Before any equipment or material may be purchased under the provisions of this act, the city engineer of such city, and an engineer of the board of public utilities or some other qualified person designated by the governing body of the city shall make under oath an estimate of the cost of such equipment and material together with detailed plans and specifications for such equipment and material to be used, and file the same in the office of the city clerk, and no bonds shall be issued in excess of said estimate.
K.S.A. 13-1234c