Fuse system for a power circuit

A safety device for a power circuit includes a circuit 8 for converting a first voltage to a second voltage including two fuses 5A, 5B whereby if a fuse blows in one arbitrary circuit the failure of the fuse in the other circuit will be induced automatically by a heater 30 or a logic circuit. Alternatively, displacement of the blown fuse element 55B causes the other fuse to blow, Fig 5B.