[RFI] Lightning Protection

Dale Svetanoff svetanoff at earthlink.net
Sun Jul 1 15:17:59 PDT 2012

Fred, Pete, and all of the other persons posting on this topic:

First, many thanks to everyone for contributing their thoughts,
suggestions, or questions to this topic.  In my 50 years of hamming, I have
found that lightning ranks as one of the most misunderstood natural
phenomena out there, second only (maybe) to propagation theories.  This
thread has done a lot of good in clearing up some of the misconceptions.

I'll start by saying that the comments by Jim, K9YC, should be mandatory
reading for anyone with an interest in the subject.  Then, follow up with a
visit to the ARRL web site for more info.  You can get an excellent
realization of what a fixed station grounding plan should look like if you
can manage your way into a web site that offers free downloads of US Mil
specs; the document to get is MIL-HDBK-419A.  It is a huge volume of some
900 or so pages, but the discussions in that document on grounding SYSTEMS
are worth the download time.  (NO, I do not have a current link to paste in
for this document.  I got my file many years ago thru a commercial source
that supplied MIL docs [which are not subject to copyright protection] to
commercial customers for a fee.)  There is also the booklet produced some
years ago by PolyPhaser, titled "The Grounds of Lightning Protection".  

I think I have said this before on this reflector, but I'll say it again: 
My station has taken 2 direct lightning hits to my main tower (I have 3 of
them) and there has been ZERO loss of equipment in the shack or house. 
Yes, stuff on the tower fried, but that's to be expected.  The key is
avoiding damage to the shack, your equipment, and (of course) yourself and
your family.  When the house was being built in 2000, I studied
MIL-HDBK-419A and the PolyPhaser booklet.  My conclusions for design of the
grounding and lightning protection system were as follows:

1.  Power entrance was at south end of the house, shack would be in the
northeast corner.  The main breaker panel is equipped with a whole house
surge protector, which also provides protectors for the TV antenna and POTS
phone lines.   

2.  One tower (40 foot) is located at the south end of the house for TV
antenna (with rotator), plus 2m and 70cm antennas for close-in work.  The
main tower (77 feet + masting = 100 foot total), is used exclusively for
VHF and UHF operations and is located about 40 feet from NE corner of house
and shack.  The HF tower (48 feet) is located 150 feet to the north and
beyond the main tower, or nearly 200 feet from the shack.

3.  The power entrance has the usual driven ground rod for bonding the
neutrals and green wire grounds that run to the outlets and direct wired
equipment (including the well pump, which has about 50 feet of wire buried
below ground, then descends another 225 feet to the pump).  I surrounded
the house foundation with a loop of #2 AWG bare stranded copper wire,
buried about 1 foot below grade.  The loop is tied into a network of 13
ground rods, each 8 feet long and spaced every 15 feet, around the
perimeter of the foundation.  Bonding between the buried wire and the rods
is mostly via Cad-Weld connections.  (I ran out of weld charges, so had to
make some bonds with clamps, which were sealed after connecting to minimize
corrosion effects.)  I bonded this "ground ring" to the AC power entrance
ground with the blessings of the local Alliant Energy engineer.  My
electrician refused to do the bonding, so I did it myself.  The power
engineer was full of praise for the installation.

4.  Each tower has its own "grounding ring" around its foundation, and all
3 legs of each tower are bonded to the ring.  Those 3 tower rings are, in
turn, bonded to the ring that goes around the foundation.  These concepts
are clearly shown in MIL-HDBK-419A.

5.  An aluminum entrance box was mounted at each end of the house and
bonded to the ring ground with more #2 AWG bare wire.  A small box was used
on the south end for the TV tower, but a much larger box was used on the
north end of the house for the more than a dozen coaxes and control lines
coming from the two tower at that end of the house.  The lightning
protectors for ALL cables were installed in these boxes, and the cables go
into the house from the back side of the boxes.

6.  Now, to the SINGLE point grounding scheme:  the entrance box on the
north (shack) side of the house is, of course, bonded to the buried ring
ground.  When I drilled out the box for installing all of the lightning
protectors, I allowed for 3 drilled and tapped 1/4-20 holes for brass bolts
to extend into the shack for the purpose of attaching heavy ground cables
from each of my operating positions (there are 3 such positions).  The
equipment located in each of the operating positions is then connected to a
bus bar or any sort of grounding system "hub" (which I believe is what Pete
is doing with his copper bus in his posting).  This scheme provides single
point grounding for each of the operating positions - very important.  The
GOAL of single point grounding is make all parts of the system rise and
fall in unison when lightning current strikes, but to not pass the current
from one part of the system thru any other part of the system.  Keep that
concept in mind.  

7.  YES, this makes for a large loop ground system, but it is one that
dissipate the current when 10s of thousands of amps flow during a lightning
strike.  NO, I do not have ground loop hum.  All parts of the system can
achieve nearly equal potentials during a strike, and that is what prevents
damage to connected equipment.  Note that by having all 3 operating
positions tied into the entrance box with separate grounding cables, the
equipment at each operating position will have the same ground potential as
the entrance box itself.  Think of this as a "star" configuration, with all
of these ground leads radiating out from star center (the protetcor box).  

Fred, I also have a few comments to points you made below:

8.  Yes, lightning will go wherever it wants, but what it wants is the
lowest impedance path to ground.  The strike you describe at your late
friend's place could have resulted in much less damage had he installed a
protection and grounding system similar to what I have described.  

9.  Lightning rods (which date back to Ben Franklin's times) are not
beneficial unless the grounding cables /wires to which they are connected
provide a low impedance path to ground for any lightning that gets
attracted to them.  All too often, out here in rural areas, I have seen
grounding cables to lightning rods run such that they have bends and kinks
in them, surely one reason that a lot of barns burned down that had rods
atop them.

10.  Phone lines, buried or not, should all be equipped with lightning
protectors.  Standard telco practices have mandated that for years, but the
big problem is that the protectors are useless unless the ground to which
they are connected has a low-Z path for the lightning.  Remember, lightning
invokes the rules of AC (or RF) theory when it comes to impedance.  Think
of it this way: the plasma you see is the conductor (or inductor), the
stray capacitance to earth ground is the resonating capacitance for the
tuned circuit.  Due to many variables in the length of an arc within the
strike, that is why the spectral distribution of a strike is from roughly
100 kHz to about 100 MHz, with the bulk of the energy at or below 10 MHz.

11.  Disconnecting cables prior to a storm's arrival is one way to reduce
damage in the shack or house.  However, where are those cable ends placed? 
If simply dropped onto the shack floor, then you still have the possibility
of converting the shack or house to charcoal (what I call the "Kingsford
Effect").  If you are going to yank the cables, toss them outside, away
from the building, and ground them if possible.  I have way too many cables
to worry about, so installing protectors was my only viable option.

I have not mentioned one other issue that can (and does) arise with a
strike near the house or shack:  Near Strike Lightning ("NSL") effects,
well-known to commercial airline pilots and the military.  I have
experienced NSL three times in my home - twice from the direct hits on the
big tower, and another time from a cloud-to-cloud discharge above my house.
In all cases, the resulting induced energy produced more than 600 kV of
potential inside the house (estimated by the length of air gap jumped when
the flashover occured). These effects are not reduced (or controlled) by
grounding schemes - they are induced charge, period.  For those putting
their thinking caps on, yes, building your shack inside of a Faraday cage
would reduce NSL effects.          

Again, my thanks to Pete for bringing up the subject, and to all who have
contributed.  This is one heck of a good reflector.

73, Dale
Sr. EMC Engineer               


> [Original Message]
> From: Fred Stevens K2FRD <k2frd at mac.com>
> To: <rfi at contesting.com>
> Date: 7/1/2012 3:25:22
> Subject: [RFI] Lightning Protection Re: RFI Digest, Vol 114, Issue 1
> Pete et al--
> In my 51 years of experience in ham radio including 24 years in the Army
Signal Corps, I have long learned that lightning is like the 800-lb
gorilla: it goes where it wants to go despite all the preventative measures
one takes. I come from upstate NY where lightning storms are quite common
and I know hams who have had their rigs, antennas, and homes or shacks
destroyed even though they had lightning protection devices, e.g., surge
and lightning protectors. Lightning doesn't need a direct hit to affect
anything electronically attached to the point of contact. In one instance,
Tony WB2DTW (now an SK) had a lightning strike on his beam some 40 ft from
his home. The strike hit the antenna, traveled down the coax to his rigs in
the garage, then proceeded along the power line into his home and
eventually found a suitable ground. Everything in between was destroyed
from his rigs to the kitchen blender including a major section of his
garage. He forgot one thing (see below).
> That said, at least some measures might be taken. Better something than
nothing if for no other reason than a little peace of mind. There is no
such thing as a lightning-proof system. But best protection I've seen are
old-fashioned lightning rods such as are commonly found on top of barns but
mounted on top of a mast, mounted on top of a second parallel mast, and/or
on top of a house... anything to divert the lightning strike away from rigs
and other (expensive) things. Main thing is to have the lightning rods
ABOVE the antennas and any nearby structures.
> Grounding is important but no matter how sophisticated a ground system
might be, there's other precautions one might take, e.g., if a
lightning/electrical storm appears imminent, disconnect the coax going into
your rig(s) and get it as far away from everything as possible (Tony had
done this yet his rigs were still destroyed.), and UNPLUG the rigs and the
other expensive items such as refrig, freezer, TV, computers and
peripherals. If there's a nearby (say 20+ miles) lightning storm, you'll
hear the crashes on whatever band if you're on the air. Same/same landline
telephone via which lightning will travel (I know of people killed while on
the phone.).
> Some details: http://www.iceradioproducts.com/10.html (see Paragraph 3).
The League also provides a wealth of information on the subject
http://www.arrl.org/lightning-protection .
> But again, lightning goes wherever it wants.
> 73 de Fred Stevens K2FRD
> Prescott, AZ
> At 12:00 PM -0700 1/7/12, rfi-request at contesting.com wrote:
> >
> >
> >Message: 1
> >Date: Sun, 01 Jul 2012 10:28:56 -0400
> >From: Pete Smith N4ZR <n4zr at contesting.com>
> >Subject: [RFI] Single-point grounding
> >To: RFI List <rfi at contesting.com>
> >Message-ID: <4FF05EA8.6040707 at contesting.com>
> >Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> >
> >I'm not sure exactly where I should post this, but suspect that this
> >group probably has more relevant expertise than most, so please bear
> >with me.
> >
> >In the last year, I have had two expensive episodes.  In both cases, my
> >transceiver's RS-232 transceiver was fried during a lightning storm, and
> >several knowledgeable people suggested a difference in chassis potential
> >between computer and transceiver as the reason.  Their prescription for
> >avoiding a repetition was simple - connect the chassis of all of the
> >units to a single-point ground.
> >
> >My solution - which I'm asking people to critique - was to fabricate an
> >L-shaped, roughly 3x5 foot ground bus made from 3/4" copper tubing,
> >which I mounted on the back of my L-shaped operating desk. All joints
> >are silver-soldered. I then connected each of the affected units to the
> >bus with very short and heavy stranded wire, and connected the end of
> >the bus to my grounded shack entry panel (in a double-hung window).
> >
> >The DC resistance of the ground bus is very low, but the length
> >approximates a quarter wave on 10 meters, and with the units connected
> >near the ends of the bus, I wonder if I'm feeling a false sense of
> >security about the likely behavior of the bus during a nearby lightning
> >event.  Would I be better off (or no better) running heavy conductors
> >from each unit to the entry panel, even if they would have to be
> >similarly long? Or should I just give up and plan on disconnecting the
> >RS-232 connection whenever weather approaches?
> >
> >73, Pete N4ZR
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