Hi,
I did 15-20 Erico one-shot cadweld connections to ground rods last year, in
fact made still couple more couple weeks ago.
I also had problems to ignite with standard flint igniter one can buy in any
big box store. Solution: Get Erico's T320 flint igniter. Works very well
without any fumbling. It is not expensive.
Only other problem I had was that sometimes hot metal was shooting/spitting
through the bottom of the mold. Maybe caused by poor gluing of black
rubberish mold bottom to ceramic cylinder. Or maybe when setting the mold
on rod this gluing came bit apart. Anyway, part of the metal ended up on
bottom of ditch and did not stay inside mold causing poor connections if you
look Erico's own inspection criteria for connection. It happened couple
times to me and I discussed it with guy in local grounding store (Mayday
Grounding in San Diego). Solution: Get some T403 mold sealer. This is like
moist putty one can place underside the mold (or even where wires go into
mold). Did not have single problem since I used the putty. It was also not
expensive compared what couple lost one-shots cost. I think guy in store
explained that the putty is actually used for some of their bigger molds
that are not one shot kind. But based on the problem I described, he
suggested to try it and it really works well.
73 de Marko N5ZO
Paul, Thanks for sharing your experience. Regarding a hard to ignite shot of
Cadweld: The process is quite like Thermite. I would expect that you can
place a small quantity of powdered magnesium on top of the difficult shot
and use a fuse consisting of a small thin strip of magnesium ribbon to
ignite the magnesium powder.
Patrick NJ5G
On 3/29/2015 12:18 AM, Paul Christensen wrote:
Thought I would share some lessons learned while recently installing a large
ring ground system. The goal was to form a ring ground around two towers,
AC power entry point, and a small telecom shelter. We followed the
"Motorola R56 Standards and Guidelines for Communications Sites."
CADWELDS
Out of two dozen Cadweld one-shots used, only one would not ignite. That
was the first device tried. When pouring in the granules into the crucible,
it's important to: (1) NOT shake the vial; (2) slowly pour the mix; and (3)
delicately pour the final igniting power at the very end. Erico, the
manufacturer, really needs to separate the two powders into separate vials.
If the fine igniting powder accidentally becomes mixed with the granules,
then ignition absolutely, positively will not happen with any form of
igniting and you will have wasted a $10 one-shot. Don't bother heating it
either with a propane torch. It takes a spark with the igniting mix on top
to start the chain reaction.
We found children's sparklers to be an excellent spark source. Much time
can be wasted with a flint striker, especially in breezy conditions.
SILVER SOLDER
Where we did not bond with Cadweld one-shots, we used 15% silver brazing
bars. In the past, I used acetylene-air for the task. This time, I
purchased a Lincoln Electric Oxy-Acetylene torch set and wow, what a
difference. Acetylene-air produces excessive carbon/soot and quickly turns
the copper black - to the point where solder will not flow. In the past,
I'm not sure how I managed to use acetylene-air, but adding a small amount
of O2 into the mix completely burns out the carbon and with a little
practice, the right acetylene-O2 mixture will produce nothing but an intense
blue cone (a neutral flame) at the end of the torch. That cone heats the
copper surface without adding any impurities from the gas. With no flux,
the brazing bars immediately flow to the copper surface. When cooled, the
result is nearly as good and strong as an exothermic bond. Some folks have
successfully used MAPP gas, but often does not get hot enough when bonding
to large surfaces with high mass.
For the AC premise grounding, we used Cadwelds to join multiple ground rods.
#2 wire solid wire extended from the rods up the power entry panel. That
satisfied the NEC but we augmented that grounding with a 4" copper strap
ring around the perimeter of the telecom shelter.
I don't believe the current NEC (and most local codes) allows
silver-soldering in place of clamps or exothermic bonding. Just a hunch,
but I suspect the main reason is that it's too much of an art form; no two
silver-solder bonds are the same and it takes some skill to get a good bond.
By contrast, if one just follows the Cadweld instructions, the result is
repeatable.
Paul, W9AC
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