(a) The outstanding general obligation indebtedness of the city incurred for all public purposes shall not at any time exceed fifteen percent of the assessed value of all the real and personal property in the city. The restrictions imposed by law on contracting debt shall not apply to debt incurred through the issuance of revenue bonds when the only security is the revenue of the enterprise, nor to bonded indebtedness to be paid from special assessments on benefited property, nor to refunding indebtedness. In determining the debt limit of the city, there shall be deducted from the amount of the outstanding bonded indebtedness any amounts credited to or on deposit for debt retirement, and any portion of reserve funds or accounts pledged to the payment of the principal amount of any outstanding bonded indebtedness. Money may be borrowed for reasons of disaster, as permitted by Section 11.1(a)(6), beyond the limit imposed by this section, and the Council shall, at the time of the authorization of such indebtedness, provide for the fulfillments of other requirements of law relative to incurring such indebtedness.

(b) Except when delay is caused by litigation, or when a bond issue has been authorized to be issued in two or more parts or series, if any bonds are not sold, the authorization of any unsold bonds may be voided at any time by a Council resolution. If any bonds are not sold within ten years after authorization, such authorization shall be null and void as to the bonds which remain unsold.