best way to ground a tower
Bruce Fraleigh
world) and have just installed a 50' tv tower (given to me by a
neighbor, with no instructions) and am wondering about how I should
ground it. It stands about a foot from my house and has three guy
wires attached to the tower about 10' from the top. About five feet
of the tower is embedded in the ground, in about two yards of
concrete.
I am just about to pour a foundation for an addition to my house, one
side of which is about 6' away from the base of the tower. The
addition will be 20' X 26' and I have just run about 130' (in two 65'
rows about six inches apart) of 5/8" reinforcing rods in the footer
trenches. Would I be better off grounding the tower to the steel
re-bars in the footers or to a copper grounding rod driven into the
ground at the base of the tower... or both? If both, should I use a
different connecting wire for each and would it be better to drive the
grounding rod into the ground at the bottom of the footer, even though
it is a little further away from the tower or as close to the bottom
of the tower as possible? Any advice and hints would be greatly
appreciated. -Bruce
Dennis Kaylor
i think you would be much better off with 3 copper 8 foot ground rods
about 3 foot from each leg of the tower and connect with some heavy gauge
wire
now what i did i too live in florida but i am not as paranoid as most are
i just planted my tower base about a foot into the ground in the bottom of
the 3 foot hole i dug for the base then filled it with a yard of cement
and when it comes to storm i will just disconnect the coax from the rigs
and short them to ground
cause reality speaking if lightning wants your stuff it will find a away
in no matter what you do,,,,grin
good luck
BTW what part of florida you in?>
i could use someone to climb my tower and install my antennas
i am in lakeland
thanks
John Passaneau
I put 3, 8' ground rods around my tower. Each spaced about 8' from each
other. The rods are connected to one leg of the tower by short, lengths of
#6 copper wire. Then I ran #6 wire back to the house and connected it to the
house ground. All this was required by building code in my area.
I bonded the shields of the coax to the tower at the point they came away
from the tower and used a lighting arrestor on the rotor cable at the point
it came off the tower. At the point the coax entered the house I put
lighting arrestors on the coax connected to yet another ground rod. Check
out the polyphaser site for good information on how to do this at
http://www.polyphaser.com/. If the tower is aluminum, then when you connect
the ground wires to it, use ground blocks that are rated for aluminum/copper
connections.
--
John Passaneau
Penn State University, State College Pa.
W3JXP
w3...@arrl.net
"Bruce Fraleigh" <brucef...@hotmail.com> wrote in message
news:3fb5609a.02042...@posting.google.com...
Bill Otten
Check my homepage at http://home1.gte.net/res0958z/index.htm which contains
both photos and text on grounding a tower for lightning protection (I live
in Largo, FL -- right in west central Florida's lightning alley). Also check
the site at http://www.k9wk.com/litenin.html (another good one) and this
site: http://users.erols.com/n3rr/lightningprotection/index.htm . I think
you'll notice a trend in thought here. Write if you need more info....I've
got a bunch of sites from my research.
Bill KC9CS
"Bruce Fraleigh" <brucef...@hotmail.com> wrote in message
news:3fb5609a.02042...@posting.google.com...
Bill Otten
John's idea of connecting the tower ground back to the house ground is
very important. The idea being that if connected together there can be no
difference in potential between the systems. Difference of potential is 'the
path' lightning uses to find it's way around.
Bill KC9CS
"John Passaneau" <jx...@psu.edu> wrote in message
news:aa3oh7$1b...@r02n01.cac.psu.edu...
Carl R. Stevenson
"Bruce Fraleigh" <brucef...@hotmail.com> wrote in message
news:3fb5609a.02042...@posting.google.com...
> world) and have just installed a 50' tv tower (given to me by a
> neighbor, with no instructions) and am wondering about how I should
> ground it. It stands about a foot from my house and has three guy
> wires attached to the tower about 10' from the top. About five feet
> of the tower is embedded in the ground, in about two yards of
> concrete.
>
> I am just about to pour a foundation for an addition to my house, one
> side of which is about 6' away from the base of the tower. The
> addition will be 20' X 26' and I have just run about 130' (in two 65'
> rows about six inches apart) of 5/8" reinforcing rods in the footer
> trenches. Would I be better off grounding the tower to the steel
> re-bars in the footers
I would NOT, under ANY circumstances tie your tower grounding to the
rebar in your foundation footers (or a slab, etc.) ... unless you'd like
them
(the footers, slab, etc.) to explode if you take a strike ... you won't get
much
of a ground through the concrete, and all that energy will be trying to get
(flash)
from those rebars embedded in the concrete to (real) ground ... I can
envision
the results as being VERY dramatic (in a disastrous way).
Carl - wk3c
Gary Schafer
Actually the rebar makes a pretty good ground. Concrete is a good
conductor. It holds
moisture where the ground around it may be dryer. It can often times
be a better ground than
the ground rods driven in the soil. It is called a Ufer ground system.
Named after the guy that
discovered it. It should not be the only ground but it can greatly
augment your ground rods.
When towers are mounted on concrete they are usually bolted to J
bolts that go down into the
concrete. When a lightning strike occurs a large amount of the current
goes into the concrete by
the J bolts. Some people bury several feet of tower in concrete. Just
because you have ground
rods tied to the tower does not mean that a large amount of the energy
will not also go into the
concrete.
The Polyphaser site has information on Ufer grounds.
73
Gary K4FMX
Bill Otten
"Carl R. Stevenson" <wk...@fast.net> wrote in message
news:3cc5bb03$1...@news7.fast.net...
Polyphaser actually recommends using the rebar in a footer to AUGMENT the
tower ground, the idea being the lower the resistance the better. One way to
lower the resistance is to expand the ground system over many paths --
divide and conquer. In the book by PolyPhaser "Lighting Protection and
Grounding Solutions for Communication Sites", the followup to the book "The
Grounds for Lightning Protection" they make numerous reference to use of
Ufer grounds for augmentation of tower grounds.
Pages 11, 32-33, amongst others. Finally on page 81 is my favorite
reference: " Those who think that three 8 ft ground rods around the base of
a tower is a good grounding system are on the right track only if the tower
will be erected on the beach at high tide".
Finally, from the Ufer ground document on Polyphaser's website in the
technical information section:
"Concrete is a fair conductor and can be used safely and effectively to
augment your tower grounding system."
"It is a common misconception to think that a lightning strike will blow up
a concrete pad. However, consider
first, a myth-perpetuating case of an improperly designed system where the
tower leg "J"-bolts are imbedded
directly into the concrete pad. In this case, due to the poor nature of the
tower ground system, each of these Jbolts
will actually share a significant amount of strike current which in turn
will flow through the concrete. Since
the surface area interface between the J-bolts and the concrete is small,
the surge current density is very large.
The corresponding heat generated by the energy transfer can turn the
concrete moisture into steam and possibly
crack the pad. We have only seen this happen once on a mountain top in the
Nevada desert. However, a
few poorly implemented occurrences can give a valuable technique a bad
reputation.
If during construction, all of the rebar in the concrete pad becomes an
integral part of your ground system, the
overall surge current density will be several orders of magnitude lower than
the myth-perpetuating case above.
With the surge current distributed over all of the rebar there will be
little to no opportunity to develop the
temperatures necessary to vaporize the imbedded moisture. The pad will not
crack."
"As well as the Ufer ground works, it should not be used alone. We always
recommend that radials or radials
with ground rods be used as the main ground system and that the Ufer ground
be used to further reduce the
ground resistance of your system. Many tests have been done, dating back to
1968, which prove that the Ufer
is a safe and very effective way of augmenting a ground system."
My pool deck has a ground connection to the wire mesh in the concrete slab.
Reason? In the event I put up an aluminum screen cage over my Florida pool
( I live in west central Florida...right in the heart of lightning country)
it was to be connected to the ground in the wire mesh. If it was a risk of
'explosion' the design would have been otherwise. By the way...the entry and
exit ladders and handrails are also tied directly to the wire mesh....by
code.
I think perhaps more research by those who don't understand proper grounds
is warranted.
Bill KC9CS
Carl R. Stevenson
I stand corrected ... Polyphaser has a very good reputation and
if they say it's OK, I trust that ... I had envisioned the currents trying
to flash from rebar through concrete and causing flash steam explosions.
Apparently I was underestimating the ability of concrete to
conduct the current.
I agree that 3 ground rods is not enough ... I just had concerns
about the concrete being part of the grounding equation.
Carl - wk3c
"Bill Otten" <res0...@verizon.net> wrote in message
news:xAkx8.19285$uV.1...@nwrddc01.gnilink.net...
Bill Otten
Well, you're not entirely wrong here Carl. I'm just glad the entire
topic came up. It's a fascinating topic to me and one I've spent a bunch of
time researching. Florida Power Corp. has a series of lectures sponsored by
Erico, Inc. http://www.erico.com/ that covers a variety of lightning
related topics for facility managers, plant engineers, etc. I was invited to
the conferences based upon some involvement I've had with a group online
that discusses ONLY lightning and prevention
ttp://groups.yahoo.com/group/LightningProtection/ . Last year our home took
a lightning strike somewhere nearby. There was NO flash, NO thunder but I
had damage to the electrical panel in my home, and it blew the phone box off
the outside wall of my home. The utilities are underground, and the heavy
fiberglass lid covering the underground phone connections in front of my
home by the street was blown off the hole and found 90 feet away! The strike
apparently then came into or tried to exit the house on the cable tv
line....and the splitters were ruined. Two televisions which were plugged
into the accessory plugs on the back of the cable boxes were lost along with
the boxes of course. One computer not entirely unplugged took a hit via the
phone modem....it was the ONLY cable to the computer not removed at the
time. Lastly, at the rear of the house about 15 feet from the tower and
along the foundation concrete slab the strike hit the foundation and along
the baseboard in my office where my radio gear was, shattered the ceramic
floor tile and blew an 8" long X 2 " deep by 3 inch hole in the concrete. So
yes, a lightning strike can damage concrete and I learned it the hard way.
At that time I only made do with the ground provided by my tower being sunk
in the ground and having a ground rod or two connected to it. I was one of
those who disconnected his coax, unplugged my rigs, and thought all was
fine. Even then, rigs aren't safe due to the induction and magnetic effects
of a near-strike. Oddly, experts don't think the tower took a strike
directly. A solid state Heathkit antenna relay on the tower was undamaged,
all my antennas work great, and my rotor was workable (although I sent it in
for diagnostics and rebuilding as a precaution). My neighbors lost 2
computers in the strike. They didn't hear any thunderclap either. Very
strange. I only heard the pistol like sound of a tile shattering. I'm not
saying that lightning cannot damage concrete here...it's a known fact that
building edges that come to a point are prime spots for strikes to hit and
cause damage. My point is that properly done and as recommended by
PolyPhaser the wire mesh in a slab can serve to augment and improve a total
grounding system. My website mentioned earlier shows the recent improvements
to my grounding system.
73,
Bill KC9CS
Richard Harrison
"It`s a known fact that building edges that come to a point are prime
spots for strikes to hit and cause damage."
I`ve been on the tops of many high buildings with my microwave
installations. Ubiquitous are the "air terminals" (lightning rods) at
frequent intervals around the edges. Their purpose? To prevent chunks of
building material from being knocked loose by lightning and into the
streets. A lightning strike to concrete may produce instant superheated
steam from moisture retained in all concrete and blast the material
asunder. It happens somewhere every day.
I`ve also erected countless communications towers. I`ve protected the
reinforced concrete bases of these towers by a separate ground rod
connected with a low inductance, low resistance cable or strap to each
tower leg. I made an exception in Tierra del Fuego, which has never seen
a lightning flash nor heard a thunder clap. But, elsewhere, the rebars
got bypassed by external lightning grounds outside the tower bases.
Never had a split tower base. Have heard of unprotected tower bases
built by others that were split. That settles it for me forever.
Best regards, Richard Harrison, KB5WZI
Bill Otten
prime topics was the protection of buildings. Several studies were shown
relating to lightning's apparent affinity for 'edges and points' on building
roofs. Pictures of those were shown with damage where chunks of concrete had
been split off by strikes. Invariably the points of buildings were most
often hit. Wind and weather apparently team up to produce unusual static
charges to the points and edges of buildings that help to either start a
strike or attract one. Air terminals at those points was strongly
recommended.
Bill KC9CS
"Richard Harrison" <richard...@webtv.net> wrote in message
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