[TowerTalk] Lightning Protection Question

[jimlux]

Roger (K8RI) wrote:
> 
> 
> On 9/13/2010 8:58 PM, jimlux wrote:
>> Gary Schafer wrote:
>>> Simple spark gaps are not so simple. Temperature, humidity, 
>>> contamination by
>>> dirt etc will all make a difference on what voltage they arc at. Gas 
>>> tubes
>>> are much simpler and more reliable for repeatability of breakdown 
>>> voltage.
>>
>> Indeed, gas tubes are nice for that reason, BUT.. they do cost more 
>> than a couple pieces of wire (not much more), and I'm not sure that in 
>> this application you need that kind of control.  After all, the 
>> original intent here was for installation at the tower, *in addition 
>> to* the high quality protection at the shack entrance.  All you're 
>> really doing here is protecting the relatively cheap relay, or, more 
>> accurately, saving yourself the hassle of replacing it on a big strike.
>>
>> And, the breakdown voltage doesn't change all that much.  It goes as 
>> density of the air, so from -20C to +50C, you're talking about 20% 
>> variation or so. Humidity effect is very small.. maybe a couple percent.
>>
> The problem from humidity comes from condensation and that condensation 
> is far from pure, just check the PH.  It'll conduct like crazy and with 
> a .020 to .030" gap it's likely to bridge the gap creating a conductive 
> path.  OTOH after a slight burp in the impedance at a KW it'll 
> clear...or initiate an arc.

wouldn't that same condensation also bridge the relay contacts?