>
> In my experience with grounding as lightning protection, a very important
> aspect is that everything be kept at the same potential. All grounds need to
> be common with the electric service ground. The tower, metalic plumbing, and
> anything metalic of any length, must be bonded together such that the entire
> grounding system is at a common potential. Then added to that ground system
It is also REQUIRED in the NEC (National Electric Code) that ALL grounds
be bonded. I bring everything in a star to the main ground point, which in my
case is the water main.
> should be several electrodes. What is often not expressed, is that a good
> grounding system will greatly lessen the possibility of a lightning strike
> by constantly discharging the rapidly building electrostatic potential
> during a storm. An ungrounded wire antenna, in my experience, is an open
> invitation for a lightning strike.
I have ground rods at each coax entry where the coaxial lightning protectors
are.
There are ground rods at each antenna structure, including the satellite dish.
All
are eventually bonded to the main ground at the water main in as close to a star
pattern as I can make them. Will it survive a direct strike? Probably not.
But it
will help to prevent one and should do a good job of protecting everything from
the induced current of a nearby one as well.
>
> Ten years ago, when I put up my tower, I thought it would be a great idea to
> separate the tower grounding system from the electric service ground. Two
> years ago I learned that such a setup creates very large differences of
> potential in a storm. I had brought a cable from the tower ground system, in
> through the wall and lugged it to the back of the steel plate where all of
> my coax bulkhead connectors were mounted. I had wire braids with banana
> plugs hanging from this grounded plate, that I would plug into the center of
> the female bulkhead connectors, to ground the dipoles.
>
> Anyway, I took a lightning strike (melted the reflector on a beam) and where
> the tower ground passed near the romex cable feeding my equipment, there was
> signs of a fire ball and the romex jacket was blown open. Interestingly
> though, the main conductors were just scorched while the romex ground
> conductor had very obviously taken the strike. This helped equalize the
> potential difference between my tower ground and my electric system ground.
> Then there was a flashover across the duplex outlet under my desk. It
> literally blew the plugs out of the receptacle, melted parts of the
> receptacle and blew the cover apart. This helped equalize the difference of
> potential between the grounds and the electric mains.
>
> The radios were disconnected from the antennas. All that was plugged in in
> the shack was a digital clock. The clock was on top of a keyer which was
> connected to two radios. The clock exploded all over the room, melted the
> metal cover where it arced to the keyer, took out several transistors in the
> keyer and wiped out both radios. Many other electrical items in the house
> ended up in the spare parts bin also.
>
> Another interesting thing was that where the guys were anchored to the roof,
> it blew through the shingles as well as through the plywood. But only on two
> of the guys. One was untouched. The two damaged areas were where the guy
> anchors were bolted near the front and back edges of the roof. I could see
> where the aluminum drip edge under the shingles was melted where the
> lightning literally blew through the roof. This drip edge is in contact with
> the aluminum gutters and obviously there was a huge difference of potential.
> There was no metal near the third guy and no sign of damage either.
>
> I now have all grounds tied together, added surge protection to the main
> panel, and keep everything disconnected during a storm. I also have a wife,
> three kids, and a dog, who have an awsome respect (fear) for lightning.
>
> Jeff - K1LE
> East Lyme, CT
>
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