Something we found out over 20 years ago is that you have to be extremely
careful about how you ground DC systems, especially if there is any other
metal of any type in the vicinity in or on the ground. We have seen it
destroy underground pipes and even metal fence posts.
You can get stray currents from things you never even imagined, and that
current is what causes a lot of the galvanic corrosion. In one case a
previous installer had used an underground tank for a positive ground
system, and after about 5 years it was almost totally destroyed - just lucky
the tank was not used for anything but water.
To be doubly safe, best to light up the system and actually put a digital
amp meter in series with the ground wire(s). Clamp on ammeters may not work,
as sometime the current is only a few to a few hundred ma. Sometimes you can
get stray currents to objects you thought were isolated.
..................................................................................................
Northern Arizona Wind & Sun - Electricity From The Sun
Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
..................................................................................................
----- Original Message -----
From: " Jeff Yago" <[email protected]>
To: <[email protected]>; "RE-wrenches"
<[email protected]>
Sent: Sunday, February 01, 2009 10:16 PM
Subject: Re: [RE-wrenches] Galvanic compatibility of commonly usedsolar
materials
I recently inspected a large ground mount off-grid system about 3 years old
that was installed by others. I would have used a #6 bare copper ground
wire due to being exposed almost 100 feet of array length and connected to
several ground rods with no conduit, but the installer had used #10 which
still barely met code, but sure was flimsy. Anyway, this small ground wire
was sagging down in many places along the array length due to about a
quarter of the galvanized steel self-tapping screws holding the copper
against the aluminum had totally dissolved.
We always use the cadmium plated copper grounding blocks and stainless
steel screws to attach the #6 copper ground wire, and I can see now just
how fast the galvanic action can dissolve metal when you don't use
stainless steel hardware.
Jeff Yago
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