Speaking of standards, NBR 5410 is ABNT's specific norm that mentions the necessary distance for junction boxes. These rules define when you must install a box, how large it must be, how you must install it, and how inspectors evaluate compliance. This guide breaks down the actual rules inspectors check — with calculations and. Present in any type of electrical installation, the junction boxes are important for promoting the passage of the wires inside walls, as well as to connect wires to sockets and switches. Check. Learn what the NEC requires for junction boxes, from box fill calculations and grounding to outdoor use and fire-rated wall installations. NEC Code Distinction: Junction boxes follow NEC 314.