Learn what the NEC requires for junction boxes, from box fill calculations and grounding to outdoor use and fire-rated wall installations. The National Electrical Code (NEC), published as NFPA 70, sets minimum safety standards for electrical junction boxes in residential and. According to the NEC (National Electrical Code), all wire splices and electrical connections must be enclosed within an approved electrical junction box to ensure safety, accessibility, and code compliance. Always install your boxes where you can reach them later. Many people miss these steps and face problems during. The National Electrical Code (NEC) governs electrical junction box rules.