In a message dated 97-01-04 00:14:18 EST, you write:
>Question 1: How do you weld #6 copper wire to ugly old rebar?
>
Wendell -- There are two approved ground wire bonding methods. One is to
use an exothermic process such as the Cadweld molds and shots. The other is
to use compression joints; this is a mechanical nut/bolt method. You can use
split bolts or ground rod clamps. Be sure you use an antioxidant on all
compression joints.
Obviously the exothermic method is the better one but the molds, shots
and clamps will run you $100 or more to get the tools you need. Each mold is
application-specific so you may need more than one. I don't think there is a
mold for rebar so you may be left with either brazing or compression
fittings.
Obviously neither method may be applicable to your rebar cage. There are
problems with welding rebar as it tends to be made from various scrap metals
and the finished product isn't real consistent raw material-wise.
Compression joints may work if you can't braze the rebar. Also I don't know
what luck you'll have brazing copper wire to rebar. Any welding experts out
there? BTW, using your tower base as an Ufer ground is a recommended
technique to enhance a ground system.
>How should I tie the tower leg, the ground rod, and the rebar cage together?
The various ground wires should be connected the same way, either
compression or exothermic joints. Run a wire from one grounding point
underground to another; repeat as necessary.
>Where should the #6 that runs 100 foot to the ham shack entrance panel tie
to
>the tower? All the radials will run away from the house.
>
The ground wire should run over to and up the leg so that it makes a very
gentle angle; no right angles are allowed as they present a high impedance
point to the charge that's trying to get to ground.
When you say "shack entrance panel", what exactly are you describing?
This 'device' is the key to building an effective Single Point Ground System
(SPGS) that is THE recognized technique for maximum ground system
effectiveness and safety.
>Question 2: Is #6 awg solid copper ($0.20/ft) wire ok for the radial
>grounding system.
>It meets NEC codes and the Inductance decrease for #4 awg ($0.30/ft) is
>negligible. Polyphaser says #24 awg will fuse with a lightning strike, but
>no where could I ever find a minimum wire size that will not fuse.
The whole point of a ground system is to have all of the conductors at
the same voltage potential so that the voltages all rise and fall at the same
rate. If they have different potentials, then you'll get arcing and damage.
BTW, if your guywires are not insulated and not grounded, a lightning strike
will probably weld the turnbuckle threads together. Now that's a bad deal.
If your wire size meets the NEC, then you're in good shape.
>Ground Rods: I have one sunk 8 feet in solid rock under the tower, and each
>of the guy pipes are sunk 5 1/2 feet in the ground. Beyond that I see no
>further need for ground rods since they cannot be driven more than 2 to 3
>feet under the surface horizontally (solid rock is 2 - 3 foot down)and they
>cost $10 each (same as 50 feet of #6 awg copper ground wire).
>
Eight foot ground rods are just as effective when installed horizontally
as they are when installed vertically as long as they are below the frost
line. A depth of 3-4 feet is a good depth to shoot for.
This is a BIG topic and lots of books have been written on it. While
the Polyphaser book has some good technical information, it has very little
when it comes to practical information for amateur installations. I have
written a paper called "Grounding" for ham installations that may give more
specific information. You can get a free copy for an SASE to TOWER TECH, Box
572, Woodinville, WA, 98072.
73, Steve K7LXC
TOWER TECH -- professional tower supplies and services for amateurs
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