S.C. Code Ann. § 56-11-10

When used in this chapter, the term "motor carrier" means every person who operates or causes to be operated on any highways in this State road tractors, truck tractors, trucks having more than two axles, or passenger vehicles designed to seat more than twenty occupants. For the purposes of this section, the federal government, the State, counties, municipalities, churches, and any agents of them, and special mobile equipment as defined in item (11) of Section 56-3-20, must not be deemed "motor carriers".