The #1 Iron is a bit facetious, but there's an element of
truth in it. The purpose of the lightning rod (or Franklin
terminal) is to be the highest point in the area. When the
lightning starts heading down (it is called the step leader
and it jumps in ~150' increments), as it approaches, streamers
start heading upwards to meet the step leader. The purpose of
the rod is to provide the streamer most likely to find favor with
the step leader and, when they meet, create the return stroke
which is the pulsed ionized white streak we call lightning. The
concept is for you, rather than Mother Nature, to control where
the strike occurs. The other important part of lightning protection
is to have a low inductance ground so the energy will flow to the
earth and be absorbed rather than finding this path through your
brand new Yaesu FT-1000D! BTW, your Ufer should *not* be the
only grounding system but should be connected to a good ground
system as an adjunct.
Any good surge suppression system should dump the energy into
the ground system for dispersal into the earth. Because of the fast
rise times associated with lightning (on the order of a few
microseconds),
frequencies up into the GHz range are generated, although the bulk
of the damage is done by the high energy DC or near DC components.
Skin effect limits the capacity of the grounding wiring, so Poly has
always recommend wide copper strap over even 4/0 wire (forget the
ubiquitous #6; it'll work for the power company's 60 Hz, but not for the
frequencies generated by lightning). You want to provide a low
inductance
path so that all of the lightning energy goes into the earth with
minimum
impedance. So whether you choose MOVs or SADs, make sure you create
a good ground system for the shunted energy to go or it will still find
a way to
get to your new 36" TV with the surround sound feature! At best, you
will
shorten the lifespan of your protective device.
For additional info, contact Poly and purchase their book "The 'Grounds'
For Lightning and EMP Protection." If you get Tricia, tell her I said
"hello."
73
Bob Wanderer AA0CY
----------
From: Peter J. F. Shaw[SMTP:k4ldr@hitter.net]
Sent: Monday, August 02, 1999 6:37 AM
To: Bob Wanderer
Subject: Re: [TowerTalk] Lightning prot. (& bases on slopes)
Ahoy Bob:
Is ur closing remark about the #1 iron on the chimney a suggestion or
recommendation for a roof lightning rod system....or just a closing to
ur discussion on MOVs/SADs? I got something useful from ur
discussion.
I am located in the belt across Florida alleged to be the world's 2nd
highest ground strike lightning area; and on the highest ground around
(135 ft AMSL is a mountain in FL). 4 strikes last year, but no ham
gear lost. Fire in radio central and lots of household appliances
cooked. I have a Ufer system in the floor slab and MOV protectors on
AC entry, well head, etc.
My high lightning is why I was asking about the lightning rod system.
I am thinking about installing two grounded 35 ft masts at opposite
ends of the one-story house and connect them with an overhead cable.
This concept is similar to what NASA has at the Canaveral space
shuttle launch tower. There, a big insulator is on the very top with
large diameter cables going to earth like guy wires. I don't know any
details more than that.
Lightning rods or no rods? That is the question. The serving power
company lightning wizards explain that their opinion is that it is a
bad idea for a rod system to be attached to the house structure. They
say that the usual home TV antenna tower should be mounted 25 ft away
from the house and well grounded. We are in a fringe area, the TV ant
towers have to be 40-50 ft and their idea is that the higher tower
gets the lightning stroke.
I wud welcome ur comments.
Tnx 73 Pete K4LDR Citrus County, FL (55 miles North of Tampa
Airport)
P.S. Lightning is so frequent and scary up here on the hill, my pals
call me Sparky.
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