The present invention relates to an arrangement for fastening a capacitor cup within which a capacitor is accommodated. The arrangement is for fastening a capacitor cup onto an opening of a mid-plate, wherein the capacitor cup comprises a cylindrical body having an opening end and an opposite end. The arrangement comprises: a collar provided on an outer surface of the cylindrical body, closely around the opening end; at least one first engagement feature formed at the outer surface of the cylindrical body and adjacent to the collar; and, at least one second engagement feature, corresponding to the first engagement feature, formed at an edge of the opening of the mid-plate; wherein, an engagement between the first and second engagement features fastens the capacitor cup onto the opening of the mid-plate. This arrangement for fastening the capacitor cup according to the present invention eliminates additional fastening members or parts, and effectively creates and maintains an environmental seal between the electronics area and the environment.