Hi everyone. I wanted to share with you a lightning strike incident which
occurred to me last week Tue afternoon. I thought I had done a pretty good job
protecting against lightning so this came as quite a surprise. I'll try to
give you a run down of the antennas and shack as it pertains to grounding.
I have 3 towers up, one at 80', one at 50' and one at 70'. Each is a Universal
Aluminum self supporting tower which I have supplemented with a single set of
3/16" steel guy wires about 2/3 of the way up. Each tower leg has it's own 10'
ground rod connected with a 3' length of #0 wire. The towers are each
separated by 130' and are in a straight line configuration. The 80' tower has
a short 40m rotatable dipole at 90'. At the 80' level I have suspended an
inverted vee for 75m. Each of these was fed with not quite 300' of 9913F type
coax. The cables were currently lying on top of the grass as I had just
installed them 2 weeks earlier. I was just starting to play on HF after many
years on VHF SSB and MS. The 70' tower has a new X7 at 75' and the 50' tower
has a pair of 17B2 on Az/El for moonbounce.
All rotor cables and coax from all towers terminate to a 18"x18"x1/8" Aluminum
panel I have in place of one of my basement windows. The panel is at around
ground level and uses N-type feedthrus. The panel has 2 mechanical connections
for ground. Each one has attached a 3'-4' length of #6 wire that goes to 2 10'
long, 3/4" copper pipes. The panel thus has 4 ground rods. When I am not
using the shack all cables and coax are physically disconnected from the panel
(from the inside) and separated from the panel by a foot or so. For almost 10
years this setup has seemed to serve me well and I recall riding out some
terrible storms with tons of hits all around the QTH with no misfortune. All
equipment was connected to AC power but not turned on.
This last Tue afternoon a fast moving storm with a large amount of
cloud-to-ground strikes moved directly over the QTH and the 80' tower took a
hit. My wife said it sounded like a grenade went off inside the house. She
made her way downstairs only to find the entire basement 100% filled with thick
smoke. Visibility was VERY poor. She was afraid the house was on fire. Once I
got home I looked things over and discovered that I overlooked a small folded
dipole made of TV twinlead that I had tucked into the blinds just above the
panel. The dipole was purely indoors and was not touching the panel. My guess
is that it was several inches away. The panel became highly charged and arced
over to the dipole. The dipole was NOT terminated but ran close to my Aluminum
radio shack speaker for the FT-990. The speaker wire conducted the arc into the
rig. Half of the dipole is missing. Half of the speaker wire is also missing.
The connector on the back of the FT-990 got blown out and t
he back of the rig looks like it was hit with a flame thrower for about 10
seconds. The rig is dead. Of course the AL-1200 was next because it was
connected to the FT-990. Once it got into the 220 mains it found the Commander
II VHF amplifier. The tailtwister rotor is shot as are the coaxial cables from
that tower. Some additional items such as 2 routers, PC interfaces, ATV
transceiver etc are also DOA.
This has taught me that my towers are not very well grounded nor is my entrance
panel. It also has shown me that anything located near the panel is vulnerable
to flash over.
I take this opportunity to share this with you in the hopes that you can learn
something from my experience and keep yourself and your equipment safe.
online gallery http://gedas.cc
web page http://www.w8bya.com
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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