Electric fuse having composite fusible element

Abstract

An electric low-voltage current-limiting fuse completely or substantially complying with the Underwriters Laboratories Inc. Standard Class R fuses. The current carrying part of the fuse comprises a fusible element having serially arranged perforations. This part may be of silver or of copper. The current carrying part of the fuses further comprises tabs of copper bent over the rims of the casing and conductively interconnecting the ends of the fusible element with the terminal caps of the fuse. The fusible element is provided with an M-effect metal to limit the temperature rise of the fusible element and of the casing. The tabs are considerably thicker than the fusible element. If the fusible element is of silver the thickness of the tabs of copper is larger than the thickness required to fully compensate for their higher resistivity. The ratio of the thickness of a pair of tabs of copper to the thickness of a fusible element of silver depends upon the geometrical configuration of the latter and is in the range of 2:1 to somewhat less than 5:1. Since the tabs are thicker than the fusible element both cannot be joined by conventional rolling operations. Each of the pair of tabs is formed by a part separate from the fusible element. These tabs are affixed by electroconductive bonds such as, e.g. spot-welds, to the fusible element.