[TowerTalk] inductance of tubing vs bar or strip

[Roger (K8RI)]

john at kk9a.com wrote:
> My tower has had a number of direct lightning strikes and I have never seen 
> a soldered connection fail.  I am assuming that Pete is referring to using 
> copper water pipe or refrigeration tubing as a ground conductor for his 
> shack and I find it hard to believe that a strike would raise the pipe 
> temperature to 400 degrees or so and melt the solder from the fittings.
>
>   
I know the "current wisdom"  has been not to solder although code IIRC 
only says that about the  ground rod.
Looking at the required currents, if the current is high enough to melt 
solder on the station buss then that will probably be the least of the 
problems.  One thing to forget is the raising of the pipe temperature to 
melt the solder.  Under some cases you can melt the solder and only warm 
the pipe. Remember in this case the solder melts due to IR losses in the 
solder, not by conducting heat from the copper.  What is the 
"resistivity" of the copper and solder?  what is the ratio?  Silver 
solder which is readily available although it too is pricey, melts at  a 
temperature only slightly less than copper although it too comes in a 
wide range of alloys and melting points.  Soldering small parts to large 
copper pipe or tube also takes concentrated heat right at the spot of 
soldering and is not nearly as easy as soldering two wires together or 
even plumbing where the pipe is roughly the same size on each side of 
the joint.

Myself? I prefer a drilled and tapped copper buss bar 1/4" to 1/2" by 2 
to 3" if you can find it. For most stations that is only a few feet 
long. Yes, it's going to be pricey, but much easier handle  Then the 
grounding lead of #2, strap, or what ever runs to the Single Point 
Ground (SPG).  BTW drilling and tapping copper for even 1/4-20 or 1/4-28 
can be a chore and very difficult for the smaller sizes such as 12-24, 
10-24  even when using the proper cutting oil.  I also prefer the 
coarser size threads in copper. I'd use 1/4-20 or 28 as you can get 1/4" 
"crimp on" connectors that will fit a wide range of wire sizes.

After having said all that, I run the same grounding cable I use from 
the tower to the SPG through the bulkhead and into the station where I 
use compression clamps to attach the station grounds to that cable.

73

Roger (K8RI)
> John KK9A
>
>
>
> Subject: Re: [TowerTalk] inductance of tubing vs bar or strip
> From: "Dick Green WC1M"
> Date: Tue, 18 Aug 2009 13:31:11
>
> I don't know about the inductance, Pete, but my understanding is that
> soldered connections are not a good idea -- a lightning surge can melt the
> joints. I think you would need to use a mechanical clamp or something like
> Cadweld.
>
> 73, Dick WC1M
>
>
> To: TowerTalk <towertalk at contesting.com
> Subject: [TowerTalk] inductance of tubing vs bar or strip
> From: Pete Smith N4ZR
> Date: Tue, 18 Aug 2009 08:16:36
>
> Can anyone suggest where I can find a calculator for the inductance per
> foot of copper tubing compared to the same length of copper bar or
> strip?  I'm looking to understand the potential utility of using
> soldered copper tubing for a ground bus, as compared to copper strip/strap. 
>
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