NCCER Introduction to the National Electrical Code (26105-20) Practice Test

Receptacle mounting height is limited to ensure the outlets are reachable and practical for everyday use without being damaged or obstructed by furniture. In the version of the NEC used for this question, the minimum height above the finished floor for a dwelling-unit receptacle is 12 inches, measured to the center of the receptacle. That means the outlet should sit low enough to be easily reached by most people, including those who are seated or shorter, while still allowing room for furniture legs and typical room layouts.

Keep in mind that different NEC editions can set different minimums. In many current editions, the required minimum center height is 15 inches above the finished floor. So, the 12-inch figure here reflects the specific study material or edition this question is based on. The other options (18, 24, 36 inches) would place the outlets higher and make them less convenient to reach in typical living spaces.