[TowerTalk] getting the ufer ground effect with a burried

[Jeff AC0C]

The rustolemum pro spray is conductive.  I sprayed a segment of aluminum 
tubing with 3 coats of the stuff; nice and thick.  After drying a few days, 
taped some fine stranded wire spread out over the top to serve as a top 
conductor and avoid the risk of cutting into the paint and inadvertently 
touching the underlying aluminum.  It measured around 10 ohms in several 
spots with my HP 3456a in 4-wire mode.

So yes it's conductive in the sense it's closer to zero than high-z, but 
it's not conductive in the sense a #4 copper buss wire is conductive.  Given 
the surface area we are talking about I would say that the paint is not 
going to be much of an impediment in a lightning event.  It's definitely 
better than a thick layer of normal paint.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

-----Original Message----- 
From: Jim Thomson
Sent: Sunday, September 10, 2017 4:02 PM
To: towertalk at contesting.com
Subject: [TowerTalk] getting the ufer ground effect with a burried

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
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