When two metals are brought in close contact, current flows from the one metal to another due to electrochemical action. For example, when aluminium conductors and copper conductors are jointed, current can flow between the two metals due to the presence of moisture, conductive salts or dirt on the surface. This causes corrosion known as galvanic corrosion which increases contact resistance. This can result in localized heating and failure.
This can be prevented by the use of bimetallic strips and washers when an electrical connection is needed to be made with two dissimilar metals. Bimetallic strips are made by cladding two metals such as copper and aluminium. The cladding ensures proper contact between the two metals. The aluminium side of the bimetallic strip is connected to the aluminium conductor while the copper side of the bimetallic strip is connected to the copper conductor.
Bimetallic Strips are used in bus bars where sections made of different metals need to be connected. They are also used when electric equipment which usually have windings made of copper are to be connected with cables made of aluminium.