Steel Conduit, Cast Aluminum Boxes, dissimilar metals?

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renosteinke

Senior Member
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NE Arkansas
First off, products like 'Noalox" are specifically listed for this application- but, there are still a few misconceptions that need to be addressed.

The first is to note that your problem is not limited to corrosion. Rather, some materials have a tendency to 'gall.' That is, their threads tend to lock up and self-destruct under pressure or movement. Stainless steels are notorious for this; indeed, probably the worst combination is 303 stainless mating with high-alloy aluminum. This has the effect of permanently locking the parts together. Again, the use of something like 'Noalox" can help reduce this problem.

As for the corrosion between dissimilar metals, a critical element to the problem is moisture. Another contributing factor is whether the connection is actually carrying current. More current = faster corrosion.

Steel conduit is coated with zinc, which has the effect of minimizing the 'dissimilar metal' issue when it's in contact with aluminum.
 
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