----- Original Message -----
From: "Don Jones" <ko7i@comcast.net>
> Cecil,
> You are spot on. A direct ground strike will develop up to 400 kA-pk. At 5
> ohms that is a serious voltage surge. The Voltage Surge will have a very
> fast rise time (less than 100nS), the current surge will have a lower rise
> time 40uS or so. Within 1mS the impulse will have decayed back to zero.
> If your tower takes a direct strike, the grounding at the base of the
> tower
> had better be able to "take it" up.
> W8JI claims his towers have taken direct strikes and has a section of his
> web site dedicated to lightning protection. Lots of straight talk and no
> BS.
>
> I feel blessed to live in Western Washington. Very rarely do we have
> serious
> lightning activity.
> 73, Don KO7i
That's why I am concerned about guys that drive 3 ground rods at the base of
their tower and expect it will be good enough. Mine has been struck 3 times
in the last year and the net result was the loss of one hot air workstation
and a tripped breaker in an electrical panel. The tripped breaker is an
indication that I probably still have a bit of work to do. (all radio gear
was still plugged in but antennas disconnected) I have lots of 2/0 copper
in the ground as radials leading away from a ring around the base of the
tower with 10' rods driven every 20'. (probably 18 to 24 total..can't
remember) Everything is cadwelded. No clamps...they degrade...especially
when buried.
As you can see with a 400Ka current peak and a ground system as good as 5
ohms you are still talking about 2 million volts to have to sink off. Less
than 5 ohms would be more desireable but becomes difficult to attain. With
things happening so fast, distance is your friend as well...having the tower
100' from the shack buys you some time for the ground system to do it's work
hopefully decaying the energy significantly before reaching the shack
equipment and your home electrical systems. Thats why bonding those
together is important so they all come up to potential together..any
differences causes current to flow and damage to occur.
I live in one of the most lighning prone areas of the country...the Gulf
Coast of MS. Second only to the central FL area...
Cecil
K5DL
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