IDSR Series UL Class RK5 Dual-Element Time Delay Fuse With Indication. The Littelfuse IDSR Indicator fuse is the first indicating power fuse ever. Its solid-state design provides state-of-the-art reliability; it will forever change the way you look at modern circuit protection. Money is wasted each time a circuit opens and halts production. Thousands of dollars can be lost with every minute spent testing to discover the cause. The Littelfuse IDSR Indicator fuse offers you a better way. Just a simple glance a the IDSR Indicator window tells which circuit is open. The circuit can be tested and any problem corrected without unnecessary delay. No time wasted finding the faulted circuit. No system damage. And no costly down time. Applications: All general-purpose circuits, Motors, Transformers, Solenoids, Fluorescent lighting, All system components with high inrush currents.