Pennsylvania constitution
Article IX: local government
Section 12

The debt of the City of Philadelphia may be increased in such amount that the total debt of said city shall not exceed thirteen and one-half percent of the average of the annual assessed valuations of the taxable realty therein, during the ten years immediately preceding the year in which such increase is made, but said city shall not increase its indebtedness to an amount exceeding three percent upon such average assessed valuation of realty, without the consent of the electors thereof at a public election held in such manner as shall be provided by law. In ascertaining the debt-incurring capacity of the City of Philadelphia at any time, there shall be deducted from the debt of said city so much of such debt as shall have been incurred, or is about to be incurred, and the proceeds thereof expended, or about to be expended, upon any public improvement, or in construction, purchase or condemnation of any public utility, or part thereof, or facility therefore, if such public improvement or public utility, or part thereof, or facility therefore, may reasonable be expected to yield revenue in excess of operating expenses sufficient to pay the interest and sinking fund charges thereon. The method of determining such amount, so to be deducted, shall be as now prescribed, or which may hereafter be prescribed by law. In incurring indebtedness for any purpose the City of Philadelphia may issue its obligations maturing not later than fifty years from the date thereof, with provision for a sinking fund to be in equal or graded annual or other periodical installments. Where any indebtedness shall be or shall have been incurred by said City of Philadelphia for the purpose of the construction or improvement of public works or utilities of any character, from which income or revenue is to be derived by said city, or for the reclamation of land to be used in the construction of wharves or docks owned or to be owned by said city, such obligations may be in an amount sufficient to provide for, and may include the amount of the interest and sinking fund charges accruing and which may accrue thereon throughout the period of construction, and until the expiration of one year after the completion of the work for which said indebtedness shall have been incurred. No debt shall be incurred by, or on behalf of, the County of Philadelphia.