General description the 3rt1 series for switching the motors belongs to the modular system building blocks sirius and fits perfectly with the other devices of this generation the technically and mechanically compatible contactors and overload relays make it easy to build complete motor control centres if circuits 110 v and 100 ma are to be switched the auxiliary contacts of contactor 3rt1 or auxiliary relay 3rh11 should be used as these provide a high contact reliability these auxiliary