Actually, Ericsson introduced this arrangement on their ARF102 x-bar exchanges back in th 1960's. Each equipment rack had one or two 16A pluggable rack fuses at the top. The pluggable fuse actually had 2 fuse wires, the main 16A and a 1.5A alarm fuse in parallel with it. When the 16A fuse blew the 1.5A alarm fuse connected in par'l then blew and operated the alarm contacts.