An analysis has been made and a design procedure established for fuses other than those using round wire and with, or without, a restricted cross-section for part of the fuse length. Fuses of restricted section are, however, the major interest since they may be used to give different current/time characteristics by varying their dimensions. These different characteristics may be predicted accurately by the method indicated in the paper. In all the cases of semi-enclosed tin-strip fuses investigated in this way very close agreement between predicted and experimental results has been obtained.