A general purpose, one time, NON-current limiting cartridge fuse. These class K-5 fuses are for light duty circuit locations.
Protect lighting, heating and other circuits not subject to temporary surges and where available short-circuit currents are relatively low
Non one-time fuses do not have any appreciable degree of time delay and thus should not be specified in circuits where large transients or motor overloads occur
For general purpose circuits, size at amp rating of circuit
For motor circuits, size at 300 percent to 400 percent according to the nec motor ampacity tables 430.247 to 430.250, per 430.6 (A)(1)