Hi Dick,
Sorry for the confusion, silver solder is only my slang. More accurately, I am
using silver-copper brazing alloy - 80% copper, 15% silver, and 5% phosphorous.
Melting point starts at 1190F and fully liquid at 1480 F, so acetylene torch
is required. To my understanding, this method is commonly used on commercial
AM station grounds. See W8JI website, Georgia Copper, and other references.
73
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Dick
Blumenstein
Sent: Monday, October 16, 2017 9:53 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] FW: Tower Grounds
Hello Jeff-
Shortly, I am going to be using 2" wide copper strapping on my tower legs.
However, I am NOT attaching them to the tower leg bolts. Instead, I will be
clamping them on each tower leg about a foot up or so from the base and in a
GENTLE ARC, running them down to a ground rod near each tower leg, attaching
them with ground rod copper clamps below the Harger CAD weld that attaches to
the rod at the top where my #2 AWG stranded goes out to additional ground rods
(like a tree branch). I have read in the past that silver solder might explode
or melt (sorry Matt) from a lightning strike and might not hold together. I
will, of course, use stainless shim stock between the copper and the galvanized
tower leg to reduce galvanic corrosion. Since I haven't done it at this time
(soon, though), it might be a little challenging to get the copper under a
couple of stainless radiator hose type clamps and then to proceed in a
"graceful" arc down to the ground rod. We'll see how that goes for
me; which is why I selected 2" wide (and not 3" wide) copper strapping. I
heard that lightning does not like to take sharp turns, hence, the arc of
copper and not bolting to the leg bolt. Every time I want to lower my crank up
tower horizontally to the ground to work on the antenna system, I will
obviously have to remove the copper from under the stainless clamps. A bit of
a pain, but so far I have not read of a better way. At least it will allow me
to look at any corrosion that might have occurred since last time I lowered the
tower.
(BTW, a little anecdote. The electrician I used for heavy duty projects in FL,
told me that he used to work at the Kennedy Space Center. He had to CAD weld
about 2,000 (as I recall) very long ground rods around the Vertical Assembly
Building. Now, that's one heck of a ground rod system!!!)
73,
Dick, K0CAT
===================
Matt wrote on 10/16/2017 12:04 AM:
>>> Has anybody had any experience with grounding towers with flat
>>> copper
> strap v.s. using stranded wire or copper braid (tinned or untinned)?
> --jeff Wb7aht
>
> Hi Jeff,
>
> I feel that wide copper strap is an excellent choice because of its
> low impedance and outdoor durability. I used 3" x.032" copper strap from each
> tower leg to tie into my ground loop. I drilled 1.125" holes in the strap
> to fit over the anchor bolt to tower base connections (all crank-up
> towers at my station). To make clean holes, I sandwiched the strap
> between two scraps of plywood and used a forstner bit in a drill
> press. The copper strap is dielectrically isolated from the
> galvanized base and bolts to prevent galvanic corrosion using a pair of
> 1.125" ID stainless steel flat
> washers at each connection. I also coated the connections with antioxidant
> compound and it will be easy to check and service them periodically
> since they are above grade bolted connections. I also use a separate
> piece of strap to ground the copper bulkhead bar at the tower base.
> It is tied into the ground loop with the shortest possible length.
>
> The leg straps run the shortest path over the side of the concrete
> base then drop below grade where they are silver soldered to a wire ground
> loop that
> encircles the concrete foundation. There are four radial grounds that are
> CAD welded to the ground loop at the four corners and these extend out
> radially to about 50 ft each. There are 4' copper clad ground rods
> CAD welded to the radials at about 8' intervals. The tops of the rods are
> about 18" deep. I would have used 8' rods but I have really hard caliche
> that starts at 18" deep and I just could not drive them any deeper
> even using a full size jack hammer - so I cut the 8 footers in half
> and doubled up the quantity at half the spacing.
>
> I also use wide copper strap at the single point station ground panel
> to connect to a similar ground loop at the station location.
>
> Hope this info is of use to you & good luck on your project.
>
> 73
> Matt
> KM5VI
>
>
>
>
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