[TowerTalk] Grounding

[John Mardock]

If lightning propagates several thousand feet through the air to get to your 
Antenna/Shack/Home does anyone think a small gap arrestor is going to stop a 
direct hit? Silly question, yes?

John Mardock KRØP
j at mardock.us
j at KRØP.us
402-525-6111

-----Original Message----- 
From: Howard Hoyt
Sent: Wednesday, September 4, 2019 13:38
To: TowerTalk at contesting.com
Subject: [TowerTalk] Grounding

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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