Excess-current protection by h.r.c. fuses on medium-voltage circuits

The paper reviews the problems of excess and fault current protection in so far as they may be solved by the use of h.r.c. fuses, or by developments based on these fuses. Following a brief commentary on two types of fuse (non-tripping and tripping) and on the fault-clearance ability of the cartridge fuse, consideration is given to the various forms of protection afforded. A survey is made of future possibilities, with special reference to a scheme for open-circuit protection, a new time-limit fuse with an accuracy equal to the h.r.c. cartridge fuse which may supersede the overload coil with a fuse in shunt, and a solution of the earth-fault protective problem. Consideration is also given to the selection of fuses for different duties, to the economics of fused switchgear, and to the need for fuse designers to attempt a greater measure of standardization.