There shall be three branches of the classified civil service, as follows:
1. The classified departmental service.
2. The classified customs service.
3. The classified postal service.
GENERAL RULE III.
1. No person shall be appointed or employed to enter the civil service, classified in accordance with section 163 of the Revised Statutes and under the "Act to regulate and improve the civil service of the United States," approved January 16, 1883, until he shall have passed an examination or shall have been shown to be specially exempted therefrom by said act or by an exception to this rule set forth in connection with the rules regulating admission to the branch of the service he seeks to enter.
2. No noncompetitive examination shall be held except under the following conditions:
(a) The failure of competent persons to be, after due notice, competitively examined, thus making it impracticable to supply to the appointing officer in due time the names of persons who have passed a competitive examination.
(b) That a person has been during one year or longer in a place excepted from examination, and the appointing or nominating officer desires the appointment of such person to a place not excepted.
(c) That a person has served two years continuously since July 16, 1883, in a place in the departmental service below or outside the classified service, and the appointing officer desires, with the approval of the President, upon the recommendation of the Commission, to promote such person into the classified service because of his faithfulness and efficiency in the position occupied by him, and because of his qualifications for the place to which the appointing officer desires his promotion.