[time-nuts] Lightning and grounds...

Burt I. Weiner biwa at att.net
Sun Oct 4 18:32:09 UTC 2009


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, time-nuts-request at febo.com wrote
>From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
>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.
biwa at att.net
K6OQK 




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