On Wed, 4 Aug 2010 10:48:59 -0700, Dick Dievendorff wrote:
>I (will) have a main panel on the garage wall. The power company ground rod
>is right there. It's not much of a ground rod.
That's a good reason to improve on it by adding more, separated by the
distance equal to the length of the rod.
>
>There's a sub panel up in the radio room over the garage. That sub panel is
>connected to the main panel with four wires, 2 black and one white neutral
>for 220, and a separate green ground wire. Neutral is attached to the green
>ground wire only at the main panel.
Very good.
>The radio equipment will be connected to one heavy conductor (a copper or
>aluminum bar) within the shack.
>The tower is a bit more than 100 feet away. It has several ground rods. If
>lightning hits, the tower and its antennas are the most likely first
>victims.
>I'm planning to put some PolyPhaser lightning arrestors inline to the
>antenna coax, and through that effort the coax shield will be bonded to the
>tower's ground system.
As K1TTT noted a few weeks ago, those arrestors should be very close to the
protected equipment. Good practice is to a beefy conductive ground panel
(copper or other good conductor) where they enter the building next to the
gear, with that panel well bonded to ground.
>Are you advocating a separate wire 100+' heavy copper wire to connect the
>tower's ground system to the power company ground rod outside the garage?
No. I would treat the tower as a separate location. Bonding as noted
previously. At the AT&T site, the tower was right next to the building, and
their budget was infinite. That proximity demanded that the tower be bonded to
the building, and the budget allowed them to do it VERY well. :) In addition,
they designed the building, the layout of the building and the tower, and the
grounding arrangement before they started digging holes in the ground. When
you do it that way, it's a LOT easier to do it very well, and with fewer
compromises.
>Is this "single point ground"? Looks like multiple paths to ground to me.
Again, you are getting hung up on the words single point ground, which are
confusing and lead to fuzzy thinking.
>Is there a reason to run a separate wire from the shack ground plate to the
>power company ground rod, or would it suffice to connect it to the green
>wire inside the sub panel, which has a green wire to the main panel and then
>to the power company ground rod. Isn't that more "single point" than a
>separate parallel ground line?
Please take the words "single point ground" out of your vocabulary. It is
confusing things. Go back and read what I've written a half dozen times
before. :) All ground electrodes associated with your house/shack MUST be tied
together by the shortest practical path. That's power, shack, telco, CATV,
building steel if there is any, metallic plumbing if there is any. All the
gear in your shack should be bonded together by short fat copper. One big
conductor, or more big conductors in parallel to lower the impedance, should
take a junction of those shack bonds to the nearest junction of the earth
electode bonds. All of the gear in your shack must also be bonded to the green
wire at the local power outlet(s).
Don't lose sight of the fundamental reason for all of this, which is to
minimize the DIFFERENCE IN POTENTIAL between equipment that is interconnected,
to prevent current from flowing THROUGH equipment, and to direct it away from
equipment.
Another point. The more things are spread out, the more difficult it is to
minimize the potential difference between them. That's because connecting
wires have inductance, and the current from a strike will induce voltage and
current on them. To maximize lightning safety we want to minimize that
distance. The safest layout from a lightning protection point of view would
have power entry, telco, CATV, and the ham shack all right next to each other.
Few of us have the luxury of that kind of layout, so we must make the best of
what we have, or what we can do at reasonable cost (including the cost of
keeping the XYL happy).
73, Jim K9YC
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