Date: Wed, 21 Jan 2015 12:51:38 -0600
From: "john@kk9a.com" <john@kk9a.com>
To: towertalk@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
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