[TowerTalk] RF Ground is a Myth

[Jim Thomson]

Date: Wed, 21 Jan 2015 12:51:38 -0600
From: "john at kk9a.com" <john at kk9a.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] [Bulk] Re: RF Ground is a Myth

What is the purpose of grounding each tower leg? I have not done this. My
towers have tapered pier pin bases and I have lines of ground rods
connected to two legs. Even with a straight base I find it hard to believe
that connecting one leg to a fantastic ground system would be
insufficient.

John KK9A

##  You folks all missed the point.  The fellow has a big mother tower
with 14 feet between legs !! 

##  he said... 
I have a triangular tower with legs on 14 ft centers, yes, 14 feet, not 
inches.  I built it with three SEPARATE concrete foundations, one per 
leg.  It is currently tilted over so one leg is not touching its 
concrete embedded mechanical connection/mount.

##  On big towers like that, or even on smaller ones like my old trylon
which are 52 inch  corner to corner, on any of the 3 sides, you always use
at least 3 ground rods.    Besides, the new eia-RS-222-rev G spec sez  you 
require a min of TWO ground rods for the base of the tower.   The 2nd one 
is for redundancy.   The 2 x rod setup applies to small towers like 25G. 

## You also need to get below the frost line.   I talked to some old timers
who have seen the concrete base of commercial towers blown to chunks
when hit by lightening.   When u super heat concrete, it explodes. 
If the concrete base for the tower contains rebar,  you require a 
minimum of 3 inchs of concrete  coverage over any rebar, or it will rust out.  

## If you are going to to use rebar as a ufer ground,  you have to be careful that the
rebar does not contain a lot of surface rust.  Some rebar comes painted.
To really do it right, and be effective, the rebar needs to be welded, instead of
using wire ties..where they intersect. 

##  back in the 80s, when I was 400 miles north of my current qth, I installed
a large L+R brand commercial tower, 33 inch face width.   It came with a large welded
base plate that was bolted to the bottom section...with the usual pier pin setup.  
I didn’t use the pier pin setup..and instead placed the bottom section, including the
massive .375 inch thick  steel base plate..into the 6 foot deep hole.   The sections were
21.5 foot long each.   To do the grounding, we jack hammered 3 x 8 foot long, copper
clad steel ground rods  into the bottom of the 6x6x6  hole, just beyond where the tower
section was.  2 ga bare stranded cu wire was cadwelded to each rod.  other ends used
compression lugs and bolted to bottom of each of the 3 x legs. then the concrete poured.
The hole was also lined with rebar, both H and V. 

##  What I ended up with is... the grnd rods starting at 6 ft below the grnd and going on down to 
14 feet below ground.   tower sections were all angle steel, and bolted together.   350 lb per 
section.  With a lightening hit, the juice flows down the 3 tower legs..right to the bottom of the
6ft deep hole..then keeps on going into the 3 x 8 ft grnd rods.   temps would hit –17 deg C
in winter. 

##  at the telco I  worked at, while up north....we used 10 ft rods, every 10 ft..around the entire
circumference of the building.   2 ga cadwelded to each one...and other ends went to a 2 inch wide
x .25 inch thick copper buss buss, that also went the circumference of the  50 x 90 ft building. 
microwave tower on the roof was grounded  to the perimeter grnd  via  3 inch wide x .187 inch
thick copper buss bar. It went from base of microwave tower to edge of flat roof, then over the 
edge..and straight down the side of the building , aprx 25 feet, then into perimeter ground. That described
setup was done in the early 50s. 

##  some more recent sites we used 200 ft deep well holes dug, then copper straight down the center of
the 6 inch diam well hole.  Hole packed with carbon.  2 of these well holes dug.   Cost a megabuck to install.
telcos at the time wanted extremely low resistance grounding setups. 

##  im still not sold on ufer grnds. I think I would bury 2 ga stranded. bare cu wire in a trench 1st.... along side the
homes perimeter concrete basement wall...like down 2-4 feet.   that’s how we got from the base of the tower
to the spg grnd in the basement...via  a 70 ft length of 2 ga cu wire.   Rods still used at each end. 

Jim   VE7RF