S.C. Code Ann. § 7-13-1010: Additional oath of voters.

The managers at each box shall require every voter to take the following additional oath and pledge: "I do solemnly swear or affirm that I am duly qualified to vote at this primary election and that I have not voted before at this primary election or in any other party's primary election or officially participated in the nominating convention for any vacancy for which this primary is being held."