Keith, all,
I will amplify this a bit; a direct strike to anything on or within the home can be
catastrophic. I'm a broadcast engineer and I will not degrade list s/n by
elaborating how extensive grounding systems are in our broadcast facilities. Even
so I have seen some very scary results of lightning such as a helical element on an
FM panel array fused into a ball of copper, and even with these spec ground systems
I've seen damage to equipment on the ground. 6" hardline has a pretty high peak
voltage rating, 50 kV or more when pressurized and I have seen loading caps in PAs
burnt up by lightning-initiated transients, followed by the HV PS feeding the arc.
Due to my 'respect' for lightning and what I have seen it do, I have always
been very wary with my ham setup. When not in use or when lightning is
anticipated I actually disconnect the feedline where it enters the house, and
walk it 30' away under a tree and stick the PL-259 into a clean dry wine
bottle. As a result I have never suffered equipment damage in my house due to
lightning striking my ham antenna. Damage to the antenna, sure, but that was
all.
Just about a year ago I had lightning strike my TV antenna, which was on a 20' mast
grounded with an 8' rod and a gas-tube "F" connector arrrestor. The antenna
was lower than the peak of my house and under 90' trees, but lightning, likely a
side-strike found my TV antenna. It melted the end of one of the alumninum elements, and
then followed the RG-6 into my house and got to work. It destroyed the TV which was
wired ethernet connected to my router. From there it propagated everywhere wrecking
audio/video/all IT infrastructure/PCs/PV Inverters/electronics test bench equipment.
Fortunately the ham gear, not being ethernet connected was largely spared other than the
USB dongle and minor grounding damage. It vaporized Cat 6 in places, and has taken me
months and ~$30k to remediate. Thanks to an Eaton commercial TVSS in my main panel no
damage propagated via H/N/G AC wiring differentials. As a side note I HIGHLY recommend
Auto Owners Insurance, I was getting deposits in my account hours after submitting
invoices.
In order to minimize a re-occurrence I have optically coupled the Ethernet and HDMI
connections to the TV. I looked into a broadband uV level optical converter to
isolate just the TV antenna but there is currently no such animal, so as of now if
lightning hits the new antenna the TV is sacrificial. Some have asked why I just
don't do Wifi with the TV, and that its because I like 4k HD content which has not
been reliable with WiFi despite optimal TV IP configuration. Others have stated if
the TV mast ground was bonded to my house ground no damage would have happened, but
although a good idea, it is likely to have made little difference in the outcome.
The TV mast is 50 feet away from the main panel and it's ground rods. Any conductor,
even if punctuated with rods every 16 feet would have >28 uH of inductance and
high capacitance to the earth, so the resulting transient would take >100 nS to
reach the house ground and equalize the charge there. In the meanwhile due to ground
potential rise the earth around the TV ground rod and the TV coax shield are at
perhaps tens of thousands of volts of potential differential to the house AC system
and all connected devices.
As is the case with broadcast facilities, it would be optimum to have all
external utilities enter at the system grounding point as I have done at FM
stations, so maybe I will move the TV antenna...
This situation exists for most homes with TV antennas, wireless dog fences and
other wiring external to the house, so be prudent!
Just my 2¢ worth.
Howie / WA4PSC
from [Keith Dutson] NM5G
My experience is that lightning can be managed, to a point.
A direct strike to your tower can be catastrophic.
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