[TowerTalk] Lightning protection - AGAIN !

[Gary Schafer]

You got it, snake oil!
The use of an independent down conductor on towers has been claimed by some
to prevent current flow in the tower. Fat chance! The tower has much lower
inductance than any down conductor you can hang on it. Even if there wasn't
an arc over between the down conductor and the tower (the chances of an arc
over are very high with no connection at the top) the current would be
induced into the tower by the close coupling of the down conductor. 

A down conductor is a waste of money on a metal tower.
Down conductors are used on buildings successfully to provide a path where
there is no other metal conductor.

73
Gary  K4FMX

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Martin Sole
> Sent: Sunday, October 01, 2006 9:58 PM
> To: towertalk at contesting.com
> Subject: [TowerTalk] Lightning protection - AGAIN !
> 
> I know this is a topic that seems to regularly surface here, not really
> surprising I suppose, but I have a question that seem rather to go
> against what I think I understand.
> 
> Recently I have started to see a number of 'protection systems'
> installed on towers that are very different from anything that I have
> seen in the past. So far I have found little independent analysis to
> show what they do and how they work.
> 
> In essence the system seems to comprise an air terminal, mounted at the
> top of the tower. In some cases these look like a pole with a sphere at
> the top, about a foot in diameter, in other cases they look like a more
> traditional 'pointed, almost' air terminal. In both cases the terminals
> are attached to a heavy conductor, typically a 1" pvc insulated cable,
> multi strand, totally isolated from any conductive connection to the
> tower and running down to the ground system.
> 
> The 'claim' seems to be that these systems provide a way to prevent the
> top of the tower from 'looking' electrically any different from the
> surrounding earth and that any buildup charge in the area will be
> prevented.
> 
> I don't really think I understand this. What is the difference between
> such a system and one utilising the tower structure as the down
> conductor? I can understand that during a surge event the voltage
> increases at a rate whereby the down conductor inductance plays an
> important part but this scenario suggests that there should not be a
> surge event with a fast rising edge and hence resistance rather than
> inductance really is the significant factor and further that no current
> should be allowed to flow in the tower or any of it's connected parts.
> 
> What's going on here? Snake oil or 'new science'?
> 
> Martin, HS0ZED
> 
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