[RFI] Lightning Protection

David Robbins k1ttt at verizon.net
Mon Jul 2 11:12:23 PDT 2012

you can't 'discharge' the buildup of charge, there is no where for it to go since the whole area under the downward moving step leader has charge being sucked into it by the field under the leader.  the best you can hope to do is create an area with fewer local bumps in the field that generate upward streamers to meat the downward stepping leader... but this is very hard to do unless you put up a very big smooth dome, so the common practice is to put up the air terminals to create the streamers from the places you want the stroke to hit and then provide a good path for it to follow away from the structure.

Jul 2, 2012 01:51:26 PM, jim at audiosystemsgroup.com wrote:

On 7/2/2012 9:10 AM, EDWARDS, EDDIE J wrote:
> So it's an attempt to absorb the strike, not prevent it. And they also show them used on building roof tops probably to meet NEC code.

We don't "absorb" a strike -- it's the result of a buildup of charge 
between the atmosphere and the earth, and the energy in that charge can 
be massive.

The general intent of most lightning protection methods, including "air 
terminals," is to ATTRACT and DIVERT the strike into a path that is 
likely to do less damage, AND to discharge the buildup of nearby charge 
before it gets strong enough to BE a strike.

Tom, W8JI, a broadcast engineer and equipment designer who has a big ham 
station in Georgia, does NOT advocate disconnecting ANY cables. He 
insists that proper bonding architecture and lightning protection 
devices are enough. His website is worth studying.

73, Jim K9YC
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