At 12:39 AM 7/22/2007, David Gilbert wrote:
>That's an encouraging comment. I will be installing a tower here soon,
>and since I live on a rocky hillside and have never been able to drive a
>rod any deeper than three or four feet before hitting granite I was
>planning to lay out several ground wires radially in however deep a
>trench I could manage. I had been thinking of using two or three #4
>copper wires for each leg of the tower, but I noticed that 1/2 inch
>copper refrigerator tubing is not much more expensive (maybe 20%) per
>foot. I roughly calculated the cross sectional area of copper for the
>tubing versus the wire and it is approximately the same so the parity in
>cost is understandable, but it seems to me that the tubing would make
>more sense for lightning protection. Is that an incorrect perception on
>my part?
A couple or so questions and comments to help clarify what you're
trying to accomplish...
Are you building a lightning protection system, or a antenna grounding system?
Does your system need to comply with some regulatory framework (e.g.
so that your insurance cover is valid, or that you can get a building
permit and the inspector will sign off on it when done)?
Now, on to the technical issue...
Sure, 1/2" tubing (or copper strapping) would probably be a better
conductor for transients and/or RF than an solid copper wire of the
same cross sectional area. You can get copper strip in a variety of
thicknesses.. no need to get razor edged flashing or 1/4" thick
bars... something like 1/16" thick might be a good compromise between
handling and low inductance. It might be cheaper than tubing (less
work in the manufacturing process), but tubing is more available and
might actually be cheaper (higher sales volume, so less markup).
Big wire has been used for historical and practical construction
reasons.. you can get it in long lengths on a spool, it bends easily.
Back when copper was cheaper compared to labor, wire was less
expensive than tubing, etc. Remember that a lot of the current
tradition and method for lightning protection was developed by this
guy named Benjamin Franklin more than 200 years ago. (It's not called
a Franklin Air Terminal for nothing.) A lot has changed in the
manufacturing business since then, so materials and processes that
were a "good deal" in 1780 aren't necessarily the same
today. Lightning protection is a conservative business... nobody
want's to change what is known to work reasonably well without a real
good reason (Let's see, Mr. Lux, about your claim for your house
cahtching fire after being hit by lightning. You installed a
lightning protection system that differs from what we've been
insuring for the last 150 years. You say that analysis, test, and
theory show that it should work better. Claim denied.. you can
appeal in court)
Jim, W6RMK
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