, we too have a standard for house wiring,
and another standard for lightning protection, but they are not in conflict
and our standard for lightning protection is well aligned with NFPA 780 on
the downconductor size issue.

Owen

Owen Duffy wrote:
"John Gilmer" wrote in
net:

Do you expect it to vaporize and set your roof on fire?

Well, engineering of lightning protection is about design of a protection
system that will, amongst other things, survive most events so as to
continue to provide protection, and to minimise incidental damage.

So, yes, down conductors adequately sized to manage the risk of the
conductor "vapourising" is part of the scope, and physical design to
minimise the risk of side flash causing damage is also part of the scope.

It is interesting, no confusing, that you have two guides that give such
different guidance. In Australia, we too have a standard for house wiring,
and another standard for lightning protection, but they are not in conflict
and our standard for lightning protection is well aligned with NFPA 780 on
the downconductor size issue.

Owen




The thing is, AWG 6 wire won't vaporize or even melt or even get warm to
the touch. There's not enough "action" (I^2 T) in a lightning stroke to
do it. Remember that the current is high, but only lasts a matter of a
50-100 microseconds.

Say you are using AWG 10 wire which has a resistance of 1 milliohm per
foot. a 50 kA strike will dissipate 50E3^2*1E-3 = 2.5 MegaWatts.. which
is big.. but for 50 microseconds, that's only 150 joules. That same
foot of wire weighs about 1/2 an ounce (I'm sorry for the customary
units, but they are what I remember off the top of my head AWG 10 is
1/10th inch in diameter, 1 ohm/kft, and 32 ft/lb).. or about 14 grams.

Specific heat of copper is 0.38, so we have deltaT = 150/14 * 0.38
let's call it about 4 degrees C.

I should note that this is a bit optimistic.. the AC resistance for a 50
microsecond pulse will be higher than for DC because of skin effect
(skin depth at 1 MHz is 65 microns, 2.5E-3 inches, and it goes as the
square root, so even at 100kHz, it's still not much more).. so the
dissipation will be higher.

But, you've got a long ways from 30C to 1000C (melting point of copper)
and even farther to "vaporization"...

(as a practical matter, you need kiloJoules to explode a 1 meter AWG 30
copper wire.. hundreds of joules just "melts" it. )

(note also that while the peak current might be 50kA or 100kA, the
average current is substantially less..)

Mechanical stresses from magnetic fields are a bigger concern, as well
as "sideflash".

I don't remember the sources but I have concluded that the Grounding
wire should be no smaller than #6.

More than 8 feet of ground rod is of little consequence.

All ground rods should be tied together. Don't put your house between
two electrodes!

The ground rods are better directly under the structure that they are
protecting.

The system does not absorb massive high energy strikes. It starts
bleeding off the energy before the strike builds and thus minmiizes
the effect.

Home improvement stores sell #6 wire, ground rods and connectors.


On Mon, 12 Jul 2010 21:21:24 -0700 (PDT), Tom Horne
wrote:

Can anyone make a recommendation, based on actual training and
experience, as to what width and thickness of copper strap would be
needed as the down conductor from the antenna mounts at the peak of my
house roof, some twenty five feet above local terrain. I have a a
mount for an antenna at one gable end and a mount for a weather
station sensor array at the other. What thickness and width should I
use in the earth between the two Grounding Electrode Systems. I will
drive five eighths inch copper rods, each eight feet long as far out
from the foundation as I can get them or eight feet were possible. On
one end that will be only six feet due to the proximity of the
property line. At all of the other rod locations I will be able to
keep them at least eight feet from any underground obstructions. To
compensate for the proximity to the foundation wall to the first rod
I will use rod couplers and drive it to hard rock or sixteen feet
whichever comes first. I'm guessing that in keeping the remaining
rods at least eight feet out from the foundation and sixteen feet
apart that I will only have four rods total in a ring around the back
side of the house. What is the best way to attach the copper strap to
the support masts and eve brackets themselves? Do you know of
anything that will make a good connection to the one inch galvanized
iron pipes that I'm using for support masts?

Can you recommend a technique for bonding the interior grounding buss
at the operating position to the exterior vertical copper strap. I
have no idea how that is usually done.
John Ferrell W8CCW

On 7/13/2010 9:52 AM, John Ferrell wrote:
I don't remember the sources but I have concluded that the Grounding
wire should be no smaller than #6.

More than 8 feet of ground rod is of little consequence.

All ground rods should be tied together. Don't put your house between
two electrodes!

The ground rods are better directly under the structure that they are
protecting.

The system does not absorb massive high energy strikes. It starts
bleeding off the energy before the strike builds and thus minmiizes
the effect.


Exactly! May often see during an electrical disturbance little spikes
off the top point of a lightning rod doing its job.

I've been through many 'lightning events' in my day with the closest
direct strike to a neighbor's tree. Also a former wife in my old house
that was hit after she and new husband had cut all the leads to my
ground rods from high TV antennas.

Marv
W5MTV

Home improvement stores sell #6 wire, ground rods and connectors.

On Jul 13, 10:52*am, John Ferrell wrote:
I don't remember the sources but I have concluded that the Grounding
wire should be no smaller than #6.

*More than 8 feet of ground rod is of little consequence.

All ground rods should be tied together. Don't put your house between
two electrodes!

The ground rods are better directly under the structure that they are
protecting.

The system does not absorb massive high energy strikes. It starts
bleeding off the energy before the strike builds and thus minmiizes
the effect.

Home improvement stores sell #6 wire, ground rods and connectors.

On Mon, 12 Jul 2010 21:21:24 -0700 (PDT), Tom Horne



wrote:
Can anyone make a recommendation, based on actual training and
experience, as to what width and thickness of copper strap would be
needed as the down conductor from the antenna mounts at the peak of my
house roof, some twenty five feet above local terrain. *I have a a
mount for an antenna at one gable end and a mount for a weather
station sensor array at the other. *What thickness and width should I
use in the earth between the two Grounding Electrode Systems. *I will
drive five eighths inch copper rods, each eight feet long as far out
from the foundation as I can get them or eight feet were possible. *On
one end that will be only six feet due to the proximity of the
property line. *At all of the other rod locations I will be able to
keep them at least eight feet from any underground obstructions. *To
compensate for the proximity *to the foundation wall to the first rod
I will use rod couplers and drive it to hard rock or sixteen feet
whichever comes first. *I'm guessing that in keeping the remaining
rods at least eight feet out from the foundation and sixteen feet
apart that I will only have four rods total in a ring around the back
side of the house. *What is the best way to attach the copper strap to
the support masts and eve brackets themselves? *Do you know of
anything that will make a good connection to the one inch galvanized
iron pipes that I'm using for support masts?

Can you recommend a technique for bonding the interior grounding buss
at the operating position to the exterior vertical copper strap. *I
have no idea how that is usually done.

John Ferrell W8CCW

John
Would you mind sharing what you base that advise on? Much of it
appears contrary to NIST guidance on protective grounding and current
industry practice.
--
Tom Horne, W3TDH

On Thu, 15 Jul 2010 18:54:08 -0700 (PDT), Tom Horne
wrote:

On Jul 13, 10:52*am, John Ferrell wrote:
I don't remember the sources but I have concluded that the Grounding
wire should be no smaller than #6.

*More than 8 feet of ground rod is of little consequence.

All ground rods should be tied together. Don't put your house between
two electrodes!

The ground rods are better directly under the structure that they are
protecting.

The system does not absorb massive high energy strikes. It starts
bleeding off the energy before the strike builds and thus minmiizes
the effect.

Home improvement stores sell #6 wire, ground rods and connectors.


John Ferrell W8CCW

John
Would you mind sharing what you base that advise on? Much of it
appears contrary to NIST guidance on protective grounding and current
industry practice.

Parts come from the code books,
some from experience and
some from observation.

The #6 wire is out of the code book. Reason and observation leads to
the conclusion that whatever you use there is the possibility of a
lightning strike that can vaporize it. That also supports the notion
that the charge must be bled off over time (seconds?) rather than
shunted to ground instantaneously. In a moment of lapsed judgment I
installed a ground rod for an invisible dog fence on the opposite side
of the house from the electric service ground. I also allowed the
TV-Internet cable ground a few feet away. Lightning strikes carbonize
cable coax connectors. Dog fence controller factory repair is $40 per
event. After much consideration I ran a #6 wire between the power
service ground and the rods for the dog fence and cable ground rods.
Much thought was given to this because that route involved putting a
conductive path along the floor joists just beneath my bed! I
considered the fact that copper plumbing is routinely routed without
concern wherever it is needed. No more service calls to the cable
company, no more repairs needed for the dog fence controller!

I have concluded that if more than 8 foot ground rods were required
for effect or code, the supply houses would be selling them. I cannot
argue with redundancy though. THERE IS A POTENTIAL PROBLEM WITH GROUND
RODS THAT ARE NOT BONDED WITH AT LEAST #6 WIRE! Common sense dictates
that protective system be continuously bled to a common level rather
than allowed to build up a differential charge.

My observations have led me to the notion that the frail little #6
wire does not provide the path for a direct strike. It only suggest a
route for the strike. A straight direct route is more likely to be
followed to ground than a longer twisted route. Lightning is a "boss
force". It can and will ionize its own path in a seemingly whimsical
manner. A spin-off cable loop has been popular for antenna entry
points for many years. This is one of those considerations that may
not do anything but it cannot hurt either!

Whatever you do it must:
Meet code, follow the law
Satisfy the Insurance company, don't give them room to wiggle out of a
claim!
Enhance safety
Protect your property.

In spite of all the precautions and preparations that you take you can
only reduce your exposure to the natural forces in life! My dog Shadow
(a black Labrador Retriever) endorses this by retreating to the Master
Bathroom during storm conditions. Midnight, (Shadows Cat) concurs by
hiding in the basement workshop under those same conditions. I
disconnect all ham radio antennas.

At this time I seem to have my problems at bay... but I also have
professionally installed lightning rods on the house.

John Ferrell W8CCW

I have concluded that if more than 8 foot ground rods were required
for effect or code, the supply houses would be selling them. I cannot
argue with redundancy though. THERE IS A POTENTIAL PROBLEM WITH GROUND
RODS THAT ARE NOT BONDED WITH AT LEAST #6 WIRE! Common sense dictates
that protective system be continuously bled to a common level rather
than allowed to build up a differential charge.


This is actually a big problem.. counterfeit rods with UL markings on
them, and rods that are too small in diameter or too short to meet NEC
requirements.

Electrical Supply places (not the home improvement stores) have had 10
foot rods for a long time.

The NEC has required 8 feet *in the ground* for years and years (at
least 20, I think), so the only way to do that with an 8 foot rod is to
do your exothermic bond to the rod and completely bury it.

The home improvement stores don't like to stock longer rods because most
of the buyers are not "code-aware" and buy on price (hey, an 8 foot rod
is cheaper than a 10 foot rod, I'll use that). Besides, for new
construction in a lot of places, a rod isn't an acceptable primary
grounding means anyway.

And we won't even get into the grounding/bonding practices of satellite
dish and Cable TV installers. There's a great website out there with
pictures of truly lame installations.

On Tue, 13 Jul 2010 10:52:14 -0400, John Ferrell
wrote:

I don't remember the sources but I have concluded that the Grounding
wire should be no smaller than #6.

#6 is a minimum required by code here in the Midland MI area. As it's
a minimum, I would not use anything less than #2 Copper.

More than 8 feet of ground rod is of little consequence.

That depends on your soil conditions. Here I'd probably agree as the
soil is usually quite moist and just a couple feet down is just plain
wet.

However a string of ground rods tied together can be quite effective.

All ground rods should be tied together. Don't put your house between
two electrodes!

I'd put a circle of them around the house, all tied together every
16', but due to the garage and driveway, that is not possible.

The ground rods are better directly under the structure that they are
protecting.

I have a 100' 45G 10' from the NW corner of the garage. Tied into it
is a grounding system consisting of 32 or 33 8' ground rods connected
together with over 600 feet of bare #2.

This system consists of a ground rod about a foot outside the concrete
bare in like with each tower leg. The cable is clamped to each tower
leg and comes off in a curve to the ground rod and is extended out in
a straight line at least 80' with additional ground rods every 16'
(give or take a tad) This system also ties into the house electrical
ground. There is an additional run that goes directly from the ground
rod at the base of the 45G to the 25G on the West end of the shop.
From there it goes on around the shop to the mast holding the 144/440
vertical and around the south side to enter the shop to provide
grounding for the station and computers. This also ties the shop
ground (which is on a different electrical feed) to the house ground.


The system does not absorb massive high energy strikes. It starts
bleeding off the energy before the strike builds and thus minmiizes
the effect.

Mine has taken at least 17 direct hits that have been visually
verified. All that energy had to go some where.

The bleeding off theory has been pretty well discussed and discarded
on the tower talk reflector. Read up on the Polyphaser site. They have
some good information. Those lightning balls or porcupines have
proven ineffective. The major work for lightning rods and ground
systems is to divert the lightning away from the interior of buildings
and process control systems in Industry.


Home improvement stores sell #6 wire, ground rods and connectors.

Read the new NEC code for tower and antenna grounding. There is a
reason I went with #2.


On Mon, 12 Jul 2010 21:21:24 -0700 (PDT), Tom Horne
wrote:

Can anyone make a recommendation, based on actual training and
experience, as to what width and thickness of copper strap would be
needed as the down conductor from the antenna mounts at the peak of my
house roof, some twenty five feet above local terrain.

I agree with the #2 recommendation. OTOH there is nothing that will
protect an installation from the big atypical Positive lightning, or
super strikes. That's the stuff that blows holes in airplanes.

I have a a
mount for an antenna at one gable end and a mount for a weather
station sensor array at the other. What thickness and width should I
use in the earth between the two Grounding Electrode Systems. I will
drive five eighths inch copper rods, each eight feet long as far out
from the foundation as I can get them or eight feet were possible. On
one end that will be only six feet due to the proximity of the
property line. At all of the other rod locations I will be able to
keep them at least eight feet from any underground obstructions. To
compensate for the proximity to the foundation wall to the first rod
I will use rod couplers and drive it to hard rock or sixteen feet
whichever comes first. I'm guessing that in keeping the remaining
rods at least eight feet out from the foundation and sixteen feet
apart that I will only have four rods total in a ring around the back
side of the house. What is the best way to attach the copper strap to
the support masts and eve brackets themselves? Do you know of
anything that will make a good connection to the one inch galvanized
iron pipes that I'm using for support masts?

Can you recommend a technique for bonding the interior grounding buss
at the operating position to the exterior vertical copper strap. I
have no idea how that is usually done.

The Polyphaser site has a tutorial on grounding tower legs and coax
shields. this would be applicable to connecting to the 1" pipe.
Use lots on NoAlox between the strap and pipe.

73

Roger (K8RI)

John Ferrell W8CCW