Most lightning actually begins with a negative charge accumulation in the
lower areas of a convective cloud. The negative charge in the cloud repels
the electrons below it in the ground and man made things near it. There is
nothing you can do to 'bleed off' this charge. Then in most cases a
negatively charged leader starts coming down from the cloud relatively
slowly, you don't see this one unless you have a special camera or track the
radio noise it makes as it steps its way downward 50-100m at a time. as it
approaches the ground the charge on the ground concentrates until it causes
a breakdown in the air and an upward moving leader connects with the
downward moving one and then BOOM, you see and hear the current that flows.
Since the electrons must flow through something to get to/from that
attachment point to the ground there will be large currents and hence high
voltages between the attachment point and anything around it, including the
ground... this is where everyone messes up, they stick a rod in the ground
and call that 'ground' as if it is always a perfect sink for electricity.
In fact it is common for the 'ground' wire of high voltage power lines to be
hit, that is the wire above the power conductors that is attached to the
towers that are all 'grounded'... but in a good percentage of those hits the
voltage of the 'ground' gets so high that it flashes over the insulators to
the power conductors, this is called a backflash. Those insulators can be
rated for 100's of kV or even into the MV range and can't withstand the
voltage on the grounded conductor... so how do you do it with your puny
cables and tiny insulators?? You don't let the voltage across the
insulation get that high by forcing everything in the house/shack to change
voltage in step with the ground. That is really what lightning arresters
do, they usually don't take current off the center conductor to the shield
of a coax unless perhaps it was a vertical antenna that was hit. In most
cases they are increasing the voltage on the center conductor to match the
shield, or on the control wires to match the ground wire. that way when the
current gets to the sensitive device that you are trying to protect the
ground and signal wires are near the same voltage (which could be MV
different than the distant earth) so there is no danger of causing damage.
But let just one power lead not be protected and it will be the wire at a
drastically different voltage and will be the target for the infamous
backflashover, and whatever equipment is between it and the ground is toast.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Bill
Winkis (KC4PE)
Sent: Saturday, September 06, 2014 11:50
To: 'Kenneth Goodwin'
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] G-2800DXA lightning damage
Proper Grounding....????
Can we agree that a static crash/lightning/begins with a positive charge in
Mother Earth, whether it be your Air Conditioner compressor/your vertical
antenna/your tower/and on......so whatever is being charged must have a
proper ground with a proper bleed off, or the charge will continue until a
atmospherically provided path couples and then BOOM, lightning/damage to
whatever.
SO ..if one provides a proper text book ground he will have no problem to
bleed off this charging he will have zero problem
Read On...!!!!
https://www.google.com/?gws_rd=ssl#q=lighning+glen+zook
http://www.w8ji.com/station_ground.htm
Take the time to read the below...especially PolyPhasers WHITE Papers
http://www.smithspower.com/brands/polyphaser/services/media-library/white-pa
pers?page=2
-KC4PE
http://www.kc4pe.com/amateurshack.htm
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Kenneth Goodwin
Sent: Friday, September 05, 2014 3:10 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] G-2800DXA lightning damage
Agree, disconnecting everything is the only reasonable means of protection.
If your radio equipment is hooked to a power outlet and/or a computer, those
connections will have to be disconnected also unless one feels confident
enough to have the power/network/Internet/telephone connections protected.
Near field lightning hits which are the highest probability of occurring for
most nominal station configurations, will result in two common scenarios.
They obviously induce large amounts of energy into antenna systems and such
things as one's security system if it has long wired connection paths, e.g.
window sensors on one loop. Near field hits will also bring the energy
right up the ground connections as the potential level of one's land is
raised with the hit (the reason for single point grounds). Don't rely on
your Internet provider even if they have what looks like a protection device
in the cable. They just normally ground the shield connection if cable
Internet/TV/VOIP telephone is used. Same applies to one's telephone if that
is another wired connection. Since disconnecting every secondary connection
is difficult, having protection for all of those other 'connections' is
probably the next best step. Disconnecting one's antennas/control lines is
still desirable regardless since the probability of one's antennas
conducting energy is > 0. One also needs to remember the impact of today's
house insurance deductibles. Last thing I want to do with my house
insurance company is file a claim. It's why I use the ARRL Insurance
program for my most expensive radio equipment. For my secondary
connections, I use multiple UPS's for power, have a gas discharge device in
my Comcast cable as it enters the house in addition to protection at the
network box interface. My TV/Internet cable runs above ground except for
the connection from the pole to the house where it runs underground as is
normally implemented by most cable companies. In the newer neighborhoods,
underground utilities are worth every indirect penny it costs. I use surge
protection for the AC power at the breaker box and telephone line protection
(MOVs) at the line entrance to the house. I tried protecting the AC power
at the pole but the electric company didn't like that even though I own the
underground wire from the breaker box to the pole. They rightfully demand
control for everything from the power meter back. I know I can't fool
Mother Nature even with my single point ground system since I have so many
back doors. I realize the commercial people are able to do it, but they
start out with a fresh sheet of paper and can easily design adequate
lightning protection from the very beginning with a no exception single
point ground system. Ken K5RG
------------------------------
Message: 5
Date: Fri, 05 Sep 2014 07:40:21 -0600
From: Steve London <n2icarrl@gmail.com>
To: towertalk@contesting.com
Subject: [TowerTalk] G-2800DXA lightning damage
>I live in an area with high monsoon thunderstorm activity. I doubt that
>any
of the protection devices would > survive. I disconnect everything where it
enters my radio shack.
>Spencer W1GAK
I live near Spencer, and 100% concur with his recommendation. Put a Jones
plug at the control box and keep it disconnected during the thunderstorm
season unless you are actually on-the-air. If you are using a computer
connection to the control box, disconnect that also.
73,
Steve, N2IC
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