The load-isolating switch 12 is coupled to the vacuum chamber 13 and is operated by a permanent magnet actuator 14 that has fixed magnets 15, a movable armature 16,a yoke 17 and a coil 18. The coil is in series with the load switch and the vacuum chamber and the armature is coupled to a fixed point by a spring 20. The armature connects via a linkage 21 to the load switch. When a current overload occurs the actuator responds to open the contacts.
