[RE-wrenches] Incompatible Metals

[SOLARPRO at aol.com]

Peter:
 
In my experience and understanding of the relative electro-negativity or  
electrode potential of these two metals, there is not an issue for the copper 
to  erode to the point of ground failure - the aluminum goes first.  In a  
marine environment, especially salt water areas, all metals  eventually 
dissolve, much more quickly when there is galvanic action due to  dissimilar 
metals. Copper is considered more "noble" than aluminum (this is  an archaic 
chemical reference) and will erode the aluminum, eventually  causing a break 
in the surface interaction, and the galvanic action slows  or stops.. 
 
 
Patrick A.  Redgate
Ameco Solar, Inc.
7623 Somerset Blvd,
Paramount, CA 90723
_www.solarexpert.com_ (http://www.solarexpert.com/) 
_www.amecosolar.com_ (http://www.amecosolar.com/) 
562-633-4400

 
 
In a message dated 1/14/2011 10:14:16 A.M. Pacific Standard Time,  
kelly at whidbeysunwind.com writes:

Peter,
I have never understood the common practice of using bare  copper  
ground wire on and against aluminum frames and modules. It  always has  
been a dissimilar metals issue. Just look anywhere copper  has set  
against aluminum for awhile.
We use #10 green jacketed Cu  USE or XHHW conductor and strip away the  
jacket at each lug, using  No-Ox on that section of bare wire at the  
lug. The wire can be  tucked in to the module frames and with the PV   
conductors.

Kelly Keilwitz, P.E.
Whidbey Sun &  Wind
Renewable Energy  Systems
kelly at whidbeysunwind.com
360-678-7131




On Jan  14, 2011, at 7:36 AM, Peter Parrish wrote:

> One of my students who  is currently responsible for standing for  
> inspection
> at  their company encountered a inspector who made an interesting  
>  point about
> incompatible metals (i.e. copper and anodized  aluminum).
>
> The PV system in question used outdoor rated lay-in  lugs to bond the  
> rails
> to bare copper wire (so far so  good). The ground wire was then zip- 
> tied to
> the rail to  carry it to the point where it entered a junction box  
> along  with
> the rest of the PV conductors.
>
> The inspector was  concerned with the fact that the bare copper was in
> contact with the  aluminum rails and that this might cause galvanic  
>  corrosion
> and subsequent failure of the grounding.
>
> I  have never encountered this issue before and I wonder if anyone  
>  else has
> and what was the outcome.
>
> As an aside: I do  know that 10 AWG and 12 AWG  solid bare copper  
> wire can  be
> purchased "pre-tinned" (maybe not tin per se, but coated). We did  so  
> by
> mistake. We used it up, but not before one  inspector questioned its  
> use for
> the purpose of  grounding our system. We showed him the UL label on  
> the  spool
> and scraped off the coating to expose the copper core and  that  
> satisfied
> him. To this day I don't know if the use  of this wire for grounding  
> was
> among its intended  purposes.
>
> - Peter
>
> Peter T. Parrish, Ph.D.,  President
> California Solar Engineering, Inc.
> 820 Cynthia Ave.,  Los Angeles, CA 90065
> CA Lic. 854779, NABCEP Cert. 031806-26
>  peter.parrish at calsolareng.com
> Ph 323-258-8883, Mobile 323-839-6108,  Fax 323-258-8885
>
>
>  _______________________________________________
> 
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