Time-Delay Fuses

Time-Delay Fuse Graphic 1 The time-delay, or "slow blow", fuses were developed for situations where acceptable momentary overloads are encountered, such as starting a motor. As the name implies, this type of fuse will carry an overload several times the normal load for a short period of time without blowing.

Time-Delay Fuse Graphic 2The time-delay fuse has two elements. In addition to the "burn out" link of the ordinary fuse, there is a short connector with a spring attached. The connector is held in place by low melting point solder. With momentary overloads of 100 to 200 percent of the fuse rating, neither element is affected. But with a continuous overload, heat builds up in the fuse to a point where the solder melts, releasing the spring which opens the contact. If there is a short circuit, the "burn out link" melts just as in an ordinary fuse.