On 1/21/2013 5:10 PM, Dick Green WC1M wrote:
Some grounding decisions are not straightforward. For example, my AC and telco services
are on one side of the house and the station "single-point" ground is on the
other side of the house. It would have taken 150 feet of low-inductance wire and at least
10 8-foot ground rods and Cadweld shots to connect the ground systems outside the house.
So I decided to bond them together inside the house, using about 25 feet of 1/0 wire. Not
the recommended way to do it, but it my opinion a better way to ensure that the ground
systems are at the same potential.
Right. I have a similar situation with my shack. I took a "belt plus
suspenders" approach -- I ran a bare #6 around the perimeter, bonding it
to rods by the power panel, at several points around the perimeter, and
more outside the shack. Inside the shack, I have thinwall steel conduit
(EMT) between the breaker panel (entrance) and outlets under my
operating desk, which are, of course, bonded to the panel. My coax panel
is between those outlets (at floor level) and the operating desk, and
I've added a bond between the desk, the antenna panel, and the conduit.
Another example is bonding the tower ground to the single-point ground at the
house. My first tower farm is 265' from the house. Being new to tower
construction, I laid 265 feet of 1/0 ground wire in the trench running between
the two locations in order to bond the ground systems. This was not cheap, to
say the least (though it was before the big run up in copper prices.) Later, I
read an article by Polyphaser that said if the ground systems are more than 75'
apart it does no good to bond them -- the wire inductance will be too high to
make an effective connection. With this in mind, when I installed my second
tower system in a different location 220' from the house, I did not run a
separate ground wire. The Polyphaser argument made sense to me.
Yes, it's good practice, solidly based on fundamental circuit concepts.
In fact, it's also good to add common mode ferrite chokes to the cables
running between the towers and the shack to minimize noise coupling.
73, Jim K9YC
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