Product Overview

The Siemens 3RW4074-6BB44 is a SIRIUS S12 soft starter designed for standard applications. This device handles an operating current of 280 A when the ambient temperature reaches 40°C. However, the rated current decreases to 248 A if the temperature rises to 50°C. Similarly, further derating to 215 A becomes necessary at 60°C. Emitted mechanical power reaches 90,000 W at 230 V and 40°C. At 400 V and 40°C, the power rating increases significantly to 160,000 W. The 3RW4074-6BB44 includes an integrated bridging contact system alongside robust thyristors. For comprehensive motor protection, this device offers both intrinsic device protection and adjustable motor overload protection. Users can also benefit from adjustable current limitation for flexible starting performance. A red fault signal display enables rapid diagnostics, while external reset capability simplifies fault recovery.

Technical Specifications

General Specifications

Current & Power Ratings

Voltage & Frequency Specifications

Protection Functions

Mechanical Dimensions

Integrated Bridging Contact System

The 3RW4074-6BB44 features an integrated bridging contact system that bypasses the thyristors after the motor reaches full speed. Consequently, power loss and heat generation reduce significantly during continuous running. The active power loss at 40°C measures only 90 W typical. For energy-conscious applications, this efficiency proves valuable. Moreover, the bridging contact extends the operational life of the thyristors by eliminating continuous conduction losses.

Motor Protection Capabilities

Motor overload protection comes built into the Siemens 3RW4074-6BB44, with an adjustable rated current range starting from 130 A minimum. Intrinsic device protection safeguards the soft starter itself from various fault conditions. For fault recovery, external reset capability allows remote or panel-based reset without opening the cabinet. However, evaluation of thermal resistor motor protection (PTC) is not available on this model. Therefore, installations requiring thermistor inputs must use separate thermal protection devices alongside the 3RW4074-6BB44.

Current Derating at Elevated Temperatures

The 3RW4074-6BB44 requires careful current derating as the ambient temperature rises. Full rated current of 280 A remains available when the temperature holds at 40°C. Once the temperature reaches 50°C, the rated current decreases to 248 A (approximately 11% derating). At 60°C, further derating reduces the rated current to 215 A (approximately 23% derating). For short-term overloads, the continuous operating current can reach 115% of Ie at 40°C. Given these derating characteristics, proper ventilation around the soft starter remains absolutely essential for achieving full rated performance.

Control Supply & Operating Voltage

The control supply requires 230 V AC at either 50 or 60 Hz, with a tolerance of -15% to +10% for reliable operation. Meanwhile, the main circuit operating voltage spans 200 to 460 V AC, also with -15% to +10% tolerance. Operating frequency tolerance extends -10% to +10% from the 50-60 Hz nominal range. As a result, the Siemens 3RW4074-6BB44 accepts a wide range of worldwide industrial power standards without additional configuration.

Auxiliary Contacts & Wiring

This soft starter includes two NO contacts and one changeover contact for auxiliary signaling. No NC contacts are available on the 3RW4074-6BB44. Screw-type terminals connect both auxiliary and control circuits securely. For the main current circuit, busbar connection serves as the standard design. Flexible wiring options support multiple conductor cross-section configurations. At the front clamping point, finely stranded wire with conductor end processing accepts 70-240 mm². Without end processing, the acceptable range remains 70-240 mm². Stranded wire, in comparison, accepts 95-300 mm². At the back clamping point, finely stranded wire with end processing accepts 120-185 mm². Stranded wire without end processing accepts 120-240 mm². When utilizing both clamping points simultaneously, finely stranded wire with end processing requires a minimum of 2x 50 mm² and accepts up to 2x 185 mm².

Mounting & Clearance Requirements

Proper mounting position demands careful attention to ensure adequate cooling. With the additional fan installed, the vertical mounting surface allows +/-90° rotation. Furthermore, the unit tilts +/-22.5° forward and backward when the fan is present. Without the additional fan, however, vertical mounting allows only +/-10° rotation. Tilting also reduces to +/-10° in the absence of the fan. Specific clearances must be maintained around the 3RW4074-6BB44 for proper airflow. Upward clearance requires 100 mm. Sideward clearance needs only 5 mm minimum. Downward clearance requires 75 mm for cable entry and cooling.

Environmental & Ambient Conditions

The Siemens 3RW4074-6BB44 operates reliably across a wide range of environmental conditions. Ambient temperature during operation spans -25°C to +60°C. During storage, the temperature range expands to -40°C to +80°C. Derating begins at 40°C as specified in the detailed current tables. Protection class reaches IP00, meaning the device provides no enclosure protection on its own. Consequently, install the 3RW4074-6BB44 inside a suitable control cabinet for safety. Maximum installation altitude reaches 5,000 meters above sea level, while maximum cable length between soft starter and motor reaches 300 meters.

Installation Guidelines

Follow these steps for proper installation of the 3RW4074-6BB44.

1. Mount the unit vertically on a flat, non-flammable surface using screw fixing.

2. Maintain required clearances: 100 mm upward, 5 mm sideward, 75 mm downward.

3. Connect main power to the input terminals using appropriate busbars or cables.

4. Connect the motor leads to the output terminals of the 3RW4074-6BB44.

5. Wire the control supply (230 V AC) to the designated auxiliary terminals.

6. Connect external reset circuits if remote fault recovery is required for your application.

7. Set the adjustable current limit between 130 A and 280 A based on the motor FLA.

8. Apply power and configure parameters according to your specific application needs.

Note: The 3RW4074-6BB44 requires IP00 protection class installation inside a suitable cabinet. Always derate current for ambient temperatures above 40°C. Never exceed 300 meters cable length between soft starter and motor. Verify that control supply voltage is 230 V AC within the specified tolerance.

Packaging List

• One Siemens 3RW4074-6BB44 SIRIUS S12 Soft Starter

• One product documentation manual

• One set of screw terminals for auxiliary connections

• One anti-static protective bag

Common FAQs

1. How does temperature affect the current rating of the 3RW4074-6BB44?

The Siemens 3RW4074-6BB44 delivers 280 A at 40°C ambient temperature. At 50°C, the rating decreases to 248 A. At 60°C, the rating further decreases to 215 A. For this reason, always consider your installation's ambient temperature when sizing the soft starter for your motor application.

2. Does the 3RW4074-6BB44 include an integrated bypass system?

Yes, this soft starter features an integrated bridging contact system that automatically bypasses the thyristors. Once the motor reaches full speed, the bypass contacts close around the thyristors. Consequently, power loss drops to only 90 W typical during continuous running. The thyristors also experience significantly less thermal stress as a result.

3. What control supply voltage does the 3RW4074-6BB44 require?

The control supply requires 230 V AC at either 50 Hz or 60 Hz. Tolerance allows -15% to +10% variation from the nominal voltage. The main circuit operating voltage spans 200 to 460 V AC with similar tolerance. Therefore, always verify both voltages before powering the 3RW4074-6BB44 for the first time.

4. What protection functions come standard on the 3RW4074-6BB44?

Intrinsic device protection safeguards the soft starter from internal faults. Motor overload protection is also included for the connected induction motor. Adjustable current limitation allows precise control over starting torque. External reset capability simplifies fault recovery from a remote location. However, thermal resistor motor protection (PTC) is not available on this 3RW4074-6BB44.

5. What mounting clearances must I maintain for the 3RW4074-6BB44?

You must allow 100 mm clearance above the unit for proper airflow. Allow 5 mm clearance on each side of the unit as well. Finally, allow 75 mm clearance below the unit for cable entry and cooling. Without these clearances, the Siemens 3RW4074-6BB44 may overheat and derate prematurely.

Why Choose This Soft Starter?

The Siemens 3RW4074-6BB44 delivers reliable motor starting and comprehensive protection for standard industrial applications. A rated current of 280 A handles large motors up to 160 kW at 400 V. The integrated bridging contact system reduces power loss dramatically during continuous running. Adjustable current limitation provides flexible starting performance across various load types. Motor overload protection and intrinsic device protection safeguard both the motor and the starter itself. External reset capability simplifies fault recovery without opening the cabinet. For demanding motor control applications in pumps, fans, and compressors, choose the 3RW4074-6BB44.