[TowerTalk] PolyPhasing of Station and Type of Braid for Grounding Station

[K7LXC@aol.com]

In a message dated 97-11-06 11:10:12 EST, w5hvv@aeneas.net writes:

> I am in the process of "PolyPhasing" my PacketCluster
>  Node's two VHF coax lines and grounding the station equipment per their
>  instructions.  The access to the external ground rods limits me to
>  braid running through the 3" PVC runnning into the ham shack from the
>  outside, 4 feet above the ground.  (The PVC is chock-o-block full of
>  coax lines coming in from the 250 ft run [buried] to the base of the
tower).
>  
>  The particular braid I have chosen to use to run from the thick aluminum
>  plate, upon which the PolyPhaser devices are mounted, to the outside
>  grounding system is 3/4" by 1/8" tinned, copper braid.  I use copious
>  amounts of Penetrox A at all junctions and connections.
>  
>  My question is this: Having remembered a comment by someone on one of
>  the reflectors regards tinned copper braid..... Is tinned copper braid
>  of good quality (very heavy and made up of many, many small individual
>  wires) suitable for grounding when used with large washers, heavily
>  torqued nuts and bolts, and lots of Penetrox A, at all junctions?
>  
     Congratulations on your getting ahead of the curve, lightning
protection-wise. That stuff really works, doesn't it?

    I see two problems with your aforementioned scenario. First, any braid
will deteriorate rapidly particularly if it's attached to a galvanized tower
leg or is installed outside where rain will wash particulates through it.
Being attached to a tower leg is about the worst use of braid for grounding
straps because of the zinc and other materials being washed down the leg plus
the dissimilar metals problem. I would only use the braid where it was
absolutely necessary and then connect it to real solid copper wire with a
solid mechanical compression connection used everywhere else.  Braid just
doesn't last very long outdoors in my experience.

    The second problem is if you are going to be running the braid through
the PVC pipe. It's full of water so it would also contribute to the braid
deterioration.

    Can you attach your ground wire to the building entry ground bus (the
Single Point Ground System)? Does it have one? Can you attach it to the
existing ground system SOMEWHERE? Why are you using an aluminum plate? It is
not a material used in ground systems. It's another dissimilar metals
problem.

   You can achieve some temporary success with the large washers and liberal
use of an antioxidant that you describe. The braid just won't last very long.

73,  Steve  K7LXC

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