NO.642-R NS is a Bussmann (Cooper Bussmann) Class R fuse reducer that lets a 200 A Class R fuse be used in a 400 A‑rated fuse block, specifically for 600 V AC circuits. This non‑indicating variant (NS) fits fuse ferrules or blades and is designed to install in fuse blocks and panels, including dead‑front types, while preserving a secure mechanical and electrical connection. By stepping down the protection current from 400 A to 200 A, it enables retrofit or compatibility in existing electrical distribution gear without replacing the entire holder. The part carries UL Listed and CSA Certified ratings, reflecting conformity for safety and performance in 600 V Class R applications.
