[BC] Irons for silver soldering copper strap

[Bruce Doerle]

Curt,

I have a great deal respect for you but I differ on one of your points here.  When I designed our grounding system for our 477' tower, we used 19 gauge 4" wide strap which is cross-sectionally equivalent to 0000 stranded cable.  This has a thickness of 0.0416".  We used silver solder to bond the strap together as well as bonding to the jumpers for the ground rods.  The jumpers could be cadwelded to the ground rods, but the heat dissipation on the strap made it difficult to solder to the strap and cadwelding was out of the question (molds were not available then).  Now I differ with you on using flux as we used flux to prep the strap and the stranded cable.  Without the flux, it was impossible to make a secure bond between the components and solder would not flow into the stranded cable. We were using Mapp gas too.  We also felt confident that the heat dissipation on the strap would prevent joint failure from the lightning surges.  So far it seems to be working, and it was installed nearly five years ago.  I had contemplated riveting the strap sections together and using a bracket for the cable to strap bond for mechanical as well as silver solder to finish the bonding, but working with 19 gauge copper is not easy and with all those bonded connections. Without the flux, we would not have been able to make a connection as I watched the subcontractors try over and over to make a solid connection without flux.  I took some sample copper cuts home with me and tried some different approaches; only the fluxed connections were a solid bond.  The solder penetrated the stranded cable thoroughly and bonded nicely to the strap.  With all the down connections (two on each tower leg) off the tower to ground ring, we don't expect any of the bonding connections to be thermally stressed. 

Bruce

>>> Cowboy <curt at spam-o-matic.net> 10/16/2007 7:32 PM >>>
On Tuesday 16 October 2007 08:48 am, Mike McCarthy wrote:
>  There's a reason we work reasonably well with each other....we're on the 
>  same page. Though I never had any luck with MAPP and strap...

 ;)

>  I do have a Turbotorch kit. But don't use it much for that reason. .

 Works fairly well on .032 strap, and it's possible, but slow, on .064 strap.
 There are two tricks.
 1. The copper must be very, very clean.
 2. No flux !

 Flux is to prevent heat oxidation, by gassing and displacing oxygen.
 A turbo-torch burns stoichiometric, so there is no residual oxygen in
 the flame, so flux serves no purpose, and may contaminate the surface
 before the bond can be made.
 Clean, is key.

 A turbo torch ( generic ) is ideal for radial work, though the bloom of
 the flame is a bit large for expanded metal ground screen, so tends
 to burn the screen before the braze flows.

 My preference for oxy-acetelene is better control.
 Much more heat, or less, in a much smaller area, but does require
 some experience handling a torch.
 For expanded metal screen, I'll always go with the oxy-acetelene
 for just that reason.

On Tuesday 16 October 2007 08:54 am, Mike McCarthy wrote:
>    How may times do you check the joints after a major 
>  local strike?
>  
>  I always fold one strap over the other in a T or angled connection, then 
>  tighten and flow the fold. 

 I never make a folded mechanical bond !!
 The reason is that should the solder joint fail, I *want* it to open up, visibly.
 It's the same reason experienced riggers always install bolts up, with the nuts
 to the top. Should a nut back off, the bolt falls out, and you can see it.
 A bolt with no nut is a failed bond every bit as much as no bolt at all !

 The downside is that the joint has failed completely, so a second strike before
 you can get there to fix it becomes more likely to cause "issues."
 My theory is that the re-flowed bad joint from the first strike is already polarized,
 crystallized, what-have-you, enough for me to consider it failed anyway, and no
 better than unsoldered copper with nothing more than weight contact.

 As always, once discussed, if it's YOUR site, I'll do it your way.

-- 
Cowboy

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