On 5/18/2014 7:13 AM, Cecil wrote:
But don't expect it to provide a clue as to how to build a ground system for
proper lightning protection...it is concerned most about electrical safety
grounding...important but not the all inclusive answer.
I don't know what the "it" you're talking about, but I can say for
certain that MANY provisions of NEC are aimed at lightning protection.
There is excellent material on station grounding in the ARRL Handbook,
which, beginning around 2011, was written by Jim Lux, W6RMK, whose day
gig is at Jet Propulsion Labs (the guys who put us on Mars).
Many of the ideas I've seen quoted here are just plain stupid. Advice to
disconnect grounds from a building, or to disconnect antennas from
ground, is badly misguided.
By contrast, the concepts in the formal documents (Navy, NASA, AT&T
Microwave, etc.) are certainly solid, but are written for a specific
industry with specific construction and installation practices, and they
are quite solid in their recommendations. But their station
configurations are VERY different from ours. In nearly all of their
installations, equipment is bolted into steel racks, which results in
their chassis being bonded together, and for all of the AC green wires
to be common. For many (most?) of these systems, there is rarely any
outboard gear with unbalanced connections to the radio equipment.
Our systems are VERY different -- I've seen VERY few rack mount ham
stations, and the vast majority have unbalanced connections to a
computer, audio interfaces of some sort, often plugged into a different
power outlet. Thus, the grounding and bonding recommendations for our
systems must be at least somewhat different, especially within our shacks.
About ten years ago, I had the opportunity to set up a station at a
decommissioned AT&T Microwave site on a mountatintop near Sacramento,
and to study their grounding. There is a 60' x 120' building with two
floors, and a tower that's 32' x 32' at the base, 24' x 24' at the top.
I don't recall all of the details, but each tower leg had ground rods,
there were multiple rods around the perimeter of the building, bonded by
a perimeter conductor, and to the power entry ground, and to the tower
grounds. All of the gear in that facility was rack mounted.
I wrote the material on grounding for K7LXC's excellent "Up The Tower."
I should do something for my own website.
73, Jim K9YC
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