 Dielectric unions, with dielectric insulation, separate dissimilar metals (such as copper and galvanized steel) to prevent galvanic corrosion.When two dissimilar metals are in contact with an electrically conductive solution (ordinary tap water is conductive), they form an electrochemical couple which generates a voltage by electrolysis.When the metals are in direct contact with each other, the electric current from one to the other also moves metallic ions from one to the other; this dissolves one metal, depositing it on the other.