S.C. Code § 58-17-1140
No railroad corporation which has previously issued bonds shall subsequently make or execute any mortgage upon its road, equipment and franchises, or any of its property, real or personal, without including in and securing by such mortgage all bonds previously issued and all pre-existing debts and liabilities of the corporation. But nothing in this section contained shall apply to a mortgage for the purchase money of any such road, equipment, franchise or property, real or personal, or to a mortgage made or executed for the purpose, in whole or in part, of building, extending, improving or equipping such railroad, or any part thereof, or any other railroad, the greater part of whose stock is held by it, or to any pledge or hypothecation of any choses in action or other securities held or owned by it. Nor shall this section require that a mortgage executed by a corporation shall secure the payment of previously issued bonds or pre-existing debts and liabilities of the corporation when the bonds to be issued under the mortgage are intended, in whole or in part, to take up, by funding or otherwise, such previously issued bonds or pre-existing debts and liabilities or when such previously issued bonds or pre-existing debts and liabilities are secured by a pre-existing mortgage or other lien.
S.C. Code § 58-17-1140