S.C. Code Ann. § 58-13-130

If any such common carrier shall prove that no delay in violation of this chapter occurred in the transportation of such freight after receipt thereof by it, that it extended the notice that prompt shipment was required to its connecting line and that, by the exercise of due diligence, it was unable to discover the cause of delay or the name of the common carrier responsible therefor, it shall be excused from liability under this chapter.