This junction box volume calculator helps electricians and DIYers determine exactly how much space you need before wires get damaged, insulation gets pinched, or connections overheat. Learn key electrical code requirements for junction boxes, including sizing, grounding, materials, and clearance to ensure safety and efficiency. If you're planning any electrical work, one of the small but important items on your list will be the junction box. In addition, the MD4050 is equipped with three-position lock. Article Summary: Calculating the correct junction box size per the NEC 2023 involves a process known as a “box fill calculation,” primarily governed by NEC Article 314. The first step is to determine the total number of conductor equivalents in the box.