Every city of the second class A, in its corporate capacity, is authorized and empowered to enact ordinances 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 percent 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 percent upon the assessed valuation of the taxable property therein.