For box openings with any dimension less than 8 inches, what is the minimum length of conductor measured from the box opening to the end?

• A. 1 in. (25 mm)
• B. 3 in. (75 mm)
• C. 5 in. (125 mm)
• D. 7 in. (175 mm)

Answer: (B)

The idea is to keep enough free conductor outside the box so you can work safely and securely with the wiring. When a box opening is smaller than 8 inches in any dimension, a minimum of 3 inches (75 mm) of conductor must extend beyond the face of the box. This length provides enough slack to land the conductor in a terminal or clamp, accommodate a splice if needed, and allow a little pull without stressing or loosening terminations inside the box. It also helps protect the wiring if the box is reworked later or if someone needs to reach in to adjust connections. So, the best choice is 3 inches.