Lightning

Also see:

Lightning Strikes



grounding

House ground layouts

Second Floor Grounding




Rohn 45G




Rotating tower




Rohn 65G



Contesting and
Boatanchor Room



Antenna System and
my house station

 

Damage-prone installations almost always
include one or more of the following mistakes:

Cable wiring that mixes or combines various
independent systems at sensitive equipment without a common entrance
panel

Cables and wiring that routes above ground,
especially several feet above ground

An entrance or equipment ground that is not
bonded to the mains ground

An equipment ground without an entrance panel,
or that is not bonded to the entrance panel

(link to
installation map)

The following are
popular false
myths….

  • Only disconnecting antennas and equipment reduces or eliminates lighting
    damage
  • Grounding or better grounding just attracts more lighting
  • Grounding 
    feed lines and
    antennas bleeds off
    static buildup, reducing odds of having a lightning
    strike
  • Static
    dissipators
    bleed off charge, reducing the
    chance of
    lightning hits

Examination of rumors and old wives’ tales, or Internet wisdom, shows us for
nearly every claim there is a countering claim. What do we do, isolate
everything? Ground everything? Use no ground at all? Use a rod? Let charges
bleed off? Stop charges from bleeding off by not grounding?  To answer this
we have to understand where charges are, and how to deal with discharges.    

Where is the
charge piling up and
how can we equalize
or reduce the “charge pile”?

Our worry isn’t so much about charges piling up, it is about large charge
differences between two points. A charge difference creates a charge gradient or
electrical potential between two or more points. Eliminating the potential
difference requires we move charges from one point to another, balancing charges
out.  

The charge
difference is
between different
areas of clouds, and
between those clouds
and the entire earth
and anything near or
on the earth. The
real problem is the
piling up of
electrical charges
in the droplets (or
even dust particles
in bad dust storms)
collected in one
area or another of
“clouds”.
If we wanted to
reduce the charge
gradient, we would
have to create a
conductive path
capable of allowing
steady charge
movement
between the areas
with different
charge, so charge
difference could
equalize. It is
quite possible to
reduce charge
gradient between an
airplane and the
surrounding
atmosphere by
attaching wire
brushes or whiskers
to protruding parts
of the airplane.
As the perfectly-insulated airplane
travels directly
through differently charged
areas, charges can
easily migrate into
or out of static dissipators, bringing
the airplane to the
same potential as
the area it is
flying through. This
is much the same as
a conductive strap
on a well-insulated
motor vehicle
contacting the
surface of a road,
preventing tire
friction from
charging the
insulated vehicle
to a different
charge potential in
relationship to the
road (and earth).

It’s my firm belief,
based on both
reasonable logic as
well as several
reports and studies,
that grounding an antenna
(or adding metallic
whiskers or
metallic “porcupine balls”)
does nothing to reduce charge
gradient that causes
lightning. Moving
charges between the
huge volume of the
earth through a
tower into the air
immediately
surrounding the
tower and earth is
meaningless, because
the real charge
gradient is between
clouds thousands of
feet away and the
entire earth.
Unless the discharge
contacts or forms a
path connecting differently charged
areas, the ionized
area does
nothing at all. The
most it offers is a
wider blunter area
at the location of
the dissipater.
While this might
slightly increase
the the voltage
gradient of the area
immediately around
the dissipater to
the sky, it does not
alter the charge
gradient or voltage
between the cloud
and tower.

Everything I have read
detailing successful
deployment of lightning
charge dissipators has been
anecdotal at best.
In every case there
are several
alternative
explanations that
have been ignored.
For example, several
people have told me
beacon or lightning
system damage has
been reduced by
addition of a mast
and dissipators
around a beacon
light. On the other hand

investigative report
s that collect data, including data from NASA, find
lightning strikes occur at similar rates with or without dissipators.

65G lightning protection for beacon and antennas

 

 

 

In my own systems, I
have a commercial
metal antennas or
metal masts mounted
above my beacon
lights. Looking at
my Rohn 65G to the
left, you can see
almost 15-feet of
antenna above the
beacon light. The
“thin” black line
going horizontally
to the right is a
160-meter dipole
mounted at about 310
feet. The more
vertical lines are
ropes, and the
fiberglass upper
guy lines are clearly
visible.

Prior to
the installation of
the upper VHF
antenna, with only a
commonly-used short
spike sticking a few
feet above the
beacon light, I
replaced several
MOV’s and tower
flashing modules in
the tower lights.

After installing the
antenna protruding
15 feet above the
beacon light, and
bonded to the tower
below the beacon
light, this tower
has taken hundreds
of strikes without
damage to any
electronics.

The taller
low-impedance
conductor bonded to
the tower below and
away from beacon
wiring reduces
damage to things
lower on the tower.
Lightning current is
harmlessly routed
around the beacon,
rather than flowing
through a thin
lightning rod
mounted immediately
next to the beacon
and grounded to the
beacon mounting
plate. This antenna
produces the very
same improvement
credited to fancy
expensive whiskers,
without the need for
false tales about
“charge dissipation”
or “lightning
mitigation” or
“charge
equalization”.

A
second effect of
adding the mast
above the beacon was
reduction in damage
to my 160-meter 
dipole. Without the
tall antenna mast at
the top, the coax in
the 160 dipole’s
balun would
occasionally melt
during a strike.
After installing the
tall mast, there
have been no balun
failures.

Had I
installed lightning
dissipators, I would
have probably
credited these
improvements to
mitigation or
reduction of
strikes. Unless I
was watching the
tower throughout a
storm, the only way
I would know if the
tower was hit would
be by observing
damage to equipment
on the tower after
the storm passed.

 

 

 

 

 

 

 

 

 

 

Reducing how
frequently Lightning
Strikes

The problem we face
is the small cloud
mass far away from
our massive
earth is charged
more and more as a
storm progresses.
The cloud either has to
stop charging
before it reaches a
voltage breakdown
point, or there
must be a direct
path that allows it
to equalize charges
without doing
damage.
Nature eventually
takes care of this. When the
charge gradient
between the cloud
(the source of the
potential) and the
earth (just a big
charge sink or
reservoir) becomes
large enough, a
streamer forms and
paves the path for
full blown lightning
bolt.

Connecting an
antenna to earth
does nothing at all
to reduce the
likelihood of a
strike. The antenna
is already at earth
potential, the real
problem is the huge
potential difference
between the cloud
and earth. The tower
is simply a
protrusion that
lowers the breakdown
voltage between the
cloud and earth. As a
matter of fact,
grounding if
anything only makes
the problem ever so
insignificantly worse. A
grounded antenna is
solidly clamped at
earth potential,
instead of being
ever so slightly
closer to cloud
potential like an
insulated or
electrically
isolated antenna
could be. In the
large scheme of
things, none of this
affects the
likelihood of a
strike. What big
improvement would
come from several
thousand volts of
change when compared
to millions of volts
of potential
difference? The only
significant change,
if we want to reduce
direct hits, is by
reducing structure
height.

A second (but less
effective) way to
reduce how
frequently a target
is stuck is to
create a very
wide blunt target.
Having a blunt
target will
reduce the electric
field density
appearing
at one concentrated
point. This is the
same effect that
causes a wider gap
in a spark plug, or a
blunt smooth tip in
a spark plug, to
greatly
increase gap voltage
breakdown. Grounding
the shell of the
spark plug better does
not help increase
gap voltage breakdown,
and neither does
putting sharp
whiskers on the
electrode tip!

Other than reducing
tower height until
it is well below the
height of
surrounding objects,
there really is only
one reliable course
we can take to
reduce damage risks. We can provide
a low impedance path
to a wide area of
earth, routing
lightning
current around things that can be
easily damaged.
Installing towers a
reasonable distance
from buildings is a
good idea, as are
perimeter grounds
and proper cable
entrances. I’ve seen
some terrible
structural damage,
and even one fire,
caused by
terminating guylines
or tower support
brackets into
building walls. Steel guylines
should be terminated
at earth anchors
that are reasonably
well away from
buildings or
building walls. If
that isn’t possible,
use fiberglass
guylines or install
low-impedance
earthing systems
that are tied into a
building perimeter
ground. Bracketed
towers need good
grounds at the tower
base, and house
brackets should not
be near large
metallic objects in
the house. The last
thing we want is a
tower bracket arcing
through a dry wooden
attic surface to a
metal duct or attic
electrical wiring.

Anyone who thinks a
few six-foot or
60-foot deep ground
rods can dissipate
hundreds or
thousands of amperes
at frequencies from
near dc up to radio
frequencies with
negligible impedance
probably should
spend time rethinking
the frequency
spectrum of
lightning. Unless
there is a very
large highly
conductive surface
area, like a radial
field or ground mat,
it
is almost impossible
to even spread or
dissipate strike
current. With small
area grounds, no
matter how deep they
are or how good they
are at dc or 60 Hz,
there will be a
huge voltage rise
between different
points around the
strike. We have to
do our best to have
everything
in the protected
area rise in voltage at the same
same rate. Keeping
charge levels of
different things
rising and falling
at the same rate is
the primary reason we
must bond the
utility entrance
ground to the radio
shack entrance
ground. It is the
reason a
protected area
requires a low
impedance perimeter
ground buss encircling
the entire protected area.

We can’t make
problems go
away or reduce the
odds of a strike noticeable
amounts by grounding
or snake oil cures
like static
dissipators. We
can’t discharge the
clouds
intentionally. We
just have to deal
with what happens during a
strike.

See Lightning Strikes

 


grounding