[TowerTalk] Cadweld vs clamps

[Jim Lux]

On 10/23/14, 4:34 PM, Keith Dutson wrote:
> [snip]
>> REPLY:
>>
>> First, I wouldn't worry about a few microns of corrosion, especially
>> when lightning is concerned. A lightning bolt has already traveled
>> thousands of feet through an insulator (air) - another thousandth of
>> an inch of corrosion is nothing.
>>
>
> I would worry about Intermodulation from a corroded connection.  From a
> lightning protection standpoint, you could have a layer of tape in
> between: it will punch right through.  Static charge or induced voltages
> would be a problem.
> ----------------------------------------------------------------------------
> ---
>
> Thanks for pointing out the difference between lightning (plasma) and
> induced voltages.  One can do just so much with lightning mitigation, and
> the results in my experience have been poor.  However, management of lesser
> voltages is a useful task.
>
>

Very much so.  I suspect more equipment damage comes from "few kV" kinds 
of transients than from direct strikes.  The direct strike will 
flashover to the ground, and that flashover is just like a big arrester gap.

But a 3,4,5,10kV transient won't jump very far, and you won't get the 
inherent clamping from the flashover. So the full voltage winds up on 
the wire.

And from a electrical code standpoint.. a low-medium voltage feeder at 
4kV falling on your antenna or tower will probably be held off by the 
corrosion, or the wrap of tape, or whatever, and the whole thing will be 
live.

And if that winds up inside your rig, something's going to short, and 
now you have a great hot burning arc with lots of energy behind it until 
the fuse or upstream breaker trips (or the wiring in your house burns away).

Or, you'll be like the poor soul near here a couple years ago who heard 
a funny noise in the backyard went out into the wet grass and died from 
an impressive step potential from the 12kV MV distribution line that 
most likely had come down in the wind.  Then his wife and son died when 
they went to help him.

http://articles.latimes.com/2011/jan/15/local/la-me-three-dead-20110115

Folks.. *this* is why you need decent bonding and grounding for your ham 
shack.  A lot more people are killed by electrocution and stuff is 
damaged by a short to a power line than lightning.  Lightning is 
literally a 1 in a million chance.