When metal boxes are used, proper grounding is essential. 146 – Bonding Requirements: If you're using grounding-type receptacles, bonding the. 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 commercial buildings. Non‑compliance risks safety or code violations. Junction boxes may be small, but they're critical for electrical safety. 15, a junction box is required whenever: You cannot: Common Misunderstanding If a cable passes through without splicing or terminating, you may not need to install a junction box — but you must still protect the conductors according to the wiring method rules. Many people miss these steps and face problems during. NEC 250.