Refunding bonds may be sold or exchanged for outstanding bonds issued under this Article and, if sold, their proceeds, and investment earnings on them, may be applied, with any other available funds, to the purchase, redemption, or payment of the bonds being refunded, to the payment of any interest on the refunding bonds, and to the payment of any expenses in connection with the refunding. The proceeds may be invested in direct obligations of, or obligations the principal of and the interest on which are unconditionally guaranteed by, the United States of America if the obligations mature or are subject to redemption by the holders, at their option not later than the respective dates when the proceeds, together with the interest accrued thereon, will be required for the purposes intended.
N.C. Gen. Stat. § 159D-52