To borrow money on the credit of the city, and to pledge the credit and revenue thereof for the payment of the same, to an amount not exceeding five per centum upon the assessed value of the taxable property in said city, and with the consent of the people of the said city, obtained at an election held under the provisions of the Constitution and the general laws of this Commonwealth, to increase the indebtedness of such city to an amount not exceeding, in the aggregate, fifteen per centum upon the assessed valuation of the taxable property therein.
53 P.S. § 23108