A bimetallic junction sometimes is suceptible for corrosion.
One example is connection of steel and aluminum. (Specially carbon steel)
A more serious case is fastening copper and aluminum.
It will depend greatly on the environment.
It is not good practice, In minor cases it will look ugly because of superficial corrosion.
I have seen conduit runs having to be replaced because of failing components in mixed systems.
Galvanized cast malleable iron straps are compatible with aluminum. They are used in conjunction with cast malleable stand off saddles to install aluminum conduit across concrete walls. Aluminum conduit installed directly on a concrete surface is a recipe for corrosion.
Bill
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"Why not the best?"
Jimmy Carter
