S.C. Code § 7-13-810
The managers of election shall prevent any person from voting when they have good reason to believe the person has already voted. They shall refuse to allow a person to vote who is not a registered elector or who has become disqualified for any cause to vote in the voting precinct. They may also prevent any voter from consuming more than five minutes in voting, but no manager may examine, read, or handle the ballot being voted or about to be voted by a voter or interfere in any way with the voting of a voter otherwise than provided in this section. It is the duty of the managers of election to, and any elector or qualified watcher may, challenge the vote of a person who may be known or suspected not to be a qualified voter. However, the challenges by persons other than a manager must be addressed to the manager and not directly to the voter. The manager shall then present the challenge to the voter and act in accordance with the provisions provided for in this section. All challenges must be made before the time a voter deposits a paper ballot in a ballot box or casts his vote in a voting machine, and no challenge may be considered after that time. However, challenges may be made at any time before the opening of return-addressed envelopes and the removal of "Ballot Herein" envelopes from them as to absentee voters. Nothing contained from them affects the right of an elector or qualified watcher to challenge the vote of a person which is fraudulent or when the challenge is based on evidence discovered after the vote is cast. A candidate may protest an election in which he is a candidate pursuant to Section 7-17-30 when the protest is based in whole or in part on evidence discovered after the election. This evidence may include, but is not limited to, after-discovered evidence of voters who have voted in a precinct or for a district office other than the one in which they are entitled by law to vote.
S.C. Code § 7-13-810