3RW4426-1BC44 77A Soft Starter | Siemens SIRIUS

Key Features and Technical Specifications

• Operating voltage: 200–460 V AC (standard and inside-delta)
• Control supply voltage: 230 V AC at 50/60 Hz
• Rated current at 40 °C: 77 A (standard), 133 A (inside-delta)
• Emitted mechanical power: 37 kW at 400 V (standard), 75 kW at 400 V (inside-delta)
• Integrated bridging contact system and thyristors for reliable switching
• Motor overload protection and intrinsic device protection built-in
• Adjustable current limitation and inside-delta circuit support
• Three auxiliary contacts (3 NO, 1 changeover) for status feedback
• IP00 protection class for open-panel installation

The 3RW4426-1BC44 also includes an evaluation of thermal resistor motor protection, enabling accurate temperature-based protection for connected motors. Its screw terminals simplify wiring, while the compact dimensions (170 mm width, 192 mm height, 270 mm depth) fit standard enclosures.

Applications and Use Cases

This soft starter suits conveyors, pumps, fans, and compressors where smooth acceleration extends equipment life. In inside-delta mode, it manages higher power motors, making it ideal for heavy-duty machinery. The adjustable current limitation helps protect motors during startup, reducing wear on belts and gears. Additionally, the integrated bypass contactor minimizes heat dissipation during continuous operation, improving energy efficiency.

Installation and Setup

Mount the 3RW4426-1BC44 on a vertical surface, allowing 100 mm clearance above and 75 mm below for airflow. Side clearance of 5 mm is sufficient. The unit can be tilted ±90° on a vertical plane or ±22.5° forward/backward, offering installation flexibility. Connect main circuit wires using box terminals, accepting solid conductors from 2.5 to 16 mm² or stranded from 4 to 70 mm². For auxiliary circuits, screw terminals accept 2x (0.5–2.5 mm²) solid or 2x (0.5–1.5 mm²) finely stranded wires.

Ensure the control supply voltage is 230 V AC at 50 or 60 Hz, with tolerances of -15%/+10%. The operating frequency range is 50–60 Hz, with ±10% tolerance. For optimal performance, keep cable length to a maximum of 500 m.

Maintenance and Reliability

Regular inspection of the soft starter ensures long-term reliability. Check all terminal connections for tightness periodically, as thermal cycling can loosen screws. Verify that ambient temperature stays within the rated range (up to 60 °C during operation, storage from -25 °C to +80 °C). The unit's derating temperature is 40 °C, so higher ambient temperatures reduce current capacity—refer to the derating curves in the manual. Since the device includes integrated protection features, it reduces the risk of motor damage, lowering maintenance costs over time.

Compatibility and Integration

The 3RW4426-1BC44 is part of the Siemens SIRIUS family, designed for seamless integration into existing motor control systems. It supports both standard and inside-delta wiring, accommodating various motor configurations. The auxiliary contacts (3 NO, 1 changeover) provide status signals to PLCs or HMIs, enabling remote monitoring. For UL/CSA applications, the unit is rated for 20 hp at 220/230 V and 50 hp at 460/480 V in standard circuit, and up to 75 hp in inside-delta mode at 480 V.

Common Issues and Troubleshooting

If the motor fails to start, verify that the control supply voltage is present and within tolerance. Check the operating voltage settings against the motor nameplate. Overload trips may occur if the motor's rated current exceeds the adjustable range (15 A minimum). Ensure the current limitation is set correctly. For thermal issues, confirm adequate ventilation and that the mounting clearances are respected. If the display shows a fault, consult the manual for specific codes.

Product Support and Availability

The Siemens 3RW4426-1BC44 is available from AutoDCSTech. Contact us for current stock and lead times. We provide genuine parts and fast shipping to keep your operations running.