SIRIUS 3RT29 Surge Suppressors Siemens SIRIUS 3RT29 Surge Suppressors offer critical protection for DC and AC systems. These surge suppressors come in sizes S00 to S3 with or without an LED. Siemens SIRIUS 3RT29 Surge Suppressors can be plugged onto the front of size 00 contactors. Space is provided for the suppressors next to a snap-on auxiliary switch. Varistors, RC elements, or diode assemblies can be plugged onto the front of size S0 to S3 contactors.