Hi Jim,
If you have the financial means, the shields of tower coaxial
transmission lines should be bonded to the tower at or near the top AND
bottom. The idea here is to shunt as much of a strike's transient
current to the tower as possible (the metal conducting mass that can
handle the current), then effectively drive as much of the transient
current into the bonded tower and building ground system as possible --
before it enters the building and contained electronics.
Following these premises, again the shields of the coaxial lines should
be bonded to an external building ground buss bar, which (in turn)
should be grounded/bonded to the nearby building services' entrance
panel ground (electrical, phone, and cable entrance/ground). Note the
coaxial surge suppressors are typically mounted nearby the building's
cable entrance panel and ground buss bar(s), since the are also bonded
to that ground.
Moreover, the tower(s) ground system(s) should be below-grade bonded
with a large conductor (2 AWG or larger) to the building's services
entrance/ground (since these two should be close to one another and
bonded).
I believe the site tower and building bonding idea is to have any
potential transient rise/fall times to be equalized (through bonding) as
much as possible, thus reducing the potential of differential voltages
from taking out equipment. Concurrently, the other idea is to shunt as
much energy as possible to earth-ground before it enters the building.
Motorola's R56 is far more detailed than this... it follows/meets Code
and goes way beyond it. What I've said is a rudimentary summation of
external grounding/bonding -- of which I suspect more than a few will
criticize and/or expound upon. I suggest reading R56 for yourself. It is
commonly available in PDF format (about 21 MB).
Follow local Code, but know there's much more you can do to further
abate potential lightning damage. You can go beyond it for added peace
of mind. It boils down to how much you want to spend. ;)
73 de Steve, NL7W
Reference: Bonding to the External Grounding Electrode System,
Motorola's Standards and Guidelines for Communications Sites (R56),
68P81089E50-A 3/1/00 — UP, page 6-5 and others.
On 7/30/2010 9:42 AM, Jim McDonald wrote:
> I am trying to improve my grounding system, which I thought was pretty good,
> after a lightning strike in April.
>
> I now have Array Solutions control line arrestors at the base of the tower
> for my SteppIR, rotor, and DX Engineering remote antenna switch. The
> SteppIR and antenna switch lines are shielded. Should those shields be
> grounded at the bottom of the tower? How about at my grounding panel at the
> entrance to the house, where I have ICE arrestors? (I would assume so to
> both.)
>
> Jim N7US
>
>
>
>
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