Slow Blow fuses are fuses which have an inherent time delay. These fuses are widely used in motor protection circuits. These fuses help discriminate between the high inrush current of motors and a high current caused by a fault.
The time delay in the fuse is achieved by designing the fuse element with a higher mass for the same current rating. This higher mass causes the element to heat gradually in the event of an overcurrent. Thus, the fuse element takes time to heat and melt to isolate the current.