> I don't see the need for GRC conduit but do see the need
> for a grounding wire to tye the tower system to the SPG shack
> ground and service entrance ground.
I read somewhere, I think in Polyphaser's documentation, that the need to
connect the tower ground with the shack ground and service entrance ground
depends on the distance between them. As I recall, if the ground systems are
more than 75 feet apart, they don't "see" each other across the wire
connection. As I recall, the wire impedance prevents the surge from
propagating more than 75 feet. Another way to think about it is that the
wire impedance is too high for the voltages above ground at both ends to
equalize.
I'd be interested in knowledgeable comments on this issue. Before I found
that Polyphaser reference, I threw 265' of stranded 1/0 wire in the trench
between my crankup tower and shack in order to connect the ground systems.
I'm in the process of putting in another tower with its own ground system
that will be 220 feet from the shack. In the nine years since I did the
first tower, the price of 1/0 stranded wire has gone up to $2.10 per foot.
If the Polyphaser literature is correct, I'd be wasting $462 if I threw a
run of 1/0 wire in the trench to connect the tower and shack ground systems.
Another consideration is that there will be two runs of 1 5/8" heliax in the
trench. I have to believe those two 2" copper tubes will have a much lower
impedance than 1/2" of 1/0 stranded copper wire. I would think a surge would
travel up those "pipes" in preference to the 1/0 wire.
Knowledgable opinions?
73, Dick WC1M
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|