Pardon me for interloping...
One of the ways that I've always explained this is to draw a
schematic, actually more of a pictorial of the ground system and each
piece of equipment in the overall system as a block. In place of the
wires to ground, I draw a resistor symbol, including the ground and
ground lead itself. In fact, each chassis or cabinet is also one of
the resistors. By looking at it this way you can see that the ground
system path is nothing more than a low resistance voltage divider,
actually a current divider between a strike and the good earth.
When I design a broadcast transmitter plant I avoid bringing coax
(connected to the ground system) in at one end of the transmitter
cabinet and the ground connected to the other end of the cabinet,
which creates a path where the lightning surge current passes through
the cabinet/chassis and everything in between. Instead, I try and
tie the ground system and transmission lines - actually all ins and
outs to the transmitter, at one end only. This is in addition to the
grounding plate as described earlier in this thread. You want to
avoid putting any equipment between ground and the lightning strike.
Hopefully the lightning ground conductors and connections are
sufficient to not blow apart and allow the remaining force of the
strike to find another path. I've seen where heavy wide straps in
ground systems were soft soldered together. This is akin to putting
a fuse in the ground path.
As a friend once told me, "Lightning never strikes the same place
twice because the same place isn't there twice". You want to layout
and install your ground system so that your "place" has a better
chance of being there after such a spectacular event.
Burt, K6OQK
At 10:19 AM 10/4/2009, [email protected] wrote
From: "Poul-Henning Kamp" <[email protected]>
Subject: Re: [time-nuts] GPS antenna and lightning
Bob Paddock writes:
>I had one strike here that came *up* out of our 300 foot deep water well,
>when a tree several hundred yards away took a direct hit. You would
>think a 300 foot deep metal pipe filled with water would be a
good ground...
The problem is that the ground is not always a good ground...
Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California U.S.A.
[email protected]
K6OQK
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