Mersen Class J spring reinforced fuse block A choice of screw, pressure plate, box and special order stud connectors fit a wide range of stranded or solid copper or aluminum conductors. Insulators are either molded glass-filled polycarbonate (GFPC) with verified dielectric strength in excess of 2500V. SJ fuse blocks feature a unique adder block configuration which can be snapped onto 3 pole blocks to form multi-pole segmented blocks of as many poles as desired. All fuse clips are made of high conductivity tin-plated copper, with a choice of spring-reinforced or non- spring reinforced clips. Polycarbonate body material and tin-plated copper materials contact. -25 degree C minimum operating and storage temperature. Approvals: All class J fuse blocks meet the requirements of UL4248 (formerly UL512). UL listed Guide IZLT, File E52283. CSA certified class 6225, File 32169.