Siemens SIRIUS 3RT2 3-Pole Power Contactor, 37 A, 24 V DC Coil, Screw Terminals, 1NO+1NC 3RT20272BB40

Industrial control panels and motor control centers demand reliable switching for heavy loads. The Siemens 3RT20272BB40 power contactor from the SIRIUS 3RT2 series delivers exactly that: a robust 3-pole contactor rated for 37 A at AC-3, 400 V, capable of controlling motors up to 18.5 kW. Its 24 V DC coil integrates seamlessly with PLC outputs and safety relays, while screw terminals ensure secure, vibration-resistant connections. One normally open and one normally closed auxiliary contact provide flexible feedback and interlocking options. This contactor is the workhorse behind conveyor systems, pumps, fans, and machine tools in factories, processing plants, and building automation.

Key specifications

• Type: Power contactor, 3-pole, size S0
• Rated operational current (AC-3, 400 V): 37 A
• Rated operational power (AC-3, 400 V): 18.5 kW
• Control supply voltage: 24 V DC
• Auxiliary contacts: 1 NO + 1 NC
• Connection type: Screw terminals
• Rated insulation voltage: 690 V
• Rated impulse withstand voltage: 6 kV
• Mechanical endurance: 30 million switching cycles
• Electrical endurance (AC-3): 10 million switching cycles
• Protection class: IP20 (front side)
• Mounting: DIN rail or screw mounting
• Standards: IEC 60947

Why choose it

The SIRIUS 3RT2 contactor is engineered for longevity and dependable performance in demanding industrial environments. Its high mechanical and electrical endurance reduces maintenance intervals and downtime. The wide operating temperature range from -25 °C to +60 °C allows installation in harsh conditions. With screw terminals, wiring is straightforward and secure, even under vibration. The compact S0 size saves panel space while delivering full-rated power. Compliance with IEC 60947 ensures global acceptance and safety.

Ideal use cases

• Motor starting and stopping in conveyor systems
• Pump control in water treatment and HVAC
• Fan and compressor switching in industrial machinery
• Heating and lighting load control in building automation
• Integration into PLC-controlled automation systems

Good to know

The contactor is designed for AC-3 duty, which covers normal starting and switching of squirrel-cage motors. For resistive or slightly inductive loads, it can handle up to 50 A at AC-1. The 24 V DC coil is ideal for low-voltage control circuits, reducing the need for additional power supplies. Always follow local electrical codes and use appropriate protection devices such as motor circuit breakers or fuses. The contactor can be mounted on a 35 mm DIN rail or screwed directly to a backplate.