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Ground lugs on RV frames - corrosion due to different metals, moisture & road salt

Ground lugs on RV frames - corrosion due to different metals, moisture & road salt

Ground lugs on RV frames - corrosion due to different metals, moisture & road salt

Have an RV that has the commonplace ground lugs like the 1st photo. These are standard in the RV industry for ground connections to RV frames.

There is a ground connection to frame required for the 12 VDC converter/charger and also for the 120 VAC panel. Our 12 volt ground conductor is #8 (I think) solid and the 120 volt ground conductor is #8 (I think) stranded, tin plated copper. The ground lug is tin-plated aluminum and the set screw is steel with CAD (or alternative) plating. The are two lugs stacked together and attached to the frame with a steel plated self-tapping screw with unknown plating (guessing it's CAD or equiv.) The RV frame is cold rolled steel. So that is 4 different metals in contact with a galvanic index (in volts) ranging from 0.35 for copper to 0.90 for aluminum (or maybe 0.95?) and CAD plating for a difference of 0.55 - 0.60 volts. This is much higher than it should be because for "harsh" enviroments, the anodic difference should not exceed 0.15 volts and for "normal" environments, not exceed 0.25 volts.

An RV frame is normally only exposed to water which could be wet for days at a time if used on the road much and may take longer to dry out if temps are lower. Not sure what the environmental exposure would be considered to be and I think might be somewhere between "harsh" and "normal". Where it gets to be especially problematic is when RVs are delivered from Indiana throughout the US & Canada during the winter when extensive amounts of road salt are used and thus galvanic corrosion can be substantially worsened.

Our RV frame has 4 or 5 ground lugs in different locations and the 12 & 120 volt grounds mentioned above were done by stacking two of the L-shaped alumin. lugs using a single screw into the frame. There's no flat or locking washers used and I found the screw to be loose. The lugs are a corroded mess and not making a good contact and need replacing.

So I just bought a Burndy Servit Post as in 2nd photo to replace the two L-shaped alum. lugs. Burndy says it is "high" copper alloy which would have an anodic index of 0.45. I will have eliminated the aluminum lugs and it's tin plating and thus will have steel, copper, tin-plated copper and "high" copper alloy in contact. The steel frame would be the highest on the anodic scale at 0.85.

My questions are:
- will I still have an issue with corrosion?
- I would like to use serrated bronze or brass lock washers for the new stud to bite into the steel frame but cannot find them (only need two as well). Can I use steel or stainless steel lock washers along with flat brass washers or just not bother?
- would it help to coat the new lug with some type of caulk (not silicone)?
- maybe replace the tin-plated stranded copper wire with non-plated/plain copper?
- am also wondering it the L-shaped aluminum lugs are listed for wet locations and can they be stacked? I tried to find UL info. but could not.

Is there perhaps a better method like perhaps a steel stud with pre-attached (thermal welded) copper wire pigtail?


[img http://forums.mikeholt.com/attachment.php?attachme...][img http://forums.mikeholt.com/attachment.php?attachme...]

RE: Ground lugs on RV frames - corrosion due to different metals, moisture & road salt

For a lot of the switchyard stuff we do, I weld a stainless steel tab with holes for a NEMA 2 connector. The assembly is HDG and grounding connectors are bolted through using phosphor bronze bolts and Belville washers. For areas with access from only one side, the stainless steel pad is drilled and tapped for the same NEMA 2. The HDG is ground away as required for the fasteners. This combination seems to work OK.


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