[TowerTalk] getting the ufer ground effect with a burried

[Jim Thomson]

Date: Sun, 10 Sep 2017 06:28:39 -0400
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk at tm.net>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] getting the ufer ground effect with a burried
painted section

<As a personal opinion and many years of back ground I think the bare 
metal would be better. The question is "how much better?"  It depends on 
the area of painted metal in the concrete and that depends much on the 
size of the tower legs. The metal with paint is essentially a very large 
capacitor that will shunt most of the lightning strike to the UFER 
(concrete) and that concrete has a tremendous area on the exterior. Far 
more than a network of ground rods.
It would take a very powerful strike to even damage the paint.

Jim Brown gave a very good description of the voltages, currents and 
power involved.

Were it me, I'd add a ground rod out about 6" on ea side (in the 
concrete) from each tower leg in addition to an external ring of ground 
rods extending out for two 8 footers, 16' apart..

As to rust. I doubt that would be a problem "in" the concrete.  I would 
want the top 4 to 6" where it enters the concrete painted though.  There 
is a high tendency to rust where unpainted steel enters the concrete.  .

73, Roger (K8RI)

##  Does that Rustoleum cold galvanized spray bomb...conduct or not ? 
I just assumed it did... and have used it myself in the past, but never thought
to check with a dvm, etc.    Ok,  I just checked several sections in the trunk
of my car where I had the rear strut tower brace brackets welded, then doused
with rustoleum cold spray... and it reads wide open using my B+K  875-B..which
reads AC resistance at 1 khz.  My fluke 87A is over at a friends place for an
electrical job, so not available. Dead battery in my B+K 875-A..which does
measure dc resistance. 

##  Flip side to all of this is.... remember when they used to strap tower sections
together on all 3 x legs to  electrically bond the sections.   They stopped doing that
25 years ago or more... even on painted sections.  Even on AM broadcast towers
that are painted.   So if his tower did get hit with lightning, it would no doubt just
jump right through the cold galvanizing paint.    I would not rely on the ufer ground.
Install at least 2 x 8’ ground rods,  and preferably 3 of em...jack hammered into the 
ground.... with tops of ground rods below ground by 3-8 inches.   Then cadweld
RW-90, stranded 2 gauge cu to each ground rod..then  route over to each tower leg.
3 rods, and 3 cadwelds, and  1 2 gauge per rod, each 2 gauge going to one leg,
then a compression clamp, then bond to leg.  With cadwelds and tops of rods below
ground level, then cover up   with grass sods etc. 

Jim  VE7RF