The answer to 'lifespan of junction box' is that a properly installed and maintained junction box can typically last 30-50 years or more. Protection ratings such as IP and NEMA define resistance to dust, water, and. Estimated useful life (EUL) represents the anticipated operational lifespan of a system or component before replacement or major repair is expected. EUL for building systems and components reflects design and manufacturing standards. When it comes to protecting electrical connections, metal junction boxes are a popular choice due to their robustness and durability.