N.C. Gen. Stat. § 160A-480.12
The Authority may issue refunding bonds or notes for one or more of the following purposes:
Refunding bonds or notes shall be issued in accordance with the same procedures and requirements as bonds or notes. Refunding bonds issued under this section may be sold or exchanged for outstanding bonds or notes issued under this Part and, if sold, the proceeds of the refunding bonds may be applied, in addition to any authorized purposes, to the purchase, redemption, or payment of outstanding bonds or notes.
Pending the application of the proceeds of refunding bonds, with any other available funds, to the payment of the principal of and accrued interest and any redemption premium on the bonds or notes being refunded, and, if so provided or permitted in securing the same, to the payment of any interest on such refunding bonds and any expenses in connection with such refunding, such 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 which shall mature or which shall be subject to redemption by the holder thereof, at the option of such holder, not later than the respective dates when the proceeds, together with the interest accruing thereon, will be required for the purposes intended.
N.C. Gen. Stat. § 160A-480.12