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Ground System

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Diggin', Poundin', Weldin', and Fillin'
 
Like most hams with towers, I'm concerned about lightning protection. A good lightning protection system starts with a good ground system. I'm a big believer in lots of ground rods, big wire or strap to connect them, and exothermic welding (Cadweld.) This page shows how I constructed the ground system for the big tower.
 
Each of the three tower legs is connected to a 50-foot radial of 1/0 stranded copper wire. 8-foot x 5/8" Ground rods are exothermically welded to the radials at 16-foot intervals. There are four rods per leg, for a total of twelve rods.
 
When the trench digger came out to dig the cable trench, I had him cut three extra trenches for the ground radials. Unlike the cable trench, which he backfilled for me, I had to backfill the radial trenches by hand. That's because it took several days to install and weld the ground rods, and it would have been expensive to have the trench digger come back. Backfilling the radial trenches was one of the more back-breaking phases of the project.
 
 
East Radial Trench

East Radial Trench
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Here's one of the radial trenches, running uphill toward the East guy anchor. Hope I don't hit any ledge when I pound the ground rods into this trench! I'll have to backfill the radial trenches by hand.
 
Note the coil of heliax to the right.
 
 
Installing Ground Rods

Ground Rod
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Here's one of 12 ground rods I pounded into the radial trenches. This rod is ready to be cadwelded.
 
I used a hand sledge and a regular sledge hammer to pound in the rods. Some went in relatively easily and some were very difficult. It took from 10-30 minutes to install each rod, depending on the hardness of the soil and the number/size of rock obstacles. Only one rod hit an immovable obstacle, and luckily that was only six inches from being fully pounded in. I just cut off the excess rod with a hacksaw.
 
Ground rods should be installed as vertical as possible. A small level helps. If they tilt too much from the vertical, the molten weld material can drip out of the mold, ruining the weld.
 
 
New Cadweld mold system

new cadweld mold
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Here's the mold used for exothermically welding 1/0 wire to a 5/8" ground rod. The wire passes through the metal-lined hole in the side of the mold. There's an identical hole on the other side of the mold.
 
The molds used to be made of ceramic, but now are made from a fibrous material that looks like very thick styrofoam. Also shown are the mold cap, the weld cup and the weld charge (in the blue container.)
 
When Erico introduced their new Cadweld molds, they changed more than just the mold. The old ceramic molds used a two-part charge consisting of weld material and igniter powder. An inexpensive flint gun was used to ignite the powder, which in turn set off the weld material. In the new system, the igniter powder and flint gun were eliminated and the user was forced to buy a $150 electronic igniter. This was quickly and decisively rejected by the customer base, and Erico went back to the two-part charge, which is in the blue bottle.
 
 
Cleaning the ground rod

cleaning ground rod
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First step is to clean the ground rod with a wire brush designed for the purpose. The wire has to be clean as well.
 
 
Sliding the mold on the wire

sliding cadweld mold
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There are two ways to make several welds in a long run of wire. You can slide the molds on the wire or you can cut the wire at each ground rod and slip the ends into the mold. I think the former provides better overall conductivity and less impedance, so that's what I do when I can.
 
With both the old and new molds, it's pretty-much impossible to slide the mold down heavy 1/0 wire with the metal inserts in the holes. They just come out of the mold. It goes better if you remove the inserts and slide them separately from the mold. This was easy with the old ceramic molds, but the new molds are very delicate and can get torn up easily if you're not careful. If the holes get enlarged too much, and the mold is not perfectly vertical, the weld material can seep out.
 
 
Mold positioned on the ground rod

new mold on rod
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It can be tricky to get the mold on the rod. Heavy 1/0 wire has a mind of its own and sometimes wants to move the mole. You can't see it in the picture, but I've used some of the large rocks removed from the trench to hold the wires in place and keep the mold vertical.
 
The process of pinning the wires down and trying to keep the mold in the correct position puts some stress on the mold where the wires enter. The new fiber molds tend to get torn up during the process, which can lead to weld failure. The old, much more durable ceramic molds were far superior. It seems like the new system was designed by someone who never used the product in the field (especially with heavy wire) and was put on the market without anyone bothering to see how well it worked. 
 
 
Wire inside mold

wire in mold
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The wire has to be exposed inside the mold and must rest on top of the small wire on the bottom of the mold. With the old ceramic system there was no wire in the base and the wire to be welded had to sit directly on top of the ground rod.
 
 
Weld cup in place

weld cup
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Next step is to drop the weld cup into the mold. It sits on top of the wire/rod and holds the weld material. It becomes part of the weld.
 
 
Weld material

Weld material
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Loose weld material takes up most of the volume of the blue bottle. A thin layer of  igniter powder is densly packed into the very bottom of the bottle. The two substances must be kept separate. If they mix, the igniter powder won't work. The blue bottle should be kept upright and shaken as little as possible.
 
 
Weld material in mold

Weld material in mold
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You have to pour the weld material slowly and carefully into the weld cup. Vigorous action can cause the igniter powder to come loose and mix with the weld material, rendering the powder useless. Pour slowly and keep the bottle horizontal as much as possible.
 
 
Adding the igniter powder

Pouring igniter powder
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Once the weld material has been poured in the mold, you should see the densely packed igniter powder in the bottom of the bottle. It's lighter in color and finer in texture than the weld material. If it's not there, it probably got mixed in with the weld material and you'll have to find more igniter powder or empty the mold and try another bottle.
 
The mold cover is put in place and the igniter powder is slowly and carefully poured through the hole onto the weld material. Gently tap the bottom of the bottle to dislodge the igniter powder. Some of the igniter powder should fall on the lip of the hole in the cover. This helps ignite the powder below. However, the distance to the surface of the weld material is greater than with the old ceramic mold, so this doesn't work as well as it used to. 
 
 
Ready to fire

Flint gun ready to fire
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A simple flint gun is used to ignite the powder. With the new molds, you have to stick the nose of the gun right into the hole, and it takes quite a few tries. With the old molds, you could hold the gun an inch or so away from the hole and one shot usually did it.
 
 
Kaboom!

Kaboom!
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You get quite a nice light show and some smoke. Don't look directly at the mold for at least 10 seconds after ignition -- it gets very bright.
 
 
The afterglow

The afterglow
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The inside of the mold gets white hot briefly, then stays red hot for at least 30 seconds.
 
 
The aftermath

The aftermath
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A glass-like material is all that remains of the weld material and weld cup.
 
 
The weld

The weld
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You can leave the mold in place or break it off with a hammer. The weld is inside. This is a good weld, but the old ceramic molds do a nicer job. See below.
 
 
The old Cadweld mold system

Old mold
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I had some of the old ceramic molds left over from my crankup tower installation nine years ago. I also got a couple of old molds from the RF Connection recently.
 
The mold is smaller, much sturdier, and the weld cup is attached to a ceramic wafer. The charge is exactly the same.
 
 
Old mold in position to fire

Old mold ready to fire
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Note the condition of the mold. It's been slid down the wire, but it's not torn up like a new mold would be.
 
 
Old mold after firing

Old mold fired
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The old and new molds look similar at this point in the process.
 
 
Weld produced by old mold

Weld produced by old mold
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This weld looks a lot cleaner than the weld produced by the new mold. Not clear to me whether there's any difference in effectiveness.
 
Note the rubber gasket at the bottom of the rod. It was at the bottom of the mold and held the mold in place on the rod.
 
 
Single-wire mold at radial termination

Single wire termination
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The molds come in a variety of configurations for different numbers and sizes of wire. This weld at the end of a radial run was made with a one-wire mold. The other welds on this radial were made with two-wire molds, either by sliding the mold down the wire or cutting the wire at the rod (requires a hacksaw or bolt cutters.)
 
A two-wire mold can be used at the termination if you don't mind a little wire sticking out the far end. If you don't extend the wire through the second hole, the weld material will blow right out of the hole.
 
One of the rods next to the base has three wires: one back to the base, one to the next rod on the radial, and one to the NEMA cabinet that holds the lightning suppressors and switches. Nine years ago, I got a custom metal mold from RF Connection to make connections of up to four wires to a single rod. I also use this mold at the single-point ground rod, which has several wires attached. It makes even cleaner welds than the old ceramic molds.