The time-delay fuse, also known as the “slow blow” fuse, is one of the more common types of fuses. It can carry a pulse current several times the normal operating current for a short period without blowing, whereas ordinary fuses cannot carry this type of current. He was developed to encounter acceptable instantaneous overloads, such as starting a motor.

The time-delay fuse not only has the ability to react to overcurrents but also has the ability to discriminate the type of overcurrent or the amount of energy. In addition to the “blowing” part of a normal fuse, there is a short connector to which a spring is attached. The connector is held in place by low melting point solder. When an instantaneous overload reaches 100% to 200% of the fuse rating, neither element is affected, and the time-delay fuse can withstand such an overcurrent shock without causing a blowing action. However, in the case of a sustained overload, heat builds up in the fuse to the point where the solder melts, releasing the spring and opening the contacts. If a short circuit occurs, the “burnt out connection” will melt like a normal fuse. When that happens the time-delay fuse will, as usual, react quickly and blow.

The slightly slower action speed of the time-delay fuse not only does not affect its protective function, but rather enhances the protective function of the time-delay, avoiding the chance of false action, can be applied in a wider range of occasions, and play a protective role for a variety of circuits.