Siemens sirius 3rt19 contactor and 3rh19 din rail control relay siemens 3rh1921 1ca01 the siemens sirius din rail auxiliary relay 3rh1921 1ca01 has screw connections and is ideal as a contactor relay or power contactor the relay has 1 nc contact and can be fitted onto the front side of the contactor size s0 to s12 siemens 3rh1921 1ca01 auxiliary switch block din en 50005 1 pole