An adjustable starter baseplate assembly is disclosed for use in mounting a contactor unit and an overload relay unit. The baseplate assembly comprises a support plate and an adjustable extension plate. The support plate has a first mounting surface which has a plurality of threaded openings thereon at least two of which will match the mounting footprint of a contactor unit to be mounted thereon. The extension plate has slots therein which are aligned with threaded mounting holes on a second mounting surface of the support plate. An electrical component, preferably an overload relay, is mounted onto the extension plate and the same screw fasteners are used to mount the overload relay to the baseplate assembly and to secure the extension plate in the appropriate position onto the support plate. The assembly is adjustable such that it may be used with a variety of sizes of housing enclosures.