Fuseology is the study of the fuse’s fundamental operating principles. These include the ratings and operating characteristics that make the fuse an efficient overcurrent protective device (OCPD) as well as its construction that creates its unique leadership role in circuit protection. In the simplest terms, a fuse is an overcurrent protective device with a circuit-opening fusible part that is heated and severed by the passage of overcurrent through it. A fuse is comprised of all the parts that form a unit that can perform these functions. It may or may not be the complete device necessary to connect it into an electrical circuit. Electrical distribution systems can be simple or complicated. Regardless, they cannot be absolutely fail-safe and are subject to destructive overcurrent events such as overloads, ground faults or short-circuits. Harsh environments, general deterioration, damage (whether accidental or from natural causes), excessive electrical system expansion or overloading are common factors leading to overcurrent events. Reliable OCPDs like the fuse shown in Figure 1 prevent or minimize costly damage to transformers, conductors, motors and many other components and loads that make up a complete power distribution system. Reliable circuit protection is also essential to electrical safety for personnel as well as avoiding severe monetary losses from power blackouts or prolonged facility downtime.