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Spiny balls vs rods and some other notes on lightning grounds:
This subject has raised a lot of interest lately, and I am deeply
involved, so here's a bunch of words for those who are interested. Feel
free to delete!
Before you homebrew, consider ---
There some basics with these devices that are important:
1. Soldering anything to do with lightning protection is worthless - it
vaporizes with the first tickle. Mechanical clamps, machine crimps, or
"Cadweld" type assembly will work.
2. Standard galvanizing is only slightly better -- that's why towers are
hot dipped.
Heavy wall aluminum tube conduit is not bad, stainless steel is best.
Regular electrical conduit (galvanized steel) is not good. Galvanized
steel wire is good only till the sharp cut point rusts. Bronze or brass
wire is better.
3. The more sharp points the better, but very fine wire can burn up over
time.
4. A good DC path to ground is essential, so dissimilar metal junctions
can defeat the whole idea if not properly protected. Corrosion leads to
elevated resistance, then to arcing and finally, destruction.
It is very important to understand that the dissipation principle is
effective only if properly employed. One crappy little brush in a
lightning storm could do much more harm than good by instigating a flare
that provides an ionized path for a bolt to follow, whereas a sufficient
number would have wiped out the risk. One must consider HIS risk with
HIS installation in HIS geographic location and act accordingly. It would
be a bad mistake to put up a little home brew device to "test the water"
with a plan to add more later, "just in case." It is also a bad mistake
to make a homebrew that will change in time due to corrosion, working
loose, or the like. Nothing against homebrew done right, however. Years
ago we cut hundreds of 6 inch SS spikes from surplus CB whips, spun 'em
against a fine grinder to needle point, stuffed the butts into 1 inch
holes in a piece of Aluminum bar stock and peened them in to stay with
hammer and punch. Bolted it to the top plate at the bottom of a G7 and,
after losing 3 in previous years, lost nothing for years thereafter.
We've inspected brushes that have turned blue and had a few inches burned
off
the ends, and some that had no brush left at all! In such cases, more
brushes would have saved the loss, but at least the hit was avoided.
Quantity and sizes required require either professional advice or a well
educated guess.
The example I offered the other day of the main street bridge in Jax is a
good case of doing it right. I've not seen a strike count, but will bet
they are rare.
The numbered points at the beginning of these comments might seem to
indicate the need for heavy current carrying capability, which may be
misleading. The current carried in a dissipation system's path to ground
is not expected to be able to handle a strike. The absolute low
resistance continuity of the path is the critical element. If you recall
grandfather's lightning rod system, the conductor to ground was a loose
mesh, finger size copper or copper clad steel wire, a highly inductive
and therefore lossy line that helps with the dissipation process.
When we do our demo, I produce a 2-4 inch spark from globe to ball. I
next use a single sharp point, and produce only a weak 1/4 inch spark,
and then I follow with a 700 point "porcupine," as we dub it, and get
nothing at all, and one can't even feel the static ruffle of the hair on
his arm. A lead to ground from the brush instead of just my body will
produce a barely visible 1/64 inch spark. My body is the usual ground in
the show, and although we throw 20 to 30K volt bolts, the current is only
enough to cause a twitch. In a protection system, the cumulative current
from several hundred or even a dozen "Porkies) would require
proportionally larger current carrying capability in the conductor that
serves the multiple units. Just like all of the creeks becoming a river.
These dissipators are supplied in many forms: Brushes with tens,
hundreds, and thousands of wires of 6 inch to 6 foot length of various
wire sizes from .003 to .100 inch and more. Commercial units are usually
SS, old fashioned lightning rods were copper, bronze, even galvanized
steel. Long runs of brush that looks like an endless bottle brush only
larger run along parapets and superstructure (The bridge at Jax has
both). Marine use is growing rapidly.
If you decide to buy some of these devices, AVOID marine supply houses
unless you've won the lottery. The prices run 2 to 5 times higher than
anywhere else. "If you own a boat you must be rich," seems to be the
thesis!
Here I will insert some of the text we supply in our display, for a bit
more background:
"A dissipator provides an ionization discharge path at each stress point
on a
communications tower or antenna installation. By discharging these points
into
the surrounding air, the possibility of a lightning strike is greatly
reduced. There
is an additional advantage: with the reduction of static charge buildup,
there is a
reduction of noise heard in the receiver.
The stress points are the highest and outermost points on the tower or
antenna
installation. Ideally, one or more dissipators should be placed at the
top of the
tower, top of the mast, and ends of booms. None should be affixed to any
radiating or active element of the antenna.
Low voltage dissipation functions by the conduction of a small Direct
Current
(DC) to or from ground. Charged particles in the immediate atmosphere
surrounding the dissipator are neutralized by the opposite polarity on
the
charges present at the tip of each wire in the dissipator. The voltage
buildup in
the area is thus retarded and strike potential is less likely to be
reached.
Obviously a continuous DC path to ground must be provided. Normally, the
tower or mast metal is adequate for this discharge, provided that they
are
properly connected to an adequate ground. At least one 8 foot copper
covered
ground rod is required for each leg of a tower, connected with a solid
copper
(low inductance) conductor (no less than 4 AWG) to each leg. Copper bar
stock
(1/4 X 1") is better for high risk areas. Connections must be made with
positive,
low corrosion clamps or a welding process like "Cadweld." The rods should
all
be connected with a circle of the heavy copper wire; consider 3 or more
additional rods, each 6 feet from the other, connected as before, in high
risk
areas such as central Florida. This sounds like over-kill for a low
current DC
path, and it is, but it is also there for that big strike that nails us,
no matter what
we do to avoid it. A direct strike can be 18,000 amps, so, the more
current that
your system can carry to ground, the less remains to plow through all of
your
property.
Remember Grandfather's house and barn, with the lightning rods and
weather
vanes? They were and still are the best protection for the money a rural
or any
home at risk can have. They were usually connected to each other and
ground
by a loose-weave copper or copper-clad steel stranded cable. This highly
inductive path was perfect for charge dissipation, if not for a heavy
strike."
I hope this is of some value in the dissipator discussion. Please don't
hesitate to hit me for whatever else we can contribute, or for details on
units that are available. Yes, we sell them, and are getting together
economical kits, too.
73
::Press Jones, N8UG
::The Wireman, Inc.
::Landrum, SC 29356
::use n8ug@juno.com or (864) 895-4195 for tech help
::orders only use 800-727-WIRE(9473) or cqwire@juno.com
The following is left as a reference as to what sparked my treatise - I
consider it to be a way to do it all wrong - sorry - Press
<<<<On Thu, 07 Aug 1997 23:27:10 -0400 Martin Gary
<n3hrt@eagle1.eaglenet.com> writes:
>I'm not sure of the exact conductor size, its about the size of your
>index finger. There was an article in QST (or 73) that discribed the
>way
>you make these "spline balls."
>
>Go to Lowes and get some of that galvanized fence wire, cut it into
>about 2 ft. lengths. Make sure that you cut the wire at an angle, so
>that its pointed on the end. Then take a piece of 1 inch x 4 or 5 ft.
>electric conduit, cut some vertical slices into one end and spread
>them
>apart slightly. Then jam as many peices of the fence wire in it as you
>can. You only need to put the fence wire in a couple of inches. Clamp
>the wire in the conduit with a stainless steel hose clamp. Then take
>your handy-dandy torch and some good flux and solder the whole thing.
>
>Now if you spreed the wires out they will form a ball. It ends up
>looking kind of strange. Make sure you bend the conduit at the bottom
>(where you would attach it to the tower). The bend should be about 35
>degrees.. so that when attached it will stick out from the tower.
>Connect the "spline balls" to the conductor mentioned above and thats
>it.
>
>I hope this is clear enough... If its not let me know!
>73 de Martin - N3HRT.
>
>
>Russ Ellsworth wrote:
>>
>> Martin Gary wrote:
>> >
>> > Actually they do work, the power company here in Southern Maryland
>put
>> > them on all
>> > of their communications towers and they haven't been hit since.
>> > To get them to work properly you HAVE to have a GOOD ground. You
>also
>> > have to have
>> > a BIG conductor connected directly to them and to the ground
>system
>> > below.
>> > You also have to have a lot of points. Several hundred or so.
>There has
>> > to be
>> > enough surface area to let the charge bleed off before the strike.
>>
>> snip
>>
>> Martin, Do you know how big the conductors are the power company is
>> using or are they relying on the metallic towers (if they are
>metallic)?
>> These "spikey things" may be worth the effort for us Hams to install
>if
>> the professionals feel they are.
>>
>> Russ Ellsworth WA6CWV, Boise Idaho
Cadweld notes:
Hi.
Despite several postings suggesting the words `exothermic' and `welding'
be added to the TT word filter, I ordered some CadWeld ONESHOTS for use
on ground rods. A few people have asked about how they work and I have
some advice for anyone wanting to use one, so a brief posting is in
order, IMHO.
Anyway, they work fine. They are more expensive than clamps, but provide
a better connection and don't require the purchase of extra
anti-oxidants, grease, etc. As an added bonus, there's a great fireworks
show when they go off.
A few points to consider: First, BUY THE CADWELD-SUPPLIED IGNITION TOOL.
A flame simply won't launch these and most consumer-oriented flint
igniters don't project the spark far enough to enter the mold and ignite
the material.
Second, if you get the kit for two wires to one rod, try and install it
such that you have ONE wire passing through the mold to the next
connection. I didn't and the process blew one of the wires out of the
mold before it could weld. In any event, secure the wire from movement
before lighting up.
Third, if you need to mail-order, I've had excellent results with The RF
Connection (email: rfc@therfc.com). I ordered three kits, and because I
didn't have the CadWeld lighter, I needed to add some material from the
third kit to the second to achieve orbit. I mentioned this in an e-mail
to rfc and they're having the warehouse ship another package of weld
material. That's excellent customer service, as far as I'm concerned,
especially since it would not have been unreasonable for them to say that
I didn't follow the instruction, so tough noogies.
Hope that helps anyone interested in exothermic welding and didn't offend
anybody who wanted the subject BANNED from the reflector.
73, kelly.
ve4xt@mts.net
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The following is summary of the replies I received to my question about
grounding 1/2 CATV hardline to my Rohn 25G tower. Many thanks to all who
replied!
73 de Mike, AD4VH
----------------------------------------------------------------------------
---------
On Oct. 18, I wrote:
I am interested in a good method for grounding a piece of 1/2" CATV hardline
as it passes the base of my tower. I would like to get a good solid
connection, but am concerned that anything that clamps to the hardline
asymmetrically will deform or crush the relatively soft aluminum outer
conductor. The cable is jacketed, so the fixture in question would
necessarily have to open wide enough to accomodate the extra diameter of the
jacket if it were to be slipped over the end. Alternatively, I was thinking
that with something like a pair of clamp shells, they could be placed at the
ground point directly without having to feed thru the 30 remaining feet of
cable.
Anybody solved this problem already? I am hoping the there is some little
gizmo waiting for me at the local hardware store that will do the job
directly without the need for alot of modification.
73 de Mike, AD4VH...................
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----------
Jay, WX0B wrote:
Hows this for size,
slice the cover off the heliax/hardline at the base of the tower.
Use an aluminum strap you have made from some AL thin stock and clamp
into place with a stainless steel hose clamp. You should not use copper
strap because of galvanic actio.
place another stainless steel hose clamp around the tower leg to protect
the galvanization from migration and place the Aluminum strap on top of
it. Secure in place with another Stainless hose clamp on top of the
whole sandwich. Should work fine. I would also use NALOX (tm) at all
junctions to prevent AL oxide.
I would use 3M (tm) Vapor wrap to seal it all up and tape.
GL
Jay
If you find a better way copy me please.
----------------------------------------------------------------------------
---------
Dick, WJ0M wrote:
SNIP...
Hi Michael, I use ½ CATV hardline as well. It runs into a modified
electrical distribution panel for switching. Where it goes into the
panel, I've used brass plumbing hardware, ... can't recall the proper
names, but it's the same as what you'd use for copper pipe. When
fittings are tightened, it locks the feedline in place. Also use a
combination of those fittings and a modified barrel connector to get
from hardline to flex. If you desire more detail, I can check the
hardware store for the proper names and a better explanation. Clear as
mud??
CUL, 73
----------------------------------------------------------------------------
---------
J.P., AA2DU wrote:
Michael:
Polyphaser in Linden, NV, makes a device such as you are seeking.
They clmap the tower leg and the hardline shield and bond them together
to ground. I don't remember their number off hand, but they advertise
in most of the ham mags.
73, J.P. AA2DU
----------------------------------------------------------------------------
---------
Bill, KM9P wrote:
I just wrapped several wraps of braid around it and it acted like a
dampening to the force of the clamp.
73
----------------------------------------------------------------------------
---------
Pete, N4ZR wrote:
Mike, I use a bronze clamp of the sort made for clamping electrical ground
wires to house plumbing. They come in various sizes and seem to squeeze
pretty symmetrically. The teeth cut into the aluminum jacket of my hardline
(granted 3/4", not 1/2") nicely with very little pressure and no evident
deformation.
73, Pete Smith N4ZR
n4zr@contesting.com
... and not changing!
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Chuck, KE5FI wrote:
I would be interested in the answers you get. I will be using this type
cable soon.
My soloution would be to cut away 1" of rubber and solder to the
aluminum. Then cover the whole thing with a sealant.
Chuck
ke5fi@wt.net
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----------
Bill, AA4NU wrote:
Mike .... I.C.E. offers "grounding blocks" like you need, Also
Polyphaser offers straps to do the same ...
Hope this gets your pointed in the right direction !
73 Bill AA4NU
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----------
Jim, KC8MK wrote:
Mike,
Go to the hardware and get a stainless steel hose clamp.
Use some penetrox and whatever wire you are going to use to
ground it with.
Tape the whole mess up when you are done.
Scotch 130C and 88 will do the job.
73, Jim
P.S. Look for you on 160 this winter.
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---------
Denny, K8DO wrote:
Get a block of aluminum about 2.25" square... have a local machine shop drill
two holes through it.. one hole to be the right size to clamp to the leg of
the tower (or ground rod as the case may be) and the other to clamp to the
hard line (sans jacket).. then they can saw half blocks out of this to form
clamps, add 3/16" clamp bolt holes, and you are in business...
I get my aluminum from:
Dillsburg Aeroplane Works
Dillsburg, Pa
717/432-4589
Cheers ... Denny k8do@aol.com
----------------------------------------------------------------------------
---------
Roger, K2JAS wrote:
like Denny's (k8do@aol.com) idea about machining a block of aluminum and
I'm sure that the people he recommended for the aluminum stock would have
this material:
Dillsburg Aeroplane Works
Dillsburg, Pa
717/432-4589
I've seen their catalog and it is comprehensive regarding just about
anything you could ever want in aluminum tubing and supplies. However, be
prepared for a substantial bill.
Again, allow me to recommend that you (or for that matter anyone) check out
your nearest scrap metal recovery yard. It has become one of my most
favorite places to visit. Aluminum, steel, stainless, copper, tubing,
piping, wire and cables...
and believe it or not working electronic equipment too (sold by the weight)!
You name it, it's a "gold mine" not only for what's available but the prices
are ridiculously low.
Today I picked up about 40 feet of a oil and gasoline resistant jacketed
stranded copper cable. The diameter of the copper was easily 1/2 inch plus.
It weighed 12 pounds. I think I overpaid but it only cost $10 with some
other pieces of alunimum. It will make a magnificent grounding cable to run
from my roof mount tower down the side of the house to a buried 8-ft ground
rod. Two copper clamps for this cable cost me over $6 at Home Depot!
The scrap metal yard may never have exactly what you want because things
just keep coming and going. You just have to make it a habit to stop by
every once in a while and check out the stock.
73's, Roger
K2JAS@worldnet.att.net
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J.P., AA2DU wrote:
Hmmm...I'm no metallurgist but I was always taught that aluminum and
galvanized steel don't mix. That's the very reason that the use
of aluminum jacketed "CATV" hardline is not recommended for runs
going up the tower.
Polyphaser makes an excellent set of feedline to tower grounding
systems that use different metals depending on what you attach them
to. One end might be copper or aluminum and the other could be
compatible with the galvanized steel of the tower leg.
73, J.P.
----------------------------------------------------------------------------
---------
Mike, NS7Z wrote:
Industrial Communication Engineers (ICE) sells a tower mount ground block
that attach's to the legs w/ U bolts. You specify the drilled hole size
or describe your coax and they will drill the holes to match the shield
OD, less the covering. It is all stainless stell and not to costly.
They are in Indianopolis , Indiaana
73 de Mike NS7Z
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Rich, KE3Q wrote:
I'd think it'll work fine as long as you don't overtighten whatever you
clamp around it. It's common to use a hose clamp (stainless preferred)
and a wire or braid to the ground at that point. It'd be very difficult
to overtighten a hose clamp so as to deform the coax. Goop the whole
connection up with waterproofing stuff.
73 - Rich Boyd, KE3Q
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---------
Steve, N0YVY wrote:
I would use homemade clamps. I start with a piece of 3/4 inch aluminum plate
about
2 inches square. I drill the appropiate size hole through the plate for the
aluminum
jacket. Then I flip the piece 90 degrees and drill two 11/32 holes on each
side of
the center hole and perpendicular to it through the edge of the plate for
the 5/16
inch clamp/mounting bolts. Then I saw the whole thing in half and the saw
cut provides
about the right crunch. Depending on where it is going, I may make the
clamp/mounting
spacing fit a U bolt and then grind/file radious to fit tower leg. When
clamping to a
tower leg, I would use a stainless steel bolt, and a thin piece of stainless
sheet between
the aluminum block and the galvanized tower leg with lots of anti-ox
compound. Then
seal the clamp, leg and cable like it was a coax joint to keep the water out.
No moisture means no electrolysis.
It is cheap and takes me about 15 minutes to make with a drill press, band
saw and grinder.
de n0yvy steve
_______________________________________________________________________________
Michael Tope, AD4VH (ex KD8NS)
200 Easy Street
Melbourne, FL 32934
Phone: (407) 259-7494
Eail: mtope@iu.net
_______________________________________________________________________________
"It is the empty space inside the vessel that makes it useful" - Lao Tzu
David Robbins, K1TTT K1TTT@arrl.net