[TowerTalk] Grounding

[Howard Hoyt]

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.