No person shall be qualified to serve as an election officer, who shall hold, at the time of the election, any office, appointment, or employment in or under the government of the United States, or of this State, or in any city or county or any municipal board, commission or trust in any city, save only the justices of the peace, and aldermen, notaries public and persons in the militia service of the State. Nor shall any election officer be eligible to any civil office to be filled at an election at which he shall serve - save only to such subordinate municipal or local offices, below the grade of city or county officers, as shall be designated by general law.