Drop-out fuse cutout and load switching fuse cutout are of outdoor used high voltage protective device. To be connected with incoming feeder of distribution transformer or distribution lines it mainly protects transformer or lines from short circuit and overload, and on/off loading current. Drop-out fuse cutout is com-posed of insulate insulator supports and fuse tube, static contacts is fixed on two sides of insulator support and moving contact is installed on two ends of fuse tube. Fuse tube is composed of inside arc-extinguishing tube, outer phenolic compound paper tube or epoxy glass tube. Load switching fuse cutout provides enforced elastic auxiliary contacts and arc-extinguishing enclosure for switching on/off loading current.

At normally wording via fuse link tightened the fuse tube is fixed to form up of close position. In case system occur false, fault current result in fuse melt immediately and take place electric arc, which let arc-extinguishing tube being heated and explode a lot of gas. This will produce high pressure and blow off the arc along with tube. After fuse link melt moving contact has no tightened strength again, mechanism is locked and fuse tube drop out. Cutout now is in open position. When it needs to switch off during cutout loading, operator shall via insulating operating bar pull the moving contact, at its beginning main contact and auxiliary static contact is contacted still. Whiling pulling the auxiliary contact is separated between auxiliary contacts there occur electric arc and the arc will be lengthened in arc-extinguishing enclosure gap and meanwhile arc-extinguishing explode gas to blow off the arc during current passing zero.