Section 8.430 - Revenue bonds refunded, when - contents of refunding bonds1. The revenue bonds issued pursuant to the provisions of sections 8.370 to 8.450 may be refunded, in whole or in part, in any of the following circumstances: (1) When any such bonds have by their terms become due and payable and there are not sufficient funds in the interest and sinking fund provided for their payment to pay such bonds and the interest thereon;(2) When any such bonds are by their terms callable for payment and redemption in advance of their date of maturity and are duly called for payment and redemption;(3) When any such bonds are voluntarily surrendered by the holder or holders thereof for exchange for refunding bonds.2. For the purpose of refunding any bonds issued hereunder, including refunding bonds, the board may make and issue refunding bonds in the amount necessary to pay off and redeem the bonds to be refunded together with unpaid and past due interest thereon and any premium which may be due under the terms of the bonds, together also with the cost of issuing the refunding bonds, and may sell the same in like manner as is herein provided for the sale of revenue bonds, and with the proceeds thereof pay off, redeem and cancel the old bonds and coupons that have matured, or the bonds that have been called for payment and redemption, together with the past due interest and the premium, if any, due thereon, or the bonds may be issued and delivered in exchange for a like par value amount of bonds to refund which the refunding bonds were issued. No refunding bonds issued pursuant to the provisions of sections 8.370 to 8.450 shall be payable in more than forty years from the date thereof or shall bear interest at a rate in excess of six percent per annum.3. The refunding bonds shall be payable from the same sources as were pledged to the payment of the bonds refunded thereby and, in the discretion of the board, may be payable from any other sources which under sections 8.370 to 8.450 may be pledged to the payment of revenue bonds issued hereunder. Bonds of two or more issues may be refunded by a single issue of refunding bonds.