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Thread: Is this possible?

  1. #1

    Join Date
    Oct 2012
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    Gravois Mills, MO
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    Unhappy Is this possible?

    Several weeks ago we had a lighting strike about 20 feet from our house, it struck the ground between my comet CHA250B and my home made fan dipole, no damage to either antenna. However, it tripped two 20 AMP circuit breakers and took out two desktop computers (power supplies), my FT-950, two cable modems (and the HDMI board of the two TVs they were connected to), and my router. All were on except the FT-950 it was off. The only thing all these items had in common is that they all connected were to my shack ground. My IC-718 & FT8800, which were both on, and two other laptop computes (which were also on) were not affected; difference being they were not connected to the ground. The system ground is separate from the house ground which is located out on the pole that the electric meter is on. Talking to several tech's at the power company and to the tech's that replaced our cable modems think the EMF must have entered through the grounding system as it was directly wired to the grounding rod with no fuse or CB between the rod and the buss bar the items were connected to. If this a plausible, how can I protect my equipment from this happening again.

    Any thoughts on this?

  2. #2

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    Oct 2009
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    Protection from a lightning strike about 20 foot away? You'd be very, very lucky to do so. When I worked for a major mobilephone network equipment manufacturer doing EMC testing, the ports were tested to 1 kV - supposedly a simulated lightning strike 1 km away. Anything closer and there was no guarantees.

    When lightning hits the ground, the ground will be charged to tens of thousands of volts at the point of the strike. This will drop off, quite quickly away from the strike point. So, any "ground" wires or cables buried in, or on the ground will have a voltage induced in them. The further away from the strike point you get, the lower the voltage. If the two points are conductivity connected, then a current will flow. If one point is close to the strike point the other is several yards away, then the PD can be well over 1 kV, easily damaging any equipment connected to the line.

    Best protection? If we hear thunder, I go to the website http://en.blitzortung.org - If I see there are strikes within 5 km / 3 miles of our home, we unplug everything that has a wall socket, except the freezer.

    United States: http://en.blitzortung.org/live_light...aps.php?map=30
    Europe: http://en.blitzortung.org/live_light...aps.php?map=10

  3. #3
    Super Moderator 5B4AJB's Avatar
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    Quote Originally Posted by KD0QEB View Post
    no fuse or CB between the rod and the buss bar
    If static discharge can travel, maybe half a mile or a mile through open air, what effect do you think a 3mm circuit breaker gap will have?

    Set up a lightning conductor somewhere as high as you can (or put your antenna below the neighbours TV antenna height), though, as OH8GAD said, some portion of the discharge will be induced whatever you do.

    I always found it fascinating during a lightning storm to connect several neon bulbs in parallel across the antenna coax and watch them dance.

    There's a few mobile apps to track lightning strikes from that website too...

  4. #4

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    Quote Originally Posted by 5B4AJB View Post
    I always found it fascinating during a lightning storm to connect several neon bulbs in parallel across the antenna coax and watch them dance.
    Neat!

    When I lived back in the UK, I had a 3-ele beam for my 2-metre rig. One morning, it was pointing south-west-ish, towards London (I lived about 80 km north-east of London). I was listening on S20. Every now and then, the noise level rose a bit, then dropped suddenly. I then heard someone calling, but only when the noise started to rise. I tried to call the guy back and he did hear, but kept getting cut off. I told him to watch the S-meter and only transmit when the noise rose and to keep it short. We even dropped it down a channel and kept up the QSO. The storm was over London and he was in Surrey, south of London. We kept up the contact until I started to hear the thunder and the S-meter was climbing to over S9 and just before discharge, it would whack the end stop. My first and only QSO using a thunderstorm!

  5. #5

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    Only problem I see from reading the OP is that both grounds are separate. If I understand the NEC correctly, all grounds should be tied together. Not that a strike that close would be survivable by your electronics, but would keep the differential the same, being safer as a result.

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