Siemens SIRIUS 3RF2420-1AC45 Solid State Relay, 1-Phase, 20 A, 48-600 V AC, 24 V DC Control, Zero-Point Switching, Screw Terminals

In industrial switching applications, mechanical contactors wear out, generate noise, and demand frequent maintenance. The Siemens SIRIUS 3RF2420-1AC45 solid state relay eliminates these pain points by using semiconductor technology to switch loads up to 20 A at 48–600 V AC without moving parts. This single-phase relay is built for high-frequency operations, offering silent, arc-free switching and a service life that far exceeds electromechanical alternatives. With zero-point switching, it minimizes inrush currents and electromagnetic interference, protecting sensitive equipment and extending the life of connected loads.

Who is it for

This relay is ideal for machine builders, panel designers, and maintenance engineers who need reliable, high-speed switching in heating, lighting, motor, and solenoid applications. It suits environments where frequent switching, low noise, and long-term dependability are critical—such as packaging lines, plastics processing, HVAC systems, and industrial ovens. If you are replacing contactors in high-cycle applications or designing a new control panel with space constraints, this compact DIN-rail mountable unit fits seamlessly.

Main features

• Rated operational current of 20 A (AC-51) with operational voltage from 48 to 600 V AC, covering a wide range of industrial loads.
• Zero-point switching reduces inrush currents and EMI, ensuring smooth operation of resistive loads.
• Control voltage of 24 V DC allows direct interfacing with PLC outputs and standard control systems.
• Single-phase design with screw terminals for both main and control circuits, simplifying wiring and maintenance.
• Compact housing with IP20 protection, suitable for DIN rail or screw mounting in control cabinets.
• High insulation voltage (600 V) and surge voltage rating (4 kV) provide robust protection against transients.
• Wide ambient operating temperature range from -25°C to +60°C, ensuring performance in harsh environments.
• Compatible with gG fuses up to 25 A for short-circuit protection, enhancing system safety.

Specifications

• Product series: SIRIUS 3RF24
• Number of phases: 1
• Rated operational current (AC-51): 20 A
• Rated operational voltage: 48–600 V AC
• Control voltage: 24 V DC
• Switching type: Zero-point switching
• Operating frequency: 50/60 Hz
• Main circuit connection: Screw terminals
• Control circuit connection: Screw terminals
• Mounting type: DIN rail / screw mounting
• Rated insulation voltage: 600 V
• Rated surge voltage: 4 kV
• Ambient operating temperature: -25 to +60 °C
• Protection class: IP20
• Short-circuit protection (with fuse): gG: 25 A

Tips

Always use a suitable heat sink when operating near the maximum current rating to ensure optimal thermal performance and longevity. For inductive loads, consider adding a varistor or RC snubber across the relay output to suppress voltage spikes. Verify that the control signal polarity is correct for the 24 V DC input to avoid malfunction. When replacing a mechanical contactor, check the existing wiring and space; this SSR's screw terminals accept standard wire sizes, but torque specifications should be followed to prevent loose connections. For applications with frequent switching, the zero-point switching feature will reduce stress on the load and improve overall system reliability.