Date sent: Sun, 11 Apr 1999 22:39:44 -0600
From: David Leikis <dlleikis@deseretonline.com>
Send reply to: dlleikis@deseretonline.com
To: towertalk <towertalk@contesting.com>
Subject: [TowerTalk] Lightning protection grounding
> I have seen many recent postings concerning grounding methods and saw one
> that stated to run a ground conductor up the mast to the final section
> (and the others as well) to prevent any high resistance points along the
> way through the joints.
That is a waste of time with bolted or pinned masts or towers.
Most, if not all, AM BCB stations have abandoned the old idea of
welding jumpers around tower joints.
With many many thousands of pounds per square inch (the weight
is in thousands of pounds and the surface area is tenths of an inch)
pressing on those joints, the likelihood of a "high resistance
connection" is zero.
Besides that, even if there were a gap it would simply breakdown
and form a low resistance path at the first sign of any charge.
A telescoping tower MIGHT be another situation. Lightning could
arc through a insulated roller or bushing and damage it. But I know
of dozens of telescoping tower installations that have never had
problems. If it was my tower, I wouldn't worry a bit.
> concerned about the sliding joints of the installation. It seems as
> though these would definitely be high resistance and would need this
> more than any other.
High resistance won't hurt a thing, if the air gap is small and has
large surface area. A lightning bolt that travels thousands of feet
through air will not care about a 1/10 inch gap in a sliding section,
and it certainly won't damage it if the surface area is large. You'd
have so much impedance in the a parallel grounding wire, virtually
all of the current would be in the large tower structure anyway.
What is a recommended method from those that may
> have done this before? We can have some pretty severe storms here and I
> am positive (or negative) that lightning charge dissipation should be
> 'high' on my list.
Bring all the cable to the base of the tower and leave underground.
Ground the base of the tower well with ground rods and buried
radials. Treat the antenna wire entrance to the house properly, and
disconnect the wiring when you aren't using the equipment.
Most anything else is a waste of time.
73, Tom W8JI
w8ji@contesting.com
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