Siemens sirius 3rt19 contactor and 3rh19 din rail control relay siemens 3rh1921 1fa40 the siemens sirius din rail auxiliary relay 3rh1921 1fa40 has screw connections and is ideal as a contactor relay or power contactor the relay has 4 no contacts and can be fitted onto the front side of the contactor size s0 to s12 siemens 3rh1921 1fa40 mountin block din en 50005 4 closer s0 s3