When a position in the competitive classified service is to be filled, the appointing power shall notify the Civil Service Commission of the fact. The Commission shall thereupon certify to such appointing power the names and addresses of the three candidates standing highest on the eligible list for the class or grade to which such position belongs. The appointing power shall appoint to such position one of the three persons thus certified. When the eligible list contains fewer than three names, the appointing power, may appoint from such names as shall be certified. If there is not eligible list for such position, or when the eligible list has been exhausted, and until a new list can be created, names may be certified from eligible lists most nearly appropriate to the position to be filled. A person certified from an eligible list more than three times to the same or similar position may be omitted from future certifications; but certification for a temporary appointment shall not be counted as one of such certificates.