[TowerTalk] Mast bonding
Fri, 07 Apr 2000 08:39:24 EDT
I would like your comments on an idea to bond my mast to my tower. I have
seen some posts in the past referring to the vulnerability of rotors to
damage from lightning strike current that comes down the mast and through
the rotor housing. My tower is R25 with a flat top plate and a Rohn TB-3
thrust bearing. The mast is 6061-T6 aluminum, 2" od. The TB-3, with its
three centering bolts, doesn't necessarily present a solid bonded connection
to the tower frame.
Well, thunderstorm season is just about upon us here in Virginia, so I need
to get cracking (zzzzZZZZT!).
Here's the plan I have so far:
I bought 2, 48 in long, #4 gauge battery cables, having crimped lugs on each
end (not post clamp ends). I will place a band of stainless steel foil
around the mast, just below the top plate, and clamp the top lug of each
cable to the band using two stainless hose clamps. I will peen the lugs
lightly with a hammer as I tighten the clamps, to maximize the contact
patch, using antioxidant paste on all mating surfaces (under the band, too).
To protect the antioxidant from washout, I will tape the joint thoroughly.
At this point, the cables are hanging straight down, parallel with the mast.
Next, I will clamp the bottom ends to two separate tower legs in the same
fashion as the top ends. I will have to choose the bottom clamp point
carefully to leave enough slack for the cables to wind around the mast
during rotation. This should present a gently curved path of discharge from
the mast to the tower legs, 2 to 3 feet above the rotor position, with no
abrupt change of direction.
Is this similar to how any of you are accomplishing this? Please pass along
your comments and ideas.
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