Siemens 3RW4426-1BC44 Soft Starter 77A 37kW

3RW4426-1BC44 Siemens SIRIUS Soft Starter – Compact 77A Motor Control

Product Introduction

The Siemens 3RW4426-1BC44 belongs to the SIRIUS family of soft starters. It is designed for three-phase asynchronous motors in industrial applications. This model delivers a 77A operational current at 400V in standard mode. For inside-delta circuits, the rating increases to 133A. Consequently, the mechanical power output reaches 37kW in standard mode and 75kW in inside-delta configuration.

Engineers value the 3RW4426-1BC44 for its compact footprint. The unit measures only 170mm in width. This makes it ideal for space-limited control cabinets. Additionally, the integrated bypass contact system reduces heat generation during continuous operation.

Core Technical Specifications

The Siemens 3RW4426-1BC44 operates at a rated insulation voltage of 690V. It includes thyristors for smooth motor starting. Several protective functions come standard on this device. For example, you get intrinsic device protection and motor overload protection. The unit also evaluates thermistor motor protection signals.

Operational Current Values by Temperature:

• At 40°C (standard): 77A

• At 50°C (standard): 68A

• At 60°C (standard): 59A

• At 40°C (inside-delta): 133A

• At 50°C (inside-delta): 118A

• At 60°C (inside-delta): 102A

Motor Power Output at 400V and 40°C:

• Standard circuit: 37kW

• Inside-delta circuit: 75kW

For 230V applications at 40°C, the 3RW4426-1BC44 provides 18.5kW in standard mode. Inside-delta wiring increases this to 37kW. The operating voltage range spans 200 to 460V AC. Tolerance for the operating voltage is -15% to +10%. Control supply voltage is fixed at 230V AC for both 50Hz and 60Hz systems.

UL/CSA Ratings for North American Applications

The 3RW4426-1BC44 carries UL/CSA ratings for use in North America. At 220/230V in standard circuit, the horsepower rating is 20 hp at 50°C. For 460/480V standard circuit, it reaches 50 hp. When using inside-delta wiring, the ratings improve significantly. At 200/208V inside-delta, you get 30 hp. At 220/230V inside-delta, the rating is 40 hp. Finally, at 460/480V inside-delta, the 3RW4426-1BC44 delivers 75 hp.

The auxiliary contacts carry a B300 and R300 rating according to UL standards. This makes the unit suitable for typical control circuits in North American industrial panels.

Protection Features and Control Functions

This soft starter includes an integrated bypass contact system. The bypass engages after the motor reaches full speed. This reduces power loss and extends thyristor life. Additionally, a motor brake output is available for dynamic braking applications.

Auxiliary Contact Configuration:

• Number of NO contacts: 3

• Number of NC contacts: 0

• Number of changeover (CO) contacts: 1

A display provides clear fault signalling for quick diagnostics. The adjustable current limitation helps manage inrush currents. You can also use an external reset for remote operation. Furthermore, the minimum load requirement is only 8% of the rated current. The adjustable motor overload protection starts from 15A.

Power Loss and Continuous Operation

At 40°C with rated current, typical power loss is only 45W. This low loss results from the integrated bypass system. The continuous operating current can reach 115% of Ie at 40°C. This margin allows for temporary overload conditions without tripping. Such efficiency makes the 3RW4426-1BC44 suitable for continuous duty applications.

Mechanical Dimensions and Installation

Physical Dimensions:

• Width: 170 mm

• Height: 192 mm

• Depth: 270 mm

Mounting Requirements:

The Siemens 3RW4426-1BC44 uses screw fixing for installation. You can rotate the unit +/-90° on a vertical surface. Tilting up to +/-22.5° forward or backward is also permitted. For side-by-side mounting, follow these spacing rules:

• Upwards clearance: 100 mm

• Side clearance: 5 mm

• Downwards clearance: 75 mm

Maximum wire length from the starter to the motor is 500 meters. The main current circuit uses three poles. Installation altitude can reach up to 5000 meters above sea level.

Terminal and Wiring Specifications

Main current connections use box terminals. Auxiliary and control circuits connect via screw-type terminals. This design provides flexibility for different wire types.

Conductor Sizes for Main Contacts (Box Terminals):

Front clamping point:

• Solid: 2.5 to 16 mm²

• Finely stranded with end processing: 2.5 to 35 mm²

• Finely stranded without end processing: 4 to 50 mm²

• Stranded: 4 to 70 mm²

Back clamping point:

• Solid: 2.5 to 16 mm²

• Finely stranded with end processing: 2.5 to 50 mm²

• Without end processing: 10 to 50 mm²

• Stranded: 10 to 70 mm²

Using both clamping points:

• Solid: 2x (2.5 to 16 mm²)

• Finely stranded with end processing: 2x (2.5 to 35 mm²)

• Without end processing: 2x (4 to 35 mm²)

• Stranded: 2x (4 to 50 mm²)

AWG equivalents for main contacts:

• Front clamping: 10 to 2/0 AWG

• Back clamping: 10 to 2/0 AWG

• Both clamping points: 2x (10 to 1/0 AWG)

Auxiliary Contacts:

• Solid: 2x (0.5 to 2.5 mm²)

• Finely stranded with end processing: 2x (0.5 to 1.5 mm²)

• AWG: 2x (20 to 14)

• Finely stranded AWG: 2x (20 to 16)

Environmental Conditions

The 3RW4426-1BC44 operates reliably in various industrial environments. Operating ambient temperature reaches up to 60°C. However, derating begins at 40°C. Storage temperature ranges from -25°C to +80°C. Protection class is IP00 according to IEC 60529.

Frequently Asked Questions (FAQ)

1. What is the maximum motor power for the 3RW4426-1BC44?

At 400V and 40°C, this soft starter delivers 37kW in standard circuit. With inside-delta connection, the power reaches 75kW. Choose inside-delta wiring for higher power applications.

2. Does this unit work with 230V control supply?

Yes, the control circuit requires 230V AC. It works for both 50Hz and 60Hz systems. The acceptable voltage tolerance is -15% to +10%.

3. What is the minimum adjustable current setting?

The motor overload protection adjusts down to 15A. This makes the 3RW4426-1BC44 suitable for smaller motors as well. The minimum load requirement is 8% of the rated motor current.

4. How much space do I need around this soft starter?

You must maintain specific clearances for proper cooling. Leave 100mm above the unit. Allow 5mm on each side. Keep 75mm clearance below the unit. These spacing rules ensure adequate airflow.

5. Does the 3RW4426-1BC44 include an integrated bypass?

Yes, it does. The integrated bypass contact system engages after starting. This reduces power loss to only 45W during continuous operation. It also protects the thyristors from unnecessary heat stress.