S.C. Code § 11-15-540
For the payment of the principal and interest of such bonds as they respectively mature and for the creation of such sinking fund as may be necessary to provide for the prompt payment thereof, the full faith, credit, taxing power and resources of the issuer shall be irrevocably pledged, and there shall be levied and collected annually upon all taxable property of the issuer an ad valorem tax, without limitation as to rate or amount, sufficient for such purposes. The governing body of the issuer may, in its discretion, additionally secure the refunding bonds by a pledge of such revenues as were pledged to secure additionally the outstanding bonds. If such refunding bonds be additionally secured, covenants similar to those made in issuing the outstanding bonds may be made.
S.C. Code § 11-15-540