A transformer switch, such as a multi-deck tap changer, includes an assembly with a first housing coupled to a first cover. The first cover holds at least a first stationary electric contact. A second housing is formed integrally with the first cover, and is coupled to a second cover, the second cover holding at least a second stationary electric contact. The first housing and first cover together define a first interior volume within which the first stationary electric contact is disposed. The second cover and the second housing together define a second interior volume within which the second stationary electric contact is disposed. Each housing-cover coupled pair includes an interior rotor rotatable relative to the stationary electric contact in the cover of the pair. At least one movable contact is coupled to each rotor. The covers and housings can be molded from a non-conductive plastic.