Bare #4 solid Copper run across aluminum racking

[coop3339]

We have bare #4 solid Copper grounding conductor run across aluminum racking in a solar installation. It is in a semi-arid location, Denver CO. It runs along the aluminum rack for about 6'. Is there any concern for dissimilar metals in this case, per NEC or otherwise? I thought I remembered a fine print note in the code addressing bare copper ground but i cant seem to locate it. Any help would be much appreciated.

 

[jaggedben]

The wire and rack itself is not a concern, especially in a semi-arid location. It may sound bad in theory, but speaking from experience, the wire laying against the racking just doesn't present an issue. Especially #4, that's thick, I'm speaking from experience with #10 or #8.

What is important is the hardware used to bond the wire to the rack. It's gotta be stainless and/or tinplated copper. You can get very serious corrosion with tin plated aluminum lay-in lugs and non-stainless set screws (the kind that come on grounding bushings). It's best if the bonding method is UL 2703 listed.

All this is a more minor concern in a semi-arid location, I think. But your mileage may vary.