| 摘要 |
Fuses having different ratings, all of which comply with the Standard for Class L fuses of the Underwriters Laboratories Inc. The fusible elements of the fuses have identical points of reduced cross-section which fuse simultaneously on major fault currents, except one point of reduced cross-section which fuses ahead of the others. A relatively large temperature gradient prevails between the aforesaid points of reduced cross-section that fuse on short circuit current and the M-effect low fusing point overlay of the copper links that severs the current path through the latter by a diffusion process. The M-effect overlay metal may just reach its fusing point, while the immediately adjacent points of reduced cross-section may have a much higher temperature, e.g. 300 DEG to 400 DEG C. Thus the fusing M-effect metal will flow to the point of higher temperature and a rapid severing of the latter will take place. To meet the changes of heat flow the fuses having fusible element of silver to fusible element of copper requires much coarser arc-extinguishing quartz fillers that have proved to be necessary, or desirable, heretofore, in Class L fuses.
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