N.C. Gen. Stat. § 20-141.1

The Board of Transportation or local authorities within their respective jurisdictions may, by ordinance, set speed limits lower than those designated in G.S. 20-141 for areas adjacent to or near a public, private or parochial school. Limits set pursuant to this section shall become effective when signs are erected giving notice of the school zone, the authorized speed limit, and the days and hours when the lower limit is effective, or by erecting signs giving notice of the school zone, the authorized speed limit and which indicate the days and hours the lower limit is effective by an electronic flasher operated with a time clock. Limits set pursuant to this section may be enforced only on days when school is in session, and no speed limit below 20 miles per hour may be set under the authority of this section. A person who drives a motor vehicle in a school zone at a speed greater than the speed limit set and posted under this section is responsible for an infraction and is required to pay a penalty of two hundred fifty dollars ($250.00).