[RE-wrenches] Incompatible Metals

[benn kilburn]

Peter,i've been having the same concern running thru my head recently, as i've done this myself, and have compensated by now using a green jacketed bond (ground) wire for rail and module bonding.  (fyi-bonding is the CEC term for inter-connecting all metallic parts of an electrical system, i.e. frames, rails)I just strip the jacket at the lugs and use nolox on all connections.
I have not yet seen any issues with corrosion when bare copper has been supported against aluminum (frames or rails), but i am watching for it.  
I am also curious if anyone else has encountered this.... and,-to what extent  (i've seen mod frame/lug 'reduced to white powder' photos, but what about rail damage?-age of install when corrosion was first noticed
Question(s):  What triggers galvanic corrosion to take place?  ...is it unavoidable if there are dissimilar metals in contact?Does there need to be current leaking thru the dissimilar metals (connection points) for the reaction to start?
benn

DayStar Renewable Energy Inc. benn at daystarsolar.ca780-906-7807 HAVE A SUNNY DAY







> From: peter.parrish at calsolareng.com
> To: re-wrenches at lists.re-wrenches.org
> Date: Fri, 14 Jan 2011 07:36:22 -0800
> Subject: [RE-wrenches] Incompatible Metals
> 
> 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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