Littelfuse MS series external mount microswitches offer permanent blown fuse indication to PSR and PSX series high-speed square-body semiconductor fuses. They have one normally open (N.O.) and one normally closed (N.C.) contact rated for 4 A, 250 V ac. These microswitches have a visual red flap or arm indicator that releases after fuse blown condition and can also be used for resetting the microswitch contacts.