The Siemens SIRIUS 3TH4 series is a contactor relay for switching the control signals in the control circuit in railway applications. It has operating voltage of 110 V DC. The design of surge suppressor is with varistor. The contactor relays have standard-compliant terminal designations and a reliable connection technology. The type of electrical connection for auxiliary and control current circuit is through screw terminal. Due to multiplication of outputs, simultaneous switching of up to 10 auxiliary circuits is possible. The contacts are designed with positively driven operation for safety applications as well as SUVA versions. The devices are climate-resistant and have a high contact reliability. It is approved for worldwide use e.g. IEC and UL/CSA.

Protection class IP is IP20
Ambient operating temperature is -25 to +55 °C