US Patent 7307507 Fuse state indicator

A fuse state indicator for a fuse including a cylindrical fuse body and a primary fuse element therein, includes an extension member, a transparent lens, a combustible substance adjacent the lens, a secondary fuse link adjacent said combustible substance, and a curved backing layer adjacent said secondary fuse link. Said backing layer is at least partially concealed by said combustible substance when viewed through said transparent lens before the fuse has opened, and said backing layer maintains said secondary fuse link in position with respect to said combustible substance.