[BC] Irons for silver soldering copper strap

[Lamar Owen]

From: broadcast-bounces at radiolists.net on behalf of Bruce Doerle 

> 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). 

Do note that silver solder (or silver brazing) does not meet the bonding requirements of the National Electrical Code, 2005 edition.  Cadwelded (exothermic welded) or mechanical joints are required in order to meet the bonding requirements in the NEC for electrical grounds.  If you don't want trouble, don't call it a ground or use the term 'bonded' around the electrical inspector; it's an 'RF counterpoise' and they are 'connections' in that context (or the inspector might want an electrode at the end of each and every raidal...).  And do be sure to run a real ground that is really bonded to the electrical grounding electrodes; let the lightning and the electrical fault currents run that ground and leave your strap alone.  (Be sure to bond the real ground to the electrode system the RF countpoise is attached to, and don't allow any ground loops (run the 'ground' wire next to the 'low impedance RF counterpoise jumper' strap).  In NEC lingo, the RF strap is not a 'grounding' conductor, but a 'grounded' one).

Also note that the Silvaloy 15 trade brand and equivalents that contain phosphorus do not require flux of any kind to bond copper to copper; Silvaloy 45 and equivalents do need flux, but can bond other metals to copper.  Silvaloy 15 is about 16 times less expensive than Silvaloy 45; $35 or so per pound for 15, $35 or so per ounce for 45.

Other similar brands include Dynaflo, Phos-flo, and many many other trade names.  The key is that phosphporus-copper-silver alloys with high copper and low silver content don't need flux to join copper to copper. Please see http://www.silvaloy.com/docs/Tech%20Sheets/wjt-td-Silvaloy%2015.pdf http://www.w1ghz.org/10g/silvaloy.htm http://www.silvaloy.com/cuphos.php for more information; the silvaloy.com information is direct from the manufacturer, Wolverine (formerly Engelhard).  This stuff finds its primary use in HVAC work, where unfluxed copper to copper tubing joints have to hold refrigerant pressures.

Wolverine recommends flux for large work or copper alloys such as bronze and brass.  Be careful with any zinc-bearing alloy; zinc fumes are dangerous.
--
Lamar Owen
Chief Information Officer
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772
828-862-5554
www.pari.edu