Lightning Arrestors [RE-wrenches]

[Joel Davidson]

I lived for several years on the 3rd highest peak in the Ozark mountains in
northwest Arkansas at 2285 feet (short mountains but deep hollers). There was
nothing taller to the north all the way to the north pole and beyond. Nothing
taller to the west until you get to the Rocky mountains uplift. Lightning
storms would come in regularly from Lightning Alley to the west and hit my
place about 6 to 12 hours after they hit Tulsa, OK. I use to lean up against
a west-facing earthen bank and watch the storms. Lightning all around. Trees
bursting nearby. Ozone in the air. Lightning never hit my home, tv antenna,
PV array, barn and out buildings with metal roofs, metal wind tower, etc. All
ungrounded. Nearest power and telephone lines about a mile away down by the
highway. A few of my neighbors had lightning rods on their barns because
traveling salesmen in the 1950s sold them. Lots of lightning hits the Ozarks,
but very little damage to man-made things. Lightning, luck and love all start
with "L". Some people believe you get what you give, but Darwin would
probably think otherwise.

"Chuck Heath, SunPower" wrote:

> Doug Pratt writes:
> > Here's what 15 years in the renewable energy biz has
> >taught me about lightning:
> Good advice, Doug!
>
> Let me add what broadcast engineers often do at FM/TV transmitter sites:
>
> The coaxial hard-line is grounded to the tower at several points using
> stainless steel clamps as it nears the bottom of the tower. This is
> accomplished by cutting the outer plastic insulation to bond the clamp to
> the solid copper outer shell of the line. If the transmission line is
> semi-flexible, they put in one or two large loops (typically 3-4 ft. in
> diameter for 7/8 in. Heliax) where it turns 90 degrees from the tower to
> the "ice bridge" leading into the transmitter building adjacent to the
> tower.
>
> Since lightning prefers to go in a straight line, this minimizes the
> amount of lightning energy brought into the building.
>
> Reminds me of the story in HP years ago about the guy who thought putting
> in a kWH meter would solve his lightning problem. He pulled the meter
> when he thought strikes were likely, only to learn the downstrikes easily
> jumped the knife blades in the meter box.
>
> In our RE business, this could mean using shielded output cable from a
> wind genny, then cutting the vinyl insulation about every 2 ft. at a
> dozen or so places in the first 25 ft. up the tower, using stainless
> steel clamps to bond to the shielded cable.
>
> Equally important is using 4 in. wide copper strap extending out from the
> base of the tower several feet (in AM radio, this ground system is needed
> to transmit an effective signal, hence the "best" ground is salt water).
> At the outer end of each ground radial, there is a copper plated ground
> rod. Each of these are interconnected by bare copper wire, forming a
> perimeter ring around the tower. The same concept is often done to the
> transmitter building itself, with bare ground going over the roof and
> down to a perimeter ground surrounding the building, with ground rods
> connected at all corners.
>
> Another popular product with telecom/broadcasters is the Cartana
> Stati-Cat. This piece of hardware sits at the very top of the tower,
> typically on a galvanized pipe rising 8-10 ft. above the top of the
> tower. It's all stainless steel and sort of looks like a porcupine.
>      http://mwpersons.com/Cortana.html  (thanks, Sparky, for this url
> last March)
>
> And yes, Polyphaser <www.polyphaser.com> is the first choice of lightning
> protection among broadcasters, but as others have noted, not inexpensive.
>
> My own experience living 12 years on a Sierra mountaintop next to two 140
> ft. commercial broadcast towers with this protection was they never took
> a hit, but a 90 ft. dead cedar tree less than 100 ft. away was struck 3
> times.
>
> Chuck Heath _now serving California's North Coast_
>
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