Electrical Distribution Systems SYSTEM COMPONENTS AND PROTECTION DEVICESFusesA fuse is a device that protects a circuit from an overcurrent condition only. It has a fusible linkdirectly heated and destroyed by the current passing through it. A fuse contains a current-carrying element sized so that the heat generated by the flow of normal current through it doesnot cause it to melt the element; however, when an overcurrent or short-circuit current flowsthrough the fuse, the fusible link will melt and open the circuit. There are several types of fusesin use (Figure 3).Figure 3 Types of FusesThe plug fuse is a fuse that consists of a zinc or alloy strip, a fusible element enclosed inporcelain or pyrex housing, and a screw base. This type of fuse is normally used on circuitsrated at 125 V or less to ground and has a maximum continuous current-carrying capacity of 30amps.The cartridge fuse is constructed with a zinc or alloy fusible element enclosed in a cylindricalfiber tube with the element ends attached to a metallic contact piece at the ends of the tube. Thistype of fuse is normally used on circuits rated at either 250 volts or 600 volts and has amaximum continuous current-carrying capacity of 600 amps.Rev. 0 Page 5 ES-15
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