The Council may borrow money to acquire or operate any public utility when authorized to do so by the Michigan Constitution or by State law and when authorized by the electors of the City at an election wherein the question is lawfully submitted. Before the question is submitted to the electors by the Council, Council shall, by an affirmative vote of at least five (5) members, declare, by resolution, the necessity for such borrowing, the amount proposed to be borrowed and the purpose thereof. It may issue mortgage bonds therefor beyond the general limit of bonded indebtedness prescribed by this Charter, provided that the indebtedness created by such mortgage bonds shall not impose any liability upon the City, but shall be secured only by the property and revenues of such public utility, including a franchise stating the conditions under which, in case of foreclosure, the purchaser may operate the same. Such franchise shall in no case extend for a longer period than twenty (20) years from the date of the sale of such utility and franchise on foreclosure.