Their dimensions are generally around 2 inches wide by 4 inches tall, with depths varying from 1-1/2 inches to 3-1/2 inches. Typically available in depths ranging from 1-1/2 inches to 2-1/8 inches, their square shape provides ample internal volume for making multiple wire connections and. Within electrical installations regulated by NEC and UL standards, the terminology surrounding junction boxes extends well beyond simple measurements of length and width. 16 (Box Fill): For smaller conductors (6 AWG and smaller), sizing is based on total volume required. For industrial/occupational use only. 5 in³ deep PVC box or a 4" square metal box with a mud ring to ensure proper fit and ease of installation.