Siemens SIRIUS 3RW30 Soft Starter | 3.6–106 A | Stoklink

About the SIRIUS 3RW30

The SIRIUS 3RW30 is Siemens' entry-level soft starter series within the SIRIUS industrial controls portfolio. It targets applications where the primary requirement is controlled acceleration and deceleration of a three-phase induction motor — eliminating the mechanical shock and inrush current spikes associated with direct-on-line (DOL) switching — without the overhead of advanced motor management, fieldbus connectivity, or onboard diagnostics.

Commissioning is intentionally simple. Two potentiometer dials on the front face set the ramp-up time and the starting voltage pedestal. There is no display, no parameter software, and no PC interface. An engineer can commission a 3RW30 in minutes using a screwdriver and a motor datasheet, making it well suited to high-volume OEM panel builds and straightforward retrofit projects.

All models in the 3RW30 family integrate internal bypass relays. Once the motor reaches full speed, the bypass relay closes and the semiconductors are taken out of circuit, eliminating continuous thyristor losses and heat generation during steady-state running. This is a significant advantage over non-bypass designs in terms of thermal management and energy efficiency in the panel.

The footprint is genuinely compact — the smallest models start at 45 mm wide — and all variants mount directly on a standard 35 mm DIN rail, simplifying installation in tight control cabinets. The supply voltage range of 200–480 V AC covers the vast majority of industrial voltage standards worldwide.

One important constraint: the 3RW30 does not include motor overload protection. A separate overload relay (such as a SIRIUS 3RU2 or 3RB3) must be installed in the circuit to provide IEC 60947-4-1-compliant thermal protection. This is standard practice and does not add significant complexity, but it must be accounted for in the BOM and panel layout.

Where SIRIUS 3RW30 Fits in the SIRIUS Portfolio

Siemens structures the SIRIUS soft starter range into four main tiers: 3RW30 (entry-level, two-phase control, no display), 3RW40 (standard, three-phase control, onboard overload protection, basic diagnostics), 3RW50/52 (advanced, full motor management, fieldbus via IO-Link or PROFINET/PROFIBUS), and 3RW55 (high-feature, integrated bypass with full communication and advanced protection for demanding loads).

Choose the 3RW30 when: the load is a standard squirrel-cage motor, starting conditions are benign, no fieldbus integration is required, and panel space and cost are the primary drivers. Step up to the 3RW40 when integrated motor overload protection is required or when three-phase control symmetry is important. Select the 3RW50/52 or 3RW55 when the application demands PROFINET/PROFIBUS integration, advanced protection functions (thermistor, phase monitoring, load monitoring), or when the motor management data must be visible in a SCADA or TIA Portal environment.

Technical Specifications

The following specifications apply at family level across all SIRIUS 3RW30 models. Per-model current and power ratings are detailed in the model selection table below.

• Current range: 3.6 A to 106 A (motor FLC)
• Power range: 1.5 kW to 55 kW at 500 V AC
• Main circuit supply voltage (Us): 200–480 V AC, 50/60 Hz
• Control supply voltage: Derived from main circuit (no separate 24 V DC control supply required on standard variants)
• Frequency: 50 Hz / 60 Hz
• Control method: Two-phase voltage ramp (thyristor control on two phases; third phase connected through)
• Integrated bypass: Yes — internal bypass relays fitted as standard; no external bypass contactor required
• Parameterisation: Dial-based (potentiometers for ramp time and starting voltage); no display, no PC software
• Fieldbus / communication: None
• Motor overload protection: Not included — external overload relay required
• Mounting: Direct DIN-rail (35 mm), screw terminals
• Minimum width: 45 mm (3RW3013/3014 variants)
• Degree of protection: IP20 (built-in unit); suitable for installation inside a control cabinet
• Ambient operating temperature: −25 °C to +40 °C (derating applies above 40 °C up to 60 °C)
• Standards: IEC 60947-4-2, CE marked, UL listed
• Coordination type: Type 2 coordination achievable with appropriate fuse selection per Siemens coordination tables

Key Features

• Two-phase voltage ramp soft start and soft stop: The 3RW30 ramps the motor terminal voltage up from an adjustable starting pedestal to full voltage over a set ramp time, limiting inrush current and mechanical shock on start. The same principle applies in reverse for soft stop, reducing water hammer in pump circuits and protecting conveyor loads. Two-phase control keeps component count and cost low while delivering effective ramp performance for standard induction motors.
• Integrated internal bypass relays: Once the motor reaches full speed, built-in bypass relays short-circuit the thyristors, eliminating semiconductor conduction losses during normal running. This reduces panel heat dissipation, extends thyristor life, and removes the need to purchase, wire, and size a separate bypass contactor — saving both panel space and BOM cost.
• Compact 45 mm width — direct DIN-rail mounting: The smallest 3RW30 models occupy just 45 mm of rail width, making them among the most space-efficient soft starters available for sub-10 A applications. All models mount directly on a standard 35 mm DIN rail without adapter plates, simplifying installation and reducing assembly time in high-volume panel builds.
• Dial-based parameterisation — no display, no software: Two front-face potentiometers cover all commissioning needs: one sets the voltage ramp time (adjustable from approximately 1 to 5 seconds depending on model), the other sets the starting voltage pedestal. No laptop, no USB interface, and no parameter software licence is required. This is a deliberate design choice that reduces commissioning risk and training overhead in straightforward DOL replacement projects.
• No fieldbus communication: The absence of a fieldbus interface is a feature as well as a limitation. For applications where no SCADA integration is required, the 3RW30 avoids the configuration overhead, network addressing, and cybersecurity considerations associated with connected devices. It is a self-contained, deterministic switching device.
• No integrated motor overload protection — engineered transparency: By omitting onboard overload protection, Siemens keeps the 3RW30 focused and low-cost, while requiring the engineer to specify a dedicated overload relay. This forces correct protection sizing and ensures the overload relay is independently accessible for testing and resetting — a sound practice for maintenance-critical installations.

Selecting Your SIRIUS 3RW30 Model

Sizing a 3RW30 is straightforward. Follow these steps to identify the correct model for your application.

Step 1 — Determine motor full-load current (FLC). Read the rated current from the motor nameplate at the supply voltage in use. For a 400 V / 50 Hz system, use the 400 V FLC value. The 3RW30 must be selected so that its rated operational current equals or exceeds the motor FLC. Do not size on motor kW alone — the current rating is the governing parameter.

Step 2 — Match to the current lineup. The 3RW30 family spans 3.6 A to 106 A in 13 steps: 3.6, 6.5, 9, 12.5, 17.6, 25, 32, 38, 45, 63, 72, 80, and 106 A. Select the first model whose current rating meets or exceeds the motor FLC. For example, a 7.5 kW motor at 400 V drawing 15.2 A FLC requires the 17.6 A model (3RW3018); the 12.5 A model would be undersized.

Step 3 — Consider duty cycle and ambient temperature. The published current ratings apply at 40 °C ambient. If the panel operates above 40 °C, apply Siemens' published derating factors (typically 2–3% per degree above 40 °C up to 60 °C). For high duty-cycle or plug-reversing loads, consult the application data in the SIRIUS 3RW30 manual for permissible starts-per-hour limits.

Step 4 — Select a separate overload relay. The 3RW30 has no internal overload protection. Specify a SIRIUS 3RU2 or 3RB3 overload relay matched to the same current range as the soft starter and set to the motor FLC. For Type 2 short-circuit coordination, refer to the Siemens SIRIUS coordination tables to select the correct upstream fuse or circuit breaker.

Step 5 — Verify supply voltage. All 3RW30 models accept 200–480 V AC. Confirm your supply voltage falls within this range. For 525 V or 690 V systems, the 3RW30 is not suitable — consider the 3RW40 or 3RW52 families which offer extended voltage options.